MANUFACTURING PROCESS FOR QUARTZ GLASS

Description

[0001] The invention relates to a method for producing a quartz glass body comprising the process steps i.) providing and introducing a bulk material selected from silicon dioxide granules and quartz glass granules into the furnace and providing a gas, ii.) forming a glass melt from the bulk material, and iii.) forming a quartz glass body from at least a portion of the glass melt. The invention further relates to a method for producing an optical fiber, a light source, or a shaped body. Background of the invention

[0002] Quartz glass, quartz glass products, and products containing quartz glass are well-known. Likewise, various processes for manufacturing quartz glass and quartz glass bodies are already known. Nevertheless, considerable efforts continue to be made to identify manufacturing processes by which quartz glass of even higher purity, meaning the absence of impurities, can be produced. For example, some applications of quartz glass and its processed products place particularly high demands on homogeneity and purity. This is the case, for instance, with quartz glass used in optical fibers or light sources. Impurities can cause absorption in these applications. This is disadvantageous because it leads to color changes and attenuation of the emitted light. Another example of the use of high-purity quartz glass is in semiconductor manufacturing.Here, any contamination of the glass body potentially leads to defects in the semiconductors, and thus to rejects in production. The high-purity, often synthetic, quartz glass types used for these processes are therefore manufactured using very complex processes. They are expensive.

[0003] There is continued market demand for the aforementioned high-purity synthetic quartz glass and products made from it at a lower price. Therefore, efforts are underway to offer high-purity quartz glass at a lower price than before. In this regard, both more cost-effective manufacturing processes and more affordable raw material sources are being sought.

[0004] Known methods for manufacturing quartz glass bodies involve melting silicon dioxide and forming the molten quartz into glass bodies. Irregularities in a glass body, for example, due to the inclusion of gases in the form of bubbles, can lead to failure of the glass body under stress, especially at high temperatures, or preclude its use for a specific purpose. For instance, impurities in the quartz glass-forming raw material can lead to the formation of cracks, bubbles, streaks, and discoloration in the quartz glass. When used in processes for the manufacture and treatment of semiconductor components, impurities in the glass body can also be extracted and transferred to the treated semiconductor components. This occurs, for example, in etching processes and then leads to the rejection of the semiconductor blanks. Consequently, a frequently occurring problem with known manufacturing processes is insufficient quality of the quartz glass bodies.Examples of state of the art include DE 10 2012 008123 A1, SU 662 507 A1 and GB 1 254 492A.

[0005] Another aspect concerns resource efficiency. It seems advantageous to process quartz glass and its raw materials, which are generated elsewhere as byproducts, into quartz glass products, rather than using these byproducts as filler material, for example in building construction, or disposing of them costly as waste. These byproducts are often captured as fine dust in filters. This fine dust poses further problems, particularly with regard to health, occupational safety, and handling. Tasks

[0006] One object of the present invention is to overcome at least some of the disadvantages arising from the prior art.

[0007] It is an object of the invention to provide a furnace for melting substances or mixtures of substances which at least partially solves at least one, preferably several, of the problems described in the prior art.

[0008] It is an object of the invention to provide a furnace for melting substances or mixtures of substances which has long service lives under the process conditions.

[0009] It is an object of the invention to provide a furnace for melting substances or mixtures of substances which is not attacked during melting, even by water-containing or corrosive substances.

[0010] A further object of the invention is to provide a furnace through which the melt produced in it is not contaminated with material from the furnace walls.

[0011] A further object of the invention is to provide a furnace with which silicon dioxide melts can be produced, which can subsequently be solidified into silicon dioxide bodies.

[0012] It is an object of the invention to provide a furnace for melting silicon dioxide which is not attacked during melting even by aqueous or corrosive silicon dioxide species.

[0013] A further objective of the invention is to provide light guides, light sources, and components with a long service life. Components are understood to be, in particular, devices that can be used in or for use in reactors for chemical and / or physical treatment steps.

[0014] A further object of the invention is to provide reactors, conduits, and other components that are particularly suitable for specific treatment steps in semiconductor manufacturing, especially in wafer production. Examples of such specific treatment steps are plasma etching, chemical etching, and plasma doping.

[0015] Another objective of the invention is to provide light guides, light sources and glass components that are bubble-free or have few bubbles.

[0016] Another objective of the invention is to provide light guides, light sources and components made of glass that exhibit high transparency.

[0017] Another objective of the invention is to provide light guides, light sources and semiconductor devices that have low opacity.

[0018] Another objective of the invention is to provide optical fibers with low attenuation.

[0019] A further object of the invention is to provide light guides, light sources, and components that exhibit high dimensional stability. In particular, it is an object of the invention to provide light guides, light sources, and components that do not deform at high temperatures. Furthermore, it is an object of the invention to provide light guides, light sources, and components that remain dimensionally stable even when large.

[0020] Another objective of the invention is to provide light guides, light sources and components that are tear- and break-resistant.

[0021] Another objective of the invention is to provide light guides, light sources and components that can be manufactured efficiently.

[0022] Another objective of the invention is to provide light guides, light sources and components that can be manufactured cost-effectively.

[0023] Another objective of the invention is to provide light guides, light sources and components whose manufacture does not require lengthy post-treatment steps, such as tempering.

[0024] A further object of the invention is to provide light guides, light sources, and components that exhibit high resistance to temperature changes. In particular, it is an object of the invention to provide light guides, light sources, and components that exhibit low thermal expansion under strong temperature fluctuations.

[0025] Another objective of the invention is to provide light guides, light sources and components that exhibit high viscosity at high temperatures.

[0026] A further objective of the invention is to provide optical fibers, light sources, and components that exhibit high purity and low contamination with foreign atoms. Foreign atoms are understood to be components that were not intentionally introduced.

[0027] It is particularly an object of the invention to provide light guides, light sources and components containing a small amount of metallic impurities, for example Al, Ge, Ti, alkali and alkaline earth metals, Fe, Va, Cr, Cu, W and Mo.

[0028] Another objective of the invention is to provide light guides, light sources and components containing a small amount of dopants.

[0029] A further object of the invention is to provide light guides, light sources, and components that exhibit high homogeneity. Homogeneity of a property or substance is a measure of the uniformity of its distribution within a sample.

[0030] It is a particular object of the invention to provide optical fibers, light sources, and components that exhibit high material homogeneity. Material homogeneity is a measure of the uniformity of the distribution of elements and compounds contained in the optical fiber, light source, or semiconductor device, in particular OH, chlorine, metals, especially aluminum, alkaline earth metals, refractory metals, and dopants.

[0031] Another objective of the invention is to provide light guides, light sources and components that are transparent in the visible range.

[0032] A further object of the invention is to provide light guides, light sources, and components that are colorless. In particular, it is an object of the invention to provide light guides, light sources, and components that do not exhibit any absorbing stripes. It is also a particular object of the invention to provide light guides, light sources, and components that do not exhibit any colored stripes.

[0033] A further object of the invention is to provide light guides, light sources, and components that exhibit a low tendency to devitrify at elevated temperatures. A further object of the invention is to provide light guides, light sources, and components that have no or only a few crystallization nuclei.

[0034] A further object of the invention is to provide a quartz glass body suitable for use in light guides, light sources and quartz glass components, and which at least partially solves at least one, preferably several, of the problems already described.

[0035] A further object of the invention is to provide a quartz glass body with a straight shape. In particular, it is an object to provide a quartz glass body with a small bending radius. In particular, it is a further object to provide a quartz glass body with a high curl parameter.

[0036] Another task is to provide a quartz glass body in which the migration of cations is as low as possible.

[0037] Another task is to provide a quartz glass body that exhibits high homogeneity over the entire length of the quartz glass body.

[0038] In particular, it is an object of the invention to provide a quartz glass body which has a high refractive index homogeneity over the entire length of the quartz glass body.

[0039] In particular, it is an object of the invention to provide a quartz glass body which has a high homogeneity of viscosity over the entire length of the quartz glass body.

[0040] In particular, it is an object of the invention to provide a quartz glass body which has a high degree of material homogeneity over the entire length of the quartz glass body.

[0041] In particular, it is an object of the invention to provide a quartz glass body which has a high optical homogeneity over the entire length of the quartz glass body.

[0042] A further objective is to provide a quartz glass body exhibiting high symmetry, in particular a uniformly round cross-sectional shape. A further objective is to provide a quartz glass body having a uniform surface. In particular, it is an object of the invention to provide a quartz glass body free of depressions, such as notches or craters, and free of raised areas, such as dents or ridges.

[0043] Another task is to provide a quartz glass body that has a low OH content.

[0044] It is a further objective to provide a quartz glass body having a low content of metallic impurities. In particular, it is an objective of the invention to provide quartz glass bodies having a low alkaline earth metal content. It is a further objective to provide a quartz glass body having no or a very low proportion of tungsten impurities.

[0045] Another challenge is to provide a quartz glass body that contains no or very little molybdenum impurities.

[0046] In particular, it is an object of the invention to provide a quartz glass body which has no or a very low proportion of crystallization nuclei.

[0047] Another objective of the invention is to provide a quartz glass body that has a high surface purity.

[0048] A further object of the invention is to provide a method by which quartz glass bodies can be produced, by means of which at least some of the problems already described are at least partially solved.

[0049] Another objective of the invention is to provide a method by which quartz glass bodies can be manufactured more easily.

[0050] Another objective of the invention is to provide a method by which quartz glass bodies can be produced continuously.

[0051] A further object of the invention is to provide a method by which quartz glass bodies can be produced by a continuous melting and shaping process.

[0052] A further object of the invention is to provide a method by which quartz glass bodies can be formed at a higher speed.

[0053] Another object of the invention is to provide a method by which quartz glass bodies can be produced with low waste.

[0054] A further object of the invention is to provide a method by which prefabricated quartz glass bodies can be manufactured.

[0055] Another objective of the invention is to provide an automated method for manufacturing quartz glass bodies.

[0056] A further object of the invention is to provide a method for the production of quartz glass bodies in which silicon dioxide granules can be processed in a melting furnace without having to be subjected beforehand to a targeted compaction step, e.g. by a temperature treatment of more than 1000 °C.

[0057] In particular, it is an object of the invention to provide a method for the production of quartz glass bodies in which a silicon dioxide granulate with a BET of 20 m² / g or more can be introduced into a melting furnace, melted and processed into a quartz glass body.

[0058] A further object of the invention is to provide a method for the production of quartz glass bodies in which the introduction of particles and foreign atoms from the furnace, in particular from the crucible, is low.

[0059] A further object of the invention is to provide a method by which a quartz glass body can be produced while avoiding particle contamination from the crucible.

[0060] A further object of the invention is to provide a method for producing quartz glass bodies in which little or no silicon dioxide is deposited as sublimate on the edge or lid of the crucible. A further object of the invention is to provide a method for producing quartz glass bodies in which little or no refractory metals are deposited as sublimate on the edge or lid of the crucible.

[0061] In particular, it is an object of the invention to provide a method for the production of quartz glass bodies in which little or no silicon dioxide sublimate is introduced into the melt.

[0062] A further object of the invention is to provide a method for producing quartz glass bodies in which the deposition of impurities from the crucible interior on the surface of silicon dioxide material during melting is prevented.

[0063] A further object of the invention is to provide a method for the production of quartz glass bodies in which a hygroscopic silicon dioxide granulate can be processed without reducing the service life of the crucibles, in particular without causing crucible corrosion.

[0064] A further object of the invention is to provide a method for the production of quartz glass bodies in which a chlorinated silicon dioxide granulate can be processed without reducing the service life of the crucibles, in particular without causing crucible corrosion. Preferred embodiments of the invention

[0065] The independent claims contribute to at least partially fulfilling at least one of the aforementioned tasks. The dependent claims provide preferred embodiments that contribute to at least partially fulfilling at least one of the tasks.

[0066] 1111 A method for producing a quartz glass body according to claim 1.

[0067] 1121 The method according to embodiment |11|, wherein the crucible is heated by means of a resistive or an inductive heater. Preferably, the energy input into the crucible, in particular for melting a material to be melted, is not effected by heating the crucible or a material to be melted therein by means of a flame, such as a burner flame directed into or onto the crucible. The combination of crucible and material to be melted is also not heated by means of a flame.

[0068] |14| The method according to one of the embodiments ∥11| to 12 |, wherein the gas is supplied through openings of a distributor ring arranged in the crucible, the distributor ring being positioned above the molten glass.

[0069] 1151 The method according to one of the embodiments ∥11| to |14|, wherein the gas is guided from the gas inlet along the crucible wall to the gas outlet.

[0070] 1161 The method according to one of the embodiments |11| to |15|, wherein the gas is selected from the group consisting of hydrogen, nitrogen, helium, neon, argon, krypton, xenon and a combination of two or more thereof.

[0071] 1171 The method according to one of embodiments 1111 to 1161, comprising the following process step: iv. Forming a hollow body with at least one opening from the quartz glass body.

[0072] 1201 The method according to one of the foregoing embodiments comprising at least one of the following features: A] an OH content of less than 500 ppm, for example less than 400 ppm, particularly preferably less than 300 ppm; B] a chlorine content of less than 60 ppm, preferably less than 40 ppm, for example less than 40 ppm or less than 2 ppm or less than 0.5 ppm, particularly preferably less than 0.1 ppm; C] an aluminum content of less than 200 ppb, for example less than 100 ppb, particularly preferably less than 80 ppb; D] an ODC content of less than 5 × 10¹⁵ / cm³, for example in a range of 0.1 × 10¹⁵ to 3 × 10¹⁵ / cm³, particularly preferably in a range of 0.5 × 10¹⁵ to 2.0 × 10¹⁵ / cm³; E] a metal content of metals other than aluminium of less than 1 ppm, for example less than 0.5 ppm, particularly preferably less than 0.1 ppm;F] a viscosity (p=1013 hPa) in a range from logio (η (1250°C) / dPas) = ​​11.4 to logio (η (1250°C) / dPas) = ​​12.9 or logio (η (1300°C) / dPas) = ​​11.1 to logio (η (1300°C) / dPas) = ​​12.2 or logio (η (1350°C) / dPas) = ​​10.5 to logio (η (1350°C) / dPas) = ​​11.5; G] a standard deviation of the OH content of not more than 10%, based on the OH content A] of the quartz glass body; H] a standard deviation of the chlorine content of not more than 10%, based on the chlorine content B] of the quartz glass body; I] a standard deviation of the aluminium content of not more than 10%, based on the aluminium content C] of the quartz glass body; J] a refractive index homogeneity of less than 10⁻⁴; K] a cylindrical shape; L] a tungsten content of less than 1000 ppb; M] a molybdenum content of less than 1000 ppb; where ppb and ppm are each based on the total weight of the quartz glass body.

[0073] |21| A method for manufacturing an optical fiber comprising the following steps: A / Performing the process steps i.) to iii.) according to claim 1 obtaining a quartz glass body, wherein the quartz glass body is optionally first processed into a hollow body with at least one opening; B / Inserting one or more core rods into the hollow body through the at least one opening; C / Drawing the hollow body provided with the core rods into a light guide under heat.

[0074] |22| A method for manufacturing a light source comprising the following steps (i) Performing the process steps i.) to iii.) according to claim 1 to obtain a quartz glass body, wherein the quartz glass body is optionally first processed into a hollow body; (ii) optionally equipping the hollow body with electrodes; (iii) filling the hollow body with a gas.

[0075] |23| A method for producing a shaped body comprising the following steps: (1) Carrying out the process steps i.) to iii.) according to claim 1 to obtain a quartz glass body; (2) Shaping the quartz glass body to obtain the shaped body. General

[0076] In this description, range specifications also include values ​​referred to as limits. A specification of the type "in the range from X to Y" with respect to a quantity A therefore means that A can take on the values ​​X, Y, and values ​​between X and Y. Similarly, unilaterally limited ranges of the type "up to Y" for a quantity A mean values ​​Y and less than Y. Detailed description of the invention

[0077] The present invention can be carried out in a furnace (itself not the subject of the invention) comprising a crucible with a crucible wall, wherein the crucible has the following features: (a) a solid feed with an outlet, wherein the outlet of the solid feed is located inside the crucible, (b) a gas inlet and a gas outlet, wherein in the crucible the gas inlet is arranged below the outlet of the solid feed, and wherein the gas outlet is arranged at the same level as or above the outlet of the solid feed.

[0078] The furnace can include a crucible, the crucible comprising a crucible interior and a crucible wall surrounding the crucible interior. Preferably, the crucible also includes a bottom and a top. The crucible wall, and optionally the bottom and top, surround the crucible interior. The crucible is arranged in the furnace such that the bottom bounds the crucible interior downwards, the crucible wall bounds the crucible interior laterally, and the top bounds the crucible interior upwards. In the context of internals and features of the furnace and the crucible, "above," "below," "above," "below," "over," "under," and "at the same level" denote a relative arrangement of the internals and features, describing the position of one feature or internal in relation to another feature or internal with respect to mean sea level (MSL).

[0079] Preferably, the crucible comprises a solid feed with an outlet, the outlet of which is fluidly connected to the interior of the crucible. A solid feed, also referred to as a solid inlet, is an object through which a bulk material, for example, a particulate solid and optionally other substances, such as liquids or gases, can be introduced into the crucible. In principle, the solid feed can have any shape known to those skilled in the art and suitable for passage by a bulk material, for example, pipes, locks, chutes, nozzles, valves, or a vibrating section. The solid feed preferably has an inlet and the outlet already described.

[0080] Preferably, the crucible includes more than one solid feed, for example two or three or four or five or more than five solid feeds.

[0081] The solid feeder can, in principle, consist of any material known to a person skilled in the art and suitable for this purpose. Preferably, the material of the solid feeder includes at least one element selected from the group consisting of quartz glass, plastic, silicone, or combinations of two or more thereof. Particularly preferably, the solid feeder consists essentially of quartz glass.

[0082] Preferably, the crucible further comprises a gas inlet and a gas outlet. Gas can be introduced into the crucible through the gas inlet. Gas can be discharged from the crucible through the gas outlet. The gas inlet can, in principle, have any shape known to a person skilled in the art and suitable for introducing a gas, for example, a nozzle, a valve, or a tube. The gas outlet can, in principle, have any shape known to a person skilled in the art and suitable for discharging a gas, for example, a nozzle, a valve, or a tube.

[0083] According to a preferred embodiment, the crucible comprises more than one gas inlet, for example, two, three, four, five, or more than five gas inlets. According to a preferred embodiment, the crucible comprises more than one gas outlet, for example, two, three, four, five, or more than five gas outlets. Furthermore, it is possible to introduce gas into the crucible interior together with a bulk material via the solid feed.

[0084] In this invention, the gas inlet in the crucible is located below the outlet of the solid feed. Likewise, the gas outlet is arranged at the same level as, or above, the outlet of the solid feed.

[0085] In principle, any solid material can be present in the crucible of the furnace, preferably a solid that can be melted in the crucible. Preferably, silicon dioxide is present in the crucible, at least partially, as a solid. According to a preferred embodiment, the crucible contains a bulk material selected from silicon dioxide granules and quartz glass granules. The bulk material is further characterized by a plurality of particles, for example, with a particle size in the range of 20 µm to about 3 mm, or from 20 to 600 µm, particularly preferably with a particle size in the range of 100 to and including 400 µm.

[0086] According to a preferred embodiment, the gas inlet is arranged in the crucible. Preferably, the gas inlet is arranged in an annular shape within the crucible. Preferably, the annularly arranged gas inlet is positioned above a fill line of the crucible, e.g., in a region of 5 to 50 cm, particularly 5 to 10 cm above the fill line. The fill line is an imaginary or physical marking on the wall of the crucible that is not crossed by either the melt or the bulk material during operation of the crucible. Normally, the gas inlet does not come into contact with either the melt or the bulk material during operation of the crucible.

[0087] The ring-shaped gas inlet is particularly preferably configured as a distribution ring with a gas supply. The distribution ring can have several nozzles as gas outlets, preferably evenly distributed along the ring. For example, the nozzles can be formed as holes in the distribution ring. Preferably, these holes are arranged on the side facing away from the melt. More preferably, the distribution ring can be moved up and down within the crucible. This mobility allows the distribution ring to be positioned so that it never comes into contact with any melt present inside the crucible. Preferably, the distribution ring is positioned in a range of 2 to 20 cm above the surface of the melt, more preferably in a range of 5 to 10 cm above the surface of the melt. More preferably, the distribution ring is supplied via a gas supply leading through the top of the crucible.

[0088] According to a preferred embodiment, the gas inlet is provided in the crucible wall of the melting crucible. In this embodiment, the crucible wall can have holes above the fill line of the melting crucible. On the outside, these holes are fluid-conducting and connected to a gas supply. Preferably, a plurality of holes are arranged at approximately equal intervals above the fill line, distributed around the perimeter of the crucible wall. Preferably, the distance between two holes is in the range of 2 to 10 cm. Furthermore, the holes can also be arranged on several levels in the crucible wall above the fill line.

[0089] According to another preferred embodiment, the crucible has a combination of a distributor ring and a gas inlet in the wall of the crucible.

[0090] According to a further preferred embodiment, the gas outlet of the crucible is located closer to the crucible wall than to the solid feed. Preferably, the ratio of the distance of the gas outlet to the crucible wall and the distance of the gas outlet to the solid feed is in the range of 1:2 to 1:8, for example, 1:2 to 1:6, or 1:2 to 1:4.

[0091] Preferably, the distance between the gas outlet and the crucible wall is in the range of 0 to 5 cm, 2 to 10 cm, 1 to 5 cm, or 1 to 20 cm. The distance between the gas outlet and the solid feed is preferably greater; for example, for a gas outlet at a distance of 5 cm from the crucible wall, the distance between the gas outlet and the solid feed is up to 50 cm, up to 40 cm, or in the range of 5 to 30 cm.

[0092] According to a further preferred embodiment, the crucible additionally has a top surface. In this case, the gas outlet can be provided on the top surface of the crucible. Preferably, the top surface is a crucible lid. According to a further preferred embodiment, the gas outlet is provided in the wall of the crucible. Particularly preferably, the gas outlet is arranged at the upper end of the wall. In both of the aforementioned embodiments, it is particularly preferred that the gas inlet and gas outlet are arranged such that a gas flow from the gas inlet to the gas outlet can sweep across the crucible wall from bottom to top.

[0093] According to another preferred embodiment, the gas outlet is arranged in an annular shape within the furnace. Preferably, the crucible wall, or the crucible top, or both, have holes serving as gas outlets. On the outside of the crucible, these holes are fluid-conducting and connected to a gas path guide.

[0094] The crucible can, in principle, consist of any material known to those skilled in the art and suitable for melting silicon dioxide. Preferably, the crucible contains a sintered material, for example, a sintered metal. Sintered metals are understood to be metals or alloys obtained by sintering metal powders. Preferably, the crucible contains at least one element selected from the group consisting of refractory metals. Refractory metals are understood to be the metals of group 4 (Ti, Zr, Hf), group 5 (V, Nb, Ta), and group 6 (Cr, Mo, W). Preferably, the crucible contains at least one sintered metal selected from the group consisting of molybdenum, tungsten, or a combination thereof. More preferably, the crucible contains at least one further refractory metal, particularly preferably rhenium, osmium, iridium, ruthenium, or a combination of two or more thereof.

[0095] Preferably, the crucible comprises an alloy of molybdenum with a refractory metal, or tungsten with a refractory metal. Particularly preferred alloying metals are rhenium, osmium, iridium, ruthenium, or a combination of two or more thereof. According to another example, the crucible comprises an alloy of molybdenum with tungsten, rhenium, osmium, iridium, ruthenium, or a combination of two or more thereof. For example, the crucible comprises an alloy of tungsten with molybdenum, rhenium, osmium, iridium, ruthenium, or a combination of two or more thereof.

[0096] Preferably, the crucible material can be coated with a refractory metal. According to a preferred example, the sheet metal of the crucible is coated with rhenium, osmium, iridium, ruthenium, molybdenum, or tungsten, or a combination of two or more thereof.

[0097] Preferably, the crucible material and the coating have different compositions. For example, a molybdenum sheet is coated with one or more layers of rhenium, osmium, iridium, ruthenium, tungsten, or any combination of two or more of these. According to another example, a tungsten sheet is coated with one or more layers of rhenium, osmium, iridium, ruthenium, molybdenum, or any combination of two or more of these. According to yet another example, the sheet of the crucible can be made of rhenium-alloyed molybdenum or rhenium-alloyed tungsten and coated on the inside of the crucible with one or more layers comprising rhenium, osmium, iridium, ruthenium, or any combination of two or more of these.

[0098] According to a further preferred embodiment, the crucible has no coating on the surface facing the melt, selected from a material containing rhenium, iridium, osmium, or a combination thereof. Therefore, an additional coating of the crucible on the surface facing the melt is unnecessary.

[0099] The crucible can be a sheet metal crucible or a sintered crucible. A sheet metal crucible is understood to be a crucible containing at least one rolled sheet. Preferably, a sheet metal crucible has several rolled sheets. A suspended sheet metal crucible is understood to be a sheet metal crucible of the type described above, which is suspended in a furnace. A sintered crucible is understood to be a crucible made of a sintered material containing at least one sintered metal and having a density of no more than 96% of the theoretical density of the metal. Sintered metals are understood to be metals or alloys obtained by sintering metal powders. The sintered material and the sintered metal in a sintered crucible are not rolled.

[0100] Preferably, the sintering material of the sintering crucible has a density of 85% or more of the theoretical density of the sintering material, for example a density of 85% to 95% or of 90% to 94%, particularly preferably of 91% to 93%.

[0101] Preferably, the sheet metal of the crucible has a density of 95% or more of its theoretical density, for example, a density of 95% to 98% or 96% to 98%. Higher theoretical densities are even more preferred, particularly in the range of 98% to 99.95%. The theoretical density of a material corresponds to the density of a pore-free and 100% dense material. A density of the sheet metal of the crucible of more than 95% of its theoretical density can be obtained, for example, by sintering a sintered metal and subsequently densifying the sintered material. A particularly preferred method is to produce a crucible by sintering a sintered metal, rolling it to obtain a sheet, and then processing the sheet into a crucible.

[0102] The crucible can, in principle, be heated in any way known to a person skilled in the art and deemed suitable. For example, the crucible can be heated by electric heating elements (resistive heating) or by induction. In resistive heating, the energy is coupled in by radiation, whereby the solid surface is heated from the outside and transfers the energy to its inner surface. In inductive heating, the energy is coupled directly into the side wall of the crucible via coils and transferred from there to the inside of the crucible. Preferably, the crucible is heated inductively.

[0103] Preferably, the energy input into the crucible, in particular for melting a material to be melted, is not achieved by heating the crucible, or a material to be melted in it, or both, by means of a flame, such as a burner flame directed into or onto the crucible.

[0104] The crucible can have one or more heating zones, for example, one, two, or more than three heating zones, preferably one, two, or three heating zones, and particularly preferably one heating zone. The heating zones of the sintering crucible can be heated to the same or different temperatures. For example, all heating zones can be heated to the same temperature, all heating zones to different temperatures, or two or more heating zones to the same temperature and one or more heating zones to different temperatures independently of each other. Preferably, all heating zones are heated to different temperatures; for example, the temperature of the heating zones increases in the direction of material transport of the silicon dioxide granules. The temperatures of the heating zones can be controlled, for example, by the type and arrangement of the heating elements or by the positioning of the crucible in the furnace.

[0105] Preferably, the crucible has an outlet through which at least a portion of the melt formed in the crucible can be withdrawn. Preferably, the outlet of the crucible is a nozzle formed from a nozzle material. Preferably, the nozzle material comprises a pre-compacted material, for example, with a density in the range of more than 95%, for example, from 98 to 100%, particularly preferably from 99 to 99.999%, in each case based on the theoretical density of the nozzle material. Preferably, the nozzle material comprises a refractory metal, for example, molybdenum, tungsten, or a combination thereof with a refractory metal, particularly preferably molybdenum. Preferably, a nozzle containing molybdenum can have a density of 100% of the theoretical density.

[0106] The crucible is particularly suitable for the formation of glass melts.

[0107] The subject matter of the present invention relates to a method for producing a quartz glass body as specified in claim 1.

[0108] Preferably, the process according to the invention, in particular the introduction of bulk material and gas in step i) and the formation of the glass melt in step ii), is carried out in the previously described, non-inventive furnace. A so-called vertical furnace is further preferred. This means that the material is transported from a solid feed point of the furnace to a glass melt outlet essentially along the vertical direction. In this case, the solid feed point and the glass melt outlet are arranged relative to each other such that an imaginary straight line connecting the solid feed point and the glass melt outlet forms an angle with the vertical direction of no more than 30°. Step i.)

[0109] According to the invention, in step i.) A), at least one bulk material is first provided and introduced into a furnace containing a melting crucible via a solid feed. The bulk material is selected according to the invention from the group consisting of silicon dioxide granules and quartz glass granules, or a combination of both.

[0110] The silicon dioxide granules can be obtained through the following process steps: I. Providing a silicon dioxide powder; and II. Processing the silicon dioxide powder into a silicon dioxide granulate, wherein the silicon dioxide granulate has a larger particle diameter than the silicon dioxide powder, wherein the processing preferably produces a silicon dioxide granulate with granules having a spherical morphology; wherein the processing is further preferably carried out by spray granulation or roll granulation.

[0111] A powder is defined as particles of dry solid substances with a primary particle size in the range of 1 to less than 100 nm.

[0112] Silicon dioxide granules can be obtained by granulating silicon dioxide powder. Silicon dioxide granules typically have a BET surface area of ​​3 m² / g or more and a density of less than 1.5 g / cm³. Granulation refers to the process of converting powder particles into granules. During granulation, several silicon dioxide powder particles clump together, forming larger agglomerates known as "silicon dioxide granules." These are often also referred to as "silicon dioxide granule particles" or "granule particles." Collectively, the granules form a granulate; for example, the silicon dioxide granules form a "silicon dioxide granulate." The silicon dioxide granules have a larger particle diameter than the silicon dioxide powder.

[0113] The process of granulation, to convert a powder into granules, will be explained in more detail later.

[0114] In this context, silicon dioxide granules are understood to be silicon dioxide particles obtainable by comminuting a silicon dioxide body, in particular a quartz glass body. Silicon dioxide granules typically have a density of more than 1.2 g / cm³, for example in the range of 1.2 to 2.2 g / cm³, and particularly preferably of about 2.2 g / cm³. More preferably, the BET surface area of ​​silicon dioxide granules is typically less than 1 m² / g, determined according to DIN ISO 9277:2014-01.

[0115] In principle, all silicon dioxide particles suitable for a person skilled in the art are suitable. Silicon dioxide granules and silicon dioxide grains are preferred.

[0116] A particle diameter or particle size is understood to be the diameter of a particle, which is defined as "area equivalent circular diameter x Ai" according to the formula x Ai = 4 A i π This results in Ai, where Ai represents the area of ​​the particle under consideration in an image analysis. Suitable methods for determining this value include, for example, ISO 13322-1:2014 or ISO 13322-2:2009. Comparative statements such as "larger particle diameter" always mean that the referenced values ​​were determined using the same method. silicon dioxide powder

[0117] Within the scope of the present invention, it is in principle possible to obtain silicon dioxide powder from naturally occurring or synthetically produced silicon dioxide. Synthetic silicon dioxide powder is preferably used; pyrogenic silicon dioxide powder is particularly preferred.

[0118] The silicon dioxide powder can be any silicon dioxide powder containing at least two particles. Any manufacturing process known to a person skilled in the art and suitable for the present purpose is acceptable.

[0119] According to a preferred embodiment of the present invention, the silicon dioxide powder is produced as a by-product in the manufacture of quartz glass, particularly in the production of so-called soot bodies. Silicon dioxide of such origin is often also referred to as "soot dust".

[0120] A preferred source of silicon dioxide powder is silicon dioxide particles obtained during the synthetic production of soot bodies using flame hydrolysis burners. In the production of a soot body, a rotating carrier tube with a cylindrical surface is moved back and forth in a reversing motion along a row of burners. Oxygen and hydrogen, as well as the starting materials for the formation of primary silicon dioxide particles, can be supplied to the flame hydrolysis burners as burner gases. The primary silicon dioxide particles preferably have a primary particle size of up to 100 nm. The primary silicon dioxide particles produced by flame hydrolysis aggregate or agglomerate to form silicon dioxide particles with particle sizes of approximately 9 µm (DIN ISO 13320:2009-1).The primary silicon dioxide particles within the silicon dioxide particles can be identified by scanning electron microscopy, allowing their shape and size to be determined. A portion of the silicon dioxide particles are deposited onto the cylindrical surface of the rotating carrier tube. In this way, the soot body is built up layer by layer. Another portion of the silicon dioxide particles is not deposited onto the cylindrical surface of the carrier tube but is collected as dust, for example, in a filter system. This remaining portion of silicon dioxide particles forms the silicon dioxide powder, often referred to as "soot dust." Generally, the portion of silicon dioxide particles deposited on the carrier tube is larger than the portion of silicon dioxide particles collected as soot dust during soot body production, based on the total weight of the silicon dioxide particles.

[0121] Nowadays, soot dust is usually disposed of as waste in a complex and costly manner, or used without added value as filler, e.g., in road construction, as additives in the dye industry, as a raw material for tile production, and for the production of hexafluorosilicic acid, which is used for the repair of building foundations. In the case of the present invention, it is suitable as a starting material and can be processed into a high-quality product.

[0122] Silicon dioxide produced by flame hydrolysis is usually referred to as pyrogenic silicon dioxide. Pyrogenic silicon dioxide typically exists in the form of amorphous silicon dioxide primary particles or silicon dioxide particles.

[0123] According to a preferred embodiment, the silicon dioxide powder can be produced from a gas mixture by flame hydrolysis. In this case, the silicon dioxide particles are also formed in the flame hydrolysis and removed as silicon dioxide powder before agglomerates or aggregates form. Here, the silicon dioxide powder, previously referred to as soot dust, is the main product.

[0124] Siloxanes, silicon alkoxides, and inorganic silicon compounds are preferably suitable as starting materials for the formation of the silicon dioxide powder. Siloxanes are defined as linear and cyclic polyalkylsiloxanes. Preferably, polyalkylsiloxanes have the general formula Si p O p R 2p , where p is an integer of at least 2, preferably 2 to 10, particularly preferably 3 to 5, and R is an alkyl group with 1 to 8 carbon atoms, preferably 1 to 4 carbon atoms, particularly preferably a methyl group.

[0125] Siloxanes selected from the group consisting of hexamethyldisiloxane, hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4), and decamethylcyclopentasiloxane (D5), or a combination of two or more thereof, are particularly preferred. If the siloxane comprises D3, D4, and D5, D4 is preferably the main component. The main component is preferably present in a proportion of at least 70 wt.%, more preferably at least 80 wt.%, for example at least 90 wt.% or at least 94 wt.%, and particularly preferably at least 98 wt.%, in each case based on the total amount of silicon dioxide powder. Preferred silicon alkoxides are tetramethoxysilane and methyltrimethoxysilane. Preferred inorganic silicon compounds as starting material for silicon dioxide powder are silicon halides, silicates, silicon carbide, and silicon nitride. Silicon tetrachloride and trichlorosilane are particularly preferred as inorganic silicon compounds as starting material for silicon dioxide powder.

[0126] According to a preferred embodiment, the silicon dioxide powder can be produced from a compound selected from the group consisting of siloxanes, silicon alkoxides and silicon halides.

[0127] Preferably, the silicon dioxide powder is produced from a compound selected from the group consisting of hexamethyldisiloxane, hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane and decamethylcyclopentasiloxane, tetramethoxysilane and methyltrimethoxysilane, silicon tetrachloride and trichlorosilane or a combination of two or more of these, for example silicon tetrachloride and octamethylcyclotetrasiloxane, particularly preferably octamethylcyclotetrasiloxane.

[0128] Several parameters are important for the formation of silicon dioxide from silicon tetrachloride by flame hydrolysis. A preferred composition of a suitable gas mixture includes an oxygen content of 25 to 40 vol% during flame hydrolysis. The hydrogen content can be in the range of 45 to 60 vol%. The silicon tetrachloride content is preferably in the range of 5 to 30 vol%, all of the aforementioned vol% based on the total volume of the gas stream. A combination of the aforementioned volume fractions for oxygen, hydrogen, and SiCl₄ is further preferred. The flame in the flame hydrolysis preferably has a temperature in the range of 1500 to 2500 °C, for example, in the range of 1600 to 2400 °C, and particularly preferably in the range of 1700 to 2300 °C.Preferably, the primary silicon dioxide particles formed in flame hydrolysis are removed as silicon dioxide powder before agglomerates or aggregates form.

[0129] According to the invention, the silicon dioxide powder has at least one, for example at least two or at least three or at least four, particularly preferably at least five of the following features: a. a BET surface area in the range of 20 to 60 m² / g, for example 25 to 55 m² / g, or 30 to 50 m² / g, particularly preferably 20 to 40 m² / g; b. a bulk density of 0.01 to 0.3 g / cm³, for example in the range of 0.02 to 0.2 g / cm³, preferably in the range of 0.03 to 0.15 g / cm³; c. a carbon content of less than 50 ppm, for example less than 40 ppm or less than 30 ppm, particularly preferably in the range of 1 ppb to 20 ppm; d. a chlorine content of less than 200 ppm, for example less than 150 ppm or less than 100 ppm, particularly preferably in the range of 1 ppb to 80 ppm; e. an aluminum content of less than 200 ppb, for example in the range of 1 to 100 ppb, particularly preferably in the range of 1 to 80 ppb; f. a total content of metals other than aluminum of less than 5 ppm, for example of less than 2 ppm, particularly preferably in the range of 1 ppb to 1 ppm; g.at least 70 wt.% of the powder particles have a primary particle size in the range of 10 to less than 100 nm, for example in the range of 15 to less than 100 nm, particularly preferably in the range of 20 to less than 100 nm; h. a tapped density in the range of 0.001 to 0.3 g / cm³, for example in the range of 0.002 to 0.2 g / cm³ or from 0.005 to 0.1 g / cm³, preferably in the range of 0.01 to 0.06 g / cm³, also preferably in the range of 0.1 to 0.2 g / cm³, or in the range of 0.15 to 0.2 g / cm³; i. a residual moisture content of less than 5 wt.%, for example in the range of 0.25 to 3 wt.%, particularly preferably in the range of 0.5 to 2 wt.%; j. a particle size distribution D 10 in the range of 1 to 7 µm, for example in the range of 2 to 6 µm or in the range of 3 to 5 µm, particularly preferably in the range of 3.5 to 4.5 µm; k.a particle size distribution D 50 in the range of 6 to 15 µm, for example in the range of 7 to 13 µm or in the range of 8 to 11 µm, particularly preferably in the range of 8.5 to 10.5 µm; l. a particle size distribution D 90 in the range of 10 to 40 µm, for example in the range of 15 to 35 µm, particularly preferably in the range of 20 to 30 µm; . where the wt.%, ppm and ppb are each based on the total weight of the silicon dioxide powder.

[0130] The silicon dioxide powder contains silicon dioxide. Preferably, the silicon dioxide powder contains silicon dioxide in an amount of more than 95% by weight, for example, in an amount of more than 98% by weight, or more than 99% by weight, or more than 99.9% by weight, in each case based on the total weight of the silicon dioxide powder. Particularly preferably, the silicon dioxide powder contains silicon dioxide in an amount of more than 99.99% by weight, based on the total weight of the silicon dioxide powder.

[0131] Preferably, the silicon dioxide powder has a metal content of metals other than aluminum of less than 5 ppm, for example, less than 2 ppm, and particularly preferably less than 1 ppm, in each case based on the total weight of the silicon dioxide powder. Often, however, the silicon dioxide powder has a content of metals other than aluminum in an amount of at least 1 ppb. Such metals include, for example, sodium, lithium, potassium, magnesium, calcium, strontium, germanium, copper, molybdenum, tungsten, titanium, iron, and chromium. These can be present, for example, as elements, as ions, or as part of a molecule, an ion, or a complex.

[0132] Preferably, the silicon dioxide powder has a total content of other components of less than 30 ppm, for example, less than 20 ppm, particularly preferably less than 15 ppm, the ppm values ​​being based on the total weight of the silicon dioxide powder. Often, however, the silicon dioxide powder contains other components in an amount of at least 1 ppb. Other components are understood to be all components of the silicon dioxide powder that do not belong to the following group: silicon dioxide, chlorine, aluminum, OH groups.

[0133] In this context, the listing of a component, if that component is a chemical element, means that it can exist as an element or as an ion in a compound or salt. For example, the term "aluminum" includes not only metallic aluminum but also aluminum salts, aluminum oxides, and aluminum metal complexes. Similarly, the term "chlorine" includes not only elemental chlorine but also chlorides such as sodium chloride and hydrogen chloride. Often, the other components are in the same state of matter as the substance in which they are contained.

[0134] In this context, the specification of a component, when that component is a chemical compound or a functional group, means that the component can exist in the stated form, as a charged chemical compound, or as a derivative of that chemical compound. For example, the specification of the chemical substance ethanol includes not only ethanol but also ethanolates, such as sodium ethoxide. The specification "OH group" also includes silanol, water, and metal hydroxides. For example, the specification "derivative" for acetic acid also includes acetic acid esters and acetic anhydride.

[0135] Preferably, at least 70% of the silicon dioxide powder particles, based on the total number of powder particles, have a primary particle size of less than 100 nm, for example in the range of 10 to 100 nm or 15 to 100 nm, and particularly preferably in the range of 20 to 100 nm. The primary particle size is determined by dynamic light scattering according to ISO 13320:2009-10.

[0136] Preferably, at least 75% of the silicon dioxide powder particles, based on the number of powder particles, have a primary particle size of less than 100 nm, for example in the range of 10 to 100 nm or 15 to 100 nm, and particularly preferably in the range of 20 to 100 nm.

[0137] Preferably, at least 80% of the silicon dioxide powder particles, based on the number of powder particles, have a primary particle size of less than 100 nm, for example in the range of 10 to 100 nm or 15 to 100 nm, and particularly preferably in the range of 20 to 100 nm.

[0138] Preferably, at least 85% of the silicon dioxide powder particles, based on the number of powder particles, have a primary particle size of less than 100 nm, for example in the range of 10 to 100 nm or 15 to 100 nm, and particularly preferably in the range of 20 to 100 nm.

[0139] Preferably, at least 90% of the silicon dioxide powder particles, based on the number of powder particles, have a primary particle size of less than 100 nm, for example in the range of 10 to 100 nm or 15 to 100 nm, and particularly preferably in the range of 20 to 100 nm.

[0140] Preferably, at least 95% of the silicon dioxide powder particles, based on the number of powder particles, have a primary particle size of less than 100 nm, for example in the range of 10 to 100 nm or 15 to 100 nm, and particularly preferably in the range of 20 to 100 nm.

[0141] Preferably, the silicon dioxide powder has a particle size D10 in the range of 1 to 7 µm, for example in the range of 2 to 6 µm or in the range of 3 to 5 µm, particularly preferably in the range of 3.5 to 4.5 µm. Preferably, the silicon dioxide powder has a particle size D50 in the range of 6 to 15 µm, for example in the range of 7 to 13 µm or in the range of 8 to 11 µm, particularly preferably in the range of 8.5 to 10.5 µm. Preferably, the silicon dioxide powder has a particle size D90 in the range of 10 to 40 µm, for example in the range of 15 to 35 µm, particularly preferably in the range of 20 to 30 µm.

[0142] Preferably, the silicon dioxide powder has a specific surface area (BET surface area) in the range of 20 to 60 m² / g, for example 25 to 55 m² / g, or 30 to 50 m² / g, particularly preferably 20 to 40 m² / g. The BET surface area is determined according to the Brunauer, Emmet and Teller method (BET) based on DIN 66132 and is based on gas absorption at the surface to be measured.

[0143] Preferably, the silicon dioxide powder has a pH value of less than 7, for example in the range of 3 to 6.5 or 3.5 to 6 or 4 to 5.5, particularly preferably in the range of 4.5 to 5. The pH value can be determined using a single-rod measuring electrode (4% silicon dioxide powder in water).

[0144] The silicon dioxide powder preferably has the combination of features a. / b. / c. or a. / b. / f. or a. / b. / g., more preferably the combination of features a. / b. / c. / f. or a. / b. / c. / g. or a. / b. / f. / g., and particularly preferably the combination of features a. / b. / c. / f. / g.

[0145] The silicon dioxide powder preferably has the combination of features a. / b. / c., wherein the BET surface area is in a range of 20 to 40 m² / g, the bulk density is in a range of 0.05 to 0.3 g / mL and the carbon content is less than 40 ppm.

[0146] The silicon dioxide powder preferably has the combination of features a. / b. / f., wherein the BET surface area is in a range of 20 to 40 m² / g, the bulk density is in a range of 0.05 to 0.3 g / mL and the total content of metals other than aluminium is in a range of 1 ppb to 1 ppm.

[0147] The silicon dioxide powder preferably has the combination of features a. / b. / g., wherein the BET surface area is in a range of 20 to 40 m² / g, the bulk density is in a range of 0.05 to 0.3 g / mL and at least 70 wt.% of the powder particles have a primary particle size in a range of 20 to less than 100 nm.

[0148] The silicon dioxide powder further preferably exhibits the combination of features a. / b. / c. / f., wherein the BET surface area is in a range of 20 to 40 m² / g, the bulk density is in a range of 0.05 to 0.3 g / mL, the carbon content is less than 40 ppm, and the total content of metals other than aluminum is in a range of 1 ppb to 1 ppm.

[0149] The silicon dioxide powder further preferably exhibits the combination of features a. / b. / c. / g., wherein the BET surface area is in a range of 20 to 40 m² / g, the bulk density is in a range of 0.05 to 0.3 g / mL, the carbon content is less than 40 ppm, and at least 70 wt.% of the powder particles have a primary particle size in a range of 20 to less than 100 nm.

[0150] The silicon dioxide powder further preferably exhibits the combination of features a. / b. / f. / g., wherein the BET surface area is in a range of 20 to 40 m² / g, the bulk density is in a range of 0.05 to 0.3 g / mL, the total content of metals other than aluminium is in a range of 1 ppb to 1 ppm, and at least 70 wt.% of the powder particles have a primary particle size in a range of 20 to less than 100 nm.

[0151] The silicon dioxide powder particularly preferably exhibits the combination of features a. / b. / c. / f. / g., wherein the BET surface area is in the range of 20 to 40 m² / g, the bulk density is in the range of 0.05 to 0.3 g / mL, the carbon content is less than 40 ppm, the total content of metals other than aluminum is in the range of 1 ppb to 1 ppm, and at least 70 wt.% of the powder particles have a primary particle size in the range of 20 to less than 100 nm. Step II.

[0152] According to a preferred embodiment of the second subject matter of the invention, the silicon dioxide powder is processed in step II into silicon dioxide granules, wherein the silicon dioxide granules have a larger particle diameter than the silicon dioxide powder. In principle, all methods known to those skilled in the art that lead to an increase in particle diameter are suitable for this purpose.

[0153] The silicon dioxide granules have a particle diameter that is larger than the particle diameter of the silicon dioxide powder. Preferably, the particle diameter of the silicon dioxide granules is in the range of 500 to 50,000 times larger than the particle diameter of the silicon dioxide powder, for example 1,000 to 10,000 times larger, and particularly preferably 2,000 to 8,000 times larger.

[0154] Preferably, at least 90% of the silicon dioxide granules provided in step i.) are formed from pyrogenically produced silicon dioxide powder, for example at least 95 wt.% or at least 98 wt.%, particularly preferably at least 99 wt.% or more, in each case based on the total weight of the silicon dioxide granules.

[0155] According to a preferred embodiment of the second subject matter of the invention, the silicon dioxide granules used have at least one, preferably at least two or at least three or at least four, particularly preferably all of the following features: A) a BET surface area in the range of 20 m² / g to 50 m² / g; B) a mean particle size in the range of 50 to 500 µm; C) a bulk density in the range of 0.5 to 1.2 g / cm³, for example in the range of 0.6 to 1.1 g / cm³, particularly preferably in the range of 0.7 to 1.0 g / cm³; D) a carbon content of less than 50 ppm; E) an aluminum content of less than 200 ppb; F) a tapped density in the range of 0.7 to 1.2 g / cm³; G) a pore volume in the range of 0.1 to 2.5 mL / g, for example in the range of 0.15 to 1.5 mL / g; particularly preferably in a range of 0.2 to 0.8 mL / g; H) an angle of repose in a range of 23 to 26°; I) a particle size distribution D 10 in a range of 50 to 150 µm; J) a particle size distribution D 50 in a range of 150 to 300 µm; K) a particle size distribution D 90 in a range of 250 to 620 µm, where ppm and ppb are each based on the total weight of the silicon dioxide granules.

[0156] Preferably, the silicon dioxide granules have a spherical morphology. A spherical morphology is defined as a round to oval shape of the particles. The silicon dioxide granules preferably have a mean sphericity in the range of 0.7 to 1.3 SPHT3, for example, a mean sphericity in the range of 0.8 to 1.2 SPHT3, and particularly preferably a mean sphericity in the range of 0.85 to 1.1 SPHT3. The SPHT3 characteristic is described in the test methods.

[0157] Furthermore, the silicon dioxide granules preferably exhibit a mean symmetry in the range of 0.7 to 1.3 Symm3, for example, a mean symmetry in the range of 0.8 to 1.2 Symm3, and particularly preferably a mean symmetry in the range of 0.85 to 1.1 Symm3. The characteristic of the mean symmetry Symm3 is described in the test methods.

[0158] Preferably, the silicon dioxide granules have a metal content of metals other than aluminum of less than 1000 ppb, for example, less than 500 ppb, and particularly preferably less than 100 ppb, in each case based on the total weight of the silicon dioxide granules. Often, however, the silicon dioxide granules have a metal content of metals other than aluminum in an amount of at least 1 ppb. Often, the silicon dioxide granules have a metal content of metals other than aluminum of less than 1 ppm, preferably in the range of 40 to 900 ppb, for example, in the range of 50 to 700 ppb, and particularly preferably in the range of 60 to 500 ppb, in each case based on the total weight of the silicon dioxide granules. Such metals are, for example, sodium, lithium, potassium, magnesium, calcium, strontium, germanium, copper, molybdenum, titanium, iron, and chromium.These can exist, for example, as an element, as an ion, or as part of a molecule, an ion, or a complex.

[0159] The silicon dioxide granules may contain other components, for example, in the form of molecules, ions, or elements. Preferably, the silicon dioxide granules contain less than 500 ppm, for example, less than 300 ppm, and particularly preferably less than 100 ppm, of other components, based on the total weight of the silicon dioxide granules. Often, other components are present in an amount of at least 1 ppb. These other components may be selected, in particular, from the group consisting of carbon, fluoride, iodide, bromide, phosphorus, or a mixture of at least two of these.

[0160] Preferably, the silicon dioxide granules contain less than 10 ppm carbon, for example less than 8 ppm or less than 5 ppm, particularly preferably less than 4 ppm, in each case based on the total weight of the silicon dioxide granules. Often, carbon is present in the silicon dioxide granules in an amount of at least 1 ppb.

[0161] Preferably, the silicon dioxide granules contain less than 100 ppm, for example less than 80 ppm, particularly preferably less than 70 ppm, in each case based on the total weight of the silicon dioxide granules, of other components. Often, however, the other components are present in an amount of at least 1 ppb.

[0162] Preferably, Step II includes the following steps: II.1. Providing a liquid; II.2. Mixing the silicon dioxide powder with the liquid to obtain a slurry; II.3. Granulating, preferably spray-drying the slurry.

[0163] For the purposes of the present invention, a liquid is understood to be a substance or a mixture of substances that is liquid at a pressure of 1013 hPa and a temperature of 20 °C.

[0164] A "slurry" within the meaning of the present invention means a mixture of at least two substances, wherein the mixture comprises at least one liquid and at least one solid under the conditions prevailing at the time of consideration.

[0165] In principle, any substance or mixture of substances known to those skilled in the art and suitable for the intended application can be used as the liquid. Preferably, the liquid is selected from the group consisting of organic liquids and water. Preferably, the silicon dioxide powder is soluble in the liquid in an amount of less than 0.5 g / L, more preferably in an amount of less than 0.25 g / L, and most preferably in an amount of less than 0.1 g / L, where g / L is expressed as grams of silicon dioxide powder per liter of liquid.

[0166] Polar solvents are preferably suitable as the liquid. These can be organic liquids or water. Preferably, the liquid is selected from the group consisting of water, methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, and mixtures of more than one of these. Particularly preferably, the liquid is water. Particularly preferably, the liquid contains distilled or deionized water.

[0167] The silicon dioxide powder is preferably processed into a slurry. The silicon dioxide powder is practically insoluble in the liquid at room temperature, but can be introduced into the liquid in high proportions by weight while maintaining the slurry consistency.

[0168] The silicon dioxide powder and the liquid can be mixed in any way. For example, the silicon dioxide powder can be added to the liquid, or the liquid to the silicon dioxide powder. The mixture can be agitated during or after the addition. It is particularly preferred that the mixture be agitated both during and after the addition. Examples of agitation include shaking and stirring, or a combination of both. Preferably, the silicon dioxide powder can be added to the liquid while stirring. More preferably, a portion of the silicon dioxide powder can be added to the liquid, the resulting mixture being agitated, and the mixture then being mixed with the remaining portion of the silicon dioxide powder. Likewise, a portion of the liquid can be added to the silicon dioxide powder, the resulting mixture being agitated, and the mixture then being mixed with the remaining portion of the liquid.

[0169] Mixing the silicon dioxide powder and the liquid produces a slurry. Preferably, the slurry is a suspension in which the silicon dioxide powder is uniformly distributed in the liquid. "Uniformly" means that the density and composition of the slurry at any point do not deviate by more than 10% from the average density and composition, respectively, based on the total amount of slurry. A uniform distribution of the silicon dioxide powder in the liquid can be produced or maintained by agitation as previously described, or both.

[0170] Preferably, the slurry has a density in the range of 1000 to 2000 g / L, for example in the range of 1200 to 1900 g / L or 1300 to 1800 g / L, particularly preferably in the range of 1400 to 1700 g / L. The density is determined by weighing a volume-calibrated container.

[0171] According to a preferred embodiment, the slurry has at least one, for example at least two or at least three or at least four, particularly preferably at least five of the following features: a.) The slurry is transported in contact with a plastic surface; b.) The slurry is sheared; c.) The slurry has a temperature above 0°C, preferably in the range of 5 to 35°C; d.) The slurry has a zeta potential at a pH of 7 in the range of 0 to -100 mA, for example from -20 to -60 mA, particularly preferably from -30 to -45 mA; e.) The slurry has a pH in the range of 7 or more, for example from more than 7 or a pH in the range of 7.5 to 13 or from 8 to 11, particularly preferably from 8.5 to 10; f.) the slurry has an isoelectric point of less than 7, for example in a range of 1 to 5 or in a range of 2 to 4, particularly preferably in a range of 3 to 3.5; g.) the slurry has a solids content of at least 40 wt.%, for example in a range of 50 to 80 wt.%, or in a range of 55 to 75 wt.%.-%, particularly preferably in the range of 60 to 70 wt.%, in each case based on the total weight of the slurry; h.) the slurry has a viscosity according to DIN 53019-1 (5 rpm, 30 wt.%) in the range of 500 to 2000 mPas, for example in the range of 600 to 1700 mPas, particularly preferably in the range of 1000 to 1600 mPas; i.) the slurry has a thixotropy according to DIN SPEC 91143-2 (30 wt.% in water, 23 °C, 5 rpm / 50 rpm) in the range of 3 to 6, for example in the range of 3.5 to 5, particularly preferably in the range of 4.0 to 4.5; j.) The silicon dioxide particles in the slurry, in a 4 wt% slurry, have a mean particle size in suspension according to DIN ISO 13320-1 in the range of 100 to 500 nm, for example in the range of 200 to 300 nm.

[0172] Preferably, the silicon dioxide particles in a 4 wt% aqueous slurry have a particle size D 10 in the range of 50 to 250 nm, particularly preferably in the range of 100 to 150 nm. Preferably, the silicon dioxide particles in a 4 wt% aqueous slurry have a particle size D 50 in the range of 100 to 400 nm, particularly preferably in the range of 200 to 250 nm. Preferably, the silicon dioxide particles in a 4 wt% aqueous slurry have a particle size D 90 in the range of 200 to 600 nm, particularly preferably in the range of 350 to 400 nm. The particle size is determined according to DIN ISO 13320-1.

[0173] The "isoelectric point" is the pH value at which the zeta potential equals zero. The zeta potential is determined according to ISO 13099-2:2012.

[0174] Preferably, the pH of the slurry is adjusted to a value within the range mentioned above. To adjust the pH, substances such as NaOH or NH3, for example as an aqueous solution, can preferably be added to the slurry. The slurry is often agitated during this process. granulation

[0175] Silicon dioxide granules are obtained by granulating silicon dioxide powder. Granulation is the process of converting powder particles into granules. During granulation, larger agglomerates, known as "silicon dioxide granules," form through the clumping of several silicon dioxide powder particles. These are often also referred to as "silicon dioxide particles," "silicon dioxide granule particles," or "granule particles." Collectively, the granules form a granulate; for example, the silicon dioxide granules form a "silicon dioxide granulate."

[0176] In principle, any granulation process known to a person skilled in the art and suitable for granulating silicon dioxide powder can be selected in this case. Granulation processes can be categorized as either build-up granulation or compression granulation, and further as wet or dry granulation. Known methods include roll granulation in a granulating disc, spray granulation, centrifugal atomization, fluidized bed granulation, granulation using a granulating mill, compaction, roller pressing, briquetting, shell production, or extrusion.

[0177] Preferably, a silicon dioxide granulate with granules exhibiting a spherical morphology is formed during processing; the processing is further preferably carried out by spray granulation or roll granulation. More preferably, a silicon dioxide granulate with granules exhibiting a spherical morphology contains at most 50%, preferably at most 40%, more preferably at most 20%, and more preferably between 0 and 50%, between 0 and 40%, or between 0 and 20%, or between 10 and 50%, between 10 and 40%, or between 10 and 20%, the percentage being based on the total number of granules in the granulate. The granules with a spherical morphology exhibit the SPHT3 values ​​already mentioned in this description. Spray drying

[0178] According to a preferred embodiment of the first subject matter of the invention, silicon dioxide granules are obtained by spray granulation of the slurry. Spray granulation is also referred to as spray drying.

[0179] Spray drying is preferably carried out in a spray tower. For spray drying, the slurry is pressurized at an elevated temperature. The pressurized slurry is then depressurized through a nozzle and sprayed into the spray tower. As a result, droplets form, which dry instantly and initially create dry microparticles ("nuclei"). These microparticles, together with a gas stream acting upon them, form a fluidized bed. This keeps them suspended, allowing them to form a surface for the drying of further droplets.

[0180] The nozzle through which the slurry is sprayed into the spray tower preferably forms an inlet into the interior of the spray tower.

[0181] During spraying, the nozzle preferentially has a contact surface with the slurry. The "contact surface" refers to the area of ​​the nozzle that comes into contact with the slurry during spraying. Often, at least part of the nozzle is shaped like a tube through which the slurry is guided during spraying, so that the inside of the hollow tube comes into contact with the slurry.

[0182] The contact surface preferably comprises a glass, a plastic, or a combination thereof. Preferably, the contact surface comprises a glass, particularly preferably quartz glass. Preferably, the contact surface comprises a plastic. In principle, all plastics known to those skilled in the art are suitable, provided they are stable at the process temperatures and do not release any foreign atoms into the slurry. Preferred plastics are polyolefins, for example, homo- or copolymers containing at least one olefin, particularly preferably homo- or copolymers containing polypropylene, polyethylene, polybutadiene, or combinations of two or more thereof.Preferably, the contact surface consists of a glass, a plastic, or a combination thereof, for example, selected from the group consisting of fused silica and polyolefins, particularly preferably selected from the group consisting of fused silica and homo- or copolymers comprising polypropylene, polyethylene, polybutadiene, or combinations of two or more thereof. Preferably, the contact surface does not contain any metals, in particular no tungsten, titanium, tantalum, chromium, cobalt, nickel, iron, vanadium, zirconium, or manganese.

[0183] It is possible, in principle, for the contact surface and the other parts of the nozzle to be made of the same or different materials. Preferably, the other parts of the nozzle contain the same material as the contact surface. It is equally possible for the other parts of the nozzle to contain a different material than the contact surface. For example, the contact surface can be coated with a suitable material, such as glass or plastic.

[0184] Preferably, the nozzle is formed from an element selected from the group consisting of glass, plastic or a combination of glass and plastic for more than 70 wt.%, based on the total weight of the nozzle, for example to more than 75 wt.% or to more than 80 wt.% or to more than 85 wt.% or to more than 90 wt.% or to more than 95 wt.%, particularly preferably to more than 99 wt.%.

[0185] The nozzle preferably comprises a nozzle plate. The nozzle plate is preferably made of glass, plastic, or a combination of glass and plastic. Preferably, the nozzle plate is made of glass, particularly preferably quartz glass. Preferably, the nozzle plate is made of plastic. Preferred plastics are polyolefins, for example, homo- or copolymers containing at least one olefin, particularly preferably homo- or copolymers containing polypropylene, polyethylene, polybutadiene, or combinations of two or more thereof. Preferably, the nozzle plate does not contain any metals, in particular no tungsten, titanium, tantalum, chromium, cobalt, nickel, iron, vanadium, zirconium, or manganese.

[0186] The nozzle preferably comprises a spiral screw. The spiral screw is preferably made of glass, plastic, or a combination of glass and plastic. Preferably, the spiral screw is made of glass, particularly preferably quartz glass. Preferably, the spiral screw is made of plastic. Preferred plastics are polyolefins, for example, homo- or copolymers containing at least one olefin, particularly preferably homo- or copolymers containing polypropylene, polyethylene, polybutadiene, or combinations of two or more thereof. Preferably, the spiral screw does not contain any metals, in particular no tungsten, titanium, tantalum, chromium, cobalt, nickel, iron, vanadium, zirconium, or manganese.

[0187] The nozzle can also comprise further components. Preferred further components are a nozzle body, particularly preferably a nozzle body surrounding the swirl screw and the nozzle plate, a cross piece, and a baffle plate. Preferably, a nozzle comprises one or more, and particularly preferably all, of these further components. In principle, the further components can be made independently of one another from any material known to those skilled in the art and suitable for this purpose, for example, a metal-containing material, glass, or a plastic. Preferably, the nozzle body is made of glass, particularly preferably quartz glass. Preferably, the further components are made of plastic. Preferred plastics are polyolefins, for example, containing homo- or copolymers of at least one olefin, particularly preferably containing homo- or copolymers of polypropylene, polyethylene, polybutadiene, or combinations of two or more thereof.Preferably, the other components do not contain any metals, in particular no tungsten, titanium, tantalum, chromium, cobalt, nickel, iron, vanadium, zirconium and manganese.

[0188] Preferably, the spray tower has a gas inlet and a gas outlet. Gas can be introduced into the interior of the spray tower through the gas inlet and discharged through the gas outlet. It is also possible to introduce gas into the spray tower via the nozzle. Likewise, gas can be discharged through the outlet of the spray tower. Even more preferably, gas can be supplied via the nozzle and a gas inlet of the spray tower and discharged through the outlet of the spray tower.

[0189] Preferably, the interior of the spray tower contains an atmosphere selected from air, an inert gas, at least two inert gases, or a combination of air with at least one inert gas, preferably at least two inert gases. The inert gases are preferably selected from the list consisting of nitrogen, helium, neon, argon, krypton, and xenon. For example, the interior of the spray tower contains air, nitrogen, or argon, most preferably air.

[0190] Preferably, the atmosphere present in the spray tower is part of a gas stream. The gas stream is preferably introduced into the spray tower via a gas inlet and discharged via a gas outlet. It is also possible to introduce parts of the gas stream via the nozzle and discharge parts of the gas stream via a solids outlet. The gas stream can absorb further components in the spray tower. These can originate from the slurry during spray drying and pass into the gas stream.

[0191] Preferably, a dry gas stream is supplied to the spray tower. A dry gas stream is defined as a gas or gas mixture whose relative humidity at the temperature set in the spray tower is below the condensation point. A relative humidity of 100% corresponds to a water content of 17.5 g / m³ at 20°C. The gas is preferably preheated to a temperature in the range of 150 to 450°C, for example, 200 to 420°C or 300 to 400°C, and particularly preferably 350 to 400°C.

[0192] The interior of the spray tower is preferably temperature-controlled. Preferably, the temperature inside the spray tower is up to 550°C, for example 300 to 500°C, particularly preferably 350 to 450°C.

[0193] The gas stream preferably has a temperature at the gas inlet in a range of 150 to 450°C, for example from 200 to 420°C or from 300 to 400°C, particularly preferably from 350 to 400°C.

[0194] At the solids outlet, the gas outlet or both locations, the discharged gas stream preferably has a temperature of less than 170°C, for example 50 to 150°C, particularly preferably 100 to 130°C.

[0195] Preferably, the difference between the temperature of the gas flow at the inlet and the gas flow at the outlet is in a range of 100 to 330°C, for example from 150 to 300°C.

[0196] The silicon dioxide granules obtained in this way exist as an agglomerate of individual silicon dioxide powder particles. The individual silicon dioxide powder particles remain recognizable within the agglomerate. The average particle size of the silicon dioxide powder particles is preferably in the range of 10 to 1000 nm, for example, in the range of 20 to 500 nm, 30 to 250 nm, 35 to 200 nm, 40 to 150 nm, or particularly preferably in the range of 50 to 100 nm. The average particle size of these particles is determined according to DIN ISO 13320-1.

[0197] Spray drying can be carried out in the presence of auxiliary substances. In principle, any substance known to a person skilled in the art and suitable for the intended application can be used as an auxiliary substance. Examples of suitable auxiliary substances include binders. Examples of suitable binders are metal oxides such as calcium oxide, metal carbonates such as calcium carbonate, and polysaccharides such as cellulose, cellulose ethers, starch, and starch derivatives.

[0198] Particularly preferably, spray drying is carried out without auxiliary materials within the scope of the present invention.

[0199] Preferably, a portion of the silicon dioxide granules is separated before, after, or both before and after removal from the spray tower. Any suitable method known to those skilled in the art is suitable for this separation. Preferably, the separation is carried out by screening or sieving.

[0200] Preferably, before removing the silicon dioxide granules formed by spray drying from the spray tower, particles with a particle size of less than 50 µm, for example with a particle size of less than 70 µm, and particularly preferably with a particle size of less than 90 µm, are separated by classifying. Classification is preferably carried out by a cyclone, which is preferably arranged in the lower region of the spray tower, and particularly preferably above the outlet of the spray tower.

[0201] Preferably, after the silicon dioxide granules have been removed from the spray tower, particles with a particle size greater than 1000 µm, for example, with a particle size greater than 700 µm, and particularly preferably with a particle size greater than 500 µm, are separated by sieving. The sieving of the particles can, in principle, be carried out using any method known to those skilled in the art and suitable for this purpose. Preferably, the sieving is carried out using a vibrating trough.

[0202] According to a preferred embodiment, the spray drying of the slurry through a nozzle into a spray tower is characterized by at least one, for example two or three, particularly preferably all of the following features: a] Spray granulation in a spray tower; b] A pressure of the slurry at the nozzle of not more than 40 bar, for example in a range of 1.3 to 20 bar, 1.5 to 18 bar, 2 to 15 bar, or 4 to 13 bar, or particularly preferably in a range of 5 to 12 bar, wherein the pressure is specified absolutely (with respect to p = 0 hPa); c] A temperature of the droplets upon entry into the spray tower in a range of 10 to 50°C, preferably in a range of 15 to 30°C, particularly preferably in a range of 18 to 25°C.d] a temperature on the side of the nozzle facing the spray tower in a range of 100 to 450°C, for example in a range of 250 to 440°C, particularly preferably in a range of 350 to 430°C; e] a flow rate of slurry through the nozzle in a range of 0.05 to 1 m³ / h, for example in a range of 0.1 to 0.7 m³ / h or of 0.2 to 0.5 m³ / h, particularly preferably in a range of 0.25 to 0.4 m³ / h; f] a solids content of the slurry of at least 40 wt.%, for example in a range of 50 to 80 wt.%, or in a range of 55 to 75 wt.%, particularly preferably in a range of 60 to 70 wt.%.-%, in each case based on the total weight of the slurry; g] a gas inflow into the spray tower in a range of 10 to 100 kg / min, for example in a range of 20 to 80 kg / min or of 30 to 70 kg / min, particularly preferably in a range of 40 to 60 kg / min; h] a temperature of the gas stream at the inlet to the spray tower in a range of 100 to 450°C, for example in a range of 250 to 440°C, particularly preferably of 350 to 430°C; i] a temperature of the gas stream at the outlet of the spray tower of less than 170°C; j] the gas is selected from the group consisting of air, nitrogen and helium, or a combination of two or more thereof; preferably air; [k] a residual moisture content of the granules when removed from the spray tower of less than 5 wt.%, for example less than 3 wt.% or less than 1 wt.% or in a range of 0.01 to 0.5 wt.%, particularly preferably in a range of 0.1 to 0.3 wt.%.-%, in each case based on the total weight of the silicon dioxide granules produced during spray drying; l] at least 50 wt.% of the spray granules, based on the total weight of the silicon dioxide granules produced during spray drying, undergoes a flight time in the range of 1 to 100 s, for example over a period of 10 to 80 s, particularly preferably over a period of 25 to 70 s; [m] at least 50 wt.% of the spray granules, based on the total weight of the silicon dioxide granules produced during spray drying, travels a distance of more than 20 m, for example more than 30 or more than 50 or more than 70 or more than 100 or more than 150 or more than 200 or in a range of 20 to 200 m or from 10 to 150 or from 20 to 100, particularly preferably in a range of 30 to 80 m.n] The spray tower has a cylindrical geometry; o] A height of the spray tower of more than 10 m, for example, more than 15 m, more than 20 m, more than 25 m, more than 30 m, or in a range of 10 to 25 m, particularly preferably in a range of 15 to 20 m; p] Removal of particles with a size of less than 90 µm before the granules are removed from the spray tower; q] Sieving of particles with a size of more than 500 µm after the granules are removed from the spray tower, preferably on a vibrating trough; r] The exit of the droplets of the slurry from the nozzle occurs at an angle of 30 to 60 degrees opposite the vertical direction, particularly preferably at an angle of 45 degrees opposite the vertical direction.

[0203] The direction of gravity is understood to be the direction of the gravity vector.

[0204] The flight path refers to the distance a droplet of the slurry travels from exiting the nozzle through the gas chamber of the spray tower, forming a granule, until the flight and fall process is complete. The flight and fall process typically ends when the granule hits the bottom of the spray tower, or when it collides with other granules already lying on the bottom, whichever occurs first.

[0205] Flight time is the time a granule needs to travel the distance within the spray tower. Preferably, the granules follow a helical trajectory within the spray tower.

[0206] Preferably, at least 60 wt.% of the spray granules, based on the total weight of the silicon dioxide granules produced during spray drying, cover an average flight distance of more than 20 m, for example more than 30 or more than 50 or more than 70 or more than 100 or more than 150 or more than 200 or in a range of 20 to 200 m or from 10 to 150 or from 20 to 100, particularly preferably in a range of 30 to 80 m.

[0207] Preferably, at least 70 wt.% of the spray granules, based on the total weight of the silicon dioxide granules produced during spray drying, cover an average flight distance of more than 20 m, for example more than 30 or more than 50 or more than 70 or more than 100 or more than 150 or more than 200 or in a range of 20 to 200 m or from 10 to 150 or from 20 to 100, particularly preferably in a range of 30 to 80 m.

[0208] Preferably, at least 80 wt.% of the spray granules, based on the total weight of the silicon dioxide granules produced during spray drying, cover an average flight distance of more than 20 m, for example more than 30 or more than 50 or more than 70 or more than 100 or more than 150 or more than 200 or in a range of 20 to 200 m or from 10 to 150 or from 20 to 100, particularly preferably in a range of 30 to 80 m.

[0209] Preferably, at least 90 wt.% of the spray granules, based on the total weight of the silicon dioxide granules produced during spray drying, cover an average flight distance of more than 20 m, for example more than 30 or more than 50 or more than 70 or more than 100 or more than 150 or more than 200 or in a range of 20 to 200 m or from 10 to 150 or from 20 to 100, particularly preferably in a range of 30 to 80 m. Roll granulation

[0210] According to a preferred embodiment of the second subject matter of the invention, a silicon dioxide granulate is obtained by roll granulation of the slurry.

[0211] Roll granulation is achieved by stirring the slurry in the presence of a gas at elevated temperature. Preferably, roll granulation takes place in a mixing vessel equipped with a stirring tool. Preferably, the mixing vessel rotates in the opposite direction to the stirring tool. The mixing vessel also preferably has an inlet through which silicon dioxide powder can be introduced, an outlet through which silicon dioxide granules can be removed, a gas inlet, and a gas outlet.

[0212] A pin swirler is preferably used for stirring the slurry. A pin swirler is understood to be a stirring tool equipped with several elongated pins, the longitudinal axes of which are each coaxial with the axis of rotation of the stirring tool. The movement of the pins preferably describes coaxial circles around the axis of rotation.

[0213] Preferably, the slurry is adjusted to a pH of less than 7, for example to a pH in the range of 2 to 6.5, particularly preferably to a pH in the range of 4 to 6. An inorganic acid is preferably used to adjust the pH, for example an acid selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid, particularly preferably hydrochloric acid.

[0214] Preferably, the stirred tank contains an atmosphere selected from air, an inert gas, at least two inert gases, or a combination of air with at least one inert gas, preferably at least two inert gases. The inert gases are preferably selected from the list consisting of nitrogen, helium, neon, argon, krypton, and xenon. For example, the stirred tank contains air, nitrogen, or argon, with air being particularly preferred.

[0215] Preferably, the atmosphere present in the stirred tank is part of a gas stream. The gas stream is preferably introduced into the stirred tank via the gas inlet and discharged via the gas outlet. The gas stream can absorb further components within the stirred tank. These can originate from the slurry during roll granulation and pass into the gas stream.

[0216] Preferably, a dry gas stream is supplied to the stirred vessel. A "dry gas stream" is understood to be a gas or gas mixture whose relative humidity at the temperature set in the stirred vessel is below the condensation point. The gas is preferably preheated to a temperature in the range of 50 to 300°C, for example, 80 to 250°C, and particularly preferably 100 to 200°C.

[0217] Preferably, 10 to 150 m³ of gas per hour are introduced into the stirred tank for every 1 kg of slurry used, for example 20 to 100 m³ of gas per hour, particularly preferably 30 to 70 m³ of gas per hour.

[0218] The gas stream dries the slurry during stirring, forming silicon dioxide granules. The resulting granules are then removed from the stirring chamber.

[0219] Preferably, the extracted granules are further dried. Drying is preferably continuous, for example in a rotary kiln. Preferred drying temperatures are in the range of 80 to 250°C, for example in the range of 100 to 200°C, and particularly preferably in the range of 120 to 180°C.

[0220] In the context of the present invention, "continuous" with regard to a process means that the process can be operated continuously. This means that the supply and removal of substances and materials involved in the process can take place continuously during the execution of the process. It is not necessary to interrupt the process for this purpose.

[0221] Continuous as an attribute of an object, e.g. in reference to a "continuous furnace", means that this object is designed in such a way that a process or process step taking place in it can be carried out continuously.

[0222] The granules obtained by roll granulation can be sieved. Sieving can be carried out before or after drying. Sieving before drying is preferred. Preferably, granules with a particle size of less than 50 µm, for example, with a particle size of less than 80 µm, and particularly preferably with a particle size of less than 100 µm, are sieved. More preferably, granules with a particle size of more than 900 µm, for example, with a particle size of more than 700 µm, and particularly preferably with a particle size of more than 500 µm, are sieved. The sieving of larger particles can, in principle, be carried out using any method known to those skilled in the art and suitable for this purpose. Preferably, larger particles are sieved using a vibrating trough.

[0223] According to a preferred embodiment, roll granulation is characterized by at least one, for example two or three, particularly preferably all of the following features: [a] Granulation takes place in a rotating stirred vessel; [b] Granulation takes place under a gas flow of 10 to 150 kg of gas per hour and per 1 kg of slurry; [c] The gas temperature at introduction is 40 to 200°C; [d] Granules with a particle size of less than 100 µm and more than 500 µm are sieved off; [e] The granules formed have a residual moisture content of 15 to 30 wt.%; [f] The granules formed are dried at 80 to 250°C, preferably in a continuous drying tube, particularly preferably to a residual moisture content of less than 1 wt.%.

[0224] The silicon dioxide granules obtained by granulation, preferably by spray or roll granulation, also referred to as silicon dioxide granules I, are preferably treated before being processed into quartz glass bodies. This pretreatment can serve various purposes, either facilitating processing into quartz glass bodies or influencing the properties of the resulting quartz glass bodies. For example, the silicon dioxide granules I can be compacted, purified, surface-modified, or dried.

[0225] Preferably, the silicon dioxide granules I can be subjected to a thermal, mechanical or chemical treatment or a combination of two or more treatments, yielding a silicon dioxide granule 11. chemical

[0226] According to a preferred embodiment of the second subject matter of the invention, the silicon dioxide granules I have a carbon content wC(1). The carbon content wC(1) is preferably less than 50 ppm, for example in the range of less than 40 ppm or less than 30 ppm, particularly preferably in the range of 1 ppb to 20 ppm, in each case based on the total weight of the silicon dioxide granules I.

[0227] According to a preferred embodiment of the second subject matter of the invention, the silicon dioxide granules I comprise at least two particles. Preferably, the at least two particles can move relative to each other. In principle, all measures known to those skilled in the art and deemed suitable are suitable for generating this relative movement. Mixing is particularly preferred. Mixing can, in principle, be carried out in any manner. Preferably, a continuous furnace is selected for this purpose. Accordingly, the at least two particles can preferably move relative to each other by being moved in a continuous furnace, for example, a rotary kiln.

[0228] Continuous furnaces are defined as furnaces in which the loading and unloading of the furnace, the so-called charging process, is continuous. Examples of continuous furnaces include rotary kilns, roller kilns, conveyor belt kilns, drive-through kilns, and pusher kilns. Rotary kilns are preferably used for the treatment of silicon dioxide granules I.

[0229] According to a preferred embodiment of the second subject matter of the invention, silicon dioxide granules I are treated with a reactant to obtain silicon dioxide granules II. This treatment is carried out to alter the concentration of certain substances in the silicon dioxide granules. The silicon dioxide granules I may contain impurities or certain functionalities whose proportion is to be reduced, such as OH groups, carbon-containing compounds, transition metals, alkali metals, and alkaline earth metals. The impurities and functionalities may originate from the starting material or be introduced during the process. The treatment of the silicon dioxide granules I can serve various purposes. For example, the use of treated silicon dioxide granules I, i.e., silicon dioxide granules II, can simplify the processing of the silicon dioxide granules into quartz glass bodies.Furthermore, this selection allows the properties of the resulting quartz glass bodies to be tailored. For example, the silicon dioxide granules I can be purified or surface-modified. The treatment of the silicon dioxide granules I can therefore be used to improve the properties of the resulting quartz glass bodies.

[0230] Preferably, a gas or a combination of several gases is suitable as the reactant. This is also referred to as a gas mixture. In principle, all gases known to those skilled in the art that are known for the treatment mentioned and appear suitable can be used. Preferably, a gas selected from the group consisting of HCl, Cl₂, F₂, O₂, O₃, H₂, C₂F₄, C₂F₆, HClO₄, air, inert gas, e.g., N₂, He, Ne, Ar, Kr, or combinations of two or more thereof is used. Preferably, the treatment is carried out in the presence of a gas or a combination of two or more gases. Preferably, the treatment is carried out in a countercurrent or cocurrent gas flow.

[0231] Preferably, the reactant is selected from the group consisting of HCl, Cl₂, F₂, O₂, O₃, or combinations of two or more thereof. Preferably, mixtures of two or more of the aforementioned gases are used to treat silicon dioxide granules I. The presence of F, Cl, or both allows the removal of metals present as impurities in the silicon dioxide granules I, such as transition metals, alkali metals, and alkaline earth metals. Under the process conditions, these metals can form gaseous compounds with components of the gas mixture, which are subsequently carried away and thus no longer present in the granules. Furthermore, the OH content in the silicon dioxide granules I can preferably be reduced by treating the silicon dioxide granules I with these gases.

[0232] Preferably, a gas mixture of HCl and Cl₂ is used as the reactant. Preferably, the gas mixture has an HCl content in the range of 1 to 30 vol%, for example, in the range of 2 to 15 vol%, and particularly preferably in the range of 3 to 10 vol%. Also preferably, the gas mixture has a Cl₂ content in the range of 20 to 70 vol%, for example, in the range of 25 to 65 vol%, and particularly preferably in the range of 30 to 60 vol%. The remaining 100 vol% can be made up of one or more inert gases, e.g., N₂, He, Ne, Ar, Kr, or air. Preferably, the proportion of inert gas in reactants is in a range of 0 to less than 50 vol.%, for example in a range of 1 to 40 vol.% or 5 to 30 vol.%, particularly preferably in a range of 10 to 20 vol.%, in each case based on the total volume of the reactant.

[0233] O 2 , C 2 F 2 , or mixtures thereof with Cl 2 are preferably used for the purification of silicon dioxide granules I, which has been produced from a siloxane or a mixture of several siloxanes.

[0234] The reactant, in the form of a gas or gas mixture, is preferably contacted with the silicon dioxide granules as a gas stream or as part of a gas stream with a throughput in the range of 50 to 2000 L / h, for example in the range of 100 to 1000 L / h, and particularly preferably in the range of 200 to 500 L / h. A preferred embodiment of the contacting process is contact between the gas stream and the silicon dioxide granules in a continuous furnace, for example a rotary kiln. Another preferred embodiment of the contacting process is a fluidized bed process.

[0235] Treating silicon dioxide granules I with the reactant yields silicon dioxide granules II with a carbon content wC(2). The carbon content wC(2) of silicon dioxide granules II is lower than the carbon content wC(1) of silicon dioxide granules I, based on the total weight of the respective silicon dioxide granules. Preferably, wC(2) is 0.5 to 99% lower than wC(1), for example, by 20 to 80% or 50 to 95%, and particularly preferably by 60 to 99%. thermal

[0236] Preferably, the silicon dioxide granules 1 are additionally subjected to thermal or mechanical treatment, or a combination of these treatments. One or more of these additional treatments can be carried out before or during treatment with the reactant. Alternatively or additionally, the additional treatment can also be carried out on silicon dioxide granules II. The general term "silicon dioxide granules" used below includes the alternatives "silicon dioxide granules I" and "silicon dioxide granules II". Likewise, it is possible to carry out the treatments described below on both "silicon dioxide granules I" and the treated silicon dioxide granules I, the "silicon dioxide granules II".

[0237] The treatment of silicon dioxide granules can serve various purposes. For example, this treatment facilitates the processing of the silicon dioxide granules into fused silica bodies. The treatment can also influence the properties of the resulting fused silica bodies. For example, the silicon dioxide granules can be compacted, purified, surface-modified, or dried. This can reduce the specific surface area (BET). Similarly, the bulk density and mean particle size can increase due to agglomeration of silicon dioxide particles. Thermal treatment can be performed dynamically or statically.

[0238] In principle, all furnaces in which the silicon dioxide granules can be thermally treated and moved during the process are suitable for dynamic thermal treatment. Continuous furnaces are preferred for dynamic thermal treatment.

[0239] A preferred mean residence time of the silicon dioxide granules during dynamic thermal treatment is quantity-dependent. Preferably, the mean residence time of the silicon dioxide granules during dynamic thermal treatment is in the range of 10 to 180 min, for example, in the range of 20 to 120 min or 30 to 90 min. Particularly preferably, the mean residence time of the silicon dioxide granules during dynamic thermal treatment is in the range of 30 to 90 min.

[0240] In the case of a continuous process, a batch is defined as a specific portion of a stream of silicon dioxide granules, e.g., one gram, one kilogram, or one ton, for determining the residence time. The start and end of the residence period are determined by the input and output from the continuous furnace operation.

[0241] Preferably, the throughput of the silicon dioxide granules in a continuous dynamic thermal treatment process is in the range of 1 to 50 kg / h, for example in the range of 5 to 40 kg / h or 8 to 30 kg / h. Particularly preferably, the throughput is in the range of 10 to 20 kg / h.

[0242] In the case of a discontinuous process for dynamic thermal treatment, the treatment time results from the period between loading and subsequent unloading of the furnace.

[0243] In the case of a discontinuous dynamic thermal treatment process, the throughput is in the range of 1 to 50 kg / h, for example, in the range of 5 to 40 kg / h or 8 to 30 kg / h. A particularly preferred throughput is in the range of 10 to 20 kg / h. The throughput can be achieved by treating a batch of a specific quantity for one hour. According to another embodiment, the throughput can be achieved by processing a number of batches per hour, where, for example, the quantity of a batch corresponds to the throughput per hour divided by the number of batches. The treatment time then corresponds to the fraction of an hour resulting from 60 minutes divided by the number of batches per hour.Preferably, the dynamic thermal treatment of the silicon dioxide granules takes place at an oven temperature of at least 500°C, for example in the range of 510 to 1700°C or from 550 to 1500°C or from 580 to 1300°C, particularly preferably in the range of 600 to 1200°C.

[0244] The oven chamber typically maintains the specified temperature. Preferably, this temperature deviates by less than 10% above or below the specified temperature, based on the entire treatment time and the entire length of the oven, both at any point during the treatment and at any point within the oven.

[0245] Alternatively, a continuous process of dynamic thermal treatment of the silicon dioxide granules at different furnace temperatures can be carried out. For example, the furnace can maintain a constant temperature throughout the treatment time, with the temperature varying in sections along the length of the furnace. These sections can be of equal or different lengths. In this case, a temperature that increases from the furnace inlet to the furnace outlet is preferred. Preferably, the temperature at the inlet is at least 100°C lower than at the outlet, for example, 150°C lower, 200°C lower, 300°C lower, or 400°C lower. More preferably, the temperature at the outlet is at least 500°C, for example, in the range of 510 to 1700°C, 550 to 1500°C, or 580 to 1300°C, and particularly preferably in the range of 600 to 1200°C.Preferably, the inlet temperature is at least 300°C, for example, 400 to 1000°C, 450 to 900°C, 500 to 800°C, 550 to 750°C, and particularly preferably 600 to 700°C. Furthermore, any of the aforementioned temperature ranges at the furnace inlet can be combined with any of the aforementioned temperature ranges at the furnace outlet. Preferred combinations of furnace inlet and outlet temperature ranges are: Oven inlet temperature range [°C] Oven outlet temperature range [°C] 400 - 1000 510 - 1300 450 - 900 550 - 1260 480 - 850 580 - 1200 500 - 800 600 - 1100 530 - 750 630 - 1050

[0246] For the static thermal treatment of silicon dioxide granules, crucibles arranged in a furnace are preferably used. Sintered crucibles or sheet metal crucibles are suitable. Rolled sheet metal crucibles made of several riveted plates are preferred. Suitable crucible materials include, for example, refractory metals, in particular tungsten, molybdenum, and tantalum. The crucibles can also be made of graphite or, in the case of crucibles made of refractory metals, lined with graphite foil. Silicon dioxide crucibles are also preferred. Silicon dioxide crucibles are particularly preferred.

[0247] The average residence time of the silicon dioxide granules during static thermal treatment is quantity-dependent. Preferably, the average residence time of the silicon dioxide granules during static thermal treatment with a quantity of 20 kg of silicon dioxide granules is in the range of 10 to 180 min, for example in the range of 20 to 120 min, and particularly preferably in the range of 30 to 90 min.

[0248] Preferably, the static thermal treatment of the silicon dioxide granules is carried out at an oven temperature of at least 800°C, for example in the range of 900 to 1700°C or from 950 to 1600°C or from 1000 to 1500°C or from 1050 to 1400°C, particularly preferably in the range of 1100 to 1300°C.

[0249] Preferably, the static thermal treatment of the silicon dioxide granules I is carried out at a constant oven temperature. The static thermal treatment can also be carried out at a varying oven temperature. Preferably, in this case, the temperature increases during the course of the treatment, wherein the temperature at the beginning of the treatment is at least 50°C lower than at the end, for example, 70°C lower, 80°C lower, 100°C lower, or 110°C lower, and wherein the temperature at the end is preferably at least 800°C, for example, in the range of 900 to 1700°C, 950 to 1600°C, 1000 to 1500°C, or 1050 to 1400°C, particularly preferably in the range of 1100 to 1300°C. mechanically

[0250] According to a further preferred embodiment, the silicon dioxide granules I can be mechanically treated. This mechanical treatment can be carried out to increase the bulk density. The mechanical treatment can be combined with the previously described thermal treatment. Mechanical treatment prevents the agglomerates in the silicon dioxide granules, and thus the average particle size of the individual treated silicon dioxide granules, from becoming too large. An increase in the size of the agglomerates can complicate further processing or have adverse effects on the properties of the quartz glass bodies produced by the inventive method, or a combination of both effects. Furthermore, mechanical treatment of the silicon dioxide granules promotes uniform contact between the surfaces of the individual silicon dioxide granules and the gas(es).This is achieved particularly through a combination of simultaneous mechanical and chemical treatment with one or more gases. This can improve the effectiveness of the chemical treatment.

[0251] The mechanical treatment of the silicon dioxide granules can be carried out by moving two or more silicon dioxide granules in relative motion to each other, for example by rotating the tube of a rotary kiln.

[0252] Preferably, the silicon dioxide granules I are chemically, thermally, and mechanically treated. In particular, the silicon dioxide granules I undergo simultaneous chemical, thermal, and mechanical treatment.

[0253] During chemical treatment, the impurity content of the silicon dioxide granules I is reduced. For this purpose, the silicon dioxide granules I can be treated in a rotary kiln at elevated temperature under a chlorine- and oxygen-containing atmosphere. Any water present in the silicon dioxide granules I evaporates, and organic materials react to form CO and CO₂. Metal impurities can be converted into volatile, chlorine-containing compounds.

[0254] The silicon dioxide granules I are preferably treated in a chlorine- and oxygen-containing atmosphere in a rotary kiln at a temperature of at least 500°C, preferably in a temperature range of 550 to 1300°C, 600 to 1260°C, 650 to 1200°C, or 700 to 1000°C, and particularly preferably in a temperature range of 700 to 900°C. The chlorine-containing atmosphere contains, for example, HCl or Cl₂ or a combination of both. This treatment reduces the carbon content.

[0255] Furthermore, alkali and iron impurities are preferably reduced. A reduction in the number of OH groups is also preferably achieved. At temperatures below 700°C, long treatment times may be required; at temperatures above 1100°C, there is a risk that the pores of the granules will close, trapping chlorine or gaseous chlorine compounds.

[0256] It is also preferable to carry out several chemical treatment steps sequentially, each with simultaneous thermal and mechanical treatment. For example, silicon dioxide granules I can first be treated in a chlorine-containing atmosphere and then in an oxygen-containing atmosphere. The resulting low concentrations of carbon, hydroxyl groups, and chlorine facilitate the melting of silicon dioxide granules II.

[0257] According to a further preferred embodiment, step II.2) is characterized by at least one, for example at least two or at least three, particularly preferably by a combination of all of the following features: N1) the reactant contains HCl, Cl₂ or a combination thereof; N2) the treatment is carried out in a rotary kiln; N3) the treatment is carried out at a temperature in the range of 600 to 900°C; N4) the reactant forms a countercurrent; N5) the reactant has a gas flow in the range of 50 to 2000 L / h, preferably 100 to 1000 L / h, particularly preferably 200 to 500 L / h; N6) the reactant has a volume fraction of inert gas in the range of 0 to less than 50 vol.%.

[0258] Preferably, the silicon dioxide granules I have a particle diameter that is larger than the particle diameter of the silicon dioxide powder. Preferably, the particle diameter of the silicon dioxide granules I is up to 300 times larger than the particle diameter of the silicon dioxide powder, for example, up to 250 times larger, up to 200 times larger, up to 150 times larger, up to 100 times larger, up to 50 times larger, up to 20 times larger, or up to 10 times larger, and particularly preferably 2 to 5 times larger.

[0259] The silicon dioxide granules obtained in this way are also referred to as silicon dioxide granules II. Silicon dioxide granules II are particularly preferably obtained from silicon dioxide granules I in a rotary kiln by means of a combination of thermal, mechanical, and chemical treatment.

[0260] The silicon dioxide granules provided in step i.) are preferably selected from the group consisting of silicon dioxide granules I, silicon dioxide granules II and a combination thereof.

[0261] "Silicon dioxide granules I" refers to silicon dioxide granules produced by granulating silicon dioxide powder obtained through the pyrolysis of silicon compounds in a fuel gas flame. The preferred fuel gases are oxyhydrogen gas, natural gas, or methane gas; oxyhydrogen gas is particularly preferred.

[0262] "Silicon dioxide granules II" refers to silicon dioxide granules produced by post-treatment of silicon dioxide granules I. These post-treatments can involve chemical, thermal, and / or mechanical processes. This is described in detail in the section on the preparation of the silicon dioxide granules (process step II of the second subject matter of the invention).

[0263] The silicon dioxide granules provided in step i.) are particularly preferably silicon dioxide granules I. Silicon dioxide granules I have at least one, for example at least two, at least three, or at least four, and particularly preferably at least five of the following features: [A] a BET surface area in the range of 20 to 50 m² / g, for example in the range of 20 to 40 m² / g; particularly preferably in the range of 25 to 35 m² / g; wherein the micropore fraction preferably amounts to a BET surface area in the range of 4 to 5 m² / g; for example in the range of 4.1 to 4.9 m² / g; particularly preferably in the range of 4.2 to 4.8 m² / g; [B] a mean particle size in the range of 180 to 300 µm; [C] a bulk density in the range of 0.5 to 1.2 g / cm³, for example in the range of 0.6 to 1.1 g / cm³, particularly preferably in the range of 0.7 to 1.0 g / cm³; [D] a carbon content of less than 50 ppm, for example less than 40 ppm or less than 30 ppm or less than 20 ppm or less than 10 ppm, particularly preferably in a range of 1 ppb to 5 ppm;[E] an aluminum content of less than 200 ppb, preferably less than 100 ppb, for example less than 50 ppb or from 1 to 200 ppb or from 15 to 100 ppb, particularly preferably in a range of 1 to 50 ppb. [F] a tapped density in a range of 0.5 to 1.2 g / cm³, for example in a range of 0.6 to 1.1 g / cm³, particularly preferably in a range of 0.75 to 1.0 g / cm³; [G] a pore volume in a range of 0.1 to 1.5 mL / g, for example in a range of 0.15 to 1.1 mL / g;particularly preferably in a range of 0.2 to 0.8 mL / g, [H] a chlorine content of less than 200 ppm, preferably less than 150 ppm, for example less than 100 ppm, or less than 50 ppm, or less than 1 ppm, or less than 500 ppb, or less than 200 ppb, or in a range of 1 ppb to less than 200 ppm, or from 1 ppb to 100 ppm, or from 10 ppb to 500 ppb, or from 10 ppb to 200 ppb, particularly preferably from 1 ppb to 80 ppb; [I] Metal content of metals other than aluminium, of less than 1000 ppb, preferably in a range of 1 to 900 ppb, for example in a range of 1 to 700 ppb, particularly preferably in a range of 1 to 500 ppb; [J] a residual moisture content of less than 10 wt.%, preferably in a range of 0.01 wt.% to 5 wt.%, for example from 0.02 to 1 wt.%, particularly preferably from 0.03 to 0.5 wt.%; ; where the wt.%, ppm and ppb are each based on the total weight of the silicon dioxide granules I.

[0264] The OH content, also known as hydroxyl group content, refers to the amount of OH groups in a material, for example, in silicon dioxide powder, silicon dioxide granules, or a quartz glass body. The OH content is determined spectroscopically in the infrared by comparing the first and third OH bands.

[0265] The chlorine content refers to the content of elemental chlorine or chloride ions in the silicon dioxide granules, silicon dioxide powder, or quartz glass body.

[0266] The term "aluminium content" refers to the amount of elemental aluminum or aluminum ions in the silicon dioxide granules, silicon dioxide powder, or quartz glass body.

[0267] Preferably, the silicon dioxide granules I have a micropore content in a range of 4 to 5 m² / g, for example in a range of 4.1 to 4.9 m² / g; particularly preferably in a range of 4.2 to 4.8 m² / g.

[0268] The silicon dioxide granules I preferably have a density in the range of 2.1 to 2.3 g / cm 3< , particularly preferably in the range of 2.18 to 2.22 g / cm 3< .

[0269] The silicon dioxide granules I preferably have a mean particle size in the range of 180 to 300 µm, for example in the range of 220 to 280 µm, particularly preferably in the range of 230 to 270 µm.

[0270] The silicon dioxide granules I preferably have a particle size D 50 in the range of 150 to 300 µm, for example in the range of 180 to 280 µm, particularly preferably in the range of 220 to 270 µm. Furthermore, the silicon dioxide granules I preferably have a particle size D 10 in the range of 50 to 150 µm, for example in the range of 80 to 150 µm, particularly preferably in the range of 100 to 150 µm. Furthermore, the silicon dioxide granules I preferably have a particle size D 90 in the range of 250 to 620 µm, for example in the range of 280 to 550 µm, particularly preferably in the range of 300 to 450 µm.

[0271] The silicon dioxide granules I preferably have the combination of features [A] / [B] / [C] or [A] / [B] / [E] or [A] / [B] / [G], more preferably the combination of features [A] / [B] / [C] / [E] or [A] / [B] / [C] / [G] or [A] / [B] / [E] / [G], and particularly preferably the combination of features [A] / [B] / [C] / [E] / [G].

[0272] The silicon dioxide granules I preferably have the combination of features [A] / [B] / [C], wherein the BET surface area is in a range of 20 to 40 m² / g, the mean particle size is in a range of 180 to 300 µm and the bulk density is in a range of 0.6 to 1.1 g / mL.

[0273] The silicon dioxide granules I preferably have the combination of features [A] / [B] / [E], wherein the BET surface area is in a range of 20 to 40 m² / g, the mean particle size is in a range of 180 to 300 µm and the aluminium content is in a range of 1 to 50 ppb.

[0274] The silicon dioxide granules I preferably have the combination of features [A] / [B] / [G], wherein the BET surface area is in a range of 20 to 40 m² / g, the mean particle size is in a range of 180 to 300 µm and the pore volume is in a range of 0.2 to 0.8 mL / g.

[0275] The silicon dioxide granules I preferably have the combination of features [A] / [B] / [C] / [E], wherein the BET surface area is in a range of 20 to 40 m² / g, the mean particle size is in a range of 180 to 300 µm, the bulk density is in a range of 0.6 to 1.1 g / mL and the aluminium content is in a range of 1 to 50 ppb.

[0276] The silicon dioxide granules I preferably have the combination of features [A] / [B] / [C] / [G], wherein the BET surface area is in a range of 20 to 40 m² / g, the mean particle size is in a range of 180 to 300 µm, the bulk density is in a range of 0.6 to 1.1 g / mL and the pore volume is in a range of 0.2 to 0.8 mL / g.

[0277] The silicon dioxide granules I preferably have the combination of features [A] / [B] / [E] / [G], wherein the BET surface area is in a range of 20 to 40 m² / g, the mean particle size is in a range of 180 to 300 µm, the aluminium content is in a range of 1 to 50 ppb and the pore volume is in a range of 0.2 to 0.8 mL / g.

[0278] The silicon dioxide granules I preferably have the combination of features [A] / [B] / [C] / [E] / [G], wherein the BET surface area is in a range of 20 to 40 m² / g, the mean particle size is in a range of 180 to 300 µm, the bulk density is in a range of 0.6 to 1.1 g / mL, the aluminium content is in a range of 1 to 50 ppb and the pore volume is in a range of 0.2 to 0.8 mL / g.

[0279] Particle size refers to the size of the aggregated particles present in a silicon dioxide powder, slurry, or silicon dioxide granules. Mean particle size is the arithmetic mean of all particle sizes in the specified substance. The D50 value indicates that 50% of the particles, relative to the total number of particles, are smaller than the specified value. The D10 value indicates that 10% of the particles, relative to the total number of particles, are smaller than the specified value. The D90 value indicates that 90% of the particles, relative to the total number of particles, are smaller than the specified value. Particle size is determined using a dynamic image analysis method according to ISO 13322-2:2006-11.

[0280] The silicon dioxide granules provided in step i.) are particularly preferably silicon dioxide granules II. Silicon dioxide granules II have at least one, for example at least two, at least three, or at least four, and particularly preferably at least five of the following features: (A) a BET surface area in the range of 10 to 35 m² / g, for example in the range of 10 to 30 m² / g, particularly preferably in the range of 20 to 30 m² / g; (B) a mean particle size in the range of 100 to 300 µm, for example in the range of 150 to 280 µm or from 200 to 270 µm, particularly preferably in the range of 230 to 260 µm; (C) a bulk density in the range of 0.7 to 1.2 g / cm³, for example in the range of 0.75 to 1.1 g / cm³, particularly preferably in the range of 0.8 to 1.0 g / cm³; (D) a carbon content of less than 5 ppm, for example less than 4.5 ppm or in a range of 1 ppb to 4 ppm, particularly preferably less than 4 ppm; (E) an aluminium content of less than 200 ppb, for example less than 150 ppb or less than 100 ppb or from 1 to 150 ppb or from 1 to 100 ppb, particularly preferably in a range of 1 to 80 ppb;(F) Tapped density in the range of 0.7 to 1.2 g / cm³, for example in the range of 0.75 to 1.1 g / cm³, particularly preferably in the range of 0.8 to 1.0 g / cm³; (G) a pore volume in the range of 0.1 to 2.5 mL / g, for example in the range of 0.2 to 1.5 mL / g; particularly preferably in the range of 0.4 to 1 mL / g; (H) a chlorine content of less than 500 ppm, preferably less than 400 ppm, for example less than 350 ppm or preferably less than 330 ppm or in the range of 1 ppb to 500 ppm or from 10 ppb to 450 ppm, particularly preferably from 50 ppb to 300 ppm; (I) a metal content of metals other than aluminium of less than 1000 ppb, for example in a range of 1 to 400 ppb, particularly preferably in a range of 1 to 200 ppb; (J) a residual moisture content of less than 3 wt.%, for example in a range of 0.001 wt.% to 2 wt.%, particularly preferably from 0.01 to 1 wt.%; where the wt.%, ppm and ppb are each based on the total weight of the silicon dioxide granules II.

[0281] Preferably, the silicon dioxide granules II have a micropore content in a range of 1 to 2 m² / g, for example in a range of 1.2 to 1.9 m² / g, particularly preferably in a range of 1.3 to 1.8 m² / g.

[0282] The silicon dioxide granules II preferably have a density in the range of 0.5 to 2.0 g / cm³, for example from 0.6 to 1.5 g / cm³, and particularly preferably from 0.8 to 1.2 g / cm³. The density is determined according to the method described in the test methods.

[0283] Silicon dioxide granules II preferably have a particle size D 50 in the range of 150 to 250 µm, for example in the range of 180 to 250 µm, particularly preferably in the range of 200 to 250 µm. Silicon dioxide granules II more preferably have a particle size D 10 in the range of 50 to 150 µm, for example in the range of 80 to 150 µm, particularly preferably in the range of 100 to 150 µm. Silicon dioxide granules II more preferably have a particle size D 90 in the range of 250 to 450 µm, for example in the range of 280 to 420 µm, particularly preferably in the range of 300 to 400 µm.

[0284] The silicon dioxide granules II preferably have the combination of features (A) / (B) / (D) or (A) / (B) / (F) or (A) / (B) / (I), more preferably the combination of features (A) / (B) / (D) / (F) or (A) / (B) / (D) / (I) or (A) / (B) / (F) / (I), and particularly preferably the combination of features (A) / (B) / (D) / (F) / (I).

[0285] The silicon dioxide granules II preferably have the combination of features (A) / (B) / (D), wherein the BET surface area is in a range of 10 to 30 m² / g, the mean particle size is in a range of 150 to 280 µm and the carbon content is less than 4 ppm.

[0286] The silicon dioxide granules II preferably have the combination of features (A) / (B) / (F), wherein the BET surface area is in a range of 10 to 30 m² / g, the mean particle size is in a range of 150 to 280 µm and the tapped density is in a range of 0.8 to 1.0 g / mL.

[0287] The silicon dioxide granules II preferably have the combination of features (A) / (B) / (I), wherein the BET surface area is in a range of 10 to 30 m² / g, the mean particle size is in a range of 150 to 280 µm and the metal content of metals other than aluminium is in a range of 1 to 400 ppb.

[0288] The silicon dioxide granules II preferably have the combination of features (A) / (B) / (D) / (F), wherein the BET surface area is in a range of 10 to 30 m² / g, the mean particle size is in a range of 150 to 280 µm, the carbon content is less than 4 ppm and the tapped density is in a range of 0.8 to 1.0 g / mL.

[0289] The silicon dioxide granules II preferably have the combination of features (A) / (B) / (D) / (I), wherein the BET surface area is in a range of 10 to 30 m² / g, the mean particle size is in a range of 150 to 280 µm, the carbon content is less than 4 ppm, and the metal content of metals other than aluminium is in a range of 1 to 400 ppb.

[0290] The silicon dioxide granules II preferably have the combination of features (A) / (B) / (F) / (I), wherein the BET surface area is in a range of 10 to 30 m² / g, the mean particle size is in a range of 150 to 280 µm, the tapped density is in a range of 0.8 to 1.0 g / mL and the metal content of metals other than aluminium is in a range of 1 to 400 ppb.

[0291] The silicon dioxide granules II preferably have the combination of features (A) / (B) / (D) / (F) / (I), wherein the BET surface area is in a range of 10 to 30 m² / g, the mean particle size is in a range of 150 to 280 µm, the carbon content is less than 4 ppm, the tapped density is in a range of 0.8 to 1.0 g / mL and the metal content of metals other than aluminium is in a range of 1 to 400 ppb.

[0292] Quartz glass granules can be obtained by crushing a quartz glass body. Crushing the quartz glass body can, in principle, be carried out by any method known to those skilled in the art and suitable for this purpose. Preferably, the quartz glass body is crushed mechanically or electromechanically. Electromechanical crushing is particularly preferred. Electromechanical crushing is preferably carried out using high-voltage discharge pulses.

[0293] Preferably, the quartz glass body is comminuted into particles with a particle size D 50 in the range of 50 µm to 5 mm. It is preferred to comminute the quartz glass body into quartz glass granules with a particle size D 50 in the range of 50 µm to 500 µm, for example in the range of 75 to 350 µm, particularly preferably in the range of 100 to 250 µm. It is also preferred to comminute the quartz glass body into quartz glass granules with a particle size D 50 in the range of 500 µm to 5 mm, for example in the range of 750 µm to 3.5 mm, particularly preferably in the range of 1 to 2.5 mm.

[0294] In a further embodiment, the quartz glass body is first comminuted electromechanically and then mechanically. Preferably, the electromechanical comminution is carried out as described above. Preferably, the quartz glass body is electromechanically comminuted to particles with a particle size D 50 of at least 2 mm, for example in a range of 2 to 50 mm or 2.5 to 20 mm, particularly preferably in a range of 3 to 5 mm.

[0295] Mechanical comminution is preferably carried out by pressure comminution, impact comminution, blow comminution, shearing or friction, preferably with the aid of crushers or mills, for example with the aid of jaw crushers, roller crushers, cone crushers, impact crushers, hammer crushers, shredders or ball mills, particularly preferably with the aid of jaw crushers or roller crushers.

[0296] The bulk material preferably comprises a combination of silicon dioxide granules and quartz glass granules. Preferred ratios of silicon dioxide granules to quartz glass granules are, for example, 30:70, 50:50, and 70:30, each expressed as a percentage by weight and based on the total weight of the bulk material.

[0297] The bulk material is introduced into the crucible via a solid feeder. Suitable solid feeders include any device known to those skilled in the art and suitable for the present purpose, in particular a filling tube. Preferably, the solid feeder is located approximately in the center of the crucible, with the center being defined as the area enclosed by the crucible wall. Preferably, the solid feeder passes through the top of the crucible. Furthermore, the solid feeder can additionally have one or more airlocks, e.g., a rotary valve or flaps. Particularly preferably, no airlocks are required in the present process. Particularly preferably, a cone of unmelted or partially melted bulk material forms in the crucible when the bulk material is introduced.Preferably, this cone of material is so large that it extends from the surface of the melt in the crucible to the outlet of the solid feed and seals it.

[0298] According to a further preferred embodiment, the solid feeder on the side facing the bulk material during operation has no coating, in particular no coating comprising at least one material selected from the group consisting of rhenium, iridium, osmium, or a combination of two or more thereof.

[0299] According to another preferred embodiment, the solid feeder does not include a glass insert, for example, made of quartz glass. Such an insert can be provided, in particular, inside a solid feeder to prevent contamination of the bulk material with components of the solid feeder, for example, due to corrosion of the material forming the solid feeder. Such an insert is sometimes also referred to as a casing tube.

[0300] In this context, silicon dioxide granules, also referred to as quartz glass granules, are silicon dioxide particles obtained by comminuting a silicon dioxide body, particularly a quartz glass body. Silicon dioxide granules typically have a density greater than 1.2 g / cm³, for example, in the range of 1.2 to 2.2 g / cm³, and particularly preferably of about 2.2 g / cm³. More preferably, the BET surface area of ​​silicon dioxide granules is typically less than 1 m² / g, determined according to DIN ISO 9277:2014-01.

[0301] Preferably, the quartz glass granules have at least one, for example at least two or at least three or at least four, particularly preferably at least five of the following features: I / an OH content of less than 500 ppm, for example less than 400 ppm, particularly preferably less than 300 ppm; II / a chlorine content of less than 60 ppm, preferably less than 40 ppm, for example less than 40 ppm or less than 2 ppm or less than 0.5 ppm, particularly preferably less than 0.1 ppm; III / an aluminum content of less than 1000 ppb, for example less than 500 ppb, particularly preferably less than 200 ppb; IV / a BET surface area of ​​less than 1 m² / g, for example less than 0.5 m² / g, particularly preferably less than 0.2 m² / g; V / a bulk density in the range of 1.1 to 1.4 g / cm³, for example in the range of 1.15 to 1.35 g / cm³, particularly preferably in the range of 1.2 to 1.3 g / cm³; VI / a particle size D 50 for the melt feed in the range of 50 to 500 µm, for example in the range of 75 to 350 µm, particularly preferably in the range of 100 to 250 µm;VIII a particle size D 50 for the slurry application 0.5 to 5 mm, for example in a range of 750 µm to 3.5 mm, particularly preferably in a range of 1 to 2.5 mm; VIII / a metal content of metals other than aluminium of less than 2000 ppb, for example of less than 500 ppb, particularly preferably of less than 100 ppb; IX / a viscosity (p=1013 hPa) in a range from log 10 (η (1250°C) / dPas) = ​​11.4 to log 10 (η (1250°C) / dPas) = ​​12.9 and / or log 10 (η (1300°C) / dPas) = ​​11.1 to log 10 (η (1300°C) / dPas) = ​​12.2 and / or log 10 (η (1350°C) / dPas) = ​​10.5 to log 10 (η (1350°C) / dPas) = ​​11.5; ; where ppm and ppb are each based on the total weight of the quartz glass grains.

[0302] The quartz glass grain preferably has the combination of features I / / II / / III / or I / / II / / IV / or I / / II / / V / , more preferably the combination of features I / / III / / III / IV / or I / / II / / III / V / or V / II / / IV / V / , and particularly preferably the combination of features I / II / / III / IV / V / .

[0303] The quartz glass granules preferably exhibit the combination of features I / / II / / III / , wherein the OH content is less than 400 ppm, the chlorine content is less than 40 ppm and the aluminium content is less than 200 ppb.

[0304] The quartz glass granules preferably have the feature combination I / III / IN I, the OH content is less than 400 ppm, the chlorine content is less than 40 ppm and the BET surface area is less than 0.5 m² / g.

[0305] The quartz glass granules preferably have the combination of features I / / II / / V / , wherein the OH content is less than 400 ppm, the chlorine content is less than 40 ppm and the bulk density is in a range of 1.15 to 1.35 g / cm 3<.

[0306] The quartz glass granules preferably have the combination of features I / / II / / III / IV / , wherein the OH content is less than 400 ppm, the chlorine content is less than 40 ppm, the aluminium content is less than 200 ppb and the BET surface area is less than 0.5 m² / g.

[0307] The quartz glass granules preferably have the combination of features I / / II / / III / V / , wherein the OH content is less than 400 ppm, the chlorine content is less than 40 ppm, the aluminium content is less than 200 ppb and the bulk density is in a range of 1.15 to 1.35 g / cm 3<.

[0308] The quartz glass granules preferably have the combination of features I / / II / / IV / V / , wherein the OH content is less than 400 ppm, the chlorine content is less than 40 ppm, the BET surface area is less than 0.5 m² / g and the bulk density is in a range of 1.15 to 1.35 g / cm³.

[0309] The quartz glass granules preferably have the combination of features I / / II / / III / IV / V / , wherein the OH content is less than 400 ppm, the chlorine content is less than 40 ppm, the aluminium content is less than 200 ppb, the BET surface area is less than 0.5 m² / g and the bulk density is in a range of 1.15 to 1.35 g / cm³.

[0310] The gas provided in step i.) B) is supplied at least partially to the crucible through at least one gas inlet, wherein the at least one gas inlet is arranged below the solid feed. The arrangement and design of the gas inlet are the embodiments described in the first subject matter of the invention for the gas inlet of the device according to the invention.

[0311] Preferably the gas is selected from the group consisting of hydrogen, nitrogen, helium, neon, argon, krypton, xenon or a combination of two or more thereof, particularly preferably a combination of hydrogen and helium. Step ii.)

[0312] According to step ii.), a glass melt is formed from the bulk material. Typically, the bulk material is heated until a glass melt is obtained. In principle, heating the bulk material to a glass melt can be done by any method known to a person skilled in the art for this purpose. V-train for producing a glass melt

[0313] The formation of a glass melt from the bulk material, for example by heating, can be carried out by a continuous process. In the inventive process for producing a quartz glass body, the bulk material can preferably be continuously fed into a furnace, or the glass melt can be continuously removed from the furnace, or both. Particularly preferably, the bulk material is continuously fed into the furnace and the glass melt is continuously removed from the furnace.

[0314] In principle, a furnace with at least one inlet and at least one outlet is suitable for this purpose. A solids inlet is understood to be an opening through which silicon dioxide and, optionally, other substances can be introduced into the furnace. An outlet is understood to be an opening through which at least some of the silicon dioxide can be removed from the furnace. The furnace can be oriented vertically or horizontally, for example. Preferably, the furnace is oriented vertically. Preferably, at least one solids inlet is located above at least one outlet. In the context of internal components and features of a furnace, particularly an inlet and outlet, "above" means that the internal component or feature arranged "above" another is located at a higher elevation above mean sea level."Vertical" means that the direct connection between the inlet and outlet of the furnace has a deviation of no more than 30° from the vertical direction.

[0315] According to the invention, the furnace has at least one gas inlet arranged below the at least one solid feed. According to the invention, the furnace has at least one gas outlet arranged at the same level as or above the at least one solid feed.

[0316] According to the invention, the molten glass formed in step ii) is located in the lower region of the crucible. Preferably, the molten glass is covered with at least a portion of the bulk material. Preferably, the introduction of the bulk material via the solid feeder forms a cone of bulk material above the molten glass, the bulk material cone.

[0317] According to a preferred embodiment of the present invention, the furnace containing the crucible is a furnace described within the scope of the first subject matter of the invention. For the preferred features and embodiments of the furnace, reference is made to the description of the first subject matter of the invention.

[0318] According to the invention, at least a portion of the gas provided in step i.)B) is supplied to the crucible through at least one gas inlet. Preferably, the gas is supplied through openings in the wall located above the molten glass, for example, in a region 2 to 20 cm above the fill line, more preferably in a region 5 to 10 cm above the fill line. Preferably, the gas is supplied through at least one gas inlet in the gas space of the crucible. The specifications given for the gas inlet of the device according to the invention can apply to the gas inlet. Particularly preferably, the gas is supplied through openings in a distributor ring arranged in the crucible, the distributor ring being positioned above the molten glass.

[0319] According to the invention, at least a portion of the gas is discharged from the crucible through at least one gas outlet. The specifications given for the gas inlet of the device according to the invention can apply to the gas inlet.

[0320] Preferably, the gas is guided from the gas inlet on the crucible wall to the gas outlet. Particularly preferably, at least 50 vol% of the gas passes over the crucible wall between the gas inlet and gas outlet at a distance of 8 cm or less. The specifications given for the gas outlet of the device according to the invention can apply to the gas outlet.

[0321] To form a glass melt, the bulk material is heated in the crucible. Heating can be carried out in the presence of a gas or a mixture of two or more gases. During heating, water bound to the bulk material can also transition into the gas phase, thus forming another gas. The gas or the mixture of two or more gases is located in the gas space of the crucible. The gas space of the crucible is defined as the area inside the crucible that is not occupied by a solid or liquid phase. Suitable gases include, for example, hydrogen, inert gases, and two or more of these. Inert gases are defined as those gases that do not react with the materials in the crucible up to a temperature of 2400°C. Preferred inert gases are nitrogen, helium, neon, argon, krypton, and xenon, with argon and helium being particularly preferred. Heating is preferably carried out in a reducing atmosphere.This can preferably be provided by hydrogen or a combination of hydrogen and an inert gas, for example by a combination of hydrogen and helium, or of hydrogen and nitrogen, or of hydrogen and argon, particularly preferably by a combination of hydrogen and helium.

[0322] Preferably, at least a partial gas exchange of air, oxygen, and water for hydrogen, at least one inert gas, or for a combination of hydrogen and at least one inert gas is carried out on the bulk material. This at least partial gas exchange is performed on the bulk material during introduction, before heating, during heating, or during at least two of the aforementioned activities. Preferably, the bulk material is heated to melting in a gas stream of hydrogen and at least one inert gas, for example, argon or helium.

[0323] Preferably, the dew point of the gas at the outlet is less than 0°C. The dew point is defined as the temperature below which, at constant pressure, a component of the gas or gas mixture under investigation condenses. Generally, this refers to the condensation of water. The dew point is determined using a dew point hygrometer according to the measurement method described in the Methods section.

[0324] Preferably, the gas withdrawn from the furnace through the gas outlet has a dew point of less than 0°C, for example, less than -10°C or less than -20°C, upon exiting the furnace through the gas outlet. The dew point is determined according to the measurement method described in the methods section at a slight overpressure of 5 to 20 mbar. A suitable measuring device, for example, is the "Optidew" device from Michell Instruments GmbH, D-61381 Friedrichsdorf, Germany.

[0325] The dew point of the gas is preferably determined at a measuring point 10 cm or more from the gas outlet of the furnace. This distance is often between 10 cm and 5 m. Within this range – described here as "at the outlet" – the distance of the measuring point from the furnace's gas outlet is irrelevant to the dew point measurement result. The gas is conveyed from the outlet to the measuring point via a fluid-conducting medium, such as a hose or pipe. The gas temperature at the measuring point is often between 10 and 60°C, for example, 20 to 50°C, and particularly 20 to 30°C.

[0326] Suitable gases and gas mixtures have already been described. Our own tests have confirmed that the above information applies to each of the gases and gas mixtures mentioned.

[0327] According to a further preferred embodiment, the gas or gas mixture has a dew point of less than -50°C, for example less than -60°C, or less than -70°C, or less than -80°C, before entering the furnace, in particular the crucible. A dew point of -60°C is generally not exceeded. The following dew point ranges at the furnace inlet are also preferred: -50 to -100°C; -60 to -100°C; and -70 to -100°C.

[0328] According to another preferred embodiment, the dew point of the gas before entering the furnace is at least 50°C lower than at the exit from the crucible, for example, at least 60°C or even 80°C. The above specifications apply to measuring the dew point at the exit from the crucible. The same applies to measuring the dew point before entering the furnace. Since there is no source of moisture ingress and no possibility of condensation between the measurement point and the furnace, the distance between the measuring point and the gas inlet of the furnace is irrelevant.

[0329] According to a preferred embodiment, the furnace, in particular the crucible, is operated with a gas exchange rate in the range of 200 to 3000 L / h.

[0330] According to a preferred embodiment, the dew point is determined in a measuring cell, wherein the measuring cell is separated from the gas exiting through the gas outlet by a membrane. The membrane is preferably permeable to moisture. This measure protects the measuring cell from dust and other particles contained in the gas stream, which are carried out of the melting furnace, particularly a crucible, by the gas stream. This measure significantly extends the service life of a measuring probe. Service life refers to the period during which the measuring probe is neither replaced nor cleaned while the furnace is in operation.

[0331] According to a preferred embodiment, a dew point mirror measuring device is used to determine the dew point.

[0332] The dew point at the gas outlet of the furnace can be adjusted. Preferably, a method for adjusting the dew point at the furnace outlet includes the following steps: I) Providing an input material in a furnace, wherein the input material has a residual moisture content; II) Operating the furnace, wherein a gas stream is passed through the furnace; and III) Varying the residual moisture content of the input material, or the gas exchange rate of the gas stream.

[0333] Preferably, this method allows the dew point to be set to a range below 0°C, for example, below -10°C, and particularly preferably below -20°C. More preferably, the dew point can be set to a range below 0°C to -100°C, for example, below -10°C to -80°C, and particularly preferably below -20°C to -60°C.

[0334] The term "starting material" refers to silicon dioxide particles provided for the manufacture of a quartz glass body, preferably silicon dioxide granules, silicon dioxide grains, or combinations thereof. The silicon dioxide particles, granules, and grains are preferably characterized by the features described in the first subject matter.

[0335] The furnace and the gas flow are preferably characterized by the features described in the first subject matter. Preferably, the gas flow is formed by introducing gas through an inlet into the furnace and by removing gas through an outlet from the furnace. The "gas exchange rate" is understood to be the volume of gas that passes through the outlet from the furnace per unit of time. The gas exchange rate is also referred to as the gas flow rate or volumetric flow rate.

[0336] The dew point can be adjusted, in particular, by varying the residual moisture content of the input material or the gas exchange rate of the gas stream. For example, increasing the residual moisture content of the input material can raise the dew point. Decreasing the residual moisture content of the input material can lower the dew point. An increased gas exchange rate can lead to a decrease in the dew point, while a decreased gas exchange rate can result in an increased dew point.

[0337] Preferably, the gas exchange rate of the gas stream is in the range of 200 to 3000 L / h, for example from 200 to 2000 L / h, particularly preferably from 200 to 1000 L / h.

[0338] The residual moisture content of the input material is preferably in a range of 0.001 wt.% to 5 wt.%, for example from 0.01 to 1 wt.%, particularly preferably from 0.03 to 0.5 wt.%, in each case based on the total weight of the input material.

[0339] The dew point can also be influenced by other measures. Examples of such measures include the dew point of the gas stream at the furnace inlet, the furnace temperature, and the composition of the gas stream. A reduction in the dew point of the gas stream at the furnace inlet, a reduction in the furnace temperature, or a reduction in the temperature of the gas stream at the furnace outlet can lead to a reduction in the dew point of the gas stream at the outlet. The temperature of the gas stream at the furnace outlet has no influence on the dew point, provided it is above the dew point.

[0340] Varying the gas exchange rate of the gas flow is particularly preferred for adjusting the dew point at the outlet of the oven.

[0341] Preferably, the method is characterized by at least one, for example at least two or at least three, particularly preferably at least four of the following features: I} a residual moisture content of the input material in a range of 0.001 to 5 wt.%, for example from 0.01 to 1 wt.%, particularly preferably from 0.03 to 0.5 wt.%.-%, each based on the total weight of the input material; II} a gas exchange rate of the gas stream in a range of 200 to 3000 L / h, for example from 200 to 2000 L / h, particularly preferably from 200 to 1000 L / h; III} a furnace temperature in a range of 1700 to 2500°C, for example in a range of 1900 to 2400°C, particularly preferably in a range of 2100 to 2300°C; IV} a dew point of the gas stream at the inlet to the furnace in a range of -50°C to -100°C, for example from -60°C to -100°C, particularly preferably from -70°C to -100°C; V} the gas stream contains helium, hydrogen or a combination thereof, preferably helium and hydrogen in a ratio of 20:80 to 95:5; VI} a temperature of the gas at the outlet in a range of 10 to 60°C, for example from 20 to 50°C, particularly preferably from 20 to 30°C.

[0342] For example, when using silicon dioxide granules with high residual moisture, it is preferable to use a gas stream with a high gas exchange rate and a low dew point at the furnace inlet. Conversely, when using silicon dioxide granules with low residual moisture, a gas stream with a low gas exchange rate and a higher dew point at the furnace inlet can be used.

[0343] Particularly preferred when using silicon dioxide granules with a residual moisture content of less than 3 wt.% is the gas exchange rate of a gas stream containing helium and hydrogen in the range of 200 to 3000 L / h.

[0344] If silicon dioxide granules with a residual moisture content of 0.1% are fed into the furnace at a rate of 30 kg / h, a gas exchange rate of the gas stream is preferably selected, in the case of He / H₂ = 50:50 in the range of 2800 to 3000 l / h, in the case of He / H₂ = 30:70 in the range of 2700 to 2900 l / h, and a dew point of the gas stream before entering the furnace of -90 °C. This results in a dew point of less than 0 °C at the gas outlet.

[0345] When silicon dioxide granules with a residual moisture content of 0.05% are fed into the furnace at a rate of 30 kg / h, a gas exchange rate of the gas stream is preferably selected. In the case of He / H₂ = 50:50, this rate is in the range of 1900 to 2100 l / h, and in the case of He / H₂ = 30:70, it is in the range of 1800 to 2000 l / h. A dew point of the gas stream before entering the furnace of -90 °C is also preferred. This results in a dew point of less than 0 °C at the gas outlet.

[0346] If silicon dioxide granules with a residual moisture content of 0.03% are fed into the furnace at a rate of 30 kg / h, a gas exchange rate of the gas stream is preferably selected, in the case of He / H₂ = 50:50 in the range of 1400 to 1600 l / h, in the case of He / H₂ = 30:70 in the range of 1200 to 1400 l / h, and a dew point of the gas stream before entering the furnace of -90 °C. This results in a dew point of less than 0 °C at the gas outlet.

[0347] The furnace temperature for melting the bulk material is preferably in the range of 1700 to 2500°C, for example in the range of 1900 to 2400°C, particularly preferably in the range of 2100 to 2300°C.

[0348] Preferably, the residence time in the furnace is in the range of 1 to 50 hours, for example 1 to 30 hours, and particularly preferably 5 to 20 hours. In the context of the present invention, the residence time means the time required to remove a quantity of the melting furnace, in which the glass melt is formed, during the execution of the process according to the invention. The quantity of the melting furnace is the total mass of silicon dioxide present in the furnace. The silicon dioxide can be in the form of a solid or a glass melt.

[0349] Preferably, the furnace temperature increases along its length in the direction of material transport. Preferably, the furnace temperature increases by at least 100°C along its length in the direction of material transport, for example, by at least 300°C, 500°C, or 700°C, and particularly preferably by at least 1000°C. Preferably, the maximum temperature in the furnace is between 1700°C and 2500°C, for example, between 1900°C and 2400°C, and particularly preferably between 2100°C and 2300°C. The increase in furnace temperature can be uniform or according to a temperature profile.

[0350] Preferably, the furnace temperature decreases before the molten glass is removed from the furnace. Preferably, the furnace temperature decreases by 50 to 500°C before the molten glass is removed, for example by 100°C or 400°C, and particularly preferably by 150 to 300°C. Preferably, the temperature of the molten glass at the time of removal is 1750 to 2100°C, for example by 1850 to 2050°C, and particularly preferably by 1900 to 2000°C.

[0351] Preferably, the furnace temperature increases along its length in the direction of material transport and decreases before the molten glass is removed from the furnace. Preferably, the furnace temperature increases by at least 100°C along its length in the direction of material transport, for example by at least 300°C, 500°C, or 700°C, and particularly preferably by at least 1000°C. Preferably, the maximum temperature in the furnace is between 1700°C and 2500°C, for example by 1900°C and 2400°C, and particularly preferably by 2100°C and 2300°C.

[0352] Preferably, the furnace temperature decreases by 50 to 500°C before the molten glass is removed from the furnace, for example by 100°C or 400°C, particularly preferably by 150 to 300°C.

[0353] The molten glass is extracted from the furnace through the outlet, preferably via a nozzle. Step iii.)

[0354] A quartz glass body is formed from at least a portion of the molten glass, wherein the molten glass is located in the lower region of the crucible. Preferably, at least a portion of the molten glass produced in step ii) is taken and used to form the quartz glass body.

[0355] The removal of a portion of the molten glass produced in step ii) can, in principle, be carried out continuously from the melting furnace or after the production of the molten glass is complete. Preferably, a portion of the molten glass is removed continuously. The molten glass is removed from the furnace outlet, preferably via a nozzle.

[0356] The molten glass can be cooled to a temperature suitable for shaping before, during, or after removal from the mold. Cooling of the molten glass increases its viscosity. Preferably, the molten glass is cooled to a temperature sufficient to retain its shape during molding, while simultaneously enabling a quick, reliable, and efficient molding process. A person skilled in the art can easily determine the optimal viscosity for shaping by varying the temperature of the molten glass at the molding tool. Preferably, the molten glass has a temperature in the range of 1750 to 2100°C at removal, for example, 1850 to 2050°C, and particularly preferably 1900 to 2000°C.Preferably, after removal, the molten glass is cooled to a temperature of less than 500°C, for example less than 200°C or less than 100°C or less than 50°C, particularly preferably to a temperature in the range of 20 to 30°C.

[0357] The resulting quartz glass body can be solid or hollow. A solid body is understood to be a body consisting essentially of a single material. However, a solid body may contain one or more inclusions, such as gas bubbles. Such inclusions in a solid body often have a size of 65 mm³ or less, for example, less than 40 mm³, less than 20 mm³, less than 5 mm³, or less than 2 mm³, and particularly preferably less than 0.5 mm³. Preferably, a solid body contains less than 0.02 vol% of its volume, for example, less than 0.01 vol% or less than 0.001 vol%, in inclusions, in each case based on the total volume of the solid body.

[0358] The quartz glass body has an external shape. The external shape refers to the shape of the outer edge of the quartz glass body's cross-section. The external shape of the quartz glass body is preferably round, elliptical, or polygonal in cross-section with three or more vertices, for example, 4, 5, 6, 7, or 8 vertices; a round quartz glass body is particularly preferred.

[0359] Preferably, the quartz glass body has a length in the range of 100 to 10000 mm, for example from 1000 to 4000 mm, particularly preferably from 1200 to 3000 mm.

[0360] Preferably, the quartz glass body has an outer diameter in the range of 1 to 500 mm, for example in a range of 2 to 400 mm, particularly preferably in a range of 5 to 300 mm.

[0361] The shaping of the quartz glass body is achieved using a nozzle. The molten glass is fed through the nozzle. The external shape of a quartz glass body formed by the nozzle is determined by the shape of the nozzle opening. If the nozzle opening is round, a cylinder is formed. If the nozzle opening has a structure, this structure is transferred to the external shape of the quartz glass body. A quartz glass body formed using a nozzle with a structure at the opening exhibits an image of the structures running lengthwise along the glass strand.

[0362] The nozzle is integrated into the melting furnace. Preferably, it is integrated into the melting furnace as part of the crucible, and particularly preferably as part of the crucible outlet.

[0363] Preferably, at least a portion of the molten glass is extracted through the nozzle. The outer shape of the quartz glass body is formed by extracting at least a portion of the molten glass through the nozzle.

[0364] Preferably, the quartz glass body is cooled after forming to retain its shape. Preferably, the quartz glass body is cooled after forming to a temperature at least 1000°C below the temperature of the molten glass during forming, for example, at least 1500°C or at least 1800°C, particularly preferably 1900 to 1950°C. Preferably, the quartz glass body is cooled to a temperature of less than 500°C, for example, less than 200°C, less than 100°C, or less than 50°C, particularly preferably to a temperature in the range of 20 to 30°C.

[0365] According to a preferred embodiment of the second subject matter of the invention, the resulting quartz glass body can be treated with at least one measure selected from the group consisting of chemical, thermal or mechanical treatment.

[0366] Preferably, the quartz glass body undergoes chemical post-treatment. Post-treatment refers to the treatment of an already formed quartz glass body. Chemical post-treatment of the quartz glass body is understood to mean, in principle, any measure known to a person skilled in the art and suitable for altering the chemical structure or the composition of the surface of the quartz glass body, or both, through the use of substances. Preferably, the chemical post-treatment comprises at least one measure selected from the group consisting of treatment with fluorine compounds and ultrasonic cleaning.

[0367] Suitable fluorine compounds include, in particular, hydrogen fluoride and fluorine-containing acids, for example, hydrofluoric acid. The liquid preferably contains fluorine compounds in the range of 35 to 55 wt.%, more preferably in the range of 35 to 45 wt.%, the wt.% in each case based on the total amount of liquid. The remaining 100 wt.% is usually water. Deionized or demineralized water is preferably selected as the water.

[0368] Ultrasonic cleaning is preferably carried out in a liquid bath, particularly preferably in the presence of detergents. In the case of ultrasonic cleaning, fluorine compounds, for example neither hydrofluoric acid nor hydrogen fluoride, are generally not used.

[0369] The ultrasonic cleaning of the quartz glass body is preferably carried out under at least one, for example at least two or at least three or at least four or at least five, particularly preferably all of the following conditions: Ultrasonic cleaning is performed in a continuous process. The ultrasonic cleaning system has six chambers interconnected by tubes. The residence time of the quartz glass bodies in each chamber can be adjusted. Preferably, the residence time of the quartz glass bodies in each chamber is the same. Preferably, the residence time in each chamber is in the range of 1 to 120 minutes, for example, less than 5 minutes, 1 to 5 minutes, 2 to 4 minutes, less than 60 minutes, 10 to 60 minutes, or 20 to 50 minutes, particularly preferably in the range of 5 to 60 minutes. The first chamber comprises a basic medium, preferably containing water and a base, and an ultrasonic cleaner. The third chamber comprises an acidic medium, preferably containing water and an acid, and an ultrasonic cleaner. In the second chamber and in the fourth to sixth chambers, the quartz glass body is cleaned with water, preferably demineralized water.The fourth to sixth chambers are operated as a cascade with water, preferably desalinated water. Preferably, the water is only introduced into the sixth chamber and flows from the sixth to the fifth and from the fifth to the fourth chamber.

[0370] Preferably, the quartz glass body is thermally post-treated. Thermal post-treatment of the quartz glass body is understood to mean, in principle, any measure known to those skilled in the art and suitable for altering the shape or structure, or both, of the quartz glass body by applying temperature. Preferably, the thermal post-treatment comprises at least one measure selected from the group consisting of annealing, upsetting, blowing, drawing, welding, and a combination of two or more thereof. Preferably, the thermal post-treatment is carried out without the aim of material removal.

[0371] Tempering is preferably carried out by heating the quartz glass body in a furnace, preferably to a temperature in the range of 900 to 1300 °C, for example in the range of 900 to 1250 °C or from 1040 to 1300 °C, particularly preferably in the range of 1000 to 1050 °C or from 1200 to 1300 °C. Preferably, a temperature of 1300 °C is not exceeded for any continuous period of more than 1 hour during the thermal treatment; particularly preferably, a temperature of 1300 °C is not exceeded during the entire thermal treatment period. Tempering can, in principle, be carried out at reduced pressure, at normal pressure, or at increased pressure, preferably at reduced pressure, and particularly preferably in a vacuum.

[0372] Upsetting is preferably carried out by heating the quartz glass body, preferably to a temperature of about 2100°C, and then forming it during a rotating motion, preferably at a rotational speed of about 60 rpm. For example, a quartz glass body in the form of a rod can be formed into a cylinder by upsetting.

[0373] Preferably, a quartz glass body can be inflated by blowing a gas into it. For example, a quartz glass body can be formed into a large-diameter tube by inflating it. Preferably, the quartz glass body is heated to a temperature of approximately 2100°C while a rotating motion, preferably at a speed of approximately 60 rpm, is performed, and the interior is purged with a gas, preferably at a defined and controlled internal pressure of up to approximately 100 mbar. A large-diameter tube is defined as a tube with an outer diameter of at least 500 mm.

[0374] A quartz glass body can preferably be drawn. The drawing is preferably carried out by heating the quartz glass body, preferably to a temperature of about 2100°C, and then drawing it at a controlled drawing speed to the desired outer diameter of the quartz glass body. For example, lamp tubes can be formed from quartz glass bodies by drawing.

[0375] Preferably, the quartz glass body is mechanically post-treated. Mechanical post-treatment of the quartz glass body is understood to mean, in principle, any measure known to a person skilled in the art and suitable for altering the shape of the quartz glass body or dividing it into several pieces by means of an abrasive process. In particular, mechanical post-treatment includes at least one measure selected from the group consisting of grinding, drilling, honing, sawing, waterjet cutting, laser cutting, roughening by sandblasting, milling, and a combination of two or more of these.

[0376] Preferably, the quartz glass body is treated with a combination of these measures, for example, with a combination of chemical and thermal post-treatment, or chemical and mechanical post-treatment, or thermal and mechanical post-treatment, and particularly preferably with a combination of chemical, thermal, and mechanical post-treatment. Furthermore, preferably, the quartz glass body can be subjected to several of the aforementioned measures independently of one another.

[0377] According to one embodiment of the second subject matter of the invention, the method includes the following process step: iv.) Forming a hollow body with at least one opening from the quartz glass body.

[0378] The resulting hollow body has an inner and an outer shape. The inner shape refers to the cross-sectional shape of the hollow body's inner edge. The inner and outer cross-sectional shapes of the hollow body can be the same or different. The inner and outer cross-sectional shapes of the hollow body can be round, elliptical, or polygonal with three or more vertices, for example, 4, 5, 6, 7, or 8 vertices.

[0379] Preferably, the outer shape of the cross-section corresponds to the inner shape of the cross-section of the hollow body. Particularly preferably, the hollow body has a round inner and a round outer cross-section.

[0380] In another embodiment, the hollow body can differ in its inner and outer shape. Preferably, the hollow body has a round outer cross-section and a polygonal inner cross-section. Particularly preferably, the hollow body has a round outer cross-section and a hexagonal inner cross-section.

[0381] Preferably, the hollow body has a length in the range of 100 to 10000 mm, for example from 1000 to 4000 mm, particularly preferably from 1200 to 2000 mm.

[0382] Preferably, the hollow body has a wall thickness in a range of 0.8 to 50 mm, for example in a range of 1 to 40 mm or 2 to 30 mm or 3 to 20 mm, particularly preferably in a range of 4 to 10 mm.

[0383] Preferably, the hollow body has an outer diameter of 2.6 to 400 mm, for example in a range of 3.5 to 450 mm, particularly preferably in a range of 5 to 300 mm.

[0384] Preferably, the hollow body has an inner diameter of 1 to 300 mm, for example in a range of 5 to 280 mm or 10 to 200 mm, particularly preferably in a range of 20 to 100 mm.

[0385] The hollow body contains one or more openings. Preferably, the hollow body contains one opening. Preferably, the hollow body contains an even number of openings, for example, 2, 4, 6, 8, 10, 12, 14, 16, 18, or 20 openings. Preferably, the hollow body contains two openings. Preferably, the hollow body is a tube. This shape of the hollow body is particularly preferred when the optical fiber contains only one core. The hollow body can contain more than two openings. The openings are preferably arranged in pairs opposite each other at the ends of the quartz glass body. For example, each end of the quartz glass body has 2, 3, 4, 5, 6, 7, or more than 7 openings, particularly preferably 5, 6, or 7 openings. Preferred shapes are, for example, tubes, twin tubes (i.e., tubes with two parallel channels), and multi-channel rods (i.e., tubes with more than two parallel channels).

[0386] The hollow body can, in principle, be formed by any method known to those skilled in the art. Preferably, the hollow body is formed using a nozzle. Preferably, the nozzle contains a device in the center of its opening that diverts the molten glass during forming. In this way, a hollow body can be formed from a single molten glass.

[0387] The formation of a hollow body can be achieved by using a nozzle and subsequent post-processing. In principle, all methods known to those skilled in the art for producing a hollow body from a solid body are suitable as post-processing, for example, upsetting channels, drilling, honing, or grinding. A preferred post-processing method is to guide the solid body over one or more bosses, thereby forming a hollow body. Similarly, the mandrel can be inserted into the solid body, forming a hollow body. Preferably, the hollow body is cooled after formation.

[0388] Preferably, after forming the hollow body, it is cooled to a temperature of less than 500°C, for example less than 200°C or less than 100°C or less than 50°C, particularly preferably to a temperature in the range of 20 to 30°C. Pre-compaction

[0389] It is generally possible to subject the silicon dioxide granules provided in step i.) to one or more pretreatment steps before heating them in step ii.) until a glass melt is obtained. Possible pretreatment steps include thermal or mechanical treatments. For example, the silicon dioxide granules are compacted before heating in step ii.). "Crispencing" refers to a reduction in the BET surface area and a reduction in the pore volume.

[0390] The silicon dioxide granules are preferably compacted thermally by heating them or mechanically by applying pressure, for example by rolling or pressing. Compaction by heating is preferred. Particularly preferred is compaction by heating the silicon dioxide granules using a preheating section connected to the melting furnace.

[0391] The silicon dioxide is preferably compressed by heating at a temperature in the range of 800 to 1400°C, for example at a temperature in the range of 850 to 1300°C, particularly preferably at a temperature in the range of 900 to 1200°C.

[0392] In a preferred embodiment of the second subject matter of the invention, the BET surface area of ​​the silicon dioxide granules is not reduced to less than 5 m² / g before heating in step ii.), preferably not to less than 7 m² / g or not to less than 10 m² / g, and particularly preferably not to less than 15 m² / g. It is further preferred that the BET surface area of ​​the silicon dioxide granules is not reduced before heating in step ii.) compared to the silicon dioxide granules provided in step i.).

[0393] In a preferred embodiment of the second subject matter of the invention, the BET surface area of ​​the silicon dioxide granules is reduced to less than 20 m² / g, for example to less than 15 m² / g, or to less than 10 m² / g, or to a range of more than 5 to less than 20 m² / g or from 7 to 15 m² / g, particularly preferably to a range of 9 to 12 m² / g. Preferably, the BET surface area of ​​the silicon dioxide granules is reduced by less than 40 m² / g before heating in step ii) compared to the silicon dioxide granules provided in step i), for example by 1 to 20 m² / g or by 2 to 10 m² / g, particularly preferably by 3 to 8 m² / g, wherein the BET surface area after compaction is more than 5 m² / g.

[0394] The compacted silicon dioxide granules are hereinafter referred to as silicon dioxide granules III. Preferably, the silicon dioxide granules III have at least one, for example at least two, at least three, or at least four, and particularly preferably at least five of the following features: A. a BET surface area in a range of more than 5 to less than 40 m² / g, for example from 10 to 30 m² / g, particularly preferably in a range of 15 to 25 m² / g; B. a particle size D 10 in a range of 100 to 300 µm, particularly preferably in a range of 120 to 200 µm; C. a particle size D 50 in a range of 150 to 550 µm, particularly preferably in a range of 200 to 350 µm; D. a particle size D 90 in a range of 300 to 650 µm, particularly preferably in a range of 400 to 500 µm; E. a bulk density in the range of 0.8 to 1.6 g / cm³, particularly preferably from 1.0 to 1.4 g / cm³; F. a tapped density in the range of 1.0 to 1.4 g / cm³, particularly preferably from 1.15 to 1.35 g / cm³; G. a carbon content of less than 5 ppm, for example less than 4.5 ppm, particularly preferably less than 4 ppm; H. a Cl content of less than 500 ppm, particularly preferably from 1 ppb to 200 ppm. where ppm and ppb are each based on the total weight of the silicon dioxide granules III.

[0395] The silicon dioxide granules III preferably have the combination of features A. / F. / G. or A. / F. / H. or A. / G. / H., particularly preferably the combination of features A. / F. / G. / H.

[0396] The silicon dioxide granules III preferably exhibit the combination of features A. / F. / G, wherein the BET surface area is in a range of 10 to 30 m² / g, the tapped density is in a range of 1.15 to 1.35 g / mL and the carbon content is less than 4 ppm.

[0397] The silicon dioxide granules III preferably have the combination of features A. / F. / H., wherein the BET surface area is in a range of 10 to 30 m² / g, the tapped density is in a range of 1.15 to 1.35 g / mL and the chlorine content is in a range of 1 ppb to 200 ppm.

[0398] The silicon dioxide granules III preferably have the combination of features A. / G. / H., wherein the BET surface area is in a range of 10 to 30 m² / g, the carbon content is less than 4 ppm and the chlorine content is in a range of 1 ppb to 200 ppm.

[0399] The silicon dioxide granules III preferably exhibit the combination of features A. / F. / G. / H., wherein the BET surface area is in a range of 10 to 30 m² / g, the tapped density is in a range of 1.15 to 1.35 g / mL, the carbon content is less than 4 ppm and the chlorine content is in a range of 1 ppb to 200 ppm.

[0400] Preferably, a silicon component other than silicon dioxide is added in at least one process step. The addition of a silicon component other than silicon dioxide is hereinafter also referred to as silicon doping. In principle, silicon doping can take place in any process step. Preferably, silicon doping takes place in step i) or in step ii).

[0401] The silicon component other than silicon dioxide can, in principle, be added in any form, for example as a solid, as a liquid, as a gas, in solution, or as a dispersion. Preferably, the silicon component other than silicon dioxide is added as a powder. It is also preferably added as a liquid or as a gas.

[0402] The silicon component, which is different from silicon dioxide, is preferably added in an amount in the range of 1 to 100,000 ppm, for example in a range of 10 to 10,000 ppm or from 30 to 1,000 ppm or in a range of 50 to 500 ppm, particularly preferably in a range of 80 to 200 ppm, and further particularly preferably in a range of 200 to 300 ppm, in each case based on the total weight of silicon dioxide.

[0403] The silicon component other than silicon dioxide can be solid, liquid, or gaseous. If solid, it preferably has a mean particle size of up to 10 mm, for example up to 1000 µm, up to 400 µm, or in a range of 1 to 400 µm, for example 2 to 200 µm or 3 to 100 µm, particularly preferably in a range of 5 to 50 µm. The particle size specifications refer to the state of the silicon component other than silicon dioxide at room temperature.

[0404] The silicon component preferably has a purity of at least 99.5 wt.%, for example, at least 99.8 wt.%, or at least 99.9 wt.%, or at least 99.99 wt.%, particularly preferably at least 99.999 wt.%, in each case based on the total weight of the silicon component. Preferably, the silicon component has a carbon content of no more than 10 ppm, for example, no more than 50 ppm, particularly preferably no more than 1 ppm, in each case based on the total weight of the silicon component. This is particularly preferred for silicon used as a silicon component. Preferably, the silicon component has an amount of impurities selected from the group consisting of Al, Ca, Co, Cr, Cu, Fe, Ge, Hf, K, Li, Mg, Mn, Mo, Na, Nb, Ni, Ti, V, W, Zn, Zr of not more than 250 ppm, for example not more than 150 ppm, particularly preferably not more than 100 ppm, in each case based on the total weight of the silicon component.This is particularly advantageous for silicon used as a silicon component.

[0405] Preferably, a silicon component other than silicon dioxide is added in process step i.). Preferably, the silicon component other than silicon dioxide is added during the processing of the silicon dioxide powder into silicon dioxide granules (step II.). For example, the silicon component other than silicon dioxide can be added to the silicon dioxide before, during, or after granulation.

[0406] Preferably, the silicon dioxide can be Si-doped by adding the silicon-other component to the slurry containing silicon dioxide powder. For example, the silicon-other component is mixed with silicon dioxide powder and then suspended in a liquid, or the silicon-other component is added to a slurry of silicon dioxide powder in a liquid and suspended, or the silicon dioxide powder is added to a slurry or solution of the silicon-other component in a liquid and suspended.

[0407] Preferably, the silicon dioxide can be silicon-doped by adding the silicon-differentiated component during granulation. In principle, it is possible to add the silicon-differentiated component at any time during granulation. In the case of spray granulation, the silicon-differentiated component can, for example, be sprayed into the spray tower through the nozzle together with the slurry. In the case of roll granulation, the silicon-differentiated component can preferably be added in solid form or as a slurry, for example, after the slurry has been introduced into the mixing vessel.

[0408] Preferably, the silicon dioxide can be doped with Si by adding the silicon component other than silicon dioxide after granulation. For example, the silicon dioxide can be doped during the treatment of silicon dioxide granules I to form silicon dioxide granules II, preferably by adding the silicon component other than silicon dioxide during the thermal or mechanical treatment of silicon dioxide granules I.

[0409] Preferably, the silicon dioxide granules II are doped with the silicon component different from silicon dioxide.

[0410] Preferably, the silicon component, which differs from silicon dioxide, can also be added during several of the aforementioned steps, in particular during and after the thermal or mechanical treatment of the silicon dioxide granules I to form silicon dioxide granules II.

[0411] The silicon component other than silicon dioxide can, in principle, be silicon or any silicon-containing compound known to those skilled in the art and possessing reducing properties. Preferably, the silicon component other than silicon dioxide is silicon, a silicon-hydrogen compound (for example, a silane), a silicon-oxygen compound (for example, silicon monoxide), or a silicon-hydrogen-oxygen compound (for example, disiloxane). Examples of preferred silanes are monosilane, disilane, trisilane, tetrasilane, pentasilane, hexasilane, heptasilane, higher homologs and isomers of the aforementioned, as well as cyclic silanes such as cyclopentasilane.

[0412] Preferably, a silicon component different from silicon dioxide is added in process step ii.).

[0413] Preferably, the silicon component other than silicon dioxide can be added directly to the melting crucible together with the silicon dioxide granules. Preferably, silicon, as the silicon component other than silicon dioxide, can be added to the melting crucible together with the silicon dioxide granules. The silicon is preferably added as a powder, particularly in the particle size already mentioned for the silicon component other than silicon dioxide.

[0414] Preferably, the silicon component, which is different from silicon dioxide, is added to the silicon dioxide granules before they are introduced into the melting crucible. In principle, the addition can take place at any time after the granules have been formed, for example, in the preheating section, before or during the pre-compaction of silicon dioxide granules II or to silicon dioxide granules III.

[0415] Silicon dioxide granules obtained by adding a silicon component other than silicon dioxide are hereinafter referred to as "Si-doped granules". Preferably, the Si-doped granules have at least one, for example at least two, at least three, or at least four, and particularly preferably at least five of the following features: [1] a BET surface area in a range of more than 5 to less than 40 m² / g, for example from 10 to 30 m² / g, particularly preferably in a range of 15 to 25 m² / g; [2] a particle size D 10 in a range of 100 to 300 µm, particularly preferably in a range of 120 to 200 µm; [3] a particle size D 50 in a range of 150 to 550 µm, particularly preferably in a range of 200 to 350 µm; [4] a particle size D 90 in a range of 300 to 650 µm, particularly preferably in a range of 400 to 500 µm; [5] a bulk density in the range of 0.8 to 1.6 g / cm³, particularly preferably from 1.0 to 1.4 g / cm³; [6] a tapped density in the range of 1.0 to 1.4 g / cm³, particularly preferably from 1.15 to 1.35 g / cm³; [7] an amount of carbon of less than 5 ppm, for example less than 4.5 ppm, particularly preferably less than 4 ppm; [8] a Cl content of less than 500 ppm, particularly preferably from 1 ppb to 200 ppm;[9] an Al content of less than 200 ppb, particularly preferably from 1 ppb to 100 ppb;

[10] a metal content of metals other than aluminium of less than 1000 ppb, for example in a range of 1 to 400 ppb, particularly preferably in a range of 1 to 200 ppb;

[11] a residual moisture content of less than 3 wt.%, for example in a range of 0.001 wt.% to 2 wt.%, particularly preferably from 0.01 to 1 wt.%; ; where the wt%, ppm and ppb are each based on the total weight of the Si-doped granules.

[0416] In a preferred embodiment of the second subject matter of the invention, the melting energy is transferred to the silicon dioxide granules via a solid surface.

[0417] A solid surface is defined as a surface that differs from the surface of the silicon dioxide granules and does not melt or decompose at the temperatures to which the silicon dioxide granules are heated to melt. Suitable materials for the solid surface include, for example, materials suitable as crucible materials.

[0418] In principle, the solid surface can be any surface known to a person skilled in the art and suitable for this purpose. For example, the crucible itself or a separate component other than the crucible can be used as the solid surface.

[0419] The solid surface can, in principle, be heated by any method known to those skilled in the art and suitable for this purpose, in order to transfer the melting energy to the silicon dioxide granules. Preferably, the solid surface is heated by resistive or induction heating. In induction heating, the energy is coupled directly into the solid surface via coils and transferred from there to its inner surface. In resistive heating, the solid surface is heated from the outside and transfers the energy from there to its inner surface. A heating chamber gas with a lower heat capacity, for example, an argon atmosphere or an argon-containing atmosphere, is advantageous in this case. For example, the solid surface can be heated electrically or by externally applying a flame to the solid surface.Preferably, the solid surface is heated to a temperature that can transfer a sufficient amount of energy to the silicon dioxide granules and / or partially melted silicon dioxide granules to melt them.

[0420] According to a preferred embodiment of the present invention, the energy input into the crucible is not achieved by heating the crucible, or any material to be melted therein, or both, by means of a flame, such as a burner flame directed into or onto the crucible.

[0421] If a separate component is used as the solid surface, it can be brought into contact with the silicon dioxide granules in any way, for example by placing the component on the silicon dioxide granules, by inserting the component between the granules of the silicon dioxide granules, by sliding the component between the crucible and the silicon dioxide granules, or by a combination of two or more of these methods. The component can be heated before, during, or both before and during the transfer of the melting energy.

[0422] Preferably, the melting energy is transferred to the silicon dioxide granules via the inside of the crucible. The crucible is heated to the point where the silicon dioxide granules melt. The crucible is preferably heated resistively or inductively. The heat is transferred from the outside to the inside of the crucible. The solid surface of the crucible's interior transfers the melting energy to the silicon dioxide granules.

[0423] According to a further preferred embodiment of the present invention, the melting energy is not transferred to the silicon dioxide granules via a gas space. More preferably, the melting energy is not transferred to the silicon dioxide granules by igniting the silicon dioxide granules with a flame. Examples of these excluded energy transfer methods are directing one or more burner flames from above into the crucible, or onto the silicon dioxide, or both.

[0424] The above-described process relates to the manufacture of a quartz glass body.

[0425] Preferably, the quartz glass body has at least one of the following features, for example at least two or at least three or at least four, particularly preferably at least five of the following features: A] an OH content of less than 500 ppm, for example less than 400 ppm, particularly preferably less than 300 ppm; B] a chlorine content of less than 60 ppm, preferably less than 40 ppm, for example less than 40 ppm or less than 2 ppm or less than 0.5 ppm, particularly preferably less than 0.1 ppm; C] an aluminum content of less than 200 ppb, for example less than 100 ppb, particularly preferably less than 80 ppb; D] an ODC content of less than 5 × 10¹⁵ / cm³, for example in a range of 0.1 × 10¹⁵ to 3 × 10¹⁵ / cm³, particularly preferably in a range of 0.5 × 10¹⁵ to 2.0 × 10¹⁵ / cm³; E] a metal content of metals other than aluminium of less than 1 ppm, for example less than 0.5 ppm, particularly preferably less than 0.1 ppm;F] a viscosity (p=1013 hPa) in a range from log 10 (η (1250°C) / dPas) = ​​11.4 to log 10 (η (1250°C) / dPas) = ​​12.9 and / or log 10 (η (1300°C) / dPas) = ​​11.1 to log 10 (η (1300°C) / dPas) = ​​12.2 and / or log 10 (η (1350°C) / dPas) = ​​10.5 to log 10 (η (1350°C) / dPas) = ​​11.5; G] a standard deviation of the OH content of not more than 10%, preferably not more than 5%, based on the OH content A] of the quartz glass body; H] a standard deviation of the chlorine content of not more than 10%, preferably not more than 5%, based on the chlorine content B] of the quartz glass body; I] a standard deviation of the aluminum content of not more than 10%, preferably not more than 5%, based on the aluminum content C] of the quartz glass body; J] a refractive index homogeneity of less than 10⁻⁴ < ;[K] a cylindrical shape, [L] a tungsten content of less than 1000 ppb, for example less than 500 ppb or less than 300 ppb or less than 100 ppb or in a range of 1 to 500 ppb or from 1 to 300 ppb, particularly preferably in a range of 1 to 100 ppb; [M] a molybdenum content of less than 1000 ppb, for example less than 500 ppb or less than 300 ppb or less than 100 ppb or in a range of 1 to 500 ppb or from 1 to 300 ppb, particularly preferably in a range of 1 to 100 ppb; where ppb and ppm are each based on the total weight of the quartz glass body.

[0426] Preferably, the fused silica body has a metal content of metals other than aluminum of less than 1000 ppb, for example, less than 500 ppb, particularly preferably less than 100 ppb, in each case based on the total weight of the fused silica body. Often, however, the fused silica body has a content of metals other than aluminum in an amount of at least 1 ppb. Such metals are, for example, sodium, lithium, potassium, magnesium, calcium, strontium, germanium, copper, molybdenum, titanium, iron, and chromium. These can be present, for example, as elements, as ions, or as part of a molecule, an ion, or a complex.

[0427] The quartz glass body may contain other components. Preferably, the quartz glass body contains less than 500 ppm, for example, less than 450 ppm, and particularly preferably less than 400 ppm, of other components, where the ppm values ​​are based on the total weight of the quartz glass body. Examples of other components include carbon, fluorine, iodine, bromine, and phosphorus. These may be present, for example, as elements, ions, or as part of a molecule, ion, or complex. However, the quartz glass body often contains other components in an amount of at least 1 ppb.

[0428] Preferably, the quartz glass body contains carbon in an amount of less than 5 ppm, for example less than 4.5 ppm, particularly preferably less than 4 ppm, in each case based on the total weight of the quartz glass body. However, the quartz glass body often has a carbon content of at least 1 ppb.

[0429] Preferably, the quartz glass body has a homogeneously distributed amount of OH, Cl, or Al. An indicator of the homogeneity of the quartz glass body can be expressed as the standard deviation of the amount of OH, Cl, or Al. The standard deviation is the measure of the spread of the values ​​of a variable, in this case the amount of OH, chlorine, or aluminum, around their arithmetic mean. To determine the standard deviation, the concentration of the component to be determined in the sample, e.g., OH, chlorine, or aluminum, is measured at at least seven points.

[0430] The quartz glass body preferably has the feature combination A] / B] / C] or A] / B] / D] or A] / B] / F], more preferably the feature combination A] / B] / C] / D] or A] / B] / C] / F] or A] / B] / D] / F], particularly preferably the feature combination A] / B] / C] / D] / F].

[0431] The quartz glass body preferably has the combination of features A] / B] / C], wherein the OH content is less than 400 ppm, the chlorine content is less than 100 ppm and the aluminium content is less than 80 ppb.

[0432] The quartz glass body preferably has the combination of features A] / B] / D], the OH content is less than 400 ppm, the chlorine content is less than 100 ppm and the ODC content is in a range of 0.1·10 15< to 3·10 15< / cm 3<.

[0433] The quartz glass body preferably has the combination of features A] / B] / F], wherein the OH content is less than 400 ppm, the chlorine content is less than 100 ppm and the viscosity (p=1013 hPa) is in a range from log 10 (η (1250°C) / dPas) = ​​11.4 to log 10 (η (1250°C) / dPas) = ​​12.9.

[0434] The quartz glass body preferably has the combination of features A] / B] / C] / D], wherein the OH content is less than 400 ppm, the chlorine content is less than 100 ppm, the aluminium content is less than 80 ppb and the ODC content is in a range of 0.1·10 15< to 3·10 15< / cm 3<.

[0435] The quartz glass body preferably has the combination of features A] / B] / C] / F], wherein the OH content is less than 400 ppm, the chlorine content is less than 100 ppm, the aluminum content is less than 80 ppb and the viscosity (p=1013 hPa) is in a range from logio (η (1250°C) / dPas) = ​​11.4 to logio (η (1250°C) / dPas) = ​​12.9.

[0436] The quartz glass body preferably has the combination of features A] / B] / D] / F], wherein the OH content is less than 400 ppm, the chlorine content is less than 100 ppm, the ODC content is in a range of 0.1·10 15< to 3·10 15< / cm 3< and the viscosity (p=1013 hPa) is in a range of logio (η (1250°C) / dPas) = ​​11.4 to log 10 (η (1250°C) / dPas) = ​​12.9.

[0437] The quartz glass body preferably has the combination of features A] / B] / C] / D] / F], wherein the OH content is less than 400 ppm, the chlorine content is less than 100 ppm, the aluminum content is less than 80 ppb, the ODC content is in a range of 0.1·10 15< to 3·10 15< / cm 3<, and the viscosity (p=1013 hPa) is in a range of log 10 (η (1250°C) / dPas) = ​​11.4 to log 10 (η (1250°C) / dPas) = ​​12.9.

[0438] Preferably, the quartz glass body has at least one of the following features, for example at least two or at least three or at least four, particularly preferably at least five of the following features: A] an OH content of less than 500 ppm, for example less than 400 ppm, particularly preferably less than 300 ppm; B] a chlorine content of less than 60 ppm, preferably less than 40 ppm, for example less than 40 ppm or less than 2 ppm or less than 0.5 ppm, particularly preferably less than 0.1 ppm; C] an aluminum content of less than 200 ppb, for example less than 100 ppb, particularly preferably less than 80 ppb; D] an ODC content of less than 5 × 10¹⁵ / cm³, for example in a range of 0.1 × 10¹⁵ to 3 × 10¹⁵ / cm³, particularly preferably in a range of 0.5 × 10¹⁵ to 2.0 × 10¹⁵ / cm³; E] a metal content of metals other than aluminium of less than 1 ppm, for example less than 0.5 ppm, particularly preferably less than 0.1 ppm;F] a viscosity (p=1013 hPa) in a range from log 10 (η (1250°C) / dPas) = ​​11.4 to log 10 (η (1250°C) / dPas) = ​​12.9 and / or log 10 (η (1300°C) / dPas) = ​​11.1 to log 10 (η (1300°C) / dPas) = ​​12.2 and / or log 10 (η (1350°C) / dPas) = ​​10.5 to log 10 (η (1350°C) / dPas) = ​​11.5; G] a standard deviation of the OH content of not more than 10%, preferably not more than 5%, based on the OH content A] of the quartz glass body; H] a standard deviation of the chlorine content of not more than 10%, preferably not more than 5%, based on the chlorine content B] of the quartz glass body; I] a standard deviation of the aluminum content of not more than 10%, preferably not more than 5%, based on the aluminum content C] of the quartz glass body; K] a cylindrical shape;L] a tungsten content of less than 1000 ppb, for example less than 500 ppb or less than 300 ppb or less than 100 ppb or in a range of 1 to 500 ppb or from 1 to 300 ppb, particularly preferably in a range of 1 to 100 ppb; M] a molybdenum content of less than 1000 ppb, for example less than 500 ppb or less than 300 ppb or less than 100 ppb or in a range of 1 to 500 ppb or from 1 to 300 ppb, particularly preferably in a range of 1 to 100 ppb; where ppb and ppm are each based on the total weight of the quartz glass body.

[0439] A second object of the present invention is a method for manufacturing an optical fiber comprising the following steps A / Providing a hollow body with at least one opening obtainable by a method according to the first subject matter of the invention comprising step iv.), or B / Inserting one or more core rods into the quartz glass body through the at least one opening, obtaining a precursor; C / Pulling the precursor from step B / under heat, obtaining a light guide with one or more cores and a shell M1. Step A /

[0440] The quartz glass body provided in step A / is obtainable by a method according to the first subject matter of the invention, comprising, as step iv), forming a hollow body with at least one opening from the quartz glass body. The quartz glass body thus obtained particularly preferably has the features according to the third subject matter of the invention. Step B /

[0441] One or more core rods are inserted through the at least one opening in the quartz glass body (step B / ). In the context of the present invention, a core rod is defined as an object intended to be inserted into a sheath, for example a sheath M1, and processed into an optical fiber. The core rod has a quartz glass core. Preferably, the core rod comprises a quartz glass core and a first sheath layer M0 surrounding the core.

[0442] Each core rod has a shape chosen to fit inside the quartz glass body. Preferably, the outer shape of a core rod corresponds to the shape of an opening in the quartz glass body. Particularly preferably, the quartz glass body is a tube and the core rod is a rod with a round cross-section.

[0443] The diameter of the core rod is smaller than the inner diameter of the hollow body. Preferably, the diameter of the core rod is 0.1 to 3 mm smaller than the inner diameter of the hollow body, for example 0.3 to 2.5 mm smaller, or 0.5 to 2 mm smaller, or 0.7 to 1.5 mm smaller, and particularly preferably 0.8 to 1.2 mm smaller.

[0444] Preferably, the ratio of the inner diameter of the quartz glass body to the diameter of the core rod is in the range of 2:1 to 1.0001:1, for example in the range of 1.8:1 to 1.01:1 or in the range of 1.6:1 to 1.005:1 or in the range of 1.4:1 to 1.01:1, particularly preferably in the range of 1.2:1 to 1.05:1.

[0445] Preferably, an area within the quartz glass body that is not filled by the core rod can be filled with at least one other component, for example a silicon dioxide powder or silicon dioxide granules.

[0446] It is also possible for a core rod, already contained within at least one other quartz glass body, to be inserted into a quartz glass body. This second quartz glass body has an outer diameter smaller than the inner diameter of the quartz glass body. The core rod inserted into the quartz glass body may also already be contained within two or more other quartz glass bodies, for example, three, four, five, six, or more.

[0447] A quartz glass body of this type, equipped with one or more core rods, is referred to below as a "precursor". Step C /

[0448] The precursor is pulled under heat (step C / ). The resulting product is an optical fiber with one or more cores and at least one sheath M1.

[0449] Preferably, the precursor is drawn at a speed in the range of 1 to 100 m / h, for example at a speed in the range of 2 to 50 m / h or 3 to 30 m / h. Particularly preferably, the quartz glass body is drawn at a speed in the range of 5 to 25 m / h.

[0450] Preferably, the drawing process is carried out in heat at a temperature of up to 2500°C, for example at a temperature in the range of 1700 to 2400°C, particularly preferably at a temperature in the range of 2100 to 2300°C.

[0451] Preferably, the precursor is passed through an oven that heats the precursor from the outside.

[0452] Preferably, the precursor is extended until the desired thickness of the optical fiber is reached. Preferably, the precursor is elongated to 1,000 to 6,000,000 times its length, for example, to 10,000 to 500,000 times its length or to 30,000 to 200,000 times its length, in each case based on the length of the quartz glass body provided in step A. The precursor is particularly preferably elongated to 100,000 to 10,000,000 times its length, for example to 150,000 to 5,800,000 times its length, or to 160,000 to 640,000 times its length, or to 1,440,000 to 5,760,000 times its length, or to 1,440,000 to 2,560,000 times its length, in each case based on the length of the quartz glass body provided in step A.

[0453] Preferably, the diameter of the precursor is reduced by elongation by a factor in a range of 100 to 3,500, for example in a range of 300 to 3,000 or 400 to 800 or 1,200 to 2,400 or 1,200 to 1,600, each based on the diameter of the quartz glass body provided in step A / .

[0454] The optical fiber, also known as a waveguide, can contain any material suitable for conducting or guiding electromagnetic radiation, especially light.

[0455] Radiation guidance refers to the propagation of radiation along the longitudinal length of the optical fiber without significant obstruction or attenuation of the radiation intensity. The radiation is coupled into the fiber at one end. Preferably, the optical fiber guides electromagnetic radiation in a wavelength range of 170 to 5000 nm. Preferably, the attenuation of the radiation by the optical fiber in the respective wavelength range is in the range of 0.1 to 10 dB / km. Preferably, the optical fiber has a transmission rate of up to 50 Tbit / s.

[0456] The optical fiber preferably has a curl parameter of more than 6 m. According to the invention, the curl parameter is understood to be the bending radius of a fiber, e.g., an optical fiber or a sheath M1, which is established when the fiber is freely moving without external force being applied.

[0457] The optical fiber is preferably designed to be flexible. Flexible in the sense of the invention means that the optical fiber is characterized by a bending radius of 20 mm or less, for example, 10 mm or less, and particularly preferably less than 5 mm or less. A bending radius is defined as the smallest radius that can be formed without causing the optical fiber to break and without impairing its ability to conduct radiation. Impairment occurs when the light transmitted through a bend in the optical fiber is attenuated by more than 0.1 dB. The attenuation is preferably specified at a reference wavelength of 1550 nm.

[0458] Preferably, the quartz consists of silicon dioxide with less than 1 wt.% of other substances, for example, with less than 0.5 wt.% of other substances, particularly preferably with less than 0.3 wt.% of other substances, in each case based on the total weight of the quartz. More preferably, the quartz contains at least 99 wt.% silicon dioxide, based on the total weight of the quartz.

[0459] The optical fiber preferably has an elongated shape. Its shape is defined by its longitudinal extent L and its cross-sectional area Q. The optical fiber preferably has a round outer wall along its longitudinal extent L. The cross-sectional area Q of the optical fiber is always determined in a plane perpendicular to the outer wall of the optical fiber. If the optical fiber is curved along its longitudinal extent L, the cross-sectional area Q is determined perpendicular to the tangent at a point on the outer wall of the optical fiber. The optical fiber preferably has a diameter dL in the range of 0.04 to 1.5 mm. The optical fiber preferably has a length in the range of 1 m to 100 km.

[0460] According to the invention, the optical fiber comprises one or more cores, for example, one core, two cores, three cores, four cores, five cores, six cores, seven cores, or more than seven cores, particularly preferably one core. Preferably, more than 90%, for example, more than 95%, particularly preferably more than 98%, of the electromagnetic radiation transmitted through the optical fiber is guided in the cores. The wavelength ranges for the transmission of light in the cores are those already specified for the optical fiber and are considered preferred. Preferably, the material of the cores is selected from the group consisting of glass or quartz glass, or a combination of both, particularly preferably quartz glass. The cores can be made independently of one another from the same material or from different materials. Preferably, all cores are made of the same material, particularly preferably quartz glass.

[0461] Each core has a cross-section QK, preferably round, and an elongated shape with length LK. The cross-section QK of one core is independent of the cross-section QK of any other core. The cross-sections QK of the cores can be the same or different. Preferably, the cross-sections QK of all cores are the same. The cross-section QK of a core is always determined in a plane perpendicular to the outer wall of the core or the outer wall of the optical fiber. If a core is curved in its longitudinal extent, the cross-section QK is determined perpendicular to the tangent at a point on the outer wall of that core. The length LK of one core is independent of the length LK of any other core. The lengths LK of the cores can be the same or different. Preferably, the lengths LK of all cores are the same. Each core preferably has a length LK in the range of 1 m to 100 km. Each core has a diameter dK.The diameter dK of a core is independent of the diameter dK of each other core. The diameters dK of the cores can be the same or different. Preferably, the diameters dK of all cores are the same. Preferably, the diameter dK of each core lies in a range of 0.1 to 1000 µm, for example, from 0.2 to 100 µm or from 0.5 to 50 µm, and particularly preferably from 1 to 30 µm.

[0462] Each core exhibits at least one refractive index profile perpendicular to its maximum core extent. "Refractive index profile" means that the refractive index is constant or changes perpendicular to the maximum core extent. The preferred refractive index profile is a concentric profile, for example, a concentric profile in which a first region with the maximum refractive index is located at the center of the core, followed by a further region with a lower refractive index. Preferably, each core exhibits only one refractive index profile over its length LK. The refractive index profile of a core is independent of the refractive index profile of any other core. The refractive index profiles of the cores can be the same or different. Preferably, the refractive index profiles of all cores are the same. In principle, it is also possible for a core to exhibit a multitude of different refractive index profiles.

[0463] Each refractive index profile perpendicular to the maximum core expansion has a maximum refractive index nK. Each refractive index profile perpendicular to the maximum core expansion can also have further lower refractive indices. The lowest refractive index of the refractive index profile is preferably not more than 0.5 lower than the maximum refractive index nK of the refractive index profile. The lowest refractive index of the refractive index profile is preferably 0.0001 to 0.15, for example 0.0002 to 0.1, and particularly preferably 0.0003 to 0.05 lower than the maximum refractive index nK of the refractive index profile.

[0464] Preferably, the core has a refractive index n Kin a range of 1.40 to 1.60, for example in a range of 1.41 to 1.59, particularly preferably in a range of 1.42 to 1.58, in each case determined at a reference wavelength of λr = 589 nm (sodium D-line), at a temperature of 20°C and at standard pressure (p = 1013 hPa). See section Test Methods for further details. The refractive index n K The refractive index of a nucleus is independent of its refractive index. n K each additional nucleus. The refractive indices n K The refractive indices of the nuclei can be the same or different. The refractive indices are preferred. n K all kernels are the same.

[0465] Preferably, each core of the optical fiber has a density in the range of 1.9 to 2.5 g / cm³, for example, in the range of 2.0 to 2.4 g / cm³, and particularly preferably in the range of 2.1 to 2.3 g / cm³. Preferably, the cores have a residual moisture content of less than 100 ppb, for example, less than 20 ppb or less than 5 ppb, and particularly preferably less than 1 ppb, in each case based on the total weight of the core. The density of a core is independent of the density of any other core. The densities of the cores can be the same or different. Preferably, the densities of all cores are the same.

[0466] If an optical fiber contains more than one core, each core is characterized by the features described above, independent of the other cores. It is preferred that all cores have the same features.

[0467] According to the invention, the cores are surrounded by at least one shell M1. The shell M1 preferably surrounds the cores over their entire length. Preferably, the shell M1 surrounds the cores to at least 95%, for example, at least 98% or at least 99%, and particularly preferably 100% of the outer surface, i.e., the entire outer wall, of the cores. Often, the cores are completely surrounded by the shell M1 except for the ends (the last 1-5 cm in each case). This serves to protect the cores from mechanical damage.

[0468] The shell M1 can contain any material, including silicon dioxide, that has a lower refractive index than at least one point P along the cross-section QK of the core. Preferably, this at least one point along the cross-section QK of the core is the point located at the center of the core. More preferably, the point P along the cross-section QK of the core is the point that exhibits a maximum of the refractive index. n Kmax in its core. Preferably, the shell M1 has a refractive index n M1 on, which is at least 0.0001 lower than the refractive index of the nucleus n K at least one point along the cross-sectional area Q of the core. Preferably, the shell M1 has a refractive index n M1 on, which is lower than the refractive index of the nucleus in a range of 0.0001 to 0.5, for example in a range of 0.0002 to 0.4, particularly preferably in a range of 0.0003 to 0.3 n K .

[0469] The envelope M1 preferably has a refractive index n M1 in a range of 0.9 to 1.599, for example in a range of 1.30 to 1.59, particularly preferably in a range of 1.40 to 1.57. Preferably, the sheath M1 forms a region of the optical fiber with a constant refractive index. n M1 .A region with a constant refractive index is defined as a region in which the refractive index does not deviate by more than 0.0001 from the mean value of the refractive index. n M1 differs in this area.

[0470] In principle, the optical fiber can include further layers. Preferably, at least one of the further layers, preferably several or all, has a refractive index that is lower than the refractive index. n K each core. Preferably, the optical fiber has one, two, three, four, or more than four additional shells surrounding the shell M1. Preferably, the additional shells surrounding the shell M1 have a refractive index lower than the refractive index n M1 the M1 case.

[0471] Preferably, the optical fiber has one, two, three, four, or more than four additional shells that surround the cores and are themselves surrounded by the shell M1, i.e., located between the cores and the shell M1. Furthermore, preferably, the additional shells located between the cores and the shell M1 have a refractive index that is higher than the refractive index of the core. n M1 the M1 case.

[0472] Preferably, the refractive index decreases from the core of the optical fiber to the outermost layer. This decrease can be stepwise or continuous. The decrease in the refractive index can be divided into different sections. More preferably, the refractive index can decrease stepwise in at least one section and continuously in at least one other section. The steps can be of equal or different magnitudes. It is also possible to include sections with increasing refractive indexes between sections with decreasing refractive indexes.

[0473] The different refractive indices of the various shells can be adjusted, for example, by doping the shell M1, the other shells and / or the cores.

[0474] Depending on the manufacturing process, a core may already possess a first cladding layer M0 after its fabrication. This cladding layer M0, immediately adjacent to the core, is sometimes also referred to as the integral cladding layer. The cladding layer M0 is closer to the core's center than the shell M1 and, if present, the other shells. The cladding layer M0 generally does not serve to conduct light or radiation. Rather, the cladding layer M0 contributes to ensuring that the radiation remains within the core and is transported there. The radiation conducted within the core is thus preferentially reflected at the interface between the core and the cladding layer M0. This interface from the core to the cladding layer M0 is preferably characterized by a change in refractive index. The refractive index of the cladding layer M0 is preferably lower than the refractive index nK of the core.Preferably, the cladding layer M0 contains the same material as the core, but has a lower refractive index than the core due to doping or additives.

[0475] Preferably, at least the shell M1 consists of silicon dioxide and has at least one, preferably several or all of the following features: a) an OH content of less than 10 ppm, for example less than 5 ppm, particularly preferably less than 1 ppm; b) a chlorine content of less than 60 ppm, preferably less than 40 ppm, for example less than 20 or less than 2 ppm, particularly preferably less than 0.5 ppm; c) an aluminum content of less than 200 ppb, preferably less than 100 ppb, for example less than 80 ppb, particularly preferably less than 60 ppb; d) an ODC content of less than 5 × 10¹⁵ / cm³, for example in a range of 0.1 × 10¹⁵ to 3 × 10¹⁵ / cm³, particularly preferably in a range of 0.5 × 10¹⁵ to 2.0 × 10¹⁵ / cm³; e) a metal content of metals other than aluminium of less than 1 ppm, for example less than 0.5 ppm, particularly preferably less than 0.1 ppm;f) a viscosity (p=1013 hPa) in a range from log 10 (η (1250°C) / dPas) = ​​11.4 to log 10 (η (1250°C) / dPas) = ​​12.9 and / or log 10 (η (1300°C) / dPas) = ​​11.1 to log 10 (η (1300°C) / dPas) = ​​12.2 and / or log 10 (η (1350°C) / dPas) = ​​10.5 to log 10 (η (1350°C) / dPas) = ​​11.5; g) a curl parameter of more than 6 m; h) a standard deviation of the OH content of not more than 10%, preferably not more than 5%, based on the OH content a) of shell M1; i) a standard deviation of the chlorine content of not more than 10%, preferably not more than 5%, based on the chlorine content b) of the shell M1; j) a standard deviation of the aluminum content of not more than 10%, preferably not more than 5%, based on the aluminum content c) of the shell M1; k) a refractive index homogeneity of less than 1 × 10⁻⁴; l) a transformation point Tg in a range of 1150 to 1250°C, particularly preferably in a range of 1180 to 1220°C; where ppb and ppm are each based on the total weight of the shell M1.

[0476] Preferably, the shell exhibits a refractive index homogeneity of less than 1 × 10⁻⁴. Refractive index homogeneity refers to the maximum deviation of the refractive index at any point in a sample, for example, a shell M1 or a quartz glass body, relative to the mean value of all refractive indices determined on the sample. To determine the mean value, the refractive index is measured at at least seven points.

[0477] Preferably, the shell M1 has a metal content of metals other than aluminum of less than 1000 ppb, for example, less than 500 ppb, particularly preferably less than 100 ppb, in each case based on the total weight of the shell M1. Often, however, the shell M1 has a content of metals other than aluminum in an amount of at least 1 ppb. Such metals are, for example, sodium, lithium, potassium, magnesium, calcium, strontium, germanium, copper, molybdenum, titanium, iron, and chromium. These can be present, for example, as elements, as ions, or as part of a molecule, an ion, or a complex.

[0478] The shell M1 can contain other components. Preferably, the shell M1 contains less than 500 ppm, for example less than 450 ppm, and particularly preferably less than 400 ppm, of other components, where the ppm values ​​are based on the total weight of the shell M1. Examples of other components include carbon, fluorine, iodine, bromine, and phosphorus. These can be present, for example, as elements, ions, or as part of a molecule, an ion, or a complex. However, the shell M1 often contains other components in an amount of at least 1 ppb.

[0479] Preferably, the shell M1 contains carbon at a concentration of less than 5 ppm, for example less than 4 ppm or less than 3 ppm, particularly preferably less than 2 ppm, in each case based on the total weight of the shell M1. Often, however, the shell M1 has a carbon content of at least 1 ppb.

[0480] Preferably, the shell M1 has a homogeneously distributed amount of OH, Cl or Al.

[0481] In a preferred embodiment of the optical fiber, the sheath M1 has a weight fraction of at least 80% by weight, for example at least 85% by weight, and particularly preferably at least 90% by weight, in each case based on the total weight of the sheath M1 and the cores. Preferably, the sheath M1 has a weight fraction of at least 80% by weight, for example at least 85% by weight, and particularly preferably at least 90% by weight, in each case based on the total weight of the sheath M1, the cores, and the further sheaths located between the sheath M1 and the cores. Preferably, the sheath M1 has a weight fraction of at least 80% by weight, for example at least 85% by weight, and particularly preferably at least 90% by weight, in each case based on the total weight of the optical fiber.

[0482] Preferably, the shell M1 has a density in the range of 2.1 to 2.3 g / cm³, particularly preferably in the range of 2.18 to 2.22 g / cm³.

[0483] A third subject matter of the present invention relates to a method for manufacturing a light source comprising the following steps: (i) Providing (ii) (i-1) a hollow body with at least one opening obtainable by a method according to the first subject matter of the invention comprising step iv.); (ii) optionally equipping the hollow body with electrodes; (iii) filling the hollow body with a gas. Step (i)

[0484] In step (i), a hollow body is provided. The hollow body provided in step (i) includes at least one opening, for example one opening or two openings or three openings or four openings, particularly preferably one opening or two openings.

[0485] Preferably, in step (i), a hollow body with at least one opening, obtainable by a method according to the first subject matter of the invention comprising step iv), is provided (step (i-1)). Preferably, the hollow body has the features described in the first subject matter of the invention.

[0486] The processing of the quartz glass body into a hollow body with one opening can, in principle, be carried out using any method known to those skilled in the art and suitable for the production of hollow glass bodies with one opening. Suitable methods include, for example, pressing, blowing, suction, or combinations thereof. It is also possible to form a hollow body with one opening from a hollow body with two openings by closing one opening, for example, by fusing them together.

[0487] The resulting hollow body preferably has the features described in the second and third subject matter of the invention.

[0488] The hollow body consists of a material containing silicon dioxide, preferably in an amount in the range of 98 to 100 wt.%, for example in the range of 99.9 to 100 wt.%, particularly preferably 100 wt.%, in each case based on the total weight of the hollow body.

[0489] The material from which the hollow body is made preferably has at least one, preferably several, for example two, or preferably all of the following features: HK1. a silicon dioxide content preferably more than 95 wt.%, for example more than 97 wt.%, particularly preferably more than 99 wt.%, based on the total weight of the material; HK2. a density in the range of 2.1 to 2.3 g / cm³, particularly preferably in the range of 2.18 to 2.22 g / cm³; HK3. a light transmittance at at least one wavelength in the visible range of 350 to 750 nm in a range of 10 to 100%, for example in a range of 30 to 99.99%, particularly preferably in a range of 50 to 99.9%, based on the amount of light generated inside the hollow body; HK4. an OH content of less than 500 ppm, for example less than 400 ppm, particularly preferably less than 300 ppm; HK5. a chlorine content of less than 60 ppm, preferably less than 40 ppm, for example less than 40 ppm or less than 2 ppm or less than 0.5 ppm, particularly preferably less than 0.1 ppm; HK6. an aluminium content of less than 200 ppb, for example less than 100 ppb, particularly preferably less than 80 ppb; HK7. a carbon content of less than 5 ppm, for example less than 4.5 ppm, particularly preferably less than 4 ppm; HK8. an ODC fraction of less than 5*10 15< / cm 3< ; HK9. a metal content of metals other than aluminium of less than 1 ppm, for example less than 0.5 ppm, particularly preferably less than 0.1 ppm; HK10. a viscosity (p=1013 hPa) in a range from log 10 η (1250°C) = 11.4 to log 10 η (1250°C)=12.4 and / or log 10 η (1300°C) = 11.1 to log 10 η (1350°C)=12.2 and / or log 10 η (1350°C) = 10.5 to log 10 η (1350°C)=11.5; HK11. a transformation point Tg in a range of 1150 to 1250°C, particularly preferably in a range of 1180 to 1220°C; where ppm and ppb are each based on the total weight of the hollow body. Step (ii)

[0490] Preferably, the hollow body from step (i) is fitted with electrodes, preferably two electrodes, before being filled with a gas. Preferably, the electrodes are connected to an electrical current supply. Preferably, the electrodes are connected to a lamp socket.

[0491] The electrode material is preferably selected from the group of metals. In principle, any metal can be selected as the electrode material that is not oxidized, corroded, melted, or otherwise impaired in its shape or conductivity during the operating conditions of the lamp. The electrode material is preferably selected from the group consisting of iron, molybdenum, copper, tungsten, rhenium, gold, and platinum, or at least two of these, with tungsten, molybdenum, or rhenium being preferred. Step (iii)

[0492] The hollow body provided in step (i) and optionally fitted with electrodes in step (ii) is filled with a gas.

[0493] Filling can be carried out using any method known to a person skilled in the art and suitable for filling. Preferably, a gas is introduced into the hollow body through the at least one opening.

[0494] Preferably, the hollow body is evacuated before being filled with a gas, preferably to a pressure of less than 2 mbar. The hollow body is then filled with the gas by introducing it. These steps can be repeated to minimize contamination with air, especially oxygen. Preferably, these steps are repeated at least twice, for example at least three times or at least four times, and particularly preferably at least five times, until the amount of contamination with other gases such as air, especially oxygen, is sufficiently low. This procedure is particularly preferred for filling hollow bodies with an opening.

[0495] If a hollow body has two or more openings, it is preferably filled through one of the openings. The air present in the hollow body before filling with gas can escape through at least one other opening. The gas is passed through the hollow body until the amount of impurities with other gases, such as air, especially oxygen, is sufficiently low.

[0496] Preferably, the hollow body is filled with an inert gas or a combination of two or more inert gases, for example, nitrogen, helium, neon, argon, krypton, xenon, or a combination of two or more thereof, particularly preferably with krypton, xenon, or a combination of nitrogen and argon. Other preferred filling materials for hollow bodies of lighting devices are deuterium and mercury.

[0497] Preferably, the hollow body is sealed after being filled with a gas, so that the gas does not escape during further processing, so that no air from the outside enters during further processing, or both. Sealing can be achieved by melting or by attaching a closure. Suitable closures include, for example, quartz glass closures, which are melted onto the hollow body, or lamp bases. Preferably, the hollow body is sealed by melting.

[0498] The light source according to the fifth subject matter of the invention comprises a hollow body and optionally electrodes. The light source preferably has at least one, for example at least two, at least three, or at least four, and particularly preferably at least five of the following features: i. a volume in a range of 0.1 cm³ to 10 m³, for example in a range of 0.3 cm³ to 8 m³, particularly preferably in a range of 0.5 cm³ to 5 m³; ii. a length in a range of 1 mm to 100 m, for example in a range of 3 mm to 80 m, particularly preferably in a range of 5 mm to 50 m; iii. a beam angle in a range of 2° to 360°, for example in a range of 10° to 360°, particularly preferably in a range of 30° to 360°; iv. an emission of light in a wavelength range of 145 to 4000 nm, for example in a range of 150 to 450 nm, or of 800 to 4000 nm, particularly preferably in a range of 160 to 280 nm; v. a power output in the range of 1 mW to 100 kW, particularly preferably in the range of 1 kW to 100 kW, or in the range of 1 to 100 watts.

[0499] A fourth object of the present invention relates to a method for producing a molded body comprising the following steps: (1) Carrying out the process steps i.) to iii.) according to claim 1 to obtain a quartz glass body; (2) Shaping the quartz glass body to obtain the shaped body.

[0500] The quartz glass body provided in step (1) is a quartz glass body obtainable by a method according to the first subject matter of the invention. Preferably, the quartz glass body provided has the features of the first subject matter of the invention. Step (2)

[0501] In principle, all methods known to those skilled in the art and suitable for shaping quartz glass are suitable for shaping the quartz glass body provided in step (1). Preferably, the quartz glass body is shaped into a form as described in the second, fourth, and fifth articles of the invention. More preferably, the form can be created using techniques known to glassblowers.

[0502] The molded body can, in principle, take on any shape that can be formed from quartz glass. Preferred molded bodies include, for example: Hollow bodies with at least one opening, such as round-bottom flasks and column flasks, attachments and closures for such hollow bodies, open articles such as trays and boats (wafer racks), crucibles, both open and closable, plates and windows, cuvettes, tubes and hollow cylinders, for example reaction tubes, profile tubes, rectangular chambers, rods, bars and blocks, for example in round or square, symmetrical or asymmetrical design, tubes and hollow cylinders closed at one or both ends, domes and bells, flanges, lenses and prisms, welded parts, bent parts, for example convex or concave surfaces and plates, bent rods and tubes.

[0503] According to a preferred embodiment, the molded body can be treated after molding. In principle, all methods described within the scope of the second subject matter of the invention that are suitable for post-processing the quartz glass body are suitable for this purpose. Preferably, the molded body can be mechanically machined, for example by drilling, honing, external grinding, grinding, or drawing. Figures

[0504] Fig. 1 Flowchart (Process for manufacturing a quartz glass body) Fig. 2 Flowchart (Process for producing silicon dioxide granules I) Fig. 3 Flowchart (Process for producing silicon dioxide granules II) Fig. 4 Flowchart (Procedure for manufacturing an optical fiber) Fig. 5 Flowchart (Procedure for manufacturing a light source) Fig. 6 Flowchart (Process for producing a quartz glass granule) Fig. 7Schematic representation of a hanging crucible in a furnace (not according to the invention) Fig. 8 Schematic representation of a standing crucible in a furnace (not according to the invention) Fig. 9 Schematic representation of a crucible with a flushing ring Fig. 10 schematic representation of a spray tower Fig. 11 Schematic representation of a cross-section of an optical fiber Fig. 12 Schematic representation of a top view of a light guide Fig. 13 Schematic representation of a crucible with a dew point measuring device (not according to the invention) Fig. 14 Flowchart (Procedure for manufacturing a molded body) Description of the characters

[0505] Figure 1Figure 1 shows a flowchart containing steps 101 to 104 of a process 100 for producing a quartz glass body according to the present invention. In a first step 101, silicon dioxide granules are provided. In a second step 102, a glass melt is formed from the silicon dioxide granules.

[0506] Preferably, molds are used for melting that can be placed in and removed from a furnace. Such molds are often made of graphite. They produce a negative mold of the casting. The silicon dioxide granules are poured into the mold and, in the third step 103, are first melted in the mold. Subsequently, the quartz glass body forms in the same mold as the melt cools. This body is then removed from the mold and further processed, for example, in an optional step 104. This procedure is discontinuous. The melting preferably takes place at reduced pressure, especially under vacuum. It is also possible to temporarily expose the furnace to a reducing, hydrogen-containing atmosphere during step 103.

[0507] In another procedure, suspended or upright crucibles are preferably used as melting pots. Melting preferably takes place in a reducing, hydrogen-containing atmosphere. In a third step 103, a quartz glass body is formed. The formation of the quartz glass body is preferably carried out by removing at least a portion of the molten glass from the crucible and cooling it. The removal is preferably carried out through a nozzle at the lower end of the crucible. In this case, the shape of the quartz glass body can be determined by the design of the nozzle. For example, solid bodies can be obtained. Hollow bodies are obtained, for example, if a mandrel is additionally provided in the nozzle. This exemplary process for the production of quartz glass bodies, and in particular step 103, is preferably carried out continuously. A hollow body can be formed from a solid quartz glass body in an optional step 104.

[0508] Figure 2Figure 1 shows a flowchart containing steps 201, 202, and 203 of a process 200 for the production of silicon dioxide granules I. In a first step 201, a silicon dioxide powder is provided. A silicon dioxide powder is preferably obtained from a synthetic process in which a silicon-containing material, for example, a siloxane, a silicon alkoxide, or a silicon halide, is reacted to form silicon dioxide in a pyrogenic process. In a second step 202, the silicon dioxide powder is mixed with a liquid, preferably water, to obtain a slurry. In a third step 203, the silicon dioxide contained in the slurry is converted into silicon dioxide granules. Granulation is carried out by spray granulation.For this purpose, the slurry is sprayed through a nozzle into a spray tower and dried, forming granules, with the contact surface between the nozzle and the slurry containing a glass or a plastic.

[0509] Figure 3 Figure 1 shows a flowchart containing steps 301, 302, 303 and 304 of a process 300 for the production of silicon dioxide granules II. Steps 301, 302 and 303 proceed according to steps 201, 202 and 203 according to Figure 201, 202 and 203. Figure 2 In step 304, the silicon dioxide granules I obtained in step 303 are processed into silicon dioxide granules II. This is preferably done by heating the silicon dioxide granules I in a chlorine-containing atmosphere.

[0510] Figure 4Figure 1 shows a flowchart containing steps 401, 403, and 404, as well as the optional step 402, of a process for manufacturing an optical fiber. In the first step 401, a quartz glass body is provided, preferably a quartz glass body manufactured according to process 100. Such a quartz glass body can be solid or hollow. From a solid quartz glass body provided in step 401, a hollow quartz glass body is formed in a second step 402 according to step 104. In a third step 403, one or more core rods are inserted into the hollow quartz glass body. In a fourth step 404, the quartz glass body provided with one or more core rods is processed into an optical fiber. For this purpose, the quartz glass body provided with one or more core rods is preferably heated to soften it and elongated until the desired optical fiber thickness is achieved.

[0511] Figure 5Figure 1 shows a flowchart comprising steps 501, 503, and 504, as well as the optional step 502, of a process for manufacturing a light source. In the first step 501, a quartz glass body is provided, preferably a quartz glass body manufactured according to process 100. Such a quartz glass body can be solid or hollow. If the quartz glass body provided in step 501 is solid, it is optionally formed into a hollow quartz glass body according to step 104 in a second step 502. In an optional third step, the hollow quartz glass body is fitted with electrodes. In a fourth step 504, the hollow quartz glass body is filled with a gas, preferably argon, krypton, xenon, or a combination thereof. Preferably, a solid quartz glass body is first provided (501), formed into a hollow body (502), fitted with electrodes (503), and filled with a gas (504).

[0512] Figure 6Figure 601 shows a flowchart containing steps 601 to 604 of a process for producing a quartz glass granule 600. In a first step 601, silicon dioxide granules are provided. In a second step 602, a glass melt is formed from the silicon dioxide. Preferably, the silicon dioxide granules are introduced into a crucible and then heated until a glass melt forms. The melting preferably takes place in a reducing, hydrogen-containing atmosphere. In a third step 603, a quartz glass body is formed. The formation of the quartz glass body is preferably carried out by removing at least a portion of the glass melt from the crucible and cooling it. The removal is preferably carried out through a nozzle at the lower end of the crucible. The shape of the quartz glass body can be determined by the design of the nozzle. The production of quartz glass bodies, and in particular step 603, is preferably carried out continuously.In a fourth step 604, the quartz glass body is crushed, preferably by high voltage discharge pulses, while retaining a quartz glass grain structure.

[0513] In Figure 7(Not according to the invention) a furnace 800 with a suspended crucible is shown. The crucible 801 is suspended within the furnace 800. The crucible 801 has a suspension 802 in its upper region, as well as a solids inlet 803 and a nozzle 804 as an outlet. The crucible 801 is filled with silicon dioxide granules 805 via the solids inlet 803. During operation, silicon dioxide granules 805 are present in the upper region of the crucible 801, while a glass melt 806 is present in the lower region of the crucible 801. The crucible 801 can be heated by heating elements 807, which are arranged on the outside of the crucible wall 810. The furnace also has an insulating layer 809 between the heating elements 807 and the outer furnace wall 808. The space between the insulating layer 809 and the crucible wall 810 can be filled with a gas and has a gas inlet 811 and a gas outlet 812 for this purpose. A quartz glass body 813 can be removed from the furnace through the nozzle 804.

[0514] In Figure 8 (Not according to the invention) a furnace 900 with a vertical crucible is shown. The crucible 901 is arranged vertically in the furnace 900. The crucible 901 has a base 902, a solids inlet 903, and a nozzle 904 as an outlet. The crucible 901 is filled with silicon dioxide granules 905 via the inlet 903. During operation, silicon dioxide granules 905 are present in the upper region of the crucible, while a glass melt 906 is present in the lower region of the crucible. The crucible can be heated by heating elements 907, which are arranged on the outside of the crucible wall 910. The furnace also has an insulating layer 909 between the heating elements 907 and the outer furnace wall 908. The space between the insulating layer 909 and the crucible wall 910 can be filled with a gas and therefore has a gas inlet 911 and a gas outlet 912. A quartz glass body 913 can be removed from the crucible 901 through the nozzle 904.

[0515] In Figure 9A preferred embodiment of a crucible 1000 is shown. The crucible 1000 has a solids inlet 1001 and a nozzle 1002 as an outlet. The crucible 1000 is filled with silicon dioxide granules 1003 via the solids inlet 1001. During operation, silicon dioxide granules 1003 are present in the upper region of the crucible 1000 as a cone 1004, while a glass melt 1005 is present in the lower region of the crucible. The crucible 1000 can be filled with a gas. It has a gas inlet 1006 and a gas outlet 1007. The gas inlet is a purge ring attached to the crucible wall above the silicon dioxide granules. The gas is released through the purge ring (with a gas supply not shown here) inside the crucible just above the melt level and / or the pile near the crucible wall and flows towards the gas outlet 1007, which is arranged in a ring shape in the lid 1008 of the crucible 1000.The resulting gas stream 1010 moves along the crucible wall and washes over it. A quartz glass body 1009 can be removed from the crucible 1000 through the nozzle 1002.

[0516] In Figure 10A preferred embodiment of a spray tower 1100 for spray granulating silicon dioxide is shown. The spray tower 1100 comprises a feeder 1101 through which a pressurized slurry containing silicon dioxide powder and a liquid is fed to the spray tower. At the end of the feeder is a nozzle 1102 through which the slurry is finely dispersed into the spray tower. Preferably, the nozzle is oriented obliquely upwards so that the slurry is sprayed into the spray tower as fine droplets in the direction of the nozzle orientation and then falls downwards in an arc driven by gravity. A gas inlet 1103 is located at the upper end of the spray tower. By introducing a gas through the gas inlet 1103, a gas flow is generated that opposes the exit direction of the slurry from the nozzle 1102. The spray tower 1100 also comprises a classifying device 1104 and a sieving device 1105.Particles smaller than a defined size are extracted by the classifier 1104 and removed through the discharge 1106. The suction power of the classifier 1104 can be adjusted according to the particle size of the particles being extracted. Particles larger than a defined size are sieved by the sieving device 1105 and removed through the discharge 1107. The sieve permeability of the sieving device 1105 can be selected according to the particle size of the particles to be sieved. The remaining particles, silicon dioxide granules of the desired particle size, are removed through the outlet 1108.

[0517] In Figure 11 A schematic cross-section through a light guide 1200 according to the invention is shown, which has a core 1201 and a shell M1 1202 surrounding the core 1201.

[0518] Figure 12Figure 1 schematically shows a top view of a fiber optic cable 1300, which has a cable-like structure. To illustrate the arrangement of the core 1301 and the sheath M1 1302 around the core 1301, a portion of the core 1301 is shown without the sheath M1 1302. Typically, however, the core 1301 is completely encased in the sheath M1 1302 along its entire length.

[0519] Figure 13Figure 1 (not according to the invention) shows a crucible 1400. The crucible has a solid inlet 1401 and an outlet 1402. During operation, silicon dioxide granules 1403 are present in a cone 1404 in the upper part of the crucible 1400, while a glass melt 1405 is present in the lower part of the crucible. The crucible 1400 has a gas inlet 1406 and a gas outlet 1407. The gas inlet 1406 and the gas outlet 1407 are arranged above the cone 1404 of silicon dioxide granules 1403. The gas outlet 1406 comprises a line for gas supply 1408 and a device 1409 for measuring the dew point of the exiting gas. The device 1409 comprises a dew point mirror hygrometer (not shown here). The distance between the crucible and the dew point measuring device 1409 can vary. A quartz glass body 1410 can be removed through the outlet 1402 of the crucible 1400.

[0520] Figure 14Figure 1 shows a flowchart containing steps 1601 and 1602 of a process for manufacturing a shaped body. In the first step, 1601, a quartz glass body is provided, preferably a quartz glass body manufactured according to process 100. Such a quartz glass body can be solid or hollow. In a second step, 1602, a shaped body is formed from a solid quartz glass body provided in step 1601. Test methods a. Fictitious temperature

[0521] The fictitious temperature is determined by Raman spectroscopy based on the Raman scattering intensity at approximately 606 cm⁻¹. The procedure and evaluation are described in the article by Pfleiderer et al.; "The UV-induced 210 nm absorption band in fused Silica with different thermal history and stoichiometry"; Journal of Non-Crystalline Solids, Volume 159 (1993), pages 145-153. b. OH content

[0522] The OH content of the glass is determined by infrared spectroscopy. The method described by DM Dodd & DM Fraser in "Optical Determinations of OH in Fused Silica" (JAP 37, 3991 (1966)) is used. Instead of the instrument specified therein, an FTIR spectrometer (Fourier-transform infrared spectrometer, currently the PerkinElmer System 2000) is employed. The spectra can, in principle, be evaluated at either the absorption band at approximately 3670 cm⁻¹ or the absorption band at approximately 7200 cm⁻¹. The selection of the band used is based on the rule that the transmission loss due to OH absorption is between 10 and 90%. c. Oxygen Deficiency Centers (ODCs)

[0523] For quantitative detection, the ODC(I) absorption at 165 nm is determined by means of a transmission measurement on a sample between 1-2 mm thick using a vacuum UV spectrometer, model VUVAS 2000, from McPherson, Inc. (USA).

[0524] Then the following applies: N = α / σ with N = Defect concentration [1 / cm 3< ] α = Optical absorption [1 / cm, basis e] of the ODC(I) band σ = Cross section [cm 2< ] where the cross-section σ=7.5·10 -17 cm 2 is used (from L. Skuja, "Color Centers and Their Transformations in Glassy SiO2", Lectures of the summer school "Photosensitivity in optical Waveguides and glasses", July 13-18 1998, Vitznau, Switzerl and). d. Elementary analysis

[0525] d-1) Massive samples are crushed. For purification, approximately 20 g of the sample is placed in an HF-resistant container, completely covered with HF, and thermally treated at 100°C for one hour. After cooling, the acid is discarded and the sample is rinsed several times with ultrapure water. The container is then dried in a drying oven.

[0526] Approximately 2 g of the solid sample (broken material, cleaned as above; dust, etc., directly without pretreatment) are weighed into an HF-resistant digestion vessel and mixed with 15 ml of HF (50 wt%). The digestion vessel is sealed and heated at 100°C until the solid sample is completely dissolved. The vessel is then opened and heated again at 100°C until the solution has completely evaporated. During this process, the digestion vessel is replenished three times with 15 ml of ultrapure water. One ml of HNO₃ is added to the digestion vessel to dissolve any precipitated impurities, and the volume is then increased to 15 ml with ultrapure water. The sample solution is now ready. d-2) Measurement ICP-MS / ICP-OES

[0527] Whether OES or MS is used depends on the expected elemental concentration. Typical limits of detection for MS are 1 ppb, and for OES 10 ppb (both based on the weighed sample volume). The determination of the elemental concentration with the instruments is carried out according to the instrument manufacturers' instructions (ICP-MS: Agilent 7500ce; ICP-OES: Perkin Eimer 7300 DV) and using certified reference solutions for calibration. The elemental concentration determined by the instruments in the solution (15 ml) is then converted to the original sample weight (2 g).

[0528] Note: It is important to ensure that the acid, containers, water, and equipment are of sufficient purity to accurately determine the element concentrations to be detected. This is verified by digesting a blank sample without quartz glass.

[0529] The following elements are determined in this way: Li, Na, Mg, K, Ca, Fe, Ni, Cr, Hf, Zr, Ti, (Ta), V, Nb, W, Mo, Al.

[0530] d-3) The determination of liquid samples is carried out as described above, except that the sample preparation according to step d-1) is omitted. 15 ml of the liquid sample are added to the digestion vessel. Conversion to an original weight is not necessary. e. Density determination of a liquid

[0531] To determine the density of a liquid, a precisely defined volume of the liquid is weighed into a measuring vessel that is inert to the liquid and its components. The empty weight and the weight of the filled vessel are measured. The density is then calculated by dividing the difference between the two weight measurements by the volume of liquid introduced into the vessel. f. Detection of fluoride

[0532] 15 g of a quartz glass sample are crushed and treated in nitric acid at 70°C for purification. The sample is then rinsed several times with ultrapure water and subsequently dried. 2 g of the sample are weighed into a nickel crucible and layered with 10 g of Na₂CO₃ and 0.5 g of ZnO. The crucible is sealed with a nickel lid and annealed at 1000°C for one hour. The nickel crucible is then filled with water and boiled until the melt cake has completely dissolved. The solution is transferred to a 200 ml volumetric flask and made up to 200 ml with ultrapure water. After settling of the undissolved components, 30 ml are removed and transferred to a 100 ml volumetric flask. 0.75 ml of glacial acetic acid and 60 ml of TISAB are added, and the solution is made up to 200 ml with ultrapure water. The sample is then transferred to a 150 ml beaker.

[0533] The fluoride content of the sample solution is determined using an ion-sensitive (fluoride) electrode suitable for the expected concentration range and a display device as specified by the manufacturer. In this case, a fluoride ion-selective electrode and reference electrode F-500 with R503 / D are used with a pMX 3000 / pH / ION from Wissenschaftlich-Technische Werkstätten GmbH. The fluoride concentration in the quartz glass is calculated using the fluoride concentration in the solution, the dilution factor, and the sample weight. G. Detection of chlorine (>= 50 ppm)

[0534] 15 g of a quartz glass sample are crushed and treated with nitric acid at approximately 70°C for purification. The sample is then rinsed several times with ultrapure water and subsequently dried. 2 g of the sample are placed in a PTFE insert of a pressure vessel, mixed with 15 mL of NaOH (c = 10 mol / L), sealed with a PTFE lid, and placed in the pressure vessel. The pressure vessel is sealed and thermally treated at approximately 155°C for 24 hours. After cooling, the PTFE insert is removed, and the solution is completely transferred to a 100 mL volumetric flask. 10 mL of HNO₃ (65 wt%) and 15 mL of acetate buffer are added, the mixture is allowed to cool, and the volume is made up to 100 mL with ultrapure water. The sample is then transferred to a 150 mL beaker. The sample has a pH between 5 and 7.

[0535] The chloride content of the measuring solution is determined using an ion-sensitive (chloride) electrode suitable for the expected concentration range and a display device according to the manufacturer's specifications, in this case an electrode type Cl-500 and reference electrode type R-503 / D on a pMX 3000 / pH / ION from Wissenschaftlich-Technische Werkstätten GmbH. h. Chlorine content (< 50 ppm)

[0536] Chlorine concentrations of < 50 ppm down to 0.1 ppm in fused silica are determined using neutron activation analysis (NAA). For this purpose, three core samples, each 3 mm in diameter and 1 cm long, are extracted from the fused silica specimen under investigation. These are sent to a research institute for analysis, in this case, the Institute of Nuclear Chemistry at Johannes Gutenberg University in Mainz. To prevent chlorine contamination of the samples, an agreement is made with the research institute to thoroughly clean the samples in an RF bath on-site immediately before measurement. Each core sample is measured multiple times. The results and the core samples are then returned by the research institute. i. Optical properties

[0537] The transmission of quartz glass samples is determined using commercial grating or FTIR spectrometers from Perkin Eimer (Lambda 900 [190-3000 nm] or System 2000 [1000-5000 nm]). The choice depends on the required measurement range.

[0538] To determine the absolute transmission, the samples are polished plane-parallel (surface roughness RMS < 0.5 nm) and the surface is cleaned of all residues by ultrasonic treatment after polishing. The sample thickness is 1 cm. In case of expected significant transmission loss due to contamination, doping, etc., a thicker or thinner sample can be selected to remain within the instrument's measuring range. A sample thickness (gauge length) is chosen at which only minimal artifacts occur due to the beam passing through the sample, while simultaneously measuring a sufficiently detectable effect.

[0539] To measure opacity, the sample is placed in front of an Ulbrich sphere in the beam path. The opacity is calculated from the measured transmittance value T according to the formula: O = 1 / T = I 0 / I. j. Refractive index and refractive index distribution on a tube or rod

[0540] The refractive index distribution of tubes / rods can be characterized using a York Technology Ltd. Preform Profiler P102 or P104. For this purpose, the rod is placed horizontally in the measuring chamber, which is then sealed tightly. The chamber is then filled with an immersion oil that has a refractive index at the test wavelength of 633 nm, very similar to that of the outermost glass layer at 633 nm. The laser beam then passes through the measuring chamber. A detector is mounted behind the measuring chamber (in the beam direction) to determine the deflection angle (beam entry versus beam exit). Assuming radial symmetry of the rod's refractive index distribution, the diametrical refractive index profile can be reconstructed using an inverse Abel transform. These calculations are performed by the software of the instrument manufacturer, York.

[0541] The refractive index of a sample is determined analogously to the above description using the York Technology Ltd. Preform Profiler P104. For isotropic samples, measuring the refractive index distribution yields only one value: the refractive index. k. Carbon content

[0542] The quantitative determination of the surface carbon content of silicon dioxide granules and silicon dioxide powder is carried out on a Leco Corporation RC612 carbon analyzer, USA, by the complete oxidation of all surface carbon contaminants (except SiC) to carbon dioxide with oxygen. For this purpose, 4.0 g of a sample is weighed out and placed in a quartz glass boat in the carbon analyzer. The sample is then surrounded by pure oxygen and heated to 900 °C for 180 seconds. The CO₂ produced is detected by the infrared detector of the carbon analyzer. Under these measurement conditions, the detection limit is ≤ 1 ppm (ppm by weight) of carbon.

[0543] A quartz glass boat suitable for this analysis with the aforementioned carbon analyzer is available as a consumable for the LECO analyzer with LECO number 781-335 from laboratory supply companies, in this case from Deslis Laborhandel, Flurstraße 21, D-40235 Düsseldorf (Germany), Deslis part number LQ-130XL. Such a boat has dimensions of approximately 25 mm (width) / 60 mm (length) / 15 mm (height). The quartz glass boat is filled halfway with sample material. For silicon dioxide powder, a sample weight of 1.0 g can be achieved. The lower detection limit is then <1 ppm carbon by weight. With the same fill level, a sample weight of 4 g of silicon dioxide granules (average particle size in the range of 100 to 500 µm) can be achieved in the same quartz glass boat. The lower detection limit is then around 0.1 ppm of carbon by weight.The lower detection limit is reached when the measurement surface integral of the sample is no larger than three times the measurement surface integral of a blank sample (blank sample = procedure as above, but with an empty quartz glass boat). 1. Curl parameters

[0544] The curl parameter (also called "fibre curl") is determined according to DIN EN 60793-1-34:2007-01 (German version of the standard IEC 60793-1-34:2006). Measurement is performed according to the method ("extrema technique") described in Annex A, sections A.2.1, A.3.2 and A.4.1. m. damping

[0545] The attenuation is determined according to DIN EN 60793-1-40:2001 (German version of IEC 60793-1-40:2001). Measurements are taken using the method described in the Annex ("cut-back method") at a wavelength λ=1550 nm. n. viscosity of the slurry

[0546] The slurry is adjusted to a concentration of 30 wt% solids content using demineralized water (Direct-Q 3UV, Millipore, water quality: 18.2 MΩcm). The viscosity is then measured using an Anton-Paar MCR102 viscometer. The viscosity is measured at 5 revolutions per minute (rpm) at a temperature of 23 °C and an atmospheric pressure of 1013 hPa. O. Thixotropy

[0547] The slurry is adjusted to a solids content of 30 wt% with demineralized water (Direct-Q 3UV, Millipore, water quality: 18.2 MΩcm). The thixotropy is then determined using an Anton-Paar MCR102 with a cone-plate setup. The viscosity is measured at 5 and 50 revolutions per minute (rpm). The ratio of these two values ​​yields the thixotropy index. The measurement is performed at a temperature of 23 °C. p. Zeta potential of the slurry

[0548] A zeta potential cell (Flow Cell, Beckman Coulter) is used for zeta potential measurements. The sample is dissolved in demineralized water (Direct-Q 3UV, Millipore, water quality: 18.2 MΩcm) to obtain a 20 mL solution with a concentration of 1 g / L. The pH is adjusted to 7 by adding HNO₃ solutions with concentrations of 0.1 mol / L and 1 mol / L and a NaOH solution with a concentration of 0.1 mol / L. Measurements are taken at a temperature of 23 °C. q. Isoelectric point of the slurry

[0549] A zeta potential cell (Flow Cell, Beckman Coulter) and an autotitrator (DelsaNano AT, Beckman Coulter) are used to determine the isoelectric point. The sample is dissolved in demineralized water (Direct-Q 3UV, Millipore, water quality: 18.2 MΩcm) to obtain a 20 mL solution with a concentration of 1 g / L. The pH is varied by adding HNO₃ solutions with concentrations of 0.1 mol / L and 1 mol / L and a NaOH solution with a concentration of 0.1 mol / L. The isoelectric point is the pH value at which the zeta potential is 0. It is measured at a temperature of 23 °C. r. pH value of the slurry

[0550] The pH value of the slurry is measured using a WTW 3210 from Wissenschaftlich-Technische-Werkstätten GmbH. The pH 3210 Set 3 electrode from WTW is used. Measurements are taken at a temperature of 23 °C. s. solids content

[0551] A sample weight m1 is heated to 500 °C for 4 hours and weighed again after cooling (m2). The solids content w is calculated as m2 / m1 * 100 [wt. %]. t. bulk density

[0552] The bulk density is determined according to DIN ISO 697:1984-01 using an SMG 697 from Powtec. The bulk material (silicon dioxide powder or granules) does not form lumps. u. Tapped density (granules)

[0553] The tapped density is measured according to the standard DIN ISO 787:1995-10. v. Determination of the pore size distribution

[0554] The pore size distribution is determined according to DIN 66133 (with a surface tension of 480 mN / m and a contact angle of 140°). For measuring pore sizes smaller than 3.7 nm, the Pascal 400 from Porotec is used. For measuring pore sizes from 3.7 nm to 100 µm, the Pascal 140 from Porotec is used. The sample is subjected to pressure treatment before measurement. A manual hydraulic press (order no. 15011 from Specac Ltd., River House, 97 Cray Avenue, Orpington, Kent BR5 4HE, UK) is used for this purpose. 250 mg of sample material are weighed into a Specac Ltd. pellet die with an inner diameter of 13 mm and a load of 1 t is applied according to the display. This load is held for 5 seconds and adjusted if necessary. The sample is then relaxed and dried for 4 hours at 105 ± 2°C in a circulating air drying oven.

[0555] The sample is weighed into the type 10 penetrometer to an accuracy of 0.001 g and, for good measurement reproducibility, is selected so that the stem volume used, i.e., the percentage of mercury consumed to fill the penetrometer, is between 20% and 40% of the total mercury volume. The penetrometer is then slowly evacuated to 50 µm Hg and held at this pressure for 5 minutes. The following parameters are directly reported by the instrument's software: total pore volume, total pore surface area (assuming cylindrical pores), average pore radius, modal pore radius (most frequent pore radius), and peak n.2 pore radius (µm). w. Primary particle size

[0556] The primary particle size is measured using a Zeiss Ultra 55 scanning electron microscope (SEM). The sample is suspended in demineralized water (Direct-Q 3UV, Millipore, water quality: 18.2 MΩcm) to obtain an extremely dilute suspension. The suspension is treated with an ultrasonic probe (UW 2070, Bandelin electronic, 70 W, 20 kHz) for 1 minute and then applied to a carbon adhesive pad. x. Average particle size in suspension

[0557] The mean particle size in suspension is measured using a Mastersizer 2000, available from Malvern Instruments Ltd., UK, according to their operating instructions, using the laser diffraction method. The sample is suspended in demineralized water (Direct-Q 3UV, Millipore, water quality: 18.2 MΩcm) to obtain 20 mL of suspension with a concentration of 1 g / L. The suspension is then treated with an ultrasonic probe (UW 2070, Bandelin electronic, 70 W, 20 kHz) for 1 minute. y. Particle size and grain size of the solid

[0558] The particle size and grain size of the solid are measured using a Camsizer XT, available from Retsch Technology GmbH, Germany, according to their operating instructions. The software outputs the D10, D50, and D90 values ​​for a sample. z. BET measurement

[0559] The static volumetric BET method according to DIN ISO 9277:2010 is used to measure the specific surface area. For the BET measurement, a "NOVA 3000" or a "Quadrasorb" (available from Quantachrome), which operates according to the SMART method ("Sorption Method with Adaptive dosing Rate"), is used. Micropore analysis is performed using the t-plot method (p / p0 = 0.1–0.3) and mesopore analysis using the MBET method (p / p0 = 0.0–0.3). The standards Alumina SARM-13 and SARM-214, available from Quantachrome, are used as reference materials. The tare weight of the measuring cells (clean and dry) is weighed. The measuring cell type is selected so that the sample material and the filling rod fill the measuring cell as much as possible, minimizing dead space. The sample material is then placed in the measuring cell. The amount of sample material is selected so that the expected measured value corresponds to 10-20 m² / g.The measuring cells are fixed in the BET measuring instrument's heating stations (without the filling rod) and evacuated to <200 mbar. The evacuation rate is set so that no material escapes from the measuring cell. In this state, the cell is baked at 200°C for 1 hour. After cooling, the sample-filled measuring cell is weighed (gross). The tare weight is then subtracted from the gross weight to obtain the net weight, which is the weight of the sample. The filling rod is then inserted into the measuring cell, and the cell is again fixed in the BET measuring instrument's heating station. Before starting the measurement, the sample designation and weight are entered into the software. The measurement is then initiated. The saturation pressure of the nitrogen gas (N₂ 4.0) is measured. The measuring cell is evacuated and cooled to 77 K using a nitrogen bath. The dead space is measured using helium gas (He 4.6). The cell is then evacuated again. A multi-point analysis with at least 5 measurement points is performed.N2 4.0 is used as the adsorptive. The specific surface area is given in m2 / g. za. Viscosity of glass bodies

[0560] The viscosity of the glass is measured using a beam viscometer type 401 from TA Instruments with the manufacturer's WinTA software (currently version 9.0) under Windows 10 according to DIN ISO 7884-4:1998-02. The span between the supports is 45 mm. Rectangular cross-section test strips are cut from areas of homogeneous material (top and bottom surfaces of the samples are finely ground to a minimum grit size of 1000). After processing, the sample surfaces have a grain size of 9 µm and a surface roughness (RA) of 0.15 µm. The test strips have the following dimensions: length = 50 mm, width = 5 mm, and height = 3 mm (length, width, height are assigned as specified in the standard). Three samples are measured, and the mean value is calculated. The sample temperature is measured using a thermocouple placed close to the sample surface. The following parameters are applied: heating rate = 25 K to a maximum of 1500 °C, load weight = 100 g, maximum deflection = 3000 µm (deviating from the norm). e.g. Dew point measurement

[0561] The dew point is determined using an Optidew dew point mirror hygrometer manufactured by Michell Instruments GmbH, D-61381 Friedrichsdorf, Germany. The measuring cell of the dew point mirror hygrometer is positioned 100 cm from the gas outlet of the furnace. The instrument and measuring cell are connected to the furnace gas outlet via a T-fitting and a hose (Swagelok PFA, outer diameter: 6 mm). The measuring cell is operated at an overpressure of 10 ± 2 mbar. The gas flow rate through the measuring cell is 1-2 standard liters / min. The measuring cell is located in a room with a temperature of 25°C, 30% relative humidity, and a mean atmospheric pressure of 1013 hPa. zc. Residual moisture

[0562] The residual moisture content of a sample of silicon dioxide granules is determined using a Mettler Toledo HX204 moisture analyzer. The instrument operates on the principle of thermogravimetry. The HX204 is equipped with a halogen lamp as its heating element. The drying temperature is 220°C. The initial sample weight is 10 g ± 10%. The "Standard" measurement method is selected. Drying continues until the weight change does not exceed 1 mg / 140 s. The residual moisture content is calculated by dividing the difference between the initial and final sample weights by the initial sample weight.

[0563] The residual moisture content of silicon dioxide powder is determined according to DIN EN ISO 787-2:1995 (2h, 105°C). Examples

[0564] The invention is further illustrated by examples below. The invention is not limited to these examples. A. 1. Production of silicon dioxide powder (OMCTS route)

[0565] The aerosol formed from the atomization of a siloxane with air (A) is introduced under pressure into a flame, which is generated by igniting a mixture of oxygen-enriched air (B) and hydrogen. A surrounding air stream (C) is then introduced, and the process mixture is subsequently cooled with process gas. The product is separated by a filter. The process parameters are given in Table 1, and the characteristics of the resulting products are given in Table 2. Experimental data for this example are provided with A1- marked with an x. 2. Modification 1: Increased carbon content

[0566] The procedure was carried out as described in A.1, but the combustion of the siloxane was conducted in such a way that a significant amount of carbon was also produced. Experimental data for this example are available with A2-x marked. Table 1 Example A1-1 A2-1 A2-2 Aerosol formation Siloxane OMCTS* OMCTS* OMCTS* supply kg / h 10 10 10 (kmol / h) (0,0337) (0,0337) (0,0337) Air supply (A) Nm 3< / h 14 10 12 Pressure barÜ 1,2 1,2 1,2 Burner supply oxygen-enriched air Nm 3< / h 69 65 68 (B) O2 content Vol.% 32 30 32 Total O2 supply Nm 3< / h 25,3 21,6 24,3 Kmol / h 1,130 0,964 1,083 Hydrogen supply Nm 3< / h 27 27 12 Kmol / h 1,205 1,205 0,536 supply -- -- carbon compound Material methane Crowd Nm 3< / h 5,5 Airflow (C) Nm 3< / h 60 60 60 Stoichiometric ratios V 2,099 1,789 2,011 X 0,938 0,80 2,023 Y 0,991 0,845 0,835 V = molar ratio of O₂ input / O₂ requirement for complete oxidation of the siloxane; X = molar ratio of O₂ / H₂; Y = (molar ratio of O₂ input / O₂ requirement for stoichiometric reaction of OMCTS + fuel gases); barÜ = overpressure; * OMCTS = octamethylcyclotetrasiloxane. Table 2 Example A1-1 A2-1 A2-2 BET m² / g 30 33 34 bulk density g / ml 0,114 +- 0,011 0,105 +- 0,011 0,103 +- 0,011 Stamped density g / ml 0,192 +- 0,015 0,178 +- 0,015 0,175 +- 0,015 Primary particle size nm 94 82 78 Particle size distribution D10 µm 3,978±0,380 5,137±0,520 4,973±0,455 Particle size distribution D50 µm 9,383±0,686 9,561±0,690 9,423±0,662 Particle size distribution D90 µm 25,622±1,387 17,362+0,921 18,722±1,218 Carbon content ppm 34±4 73±6 80±6 Chlorine content ppm < 60 < 60 < 60 Al content ppb 20 20 20 Total metal content excluding Al ppb < 700 < 700 < 700 Residual moisture % by weight 0,02-1,0 0,02-1,0 0,02-1,0 pH value in water 4% (IEP) - 4,8 4,6 4,5 Viscosity at 5 rpm, aqueous suspension 30 wt%, 23 °C mPas 753 1262 1380 alkaline earth metal content ppb 538 487 472 B. 1. Production of silicon dioxide powder (silicon source: SiCl 4 )

[0567] A quantity of silicon tetrachloride (SiCl₄) is vaporized at a temperature T and introduced at a pressure P into the flame of a burner, which is generated by igniting a mixture of oxygen-enriched air and hydrogen. The mean normalized gas flow at the burner outlet is recorded. The process mixture is subsequently cooled with process gas. The product is separated on a filter. The process parameters are given in Table 3 and the characteristics of the resulting products in Table 4. B1-x marked. 2. Modification 1: Increased carbon content

[0568] The procedure was carried out as described in B.1, but the combustion of the silicon tetrachloride was conducted in such a way that a significant amount of carbon was also produced. Experimental data for this example are available with B2-x marked. Table 3 Example B1-1 B2-1 Aerosol formation Supply of silicon tetrachloride kg / h 50 50 (kmol) (0,294) (0,294) Temperature T °C 90 90 Pressure p barÜ 1,2 1,2 Burner supply Oxygen-enriched air, Nm 3< / h 145 115 its O2 content Vol.% 45 30 supply -- carbon compound Material methane Crowd Nm 3< / h 2,0 Hydrogen supply Nm 3< / h 115 60 Kmol / h 5,13 2,678 Stoichiometric ratios X 0,567 0,575 Y 0,946 0,85 X = molar ratio O₂ / H₂; Y = mol. ratio of O₂ / O₂ input required for stoichiometric reaction with SiCl₄ + H₂ + CH₄; barÜ = gauge pressure. Table 4 Example B1-1 B2-1 BET m² / g 49 47 bulk density g / ml 0,07 ± 0,01 0,06±0,01 Stamped density g / ml 0,11 ± 0,01 0,10 ± 0,01 Primary particle size nm 48 43 Particle size distribution D10 µm 5,0±0,5 4,5±0,5 Particle size distribution D50 µm 9,3±0,6 8,7±0,6 Particle size distribution D90 µm 16,4±0,5 15,8±0,7 Carbon content ppm <4 76 Chlorine content ppm 280 330 Al content ppb 20 20 Total concentrations of Ca, Co, Cr, Cu, Fe, Ge, Hf, K, Li, Mg, Mn, Mo, Na, Nb, Ni, Ti, V, W, Zn, Zr ppb < 1300 < 1300 Residual moisture % by weight 0,02-1,0 0,02-1,0 pH value in water 4% (IEP) pH 3,8 3,8 Viscosity at 5 rpm, aqueous suspension 30 wt%, 23 °C mPas 5653 6012 alkaline earth metal content ppb 550 342 C. Steam treatment

[0569] A stream of silicon dioxide powder is introduced over the top of a vertical column. Water vapor at temperature (A) and air are supplied through the base of the column. The column is heated internally to maintain two temperatures: one at the top (B) and the other at the base (C). After exiting the column (residence time (D)), the silicon dioxide powder exhibits the properties shown in Table 6. The process parameters are listed in Table 5. Table 5 Example C-1 C-2 Recipient: Product of B1-1 B2-1 Input of reactant kg / h 100 100 Supply of water vapor kg / h 5 5 Temperature of water vapor (A) °C 120 120 Air supply Nm 3< / h 4,5 4,5 column Height m 2 2 Inner diameter mm 600 600 T (B) °C 260 260 T (C) °C 425 425 Time spent (D) s 10 10 silicon dioxide powder Table 6 Example C-1 C-2 pH value in water 4% (IEP) - 4,6 4,6 Chlorine content ppm < 60 < 60 Carbon content ppm <4 36 Viscosity at 5 rpm, aqueous suspension 30 wt%, 23 °C mPas 1523 1478

[0570] The silicon dioxide powders obtained in examples C-1 and C-2 each have a low chlorine content and a moderate pH value in suspension. The carbon content of example C-2 is higher than that of C-1. D. Treatment with neutralizing agent

[0571] A stream of silicon dioxide powder is introduced over the top of a vertical column. A neutralizing agent and air are supplied over the bottom of the column. The column is heated internally to a temperature (B) at the top and a second temperature (C) at the bottom. After exiting the column (residence time (D)), the silicon dioxide powder exhibits, in particular, the properties shown in Table 8. The process parameters are given in Table 7. Table 7 Example D-1 Recipient: Product of B1-1 Input of reactant kg / h 100 Neutralizing agent ammonia Supply of neutralizing agent kg / h 1,5 Key data Neutralizing agent Available from Air Liquide: Ammonia N38, purity ≥ 99.98% by volume Air supply Nm 3< / h 4,5 column Height m 2 Inner diameter mm 600 T (B) °C 200 T (C) °C 250 Time spent (D) s 10 silicon dioxide powder Table 8 Example D-1 pH value in water 4% (IEP) 4,8 Chlorine content ppm 210 Carbon content ppm < 4 Viscosity at 5 rpm, aqueous suspension 30 wt%, 23 °C mPas 821 E. 1. Production of silicon dioxide granules from silicon dioxide powder

[0572] A silicon dioxide powder is dispersed in demineralized water using an intensive mixer type R from Gustav Eirich. The resulting suspension is pumped by a diaphragm pump, pressurized, and dispersed into droplets through a nozzle. These droplets are dried in a spray tower and collect at the bottom. The process parameters are given in Table 9, and the properties of the resulting granules are given in Table 10. Experimental data for this example are available with E1-x marked. 2. Modification 1: Increased carbon content

[0573] The procedure is analogous to description E.1. Additionally, carbon powder is dispersed into the suspension. Experimental data for this example are available with E2-x marked. 3. Modification 2: Addition of silicon

[0574] The procedure is analogous to description E.1. Additionally, a silicon component is dispersed into the suspension. Experimental data for this example are available with E3-1 marked. Table 9 Example E1-1 E1-2 E1-3 E1-4 E1-5 E2-1 E3-1 E3-2 Recipient = product of A1-1 A2-1 B1-1 C-1 C-2 A1-1 A1-1 A2-1 Quantity of reactant kg 10 10 10 10 10 10 10 10 Carbon powder -- -- -- -- -- -- -- material C** Max. particle size 75 Crowd µm 1 g silicon component -- -- -- -- -- -- Siliziu mpulv er*** -- Material Grain size (d 50 ) 8 µm Crowd 1000 ppm Carbon content 0.5 ppm Total concentrations of Ca, Co, Cr, Cu, Fe, Ge, Hf, K, Li, Mg, Mn, Mo, Na, Nb, Ni, Ti, V, W, Zn, Zr 5 ppm Water Quality* VE VE VE VE VE VE VE VE liter 5,4 5,4 5,4 5,4 5,4 5,4 5,4 5,4 Dispersion solids content wt.% 65 65 65 65 65 65 65 65 nozzle diameter mm 2,2 2,2 2,2 2,2 2,2 2,2 2,2 2,2 temperature °C 25 25 25 25 25 25 25 25 Pressure Bear 16 16 16 16 16 16 16 16 Installation height m 6,5 6,5 6,5 6,5 6,5 6,5 6,5 6,5 Spray tower Height m 18,20 18,20 18,20 18,20 18,20 18,20 18,20 18,20 Inner diameter m 6,30 6,30 6,30 6,30 6,30 6,30 6,30 6,30 T (Gas supplied) °C 380 380 380 380 380 380 380 380 T (Exhaust air) °C 110 110 110 110 110 110 110 110 airflow m³ / h 6500 6500 6500 6500 6500 6500 6500 6500 Installation height = distance between the nozzle and the lowest point inside the spray tower in the direction of the gravity vector. * VE = fully demineralized, conductivity ≤ 0.1 µS; ** C 006011: Graphite powder, max. particle size: 75 µm, high purity (available from Goodfellow GmbH, Bad Nauheim (Germany); *** available from Wacker Chemie AG (Munich, Germany). Table 9 (continued) Example E8-11 E8-12 E8-13 E8-14 Recipient = product of A2-1 B1-1 B1-1 A1-1 Quantity of reactant kg 10 10 10 10 Carbon powder material C** Max. particle size 75 µm -- -- -- Crowd 1 g silicon component -- -- -- -- Material Water Quality* Liters VE 5.4 VE 5.4 VE 5.4 VE 5.4 Dispersion solids content wt.% 65 65 65 65 nozzle diameter mm 2,2 2,2 2,2 2,2 temperature °C 25 25 25 25 Pressure Bear 16 16 16 16 Installation height m 6,5 6,5 6,5 6,5 Spray tower Height m 18,2 18,2 18,2 18,2 Inner diameter m 6,3 6,3 6,3 6,3 T (Gas supplied) °C 380 380 380 380 T (Exhaust air) °C 110 110 110 110 airflow m³ / h 6500 6500 6500 6500 Installation height = distance between the nozzle and the lowest point inside the spray tower in the direction of the gravity vector. * VE = fully demineralized, conductivity ≤ 0.1 µS; ** C 006011: Graphite powder, max. particle size: 75 µm, high purity (available from Goodfellow GmbH, Bad Nauheim (Germany); *** available from Wacker Chemie AG (Munich, Germany). Table 10 Example E1-1 E1-2 E1-3 E1-4 E1-5 E2-1 E3-1 E3-2 BET m² / g 30 33 49 49 47 28 31 35 bulk density g / ml 0,8 ± 0,1 0,8 ± 0,1 0,8 ± 0,1 0,8 ± 0,1 0,8 ± 0,1 0,8 ± 0,1 0,8 ± 0,1 0,8 ± 0,1 Stamped density g / ml 0,9 ± 0,1 0,9 ± 0,1 0,9 ± 0,1 0,9 ± 0,1 0,9 ± 0,1 0,9 ± 0,1 0,9 ± 0,1 0,9 ± 0,1 medium particle size µm 255 255 255 255 255 255 255 255 Particle size distribution gD10 µm 110 110 110 110 110 110 110 110 Particle size distribution gD50 µm 222 222 222 222 222 222 222 222 Particle size distribution D90 µm 390 390 390 390 390 390 390 390 SPHT3 Dim-less 0,64-0,98 0,64-0,98 0,64-0,98 0,64-0,98 0,64-0,98 0,64-0,98 0,64-0,98 0,64-0,98 Aspect ratio B / L (width to length) Dim-less 0,64-0,94 0,64-0,94 0,64-0,94 0,64-0,94 0,64-0,94 0,64-0,94 0,64-0,94 0,64-0,94 Carbon content ppm < 4 39 <4 <4 32 100 <4 39 Chlorine content ppm < 60 < 60 280 <60 <60 <60 <60 < 60 Al content ppb 20 20 20 20 20 20 20 20 Total concentrations of Ca, Co, Cr, Cu, Fe, Ge, Hf, K, Li, Mg, Mn, Mo, Na, Nb, Ni, Ti, V, W, Zn, Zr ppb < 700 < 700 < 1300 < 1300 < 1300 < 700 < 700 < 700 Residual moisture % by weight < 3 <3 <3 < 3 <3 <3 < 3 < 3 alkaline earth metal content ppb 538 487 550 550 342 538 538 487 pore volume ml / g 0,33 0,33 0,45 0,45 0,45 0,33 0,33 0,33 Angle of repose ° 26 26 26 26 26 26 26 26 Table 10 (continued) Example E8-11 E8-12 E8-13 E8-14 BET m² / g 33 52 51 32 bulk density g / ml 0,8 ± 0,1 0,8 ± 0,1 0,8 ± 0,1 0,8 ± 0,1 Stamped density g / ml 0,9 ± 0,1 0,9 ± 0,1 0,9 ± 0,1 0,9 ± 0,1 medium particle size µm 255 255 255 255 Particle size distribution D10 µm 110 110 110 110 Particle size distribution D50 µm 222 222 222 222 Particle size distribution D90 µm 390 390 390 390 SPHT3 Dim-less 0,64-0,98 0,64-0,98 0,64-0,98 0,64-0,98 Aspect ratio B / L (width to length) Dim-less 0,64-0,94 0,64-0,94 0,64-0,94 0,64-0,94 Carbon content ppm 39 < 4 <4 <4 Chlorine content ppm < 60 250 260 < 60 Al content ppb 20 20 20 20 Total concentrations of Ca, Co, Cr, Cu, Fe, Ge, Hf, K, Li, Mg, Mn, Mo, Na, Nb, Ni, Ti, V, W, Zn, Zr ppb < 700 < 700 < 700 < 700 Residual moisture % by weight <3 <3 <3 <3 alkaline earth metal content ppb 468 535 530 527 pore volume ml / g 0,33 0,33 0,33 0,33 Angle of repose ° 26 26 26 26

[0575] The granules are all open-pored and exhibit a uniform, spherical shape (all confirmed by microscopic examination). They do not tend to clump or stick together. F. Cleaning of silicon dioxide granules

[0576] Silicon dioxide granules are first treated in a rotary kiln, optionally at temperature T1, with oxygen or nitrogen (see Table 11). The silicon dioxide granules are then treated in cocurrent flow with a chlorine-containing component, whereby the temperature is increased to temperature T2. The process parameters are given in Table 11, and the properties of the resulting treated granules are given in Table 12. Table 11 Example F1-1 F1-2 F1-3 F1-4 F1-5 F2-1 F3-1 F3-2 Recipient = product of E1-1 E1-2 E1-3 E1-4 E1-5 E2-1 E3-1 E3-2 rotary kiln 1) < length cm 200 200 200 200 200 200 Inner diameter cm 10 10 10 10 10 10 throughput kg / h 2 2 2 2 2 2 Rotational speed it rpm 2 2 2 2 2 2 T1 °C 1100 omitted 1100 1100 1100 omitted 1100 1100 atmosphere Pure O2 omitted Pure O2 Pure O2 Pure O2 omitted N2 N2 reactant O 2 omitted O2 O2 O 2 omitted No No Supply 300l / h omitted 3001 / h 3001 / h 300l / h omitted Residual moisture Weight- <1 <3 <1 <1 <1 <3 <1 <1 % T2 °C 1100 1100 1100 1100 1100 1100 omitted omitted Direct current Component 1: HCl l / h 50 50 50 50 50 50 omitted omitted Component 2: Cl 2 l / h 0 15 0 0 0 15 omitted omitted Component 3: N 2 l / h 50 35 50 50 50 35 omitted omitted Total direct current l / h 100 100 100 100 100 100 omitted omitted 1)< For rotary kilns, the throughput was chosen as the control variable. This means that during operation, the mass flow exiting the rotary kiln is continuously measured, and the rotational speed and / or the inclination of the rotary kiln are adjusted accordingly. For example, an increase in throughput can be achieved by a) increasing the rotational speed, or b) increasing the inclination of the rotary kiln from the horizontal, or a combination of a) and b). Table 11 (continued) Example F8-11 F8-12 F8-13 F8-14 Recipient = product of E8-11 E8-12 E8-13 E8-14 rotary kiln 1) < length cm 200 200 200 Inner diameter cm 10 10 10 throughput kg / h 2 2 2 Rotational speed rpm 2 2 2 T1 °C omitted 1100 1100 1100 atmosphere omitted Pure O2 Pure O2 Pure O2 reactant omitted O 2 O 2 O 2 Supply omitted 300l / h 300l / h 300l / h Residual moisture % by weight <3 <1 <1 <1 T2 °C 1100 1100 1100 1100 Direct current Component 1: HCl l / h 50 50 50 50 Component 2: Cl 2 l / h 15 0 0 0 Component 3: N 2 1 / h 35 50 50 50 Total direct current l / h 100 100 100 100 1)< For the rotary kiln, the throughput was chosen as the control variable. This means that during operation, the mass flow exiting the rotary kiln is continuously measured, and the rotational speed and / or the inclination of the rotary kiln are adjusted accordingly. For example, an increase in throughput can be achieved by a) increasing the rotational speed, or b) increasing the inclination of the rotary kiln from the horizontal, or a combination of a) and b). Table 12 Example F1-1 F1-2 F1-3 F1-4 F1-5 F2-1 F3-1 F3-2 BET m² / g 25 27 43 45 40 23 25 26 Carbon content ppm <4 <4 <4 <4 < 4 <4 <4 <4 Chlorine content ppm 100-200 100-200 300-400 100-200 100-200 100-200 <60 <60 Al content ppb 20 20 20 20 20 20 20 20 pore volume mm 3< / g 650 650 650 650 650 650 650 650 Total concentrations of Ca, Co, Cr, Cu, Fe, Ge, Hf, K, Li, Mg, Mn, Mo, Na, Nb, Ni, Ti, V, W, Zn, Zr ppb <200 <200 <200 <200 <200 <200 <700 <700 alkaline earth metal content ppb 115 55 95 115 40 35 136 33 Stamped density g / cm³< 0,95 ± 0,05 0,95 ± 0,05 0,95 ± 0,05 0,95 ± 0,05 0,95 ± 0,05 0,95 ± 0,05 0,95 ± 0,05 0,95 ± 0,05 Table 12 (continued) Example F8-11 F8-12 F8-13 F8-14 BET m² / g 27 49 45 25 Carbon content ppm <4 <4 <4 <4 Chlorine content ppm 100-200 300-400 300-400 100-200 Al content ppb 20 20 20 20 pore volume mm 3< / g 650 650 650 650 Total concentrations of Ca, Co, Cr, Cu, Fe, Ge, Hf, K, Li, Mg, Mn, Mo, Na, Nb, Ni, Ti, V, W, Zn, Zr ppb <200 <200 <200 <200 alkaline earth metal content ppb 58 117 119 114 Stamped density g / cm³< 0,95 ± 0,05 0,95 ± 0,05 0,95 ± 0,05 0,95 ± 0,05

[0577] The granules after the purification step show a significantly reduced carbon content in the case of F1-2, F2-1, and F3-2 (similar to low-carbon granules, e.g., Fl-1). In particular, F1-2, F1-5, F2-1, and F3-2 show a significantly lower content of alkaline earth metals. SiC formation was not observed. G. Heat treatment of silicon dioxide granules

[0578] Silicon dioxide granules are subjected to heat treatment in a rotary kiln, a pre-chamber upstream of the melting furnace and connected to it via a further intermediate chamber. The rotary kiln is characterized by a temperature profile that increases in the conveying direction. The result is further treated silicon dioxide granules. In Example G-4-2, heat treatment during mixing in the rotary kiln was omitted. The process parameters are given in Table 13, and the properties of the resulting treated granules are given in Table 14. Table 13 Example G1-1 G1-2 G1-3 G1-4 G1-5 G2-1 G3-1 G3-2 G4-1 G4-2 Recipient = product of F1-1 F1-2 F1-3 F1-4 F1-5 F2-1 F3-1 F3-2 F1-1 F1-1 Silicon components -- -- -- -- -- -- -- --- silicon powder silicon p Material ver*** ulver*** Crowd 0,01% 0,1% rotary kiln 1) < omitted length cm 200 200 200 200 200 200 200 200 200 Inner diameter cm 10 10 10 10 10 10 10 10 10 throughput kg / h 8 5 5 5 5 5 5 5 5 Rotational speed rpm 30 30 30 30 30 30 30 30 30 T1 (Inlet to rotary kiln) °C RT RT RT RT RT RT RT RT RT T2 (Outlet rotary kiln) °C 500 500 500 500 500 500 500 500 500 atmosphere Gas, flow direction Air, free convection O2, in countercurrent O2, in countercurrent O2, in countercurrent O2, in countercurrent O2, in countercurrent O2, in countercurrent O2, in countercurrent O2, in countercurrent Total gas flow rate Nm 3< / h 0,6 0,6 0,6 0,6 0,6 0,6 0,6 0,6 *** Particle size D 50 = 8 µm; Carbon content ≤ 5 ppm; Total foreign metals ≤ 5 ppm; 0.5 ppm; available from Wacker Chemie AG (Munich, Germany); RT = Room temperature (25 °C). 1)< For the rotary kilns, the throughput was chosen as the control variable. This means that during operation, the mass flow exiting the rotary kiln is continuously weighed, and then the rotational speed and / or the inclination of the rotary kiln are adjusted accordingly. For example, an increase in throughput can be achieved by a) increasing the rotational speed, or b) increasing the inclination of the rotary kiln from the horizontal, or a combination of a) and b). Table 13 (continued) Example G8-11 G8-12 G8-13 G8-14 Recipient = product of F8-11 F8-12 F8-13 F8-14 Silicon components -- -- -- -- Material Crowd rotary kiln 1) < length cm 200 200 200 200 Inner diameter cm 10 10 10 10 throughput kg / h 5 8 8 8 Rotational speed rpm 30 30 30 30 T1 (Inlet to rotary kiln) °C RT RT RT RT T2 (Outlet rotary kiln) °C 500 500 500 500 atmosphere Gas, flow direction O2, in countercurrent Air, free convection Air, free convection Air, free convection Total gas flow rate Nm 3< / h 0,6 *** Particle size D 50 = 8 µm; Carbon content ≤ 5 ppm; Total foreign metals ≤ 5 ppm; 0.5 ppm; available from Wacker Chemie AG (Munich, Germany); RT = Room temperature (25 °C). 1)< For the rotary kilns, the throughput was chosen as the control variable. This means that during operation, the mass flow exiting the rotary kiln is continuously weighed, and then the rotational speed and / or the inclination of the rotary kiln are adjusted accordingly. For example, an increase in throughput can be achieved by a) increasing the rotational speed, or b) increasing the inclination of the rotary kiln from the horizontal, or a combination of a) and b). Table 14 Example G1-1 G1-2 G1-3 G1-4 G1-5 G2-1 G3-1 G3-2 G4-1 G4-2 BET m² / g 22 23 38 42 37 22 22 21 22 24 Water content (residual moisture) ppm 500 100 100 100 100 100 500 100 500 <10000 Carbon content ppm <4 <4 <4 <4 <4 <4 <4 <4 <4 <4 Chlorine content ppm 100-200 100-200 300-400 100-200 100-200 100-200 <60 <60 100-200 100-200 Al content ppb 20 20 20 20 20 20 20 20 20 20 Total concentrations of Ca, Co, Cr, Cu, Fe, Ge, Hf, K, Li, Mg, Mn, Mo, Na, Nb, Ni, Ti, V, W, Zn, Zr ppb ≤ 200 ≤ 200 ≤ 200 ≤ 200 ≤ 200 ≤ 200 ≤ 200 ≤ 200 ≤ 200 ≤ 200 alkaline earth metal content ppb 115 55 95 115 40 35 136 33 115 115 Angle of repose ° 26 26 26 26 26 26 26 26 26 26 Table 14 (continued) Example G8-11 G8-12 G8-13 G8-14 BET m² / g 23 46 43 22 Water content (residual moisture) ppm 293 570 529 281 Carbon content ppm <4 <4 <4 < 4 Chlorine content ppm 83 300-400 300-400 84 Al content ppb 20 20 20 20 Total concentrations of Ca, Co, Cr, Cu, Fe, Ge, Hf, K, Li, Mg, Mn, Mo, Na, Nb, Ni, Ti, V, W, Zn, Zr ppb ≤ 200 ≤ 200 ≤ 200 ≤ 200 alkaline earth metal content ppb 58 117 119 114 Angle of repose ° 26 26 26 26

[0579] As a result of this treatment, G3-1 and G3-2 have a significantly reduced alkaline earth metal content compared to before (E3-1 and E3-2 respectively). H. Melting of granules to quartz glass

[0580] Silicon dioxide granules according to row 2 of Table 15 are used to manufacture a quartz glass tube in a vertical crucible drawing process. The setup of the vertical furnace for example H5-1 including a standing crucible is in Figure 8 shown schematically; for all other examples with a hanging crucible, see below. Figure 7As a schematic diagram. The silicon dioxide granules are added via the solid feed, and the interior of the crucible is purged with a gas mixture. A glass melt forms in the crucible, upon which rests a cone of silicon dioxide granules. In the lower part of the crucible, molten glass is extracted from the glass melt through a drawing nozzle (possibly with a mandrel) and drawn vertically downwards as a pipe string. The throughput of the system is determined by the weight and viscosity of the glass melt above the nozzle and the orifice size defined by the nozzle. By varying the amount of silicon dioxide granules supplied and the temperature, the throughput can be adjusted to the desired level. The process parameters are given in Tables 15 and 17, and, where applicable, Table 19; the properties of the resulting quartz glass bodies are given in Tables 16 and 18.

[0581] In Example H7-1 and H8-11 to H8-14A gas distribution ring is arranged in the crucible, which supplies the purge gas near the surface of the molten glass. An example of such an arrangement is shown below. Figure 9 .

[0582] In Example H8-1 to H8-4 The dew point was determined at the gas outlet. The measuring principle is in Figure 13 shown. The gas flow travels a distance of 100 cm between the outlet of the melting pot and the dew point measuring point. Table 15 Example H1-1 H1-2 H1-3 H1-4 H1-5 H3-1 H3-2 H4-1 H4-2 Recipient = product of G1-1 G1-2 G1-3 G1-4 G1-5 G3-1 G3-2 G4-1 G4-2 Melting pot type Hanging tin pot Hanging tin pot Hanging tin pot Hanging tin pot Hanging tin pot Hanging tin pot Hanging tin pot Hanging tin pot Hanging tin pot Metal type tungsten tungsten tungsten tungsten tungsten tungsten tungsten tungsten tungsten length cm 200 150 150 150 150 200 150 200 200 Inner diameter cm 40 25 25 25 25 40 25 40 40 throughput kg / h 30 20 20 20 20 30 20 30 30 T1 (Gas space crucible) °C 300 300 300 300 300 300 300 300 300 T2 (glass melt) °C 2100 2100 2100 2100 2100 2100 2100 2100 2100 T3 (nozzle) °C 1900 1900 1900 1900 1900 1900 1900 1900 1900 Atmosphere / purge gas He concentration Vol. 50 50 50 50 50 50 50 50 50 H 2 concentration Vol. 50 50 50 50 50 50 50 50 50 Total gas flow rate Nm 3< / h 4 4 4 4 4 2 4 2 2 O 2 ppm ≤100 ≤100 ≤100 ≤100 ≤100 ≤100 ≤100 ≤100 ≤100 Table 16 Example H1-1 H1-2 H1-3 H1-4 H1-5 H3-1 H3-2 H4-1 H4-2 Carbon content ppm < 4 < 4 < 4 < 4 < 4 < 4 < 4 < 4 < 4 Chlorine content ppm 100-200 100-200 300-400 100-200 100-200 <60 <60 100-200 100-200 Al content ppb 20 20 20 20 20 20 20 20 20 Total concentrations of Ca, Co, Cr, Cu, Fe, Ge, Hf, K, Li, Mg, Mn, Mo, Na, Nb, Ni, Ti, V, W, Zn, Zr ppb <400 <400 <400 <400 <400 <400 <400 <400 <400 OH content ppm 400 400 400 400 400 80 400 80 80 alkaline earth metal content ppb 115 55 95 115 40 136 33 115 115 ODC content 1 / cm 3< 4*10 15< 2*10 16< 4*10 15< 4*10 15< 4*10 15< 5*10 18< 2*10 16< 5*10 18< 8*10 18< pore volume mL / g 0,1 0,1 0,1 0,1 0,1 0,1 0,1 0,1 0,1 Outer diameter of pipe string / quartz glass body cm 19,7 3,0 19,7 19,7 19,7 19,7 3,0 19,7 19,7 viscosity @1250°C Lg(η / dPas) 11,69±0,13 11,69±0,13 11,69±0,13 11,69±0,13 11,69±0,13 12,16±0,2 11,69±0,13 12,16±0,2 12,16±0,2 @1300°C 11,26±0,1 11,26±0,1 11,26±0,1 11,26±0,1 11,26±0,1 11,49±0,15 11,26±0,1 11,49±0,15 11,49±0,15 @1350°C 10,69±0,07 10,69±0,07 10,69±0,07 10,69±0,07 10,69±0,07 10,88±0,1 10,69±0,07 10,88±0,1 10,88±0,1 "±" values ​​represent the standard deviation. Table 17 Example H5-1 H6-1 H7-1 H8-1 H8-2 H8-3 H8-4 Recipient = product of G1-1 G1-1 G1-1 G1-1 G1-1 G1-1 G1-1 Melting pot type Standing sintering crucible Hanging sintering crucible Hanging tin pot Hanging tin pot Hanging tin pot Hanging tin pot Hanging tin pot Metal type tungsten tungsten tungsten tungsten tungsten tungsten tungsten Additional additions or extensions -- -- Gas distributor r-ring Dew point measurement Dew point measurement Dew point measurement Dew point measurement length cm 250 250 200 200 200 200 200 Inner diameter cm 40 36 40 40 40 40 40 throughput kg / h 40 35 30 30 30 30 30 T1 (Gas space crucible) °C 300 400 300 300 300 300 300 T2 (glass melt) °C 2100 2150 2100 2100 2100 2100 2100 T3 (nozzle) °C 1900 1900 1900 1900 1900 1900 1900 atmosphere He concentration Vol. 30 50 50 50 50 50 50 H 2 concentration Vol. 70 50 50 50 50 50 50 Total gas flow rate Nm 3< / h 4 4 8 8 4 3 2 O 2 ppm <100 <100 ≤10 ≤100 ≤100 ≤100 ≤100 Table 17 (continued) Example H8-11 H8-12 H8-13 H8-14 Recipient = product of G8-11 G8-12 G8-13 G8-14 Melting pot type Hanging tin pot Hanging tin pot Hanging tin pot Hanging tin pot Metal type tungsten tungsten tungsten tungsten Additional entry or Gas distributor- Gas distributor- Gas distributor- Gas distributor- Extension(s) ring ring ring ring length 200 200 200 200 Inner diameter 40 40 40 40 throughput 30 30 30 30 T1 (Gas space crucible) 300 300 300 300 T2 (glass melt) 2100 2100 2100 2110 T3 (nozzle) 1900 1920 1920 1910 atmosphere H e K onzentration 30 30 30 30 H 2 K onzentration 70 70 70 70 D Total gas flow rate 4 6 6 4 O 2 ≤100 ≤100 ≤100 ≤100 Dew point of the gas stream before being fed to the melting pot -90 -90 -90 -90 Dew point of the gas flow after removal from the crucible -7,1 -2,8 -3,7 -6,9 Table 18 Example H5-1 H6-1 H7-1 H8-1 H8-2 Carbon content ppm <4 <4 <4 <4 <4 Chlorine content ppm 100-200 100-200 100-200 100-200 100-200 Al content ppb 20 20 20 20 20 Total concentrations of Ca, Co, Cr, Cu, Fe, Ge, Hf, K, Li, Mg, Mn, Mo, Na, Nb, Ni, Ti, V, W, Zn, Zr ppb <400 <400 <400 <400 <400 OH content ppm 400 400 400 250 400 alkaline earth metal content ppb 115 115 115 115 115 ODC content 1 / cm 3< <4*10 15< <4*10 15< <4*10 15< <4*10 15< <4*10 15< Salary to W, Mo, Re, Ir, Os ppb <300 <300 <100 <50 <100 Outer diameter of pipe string / quartz glass body cm 26,0 19,7 19,7 19,7 19,7 viscosity @1250°C Lg(η / dPas) 11,69±0,13 11,69±0,13 11,69±0,13 12,06±0,15 11,69+0,13 @1300°C 11,26±0,1 11,26±0,1 11,26±0,1 11,38±0,1 11,26±0,1 @1350°C 10,69±0,07 10,69±0,07 10,69±0,07 10,75±0,08 10,69±0,07 Table 18 (continued) Example H8-3 H8-4 H8-11 H8-12 H8-13 H8-14 Carbon content ppm < 4 <4 <4 <4 <4 <4 Chlorine content ppm 100-200 100-200 <60 100-200 100-200 <60 Al content ppb 20 20 29 35 34 18 Total concentrations of Ca, Co, Cr, Cu, Fe, Ge, Hf, K, Li, Mg, Mn, Mo, Na, Nb, Ni, Ti, V, W, Zn, Zr ppb <400 <400 <1200 <1200 <1200 <900 OH content ppm 500 800 211 454 446 410 alkaline earth metal content ppb 115 115 58 117 119 114 ODC content 1 / cm 3< <4*10 15< <4*10 15< <3*10 15< <4*10 15< <4*10 15< <4*10 15< Salary to W, Mo, Re, Ir, Os ppb <5000 100000 79 335 241 52 Outer diameter of pipe string / quartz glass body cm 19,7 19,7 19,7 19,7 19,7 19,7 viscosity @1250°C Lg(η / dPas) 11,69±0,13 11,63±0,13 11,69±0,14 11,63±0,13 11,63±0,13 11,69±0,13 @1300°C 11,26±0,1 11,22±0,1 11,26±0,2 11,22±0,1 11,22±0,1 11,26±0,1 @1350°C 10,69±0,07 10,65±0,07 10,69±0,08 10,65±0,07 10,65±0,07 10,69±0,07 Table 19 Example H-7-1 H8-1 H8-2 H8-3 H8-4 Distribution ring (gas inlet in the crucible), h...

Claims

1. A method for producing a quartz glass body, comprising the following method steps: i) A) providing and introducing at least one bulk material via a solids feed into a furnace comprising a crucible, wherein silicon dioxide granulate from pyrogenically produced silicon dioxide powder is used as the bulk material, wherein the silicon dioxide granulate has a BET surface area in a range of from 20 to 50 m2 / g; B) providing a gas; ii) forming a glass melt from the bulk material in the crucible; iii) forming a quartz glass body from at least part of the glass melt, wherein at least some of the gas is supplied to the crucible through at least one gas inlet and discharged through at least one gas outlet, wherein the at least one gas inlet is arranged below the at least one solids feed, wherein the gas outlet is arranged at the same height as or above the outlet of the solids feed; wherein the gas is supplied through a gas inlet in the gas space of the crucible; where the glass melt is located in the lower region of the crucible, wherein the crucible is heated by means of electrical heating elements, in particular by means of a resistive or an inductive heater.

2. The method according to claim 1, wherein the gas is supplied through openings in a distributor ring arranged in the crucible, wherein the distributor ring is positioned above the glass melt.

3. The method according to any of claims 1 to 2, wherein the gas is guided from the gas inlet along the crucible wall to the gas outlet.

4. The method according to any of claims 1 to 3, wherein the gas is selected from the group consisting of hydrogen, nitrogen, helium, neon, argon, krypton, xenon and a combination of two or more thereof.

5. The method according to any of claims 1 to 4, comprising the following method step: iv.) forming a hollow body comprising at least one opening from the quartz glass body.

6. A method according to any of claims 1 to 5 wherein the quartz glass body has at least one of the following features: A] an OH content of less than 500 ppm; B] a chlorine content of less than 60 ppm; C] an aluminum content of less than 200 ppb; D] an ODC content of less than 5 • 1015 / cm3; E] a metal content of metals that are different from aluminum of less than 1 ppm; F] a viscosity (p=1013 hPa) in a range of from log10 (η (1250°C) / dPas) = 11.4 to log 10 ( η (1250 ° C) / dPas) = 12 .9 or log 10 ( η (1300 ° C) / dPas) = 11 .1 to log 10 ( η (1300 ° C) / dPas) = 12 .2 or log 10 ( η (1350 ° C) / dPas) = 10 .5 to log 10 ( η (1350 ° C) / dPas) = 11 .5; K] a cylindrical shape; L] a tungsten content of less than 1000 ppb; M] a molybdenum content of less than 1000 ppb, wherein the ppb and ppm are each based on the total weight of the quartz glass body.

7. A method for producing a light guide, comprising the following steps: A / carrying out method steps i.) to iii.) according to claim 1 to obtain a quartz glass body, wherein the quartz glass body is optionally first processed to form a hollow body comprising at least one opening; B / inserting one or more core rods into the hollow body through the at least one opening; C / drawing the hollow body provided with the core rods in the heat to form a light guide.

8. A method for producing a lighting means, comprising the following steps: (i) carrying out method steps i.) to iii.) according to claim 1 to obtain a quartz glass body, wherein the quartz glass body is optionally first processed to form a hollow body; (ii) optionally fitting the hollow body with electrodes; (iii) filling the hollow body with a gas.

9. A method for producing a shaped body, comprising the following steps: (1) carrying out method steps i.) to iii.) according to claim 1 to obtain a quartz glass body; (2) shaping the quartz glass body to obtain the shaped body.