Method for producing a sio 2-soot body having a diffusion barrier

Abstract

The invention relates to a method for producing a quartz glass body, in which firstly a SiO2 soot body having a compression layer is produced, the SiO2 soot body is vitrified to form a quartz glass body, and then the compression layer is removed again. The present invention also relates to a quartz glass body which can be obtained in accordance with the method according to the invention, and to a quartz glass body which has a doping of fluorine and / or chlorine in a concentration of 1000 wt. ppm to 20000 wt. ppm, more preferably 1500 wt. ppm to 17000 wt. ppm, wherein the doping is distributed homogeneously over the quartz glass body.

Description

[0001] Porous diffusion barrier

[0002] DESCRIPTION

[0003] TECHNICAL AREA

[0004] According to a first aspect of the present invention, it relates to a method for producing a quartz glass body starting from a base with a densification layer. According to a second aspect, it relates to a quartz glass body obtainable by the method according to the invention.

[0005] TECHNICAL BACKGROUND

[0006] Synthetic quartz glass is produced from a silicon-containing starting material using a CVD process, through hydrolysis or oxidation, and deposited onto a moving support. A distinction can be made between external and internal deposition processes. In external deposition processes, the SiO2 particles are applied to the outside of a rotating support. Examples of external deposition processes include the so-called OVD process (Outside Vapor Phase Deposition), the VAD process (Vapour Phase Axial Deposition), and the PECVD process (Plasma-Enhanced Chemical Vapor Deposition). The best-known example of an internal deposition process is the MCVD process (Modified Chemical Vapor Deposition), in which SiO2 particles are deposited on the inner wall of a tube heated from the outside.

[0007] At sufficiently high temperatures in the area of ​​the substrate surface, the SiO2 particles undergo immediate vitrification, which is also known as "direct vitrification".

[0008] In contrast, in the so-called "soot process", the temperature during the deposition of the SiO2 particles is so low that a porous SiO2 soot layer is obtained, which is sintered into transparent quartz glass in a separate process step.

[0009] Both direct glazing and the Soot process result in a dense, transparent, high-purity, synthetic quartz glass.

[0010] In the SOOT process for manufacturing quartz glass cylinders, a porous SOOT body is first produced at temperatures below the sintering temperature and then vitrified. This sintering process is particularly suitable for producing synthetic quartz glass that is additionally doped. The doping of the synthetic quartz glass can be achieved within the SOOT process through appropriate chemical treatment of the porous SOOT body. The SOOT body is then clear-sintered in a vacuum furnace. However, this process can lead to the diffusion of gaseous components, resulting in radial and axial inhomogeneity within the sintered quartz glass body, meaning that the dopants are not homogeneously distributed. Depending on the application, the resulting diffusion profile can be detrimental to the final product.

[0011] EP 2 497 755 A discloses a process for producing fluorine-doped fibers in a sintering process, wherein, in the process step of vitrifying the soot body, diffusion of the fluorine doping is counteracted by using a fluorine-containing atmosphere during vitrification.

[0012] DE 102009024267 A discloses a process for producing a synthetic quartz glass, in which a cylindrical SiO2 soot body, having an inner area and at least one free cylindrical surface surrounding the inner area, is thermally dried and vitrified. Before vitrification, the soot body is subjected to a homogenization process in which a sealing layer is produced on the outer surface at a compression temperature, which seals the inner area from the outside.

[0013] From DE 10 2008 059 400 A, a method for producing quartz glass bodies is known in which, prior to the compaction process, the cylindrical outer surface of the molded body is provided with a gas-tight sealing layer, leaving an open-pored inner surface, and the open-pored inner surface of the molded body, now covered with the gas-tight sealing layer, is subjected to a conditioning treatment. Therefore, it is known from DE 10 2008 059 400 A that the outer surface of a quartz glass body is provided with a sealing layer. For this purpose, the cylindrical outer surface of the molded body is compacted after the production of the quartz glass body. In a first method variant, the sealing layer is produced by thermally compacting the outer surface of the molded body.In this process, the cylindrical outer surface of the porous Soot body is heated to such a high temperature that the SiO2 particles sinter densely, forming a gas-tight surface layer. Alternatively, or in addition to thermally densifying the outer surface of the molded body, a second process variant can create the sealing layer by depositing and vitrifying SiO2 particles on the outer surface of the Soot body to form a gas-tight surface coating. If the Soot body is in the form of a tube with a porous inner wall, this wall remains porous and gas-permeable.

[0014] US 4,643,751 describes a method for fabricating an optical waveguide, comprising depositing a layer of particulate silicon dioxide onto a cylindrical silicon dioxide substrate, positioning the silicon dioxide substrate with the particulate silicon dioxide-coated silicon dioxide substrate in a fused silica tube, heating the fused silica tube and the substrate contained therein, and passing a fluorine-containing gas through the tube to diffuse fluorine into the particulate silicon dioxide. This is intended to prevent the fluorine from diffusing into the core region of the substrate. The proposed measure to prevent fluorine diffusion into the core is the prior compaction of the core substrate into a substrate silica before doping with the fluorine-containing gas.US 2002 / 073740 A describes a process for producing a SiCh carbon black body in which at least one barrier layer is formed in the carbon black preform during the deposition step. The barrier layer is preferably a thin layer of vitrified glass. The barrier layer serves to reduce the migration of dopants between individual segments of the carbon black preform, for example, between a first and a second annular segment. The barrier layer described here is completely vitrified, which is technically disadvantageous because a completely vitrified layer can lead to cracking of the vitrified cylinder due to the stresses arising in the final vitrification process.

[0015] JP 2023130881 A describes a process for manufacturing an optical fiber preform. The process includes the step of producing a SiCh soot body as a tubular hollow body. This soot body has a densification layer. It should also be noted that the focus of this prior art is on the production of a core preform with a trench layer. Here, the barrier layer is intended to prevent diffusion between the outer and inner layers. DE 10 2012 007520 B describes a process for manufacturing a cylindrical component made of fluorine-containing synthetic quartz glass, which is based on the production of a SiO2 soot body by flame hydrolysis or oxidation. In this process, the soot body is first dehydrated, then loaded in a fluorine-containing atmosphere, and subsequently subjected to post-chlorination to achieve specific fluorine and chlorine concentrations.Finally, the treated soot body is vitrified, resulting in a cylindrical quartz glass component.

[0016] US 2017 / 362115 A describes a process for manufacturing halogen-doped optical elements in which silica-based soot particles are first produced by chemical vapor deposition and compacted into a soot body. This soot body is then doped in a closed system with a halogen-containing gas—especially fluorine or chlorine—at temperatures below 1200 °C. This is followed by consolidation into a glass body, during which the temperature is simultaneously increased and the halogen concentration in the system is controlled and decreased. The glasses and fiber preforms produced in this way are suitable for both EUV lithography optics and optical fibers with optimized attenuation.

[0017] The prior art does not satisfactorily solve the problem of the resulting diffusion profile of dopants. This problem arises particularly in processes where a porous sintered body is first produced, then dried at temperatures below the sintering temperature, subsequently doped, and finally clear-sintered. In the final clear-sintering step, gaseous components diffuse out, leading to radial and axial inhomogeneity of the dopant within the sintered quartz glass body. The resulting diffusion profile can be disadvantageous depending on the application of the quartz glass material. For example, in the case of fluorine doping, it can interfere with the subsequent use of the quartz glass cylinder.The resulting inhomogeneities in the tubes produced as part of a fiber preform are due to the need for a uniform fluorine distribution, particularly in the core region, to ensure optimal optical fiber properties. Based on this prior art, the present invention aims to provide a method for producing a quartz glass body, wherein the quartz glass body exhibits essentially no inhomogeneities of dopants such as fluorine and chlorine, and OH. The desired method should be as simple and cost-effective as possible and prevent the diffusion of gases, such as fluorine, chlorine, or OH. In particular, the resulting quartz glass body should exhibit a uniform distribution of dopants, especially chlorine and fluorine, as well as OH.The diffusion of OH occurs in such a way that two OH groups of the starting material diffuse out as water (H₂O), forming a Si-O-Si bond. Furthermore, the resulting quartz glass body should preferably exhibit little or no in-diffusion, which could lead to undesired reactions. These include, for example, the reduction of SiO₂ by CO, resulting in the formation of oxygen defect centers in the quartz glass body due to oxygen deficiency.

[0018] DEFINITIONS

[0019] Within the scope of the present invention, a soot body is understood to be a porous, not yet fully vitrified body made of SiO2 particles, which is deposited on a support made of SiO2 particles formed by pyrolysis or by hydrolysis.

[0020] Within the scope of the present invention, a soot body is further understood to be any porous soot body consisting of at least 80% pure SiO₂ or silica glass, the remaining portion consisting of another metal oxide. The other metal oxide may be, among other things, a titanium and / or cerium oxide. In particular, within the scope of the present invention, a soot body may contain a TiO₂ content of 4 to 12 wt.%, more preferably 5 to 11 wt.%, and even more preferably 6 to 10 wt.%, with the remaining amount corresponding to SiO₂.

[0021] Within the scope of the present invention, a quartz glass body is understood to be a substantially completely vitrified body made of SiO2 particles, which is obtained by vitrification of a soot body according to the invention.

[0022] SUMMARY

[0023] The problems described above are preferably solved within the scope of the present invention by a method for producing a quartz glass body. The method according to the invention is characterized in that a special soot body is first produced as an intermediate product, which is optionally subjected to doping, and is subsequently transformed into a quartz glass body by vitrification.

[0024] A further object of the present invention is the quartz glass body resulting from glazing.

[0025] In a first aspect, the present invention thus relates to a method for producing a quartz glass body from a SiO2 soot body, in which a tubular hollow body is deposited as a SiC>2 soot body in such a way that a first compaction layer of SiCh particles is formed in the area of ​​the inside of the tubular hollow body, which has a density of 37% to 70%, more preferably 45% to 65%, and even more preferably 50% to 60%, in each case based on fully consolidated quartz glass.

[0026] This first compaction layer is preferably located in an area radially from the inside in a zone between 0 and 15 mm.

[0027] By forming a corresponding first densification layer on the inner surface of the tubular hollow body of the soot body, the diffusion of dopants, such as fluorine or chlorine, but also OH, to the inner surface of the cylinder during further use of the soot body, i.e., in particular during drying, doping, and vitrification of the soot body into a quartz glass body according to the invention, can be prevented or reduced. In the context of the present invention, the first densification layer is a porous diffusion barrier.

[0028] The porosity of the diffusion barrier is preferably 30 to 67%, more preferably 35%. In the case of fluorine doping, the resulting inhomogeneities are problematic when the quartz glass cylinder or tubes produced therefrom are subsequently used as part of a fiber preform, since a fluorine distribution that is as uniform as possible, especially in the core region, is required for the optical fiber properties. This first densification layer provided for according to the invention can be obtained as an intermediate product in the inventive process for producing the quartz glass body by appropriate process design during the production of the soot body. Suitable process designs for forming the first densification layer are achieved, for example, by adjusting the quantity of the burner media, especially the burner gas, by adjusting the movement sequence of the soot body during its production, and / or by using a larger number of burners.In the inventive process for producing quartz glass bodies, in particular quartz glass cylinders, a porous soot body is first produced at temperatures below the sintering temperature and subsequently vitrified. If dopants are desired in the resulting quartz glass body, they are typically introduced into the soot body material after its production and before vitrification. The present invention therefore also focuses on a soot body obtainable by a soot process, which in subsequent process steps is optionally first doped and then subjected to a sintering process for vitrification.

[0029] The SiO2 soot bodies are typically deposited on a support and therefore have the geometric shape of a tubular hollow body. The term tubular hollow cylinder is used synonymously with the term hollow cylinder.

[0030] By using a compression layer according to the invention in the soot body, diffusion of gaseous components, which leads to radial and axial inhomogeneities in the sintered quartz glass body, can be avoided or at least reduced during its subsequent vitrification.

[0031] Diffusion of gaseous components from the soot body during its vitrification can lead to disadvantages, especially if the soot body is doped with foreign materials during or after its formation.

[0032] The inventive process, which will be described in more detail below, is simple and cost-effective to carry out and essentially prevents the diffusion of dopants, for example gases, in particular fluorine, chlorine and / or OH, from the vitrified body during its vitrification. In particular, the resulting vitrified vitrified body exhibits the most uniform distribution possible of dopants, for example chlorine and fluorine, and of OH, since the condensation layer prevents or reduces uncontrolled diffusion of the dopants or of OH.

[0033] DETAILED DESCRIPTION OF THE INVENTION

[0034] Method for producing a SiO2 soot body

[0035] The present invention comprises a method for producing a SiO2 soot body, characterized by the following process steps:

[0036] a. Evaporation of a silicon-containing feed material to form a feed material vapor;

[0037] b. Feeding the feedstock vapor resulting from process step a. to a reaction zone in which the feedstock is converted to SiO2 particles by pyrolysis or hydrolysis; and

[0038] c. Deposition of the SiO2 particles resulting from process step b. on a depositional surface, forming a soot body as a tubular hollow body,

[0039] wherein in process step c. the tubular hollow body of the SiO2 soot body is deposited in such a way that a first compaction layer of SiO2 particles is formed in the area of ​​the inside of the tubular hollow body, which has a density of 37% to 70%, more preferably 45% to 65%, and even more preferably 50% to 60%, in each case based on fully consolidated quartz glass.

[0040] The first compaction layer is preferably formed by the temperature applied during the deposition of the SiO2 soot particles, so that, through the aforementioned measures of adjusting the amount of burner media and the movement sequence of the soot body, the areas of the compaction layer are exposed to a higher temperature than the other areas of the soot body. This results in the compaction of the deposited SiO2 soot particles and the formation of the porous diffusion barrier.The method according to the invention is therefore characterized in particular by the fact that during the soot build-up, a densification layer is produced in the soot body by adjusting the flame stoichiometry to increase the temperature locally, and / or a densification layer is produced in the soot body by slowing down the soot body movement to increase the residence time of an area of ​​the surface of the soot body at the flame impact point, and / or a densification layer is produced in the soot body by using a larger number of burners.

[0041] The precise flame stoichiometry and the precise deceleration of the soot body movement to be applied each depend on the operational setup of the manufacturing process and can be suitably selected by a person skilled in the art based on their knowledge. Within the scope of the present invention, the intended first compression step in process step c. is preferably generated on the inside of the soot body, which is designed as a tubular hollow body, so that in a subsequent process step doping can still take place via the open-pored outer surface of the soot body, which is preferably designed as a tubular hollow cylinder.

[0042] However, within the scope of the present invention, it is not essential that the first compaction layer constitutes the innermost layer of the soot body to be produced, provided that the compaction layer is arranged radially closer to the inside of the cylindrical hollow body than to the outside of the cylindrical hollow body. In particular, it can be advantageous if the compaction layer forms the second discrete layer extending radially outwards from the inner layer of the hollow body, and if, in process step c, a first soot layer of SiCh particles is initially built up on the deposit surface, which has a density of 10% to 40%, more preferably 15% to 35%, and even more preferably 20% to 30%, in each case based on fully consolidated quartz glass.This first layer of soot does not provide an efficient diffusion barrier for dopants, but serves to simplify the removal of the soot body from the deposition surface and to avoid damage to the inner surface of the soot body.

[0043] Therefore, the present invention also includes a method for producing a SiO2 soot body, characterized by the following process steps:

[0044] a. Evaporation of a silicon-containing feed material to form a feed material vapor;

[0045] b. Feeding the feedstock vapor resulting from process step a. to a reaction zone in which the feedstock is converted to SiO2 particles by pyrolysis or hydrolysis; and

[0046] c. Deposition of the SiO2 particles resulting from process step b. on a deposition surface, forming a soot body as a tubular hollow body, wherein in process step c. the tubular hollow body of the SiCh soot body is deposited in such a way that on the deposition surface

[0047] c.1 first a first layer of SiCh particles is built up, which has a density of 10% to 40%, more preferably 15% to 35%, and even more preferably 20% to 30%, each based on fully consolidated quartz glass, and

[0048] c.2 Subsequently, on the first layer of SiO2 particles, a first compaction layer of SiO2 particles is built up, radially outwards, which has a density of 37% to 70%, more preferably 45% to 65%, and even more preferably 50% to 60%, in each case based on fully consolidated quartz glass. The density of this first layer of SiO2 particles, which is deposited on the surface of the deposit, is therefore lower than the density of the first compaction layer.

[0049] The control of the formation of a first soot layer and a first compaction layer can be achieved within the framework of this inventive method by the process designs of varying the deposition parameters (temperature and duration) already explained above.

[0050] The deposit surface can be the surface of an Alsinth, SiC or SiSiC tube.

[0051] SiO2 soot body

[0052] Within the scope of the present invention, a SiO2 soot body is first provided, which is obtainable according to the method described above.

[0053] The SiO2 soot body preferably has a first compaction layer of SiO2 particles, which has a density of 37% to 70%, more preferably 45% to 65%, and even more preferably 50% to 60%, in each case based on fully consolidated quartz glass.

[0054] The SiO2 soot body has the first compaction layer preferably arranged radially closer to the inside of the cylindrical hollow body than to the outside of the cylindrical hollow body.

[0055] The SiO2 soot body has the first compaction layer preferably radially from the inside to the outside of the tubular hollow body as a second discrete layer, while the inner layer of the tubular hollow body is formed by a first SiO2 soot layer which has a density of 10% to 40%, more preferably 15% to 35%, and even more preferably 20% to 30%, each based on fully consolidated quartz glass.

[0056] Therefore, a soot body is particularly advantageous within the scope of the present invention, in which

[0057] the soot body is in the form of a tubular hollow body, the innermost discrete layer of the soot body is formed by a first soot layer which has a density of 10% to 40%, based on consolidated quartz glass, and

[0058] • a first compaction layer, which has a density of 37 to 70% relative to consolidated quartz glass, adjoins the innermost discrete layer radially outwards.

[0059] Furthermore, a soot body is particularly advantageous within the scope of the present invention, in which

[0060] • the soot body is in the form of a tubular hollow body,

[0061] • the innermost discrete layer of the soot body is formed by a first soot layer, which has a density of 15% to 35%, based on consolidated quartz glass, and

[0062] • a first compaction layer, which has a density of 45 to 65% relative to consolidated quartz glass, adjoins the innermost discrete layer radially outwards.

[0063] Furthermore, a soot body is particularly advantageous within the scope of the present invention, in which

[0064] • the soot body is in the form of a tubular hollow body,

[0065] • the innermost discrete layer of the soot body is formed by a first soot layer, which has a density of 20% to 30%, based on consolidated quartz glass, and

[0066] • a first compaction layer, which has a density of 50 to 60% relative to consolidated quartz glass, adjoins the innermost discrete layer radially outwards.

[0067] Within the scope of the present invention, an immediate arrangement of the first compaction layer around an (inner) first soot layer is understood to mean that no further discrete layer is located between the first compaction layer and the inner (first) soot layer. The compaction layer and the inner soot layer then exhibit the preferred density values ​​described above.

[0068] In the case of an inner soot layer that differs from the first compaction layer, the thickness of the inner first soot layer is preferably 0.5 to 10 mm, more preferably 1 mm to 5 mm, and even more preferably 2 to 3 mm.

[0069] Therefore, within the scope of the present invention, a soot body is particularly advantageous in which the soot body is in the form of a tubular hollow body,

[0070] • the innermost discrete layer of the Soot body is formed by a first Soot layer, which has a density of 10% to 40%, based on consolidated quartz glass, • the first Soot layer has a layer thickness of 0.5 to 10 mm, and

[0071] • a first compaction layer, which has a density of 37 to 70% relative to consolidated quartz glass, adjoins the innermost discrete layer radially outwards.

[0072] Furthermore, a soot body is particularly advantageous within the scope of the present invention, in which

[0073] • the soot body is in the form of a tubular hollow body,

[0074] • the innermost discrete layer of the Soot body is formed by a first Soot layer, which has a density of 15% to 35%, based on consolidated quartz glass, • the first Soot layer has a layer thickness of 1 mm to 5 mm, and

[0075] • a first compaction layer, which has a density of 45 to 65% relative to consolidated quartz glass, adjoins the innermost discrete layer radially outwards.

[0076] Furthermore, a soot body is particularly advantageous within the scope of the present invention, in which

[0077] • the soot body is in the form of a tubular hollow body,

[0078] • the innermost discrete layer of the Soot body is formed by a first Soot layer, which has a density of 20% to 30%, based on consolidated quartz glass, • the first Soot layer has a layer thickness of 2 mm to 3 mm, and

[0079] • a first compaction layer, which has a density of 50 to 60% relative to consolidated quartz glass, adjoins the innermost discrete layer radially outwards.

[0080] In a further embodiment of the soot body, a further discrete second soot layer can be directly connected radially outwards to the compaction layer. This second soot layer can have a density of 15% to 35%, more preferably 20% to 32%, and even more preferably 25% to 29%, each based on consolidated quartz glass. Therefore, within the scope of the present invention, a soot body in which the soot body is in the form of a tubular hollow body is particularly advantageous.

[0081] • the innermost discrete layer of the Soot body is formed by a first Soot layer, which has a density of 10% to 40%, based on consolidated quartz glass, • the first Soot layer has a layer thickness of 0.5 to 10 mm,

[0082] • a first densification layer, which has a density of 37 to 70% relative to consolidated quartz glass, adjoins the innermost discrete layer radially outwards, and

[0083] • a second layer of soot, with a density of 15% to 35% relative to consolidated quartz glass, adjoins the compaction layer radially outwards.

[0084] Furthermore, a soot body is particularly advantageous within the scope of the present invention, in which

[0085] • the soot body is in the form of a tubular hollow body,

[0086] • the innermost discrete layer of the Soot body is formed by a first Soot layer, which has a density of 15% to 35%, based on consolidated quartz glass, • the first Soot layer has a layer thickness of 1 mm to 5 mm,

[0087] • a first compaction layer, which has a density of 45 to 65% relative to consolidated quartz glass, adjoins the innermost discrete layer radially outwards, and

[0088] • a second layer of soot, with a density of 20% to 32% relative to consolidated quartz glass, adjoins the compaction layer radially outwards.

[0089] Furthermore, a soot body is particularly advantageous within the scope of the present invention, in which

[0090] • the soot body is in the form of a tubular hollow body,

[0091] • the innermost discrete layer of the Soot body is formed by a first Soot layer, which has a density of 20% to 30%, based on consolidated quartz glass, • the first Soot layer has a layer thickness of 2 mm to 3 mm,

[0092] • a first compaction layer, which has a density of 50 to 60% relative to consolidated quartz glass, adjoins the innermost discrete layer radially outwards, and

[0093] • A second layer of soot, with a density of 25 to 29% relative to consolidated quartz glass, adjoins the compaction layer radially outwards. The second layer of soot can have a thickness of 100 to 190 mm, more preferably 115 to 180 mm, and even more preferably 130 to 170 mm.

[0094] Therefore, a soot body is particularly advantageous within the scope of the present invention, in which

[0095] • the soot body is in the form of a tubular hollow body,

[0096] • the innermost discrete layer of the Soot body is formed by a first Soot layer, which has a density of 10% to 40%, based on consolidated quartz glass, • the first Soot layer has a layer thickness of 0.5 to 10 mm,

[0097] • a first compaction layer, which has a density of 37 to 70% relative to consolidated quartz glass, adjoins the innermost discrete layer radially outwards,

[0098] • a second layer of soot, with a density of 15% to 35% relative to consolidated quartz glass, adjoins the compaction layer radially outwards, and

[0099] • the second layer of sod has a thickness of 100 to 190 mm.

[0100] Furthermore, a soot body is particularly advantageous within the scope of the present invention, in which

[0101] • the soot body is in the form of a tubular hollow body,

[0102] • the innermost discrete layer of the Soot body is formed by a first Soot layer, which has a density of 15% to 35%, based on consolidated quartz glass, • the first Soot layer has a layer thickness of 1 mm to 5 mm,

[0103] • a first compaction layer, which has a density of 45 to 65% relative to consolidated quartz glass, adjoins the innermost discrete layer radially outwards,

[0104] • A second layer of soot, with a density of 20% to 32% relative to consolidated quartz glass, adjoins the compacted layer radially outwards. And

[0105] • the second layer of soot has a thickness of 115 to 180 mm.

[0106] Furthermore, a soot body is particularly advantageous within the scope of the present invention, in which

[0107] • the soot body is in the form of a tubular hollow body,

[0108] • the innermost discrete layer of the Soot body is formed by a first Soot layer, which has a density of 20% to 30%, based on consolidated quartz glass, and the first Soot layer has a thickness of 2 mm to 3 mm.

[0109] • a first compaction layer, which has a density of 50 to 60% relative to consolidated quartz glass, adjoins the innermost discrete layer radially outwards,

[0110] • a second layer of soot, with a density of 25 to 29% relative to consolidated quartz glass, adjoins the compaction layer radially outwards, and

[0111] • the second layer of sod has a thickness of 130 to 170 mm.

[0112] Within the scope of the present invention, it is additionally advantageous if, in addition to a first compaction layer on the inner surface of the tubular hollow body, a second compaction layer is also present in the area of ​​the outer surface of the tubular hollow body. This second compaction layer ensures that any dopants cannot escape, or can only escape to a lesser extent, via the outer surface of the tubular hollow body during the subsequent vitrification process step.

[0113] In a further preferred embodiment, this second compaction layer of SiO2 particles has a density of 37% to 70%, more preferably 45% to 65%, and even more preferably 50% to 60%, in each case based on fully consolidated quartz glass. This not only prevents the diffusion of any dopants across the outer surface of the tubular hollow body but also ensures greater stability of the resulting hollow cylinder, thus simplifying further manipulation of the hollow body for doping and / or vitrification purposes.

[0114] The density of the second compaction layer may differ from the density of the first compaction layer.

[0115] Within the scope of the present invention, the aforementioned sealing layer is formed in the inner region of the tubular hollow body, particularly when subsequent doping of the tubular hollow body is to take place and glazing following doping generally occurs from the outside in, so that the doped hollow body is quickly sealed on the outside, while glazing on the inside occurs later, and the dopants can escape for a considerably longer period there. Therefore, a sealing layer on the inner surface of the tubular hollow body is more important than on the outer surface.

[0116] However, the respective compaction layers not only serve to fix the dopants in the soot body and enable their homogeneous distribution, they also serve to reduce or even prevent the diffusion of gases that can lead to unwanted reactions in the soot body, such as the reduction of SiÜ2 by carbon monoxide (CO) with the formation of defect centers with O deficiency.

[0117] Within the scope of the present invention, a fully vitrified quartz glass with a density of 2.21 g / cm³ is placed under a consolidated quartz glass. 3 understood and this density is taken as a reference for the percentage density values ​​in the compaction layer(s) and soot layer(s).

[0118] In the following, the term "compaction layer" is used in the singular, whereby the following information refers to both the first compaction layer on the inside of the tubular hollow body and the second compaction layer on the outside of the tubular hollow body.

[0119] The density of the compaction layer in the soot body is preferably at least 5%, more preferably at least 10%, and even more preferably at least 20% greater than the average density of the synthetic quartz glass in the soot body outside the compaction layer. In the case of a corresponding configuration of the density of the compaction layer relative to the average density of the soot body outside the compaction layer, the aforementioned problems of the present invention can be particularly well solved. Within the scope of the present invention, the compaction layer typically has a thickness of at least 0.1 mm, more preferably at least 0.3 mm, and even more preferably at least 0.5 mm.

[0120] In the context of the present invention, the compaction layer typically has a layer thickness of at most 20 mm, more preferably at most 17 mm, and even more preferably at most 15 mm.

[0121] In particular, the compaction layer within the scope of the present invention has a layer thickness of 0.1 to 20 mm, more preferably 0.3 to 17 mm, and even more preferably 0.5 to 15 mm.

[0122] Furthermore, the compaction layer can have a layer thickness of 1 to 10 mm, more preferably 2 to 8 mm, and even more preferably 3 to 7 mm.

[0123] Therefore, a soot body is particularly advantageous within the scope of the present invention, in which

[0124] • the soot body is in the form of a tubular hollow body,

[0125] • the innermost discrete layer of the soot body is formed by a first soot layer, which has a density of 10% to 40%, based on consolidated quartz glass, • a first compaction layer, which has a density of 37% to 70%, based on consolidated quartz glass, adjoins the innermost discrete layer radially outwards, and

[0126] • the thickness of the first compaction layer is 0.1 to 20 mm.

[0127] Furthermore, within the scope of the present invention, a soot body is particularly advantageous in which the soot body is in the form of a tubular hollow body,

[0128] • the innermost discrete layer of the soot body is formed by a first soot layer, which has a density of 15% to 35%, based on consolidated quartz glass, • a first compaction layer, which has a density of 45% to 65%, based on consolidated quartz glass, adjoins the innermost discrete layer radially outwards, and

[0129] • the thickness of the first compaction layer is 0.3 to 17 mm.

[0130] Furthermore, a soot body is particularly advantageous within the scope of the present invention, in which

[0131] • the soot body is in the form of a tubular hollow body,

[0132] • the innermost discrete layer of the soot body is formed by a first soot layer, which has a density of 20% to 30%, based on consolidated quartz glass, • a first compaction layer, which has a density of 50% to 60%, based on consolidated quartz glass, adjoins the innermost discrete layer radially outwards, and

[0133] • the thickness of the first compaction layer is 0.5 to 15 mm.

[0134] Furthermore, a soot body is particularly advantageous within the scope of the present invention, in which

[0135] • the soot body is in the form of a tubular hollow body,

[0136] • the innermost discrete layer of the soot body is formed by a first soot layer, which has a density of 20% to 30%, based on consolidated quartz glass, • a first compaction layer, which has a density of 50% to 60%, based on consolidated quartz glass, adjoins the innermost discrete layer radially outwards, and

[0137] • the thickness of the first compaction layer is 1 to 10 mm.

[0138] Furthermore, a soot body is particularly advantageous within the scope of the present invention, in which

[0139] • the soot body is in the form of a tubular hollow body,

[0140] • the innermost discrete layer of the soot body is formed by a first soot layer, which has a density of 20% to 30%, based on consolidated quartz glass, followed radially outwards by a first compaction layer, which has a density of 50% to 60%, based on consolidated quartz glass, and

[0141] • the thickness of the first compaction layer is 2 to 8 mm.

[0142] Furthermore, a soot body is particularly advantageous within the scope of the present invention, in which

[0143] • the soot body is in the form of a tubular hollow body,

[0144] • the innermost discrete layer of the soot body is formed by a first soot layer, which has a density of 20% to 30%, based on consolidated quartz glass, • a first compaction layer, which has a density of 50% to 60%, based on consolidated quartz glass, adjoins the innermost discrete layer radially outwards, and

[0145] • the thickness of the first compaction layer is 3 to 7 mm.

[0146] Therefore, a soot body is particularly advantageous within the scope of the present invention, in which

[0147] • the soot body is in the form of a tubular hollow body,

[0148] • the innermost discrete layer of the Soot body is formed by a first Soot layer, which has a density of 10% to 40%, based on consolidated quartz glass, • the first Soot layer has a layer thickness of 0.5 to 10 mm,

[0149] • a first densification layer, which has a density of 37 to 70% relative to consolidated quartz glass, adjoins the innermost discrete layer radially outwards, and

[0150] • the thickness of the first compaction layer is 0.1 to 20 mm.

[0151] Furthermore, a soot body is particularly advantageous within the scope of the present invention, in which

[0152] • the soot body is in the form of a tubular hollow body,

[0153] • the innermost discrete layer of the soot body is formed by a first soot layer, which has a density of 15% to 35%, based on consolidated quartz glass, • the first soot layer has a layer thickness of 0.5 to 10 mm, a first compaction layer, which has a density of 45% to 65%, based on consolidated quartz glass, adjoins the innermost discrete layer radially outwards, and

[0154] • the thickness of the first compaction layer is 0.3 to 17 mm.

[0155] Furthermore, a soot body is particularly advantageous within the scope of the present invention, in which

[0156] • the soot body is in the form of a tubular hollow body,

[0157] • the innermost discrete layer of the Soot body is formed by a first Soot layer, which has a density of 20% to 30%, based on consolidated quartz glass, • the first Soot layer has a thickness of 1 to 5 mm,

[0158] • a first compaction layer, which has a density of 50 to 60% relative to consolidated quartz glass, adjoins the innermost discrete layer radially outwards, and

[0159] • the thickness of the first compaction layer is 0.5 to 15 mm.

[0160] Furthermore, a soot body is particularly advantageous within the scope of the present invention, in which

[0161] • the soot body is in the form of a tubular hollow body,

[0162] • the innermost discrete layer of the soot body is formed by a first soot layer, which has a density of 20% to 30%, based on consolidated quartz glass, • the first soot layer has a thickness of 1 to 5 mm

[0163] • a first compaction layer, which has a density of 50 to 60% relative to consolidated quartz glass, adjoins the innermost discrete layer radially outwards, and

[0164] • the thickness of the first compaction layer is 1 to 10 mm.

[0165] Furthermore, a soot body is particularly advantageous within the scope of the present invention, in which

[0166] • the soot body is in the form of a tubular hollow body,

[0167] • the innermost discrete layer of the soot body is formed by a first soot layer, which has a density of 20% to 30%, based on consolidated quartz glass, • the first soot layer has a thickness of 2 to 3 mm, and a first compaction layer, which has a density of 50% to 60%, based on consolidated quartz glass, adjoins the innermost discrete layer radially outwards.

[0168] • the thickness of the first compaction layer is 2 to 8 mm.

[0169] Furthermore, a soot body is particularly advantageous within the scope of the present invention, in which

[0170] • the soot body is in the form of a tubular hollow body,

[0171] • the innermost discrete layer of the soot body is formed by a first soot layer, which has a density of 20% to 30%, based on consolidated quartz glass, • the first soot layer has a thickness of 2 to 3 mm

[0172] • a first compaction layer, which has a density of 50 to 60% relative to consolidated quartz glass, adjoins the innermost discrete layer radially outwards, and

[0173] • the thickness of the first compaction layer is 3 to 7 mm.

[0174] Therefore, a soot body is particularly advantageous within the scope of the present invention, in which

[0175] • the soot body is in the form of a tubular hollow body,

[0176] • the innermost discrete layer of the Soot body is formed by a first Soot layer, which has a density of 10% to 40%, based on consolidated quartz glass, • the first Soot layer has a layer thickness of 0.5 to 10 mm,

[0177] • a first compaction layer, which has a density of 37 to 70% relative to consolidated quartz glass, adjoins the innermost discrete layer radially outwards,

[0178] • the thickness of the first compaction layer is 0.1 to 20 mm, and

[0179] • a second layer of soot, with a density of 15% to 35% relative to consolidated quartz glass, adjoins the compaction layer radially outwards.

[0180] Furthermore, a soot body is particularly advantageous within the scope of the present invention, in which

[0181] • the soot body is in the form of a tubular hollow body,

[0182] • the innermost discrete layer of the Soot body is formed by a first Soot layer, which has a density of 15% to 35%, based on consolidated quartz glass, and the first Soot layer has a thickness of 0.5 to 10 mm,

[0183] • a first compaction layer, which has a density of 45 to 65% relative to consolidated quartz glass, adjoins the innermost discrete layer radially outwards,

[0184] • the thickness of the first compaction layer is 0.3 to 17 mm, and

[0185] • a second layer of soot, with a density of 15% to 35% relative to consolidated quartz glass, adjoins the compaction layer radially outwards.

[0186] Furthermore, a soot body is particularly advantageous within the scope of the present invention, in which

[0187] • the soot body is in the form of a tubular hollow body,

[0188] • the innermost discrete layer of the Soot body is formed by a first Soot layer, which has a density of 20% to 30%, based on consolidated quartz glass, • the first Soot layer has a thickness of 1 to 5 mm,

[0189] • a first compaction layer, which has a density of 50 to 60% relative to consolidated quartz glass, adjoins the innermost discrete layer radially outwards,

[0190] • the thickness of the first compaction layer is 0.5 to 15 mm, and

[0191] • a second layer of soot, with a density of 20% to 32% relative to consolidated quartz glass, adjoins the compaction layer radially outwards.

[0192] Furthermore, a soot body is particularly advantageous within the scope of the present invention, in which

[0193] • the soot body is in the form of a tubular hollow body,

[0194] • the innermost discrete layer of the Soot body is formed by a first Soot layer, which has a density of 20% to 30%, based on consolidated quartz glass, • the first Soot layer has a thickness of 1 to 5 mm,

[0195] • a first compaction layer, which has a density of 50 to 60% relative to consolidated quartz glass, adjoins the innermost discrete layer radially outwards,

[0196] • the thickness of the first compaction layer is 1 to 10 mm, and

[0197] • a second layer of soot, with a density of 20% to 32% relative to consolidated quartz glass, adjoins the compaction layer radially outwards. Furthermore, a soot body is particularly advantageous within the scope of the present invention in which

[0198] • the soot body is in the form of a tubular hollow body,

[0199] • the innermost discrete layer of the Soot body is formed by a first Soot layer, which has a density of 20% to 30%, based on consolidated quartz glass, • the first Soot layer has a layer thickness of 2 to 3 mm,

[0200] • a first compaction layer, which has a density of 50 to 60% relative to consolidated quartz glass, adjoins the innermost discrete layer radially outwards,

[0201] • the thickness of the first compaction layer is 2 to 8 mm, and

[0202] • a second layer of soot, with a density of 25% to 29% relative to consolidated quartz glass, adjoins the compaction layer radially outwards.

[0203] Furthermore, a soot body is particularly advantageous within the scope of the present invention, in which

[0204] • the soot body is in the form of a tubular hollow body,

[0205] • the innermost discrete layer of the Soot body is formed by a first Soot layer, which has a density of 20% to 30%, based on consolidated quartz glass, • the first Soot layer has a layer thickness of 2 to 3 mm,

[0206] • a first compaction layer, which has a density of 50 to 60% relative to consolidated quartz glass, adjoins the innermost discrete layer radially outwards,

[0207] • the thickness of the first compaction layer is 3 to 7 mm, and

[0208] • a second layer of soot, with a density of 25% to 29% relative to consolidated quartz glass, adjoins the compaction layer radially outwards.

[0209] Therefore, a soot body is particularly advantageous within the scope of the present invention, in which

[0210] • the soot body is in the form of a tubular hollow body,

[0211] • the innermost discrete layer of the soot body is formed by a first soot layer, which has a density of 10% to 40%, based on consolidated quartz glass, • the first soot layer has a thickness of 0.5 to 10 mm, • a first compaction layer, which has a density of 37% to 70%, based on consolidated quartz glass, adjoins the innermost discrete layer radially outwards,

[0212] • the thickness of the first compaction layer is 0.1 to 20 mm,

[0213] • a second layer of soot, with a density of 15% to 35% relative to consolidated quartz glass, adjoins the compaction layer radially outwards, and

[0214] • the second layer of sod has a thickness of 100 to 190 mm.

[0215] Furthermore, a soot body is particularly advantageous within the scope of the present invention, in which

[0216] • the soot body is in the form of a tubular hollow body,

[0217] • the innermost discrete layer of the Soot body is formed by a first Soot layer, which has a density of 15% to 35%, based on consolidated quartz glass, • the first Soot layer has a layer thickness of 0.5 to 10 mm,

[0218] • a first compaction layer, which has a density of 45 to 65% relative to consolidated quartz glass, adjoins the innermost discrete layer radially outwards,

[0219] • the thickness of the first compaction layer is 0.3 to 17 mm,

[0220] • a second layer of soot, with a density of 15% to 35% relative to consolidated quartz glass, adjoins the compaction layer radially outwards, and

[0221] • the second layer of sod has a thickness of 100 to 190 mm.

[0222] Furthermore, a soot body is particularly advantageous within the scope of the present invention, in which

[0223] • the soot body is in the form of a tubular hollow body,

[0224] • the innermost discrete layer of the Soot body is formed by a first Soot layer, which has a density of 20% to 30%, based on consolidated quartz glass, • the first Soot layer has a thickness of 1 to 5 mm,

[0225] • a first compaction layer, which has a density of 50 to 60% relative to consolidated quartz glass, adjoins the innermost discrete layer radially outwards,

[0226] the thickness of the first compaction layer is 0.5 to 15 mm, a second layer of compaction is radially outwards, the density of which is 20% to 32%, based on consolidated quartz glass, and

[0227] • the second layer of soot has a thickness of 115 to 180 mm.

[0228] Furthermore, a soot body is particularly advantageous within the scope of the present invention, in which

[0229] • the soot body is in the form of a tubular hollow body,

[0230] • the innermost discrete layer of the soot body is formed by a first soot layer, which has a density of 20% to 30%, based on consolidated quartz glass, • the first soot layer has a thickness of 1 to 5 mm

[0231] • a first compaction layer, which has a density of 50 to 60% relative to consolidated quartz glass, adjoins the innermost discrete layer radially outwards,

[0232] • the thickness of the first compaction layer is 1 to 10 mm,

[0233] • a second layer of soot, with a density of 20% to 32% relative to consolidated quartz glass, adjoins the compaction layer radially outwards, and

[0234] • the second layer of soot has a thickness of 115 to 180 mm.

[0235] Furthermore, a soot body is particularly advantageous within the scope of the present invention, in which

[0236] • the soot body is in the form of a tubular hollow body,

[0237] • the innermost discrete layer of the soot body is formed by a first soot layer, which has a density of 20% to 30%, based on consolidated quartz glass, • the first soot layer has a thickness of 2 to 3 mm

[0238] • a first compaction layer, which has a density of 50 to 60% relative to consolidated quartz glass, adjoins the innermost discrete layer radially outwards,

[0239] • the thickness of the first compaction layer is 2 to 8 mm,

[0240] • a second layer of soot, with a density of 25% to 29% relative to consolidated quartz glass, adjoins the compaction layer radially outwards, and the second layer of soot has a thickness of 130 to 170 mm. Furthermore, within the scope of the present invention, a soot body is particularly advantageous in which

[0241] • the soot body is in the form of a tubular hollow body,

[0242] • the innermost discrete layer of the soot body is formed by a first soot layer, which has a density of 20% to 30%, based on consolidated quartz glass, • the first soot layer has a thickness of 2 to 3 mm

[0243] • a first compaction layer, which has a density of 50 to 60% relative to consolidated quartz glass, adjoins the innermost discrete layer radially outwards,

[0244] • the thickness of the first compaction layer is 3 to 7 mm,

[0245] • a second layer of soot, with a density of 25% to 29% relative to consolidated quartz glass, adjoins the compaction layer radially outwards, and

[0246] • the second layer of sod has a thickness of 130 to 170 mm.

[0247] The aforementioned layer thicknesses of the compaction layer represent a compromise; on the one hand, the layer thickness should not be too large, since the material area of ​​the compaction layer is not doped and must later be drilled out (removed) when the vitrified soot body is used for certain applications, and on the other hand, the layer thickness must be sufficiently large so that the compaction layer can fulfill its function as a barrier.

[0248] Furthermore, within the scope of the present invention, it is preferred if the variation in the thickness of the densification layer along the axis of rotation of the tubular hollow body is a maximum of + / - 10%, preferably a maximum of + / - 5%. A more uniform layer thickness makes subsequent drilling out of the densification layer easier and results in less material loss of doped and vitrified quartz material.

[0249] The compression layers and the soot layers of the tubular hollow cylinder are distinguished by their densities as defined above.

[0250] As explained above, the density distribution is achieved within the scope of the present invention by adjusting the temperature at the surface of the soot body during its formation. The density of the soot body is very closely linked to its build-up temperature. Therefore, the density of the soot body can be controlled, among other things, by the following process measures, as already described:

[0251] 1. By adjusting the quantity of burner media, especially burner gas;

[0252] and / or 2. by adjusting the movement of the soot body, i.e., if the body is moved more slowly, it becomes hotter and / or

[0253] 3. by the number of burners arranged in the individual areas, since a higher number of burners can result in a higher heat input onto the surface of the soot body.

[0254] Further possibilities for producing a first compaction layer within the scope of the present invention consist of providing a SiO2 suspension coating on the deposit surface prior to the deposition of the SiO2 soot particles and / or providing a glass tube between the deposit surface and the soot body.

[0255] The density of the soot body can be determined using known methods. For example, the local density of the soot body can be determined using computed tomography by creating cross-sectional images of the soot body. The average density is then obtained by averaging over all measurement points.

[0256] Method for producing a doped SiO2 soot body

[0257] Following the production of a soot body as defined above, the soot body is generally subjected to doping in accordance with the present invention. This doping can be carried out, for example, with a halogen, in particular fluorine or chlorine. Therefore, the present invention also includes a method for producing a doped soot body. The method is characterized in that a SiCh soot body according to the foregoing is provided with at least one densification layer and the following process step is carried out:

[0258] d. Doping of the resulting SiCh soot body.

[0259] In a first embodiment of the process step d. provided according to the invention, the doping is carried out with a fluorine-containing gas, with which the soot body resulting from process step c. is acted upon.

[0260] A corresponding embodiment of the fluorination is described in European patent application EP 2977359 A and German patent application DE102012007520 B, the corresponding disclosures being incorporated into the present invention by reference.

[0261] In a second embodiment of the process step d. provided according to the invention, the doping is carried out with a chlorine-containing gas, with which the soot body resulting from process step c. is acted upon.

[0262] A corresponding embodiment of the chlorination process is described in German patent DE 10303 290 B, the corresponding disclosures of which are incorporated into the present invention by reference. Accordingly, the fluorination is carried out as doping after obtaining the soot body in process step d, preferably by the following process steps:

[0263] d.1 Removal of hydroxyl groups by subjecting the soot body to a dehydration treatment,

[0264] d.2 Loading the soot body with fluorine by treating it in a fluorine-containing atmosphere at a fluorination temperature of at least 750 °C, and d.3 Post-chlorinating the soot body loaded with fluorine by treating it in a chlorine-containing atmosphere at a post-chlorination temperature.

[0265] In the fluorination process provided according to the invention, during the dehydration treatment according to process step d.1 (removal of hydroxyl groups) in the soot body, a concentration of hydroxyl groups is preferably adjusted which, after vitrification, results in an average hydroxyl group content in the range of 1 to 300 ppm by weight.

[0266] The fluorination provided according to the invention is preferably carried out during the loading of the soot body according to process step d.2 (loading the soot body with fluorine) in such a way that after vitrification in the synthetic quartz glass an average fluorine content of at least 1500 wt. ppm results.

[0267] The fluorination provided according to the invention is preferably carried out in the soot body during the post-chlorination according to process step d.3 (post-chlorination of the fluorine-loaded soot body) in such a way that a hydroxyl group content is adjusted which, after vitrification in the synthetic quartz glass, results in an average hydroxyl group content of less than 0.3 wt. ppm, and a loading with chlorine takes place which, after vitrification in the synthetic quartz glass, results in an average chlorine content of at least 50 wt. ppm.

[0268] The soot body is therefore subjected to a multi-stage post-treatment for doping. First, dehydration is necessary, as soot bodies typically contain a high concentration of hydroxyl groups (OH groups) due to the manufacturing process. The required duration and effectiveness of the drying process depend not only on the initial hydroxyl group content and the desired average hydroxyl group content, but also significantly on the soot density.

[0269] In the dehydration treatment, the soot body is dried purely thermally by heating under vacuum (< 2 mbar) or in a chlorine-free inert gas atmosphere (noble gas or nitrogen), or alternatively or additionally, chemically using a drying reagent such as chlorine or fluorine. The dehydration treatment always takes place at an elevated temperature, although significant densification of the soot body is not desired. It is important that the concentration of hydroxyl groups in the soot body is such that—if the soot body were vitrified under vacuum at this stage of the process—the average hydroxyl group content in the quartz glass would be less than 300 ppm by weight. In the fluorine loading step, the soot body is treated at high temperature with a fluorine-containing treatment gas, such as C₂F₆, CF₄, or SiF₄.

[0270] In the subsequent post-chlorination according to process step d.3, the soot body is treated with a chlorine-containing treatment gas, such as chlorine, at approximately the same temperature or a slightly lower temperature than during the preceding fluorine loading. The post-chlorination involves loading the soot body with chlorine or further loading it with chlorine. The concentration ratio of fluorine to chlorine has proven to be a simple measure of whether this measure sufficiently smooths the fluorine distribution profile. According to the invention, this ratio does not exceed 30 (in units by weight), meaning that the average fluorine concentration is at most 30 times higher than the average chlorine concentration, and the latter is also not less than 50 ppm by weight.

[0271] A particularly preferred embodiment of the method according to the invention is one in which the soot body has a specific surface area according to BET of 7 to 16 m². 2 / g, preferably 10 to 15 m 2 / g, determined according to DIN-ISO 9277:2003-5.

[0272] The soot body can be dried before treatment with a gas containing a fluorine compound to remove any impurities present in the soot body, such as hydroxide groups (OH groups), should these be undesirable in the resulting quartz glass body. This drying can be carried out thermally and / or chemically. A particularly preferred embodiment is one in which the soot body from process step c. is dried thermally and / or chemically at a temperature in the range of 700 to 1200 °C.

[0273] The chemical drying of the soot body is preferably carried out in the presence of a chlorine-containing compound. The use of chlorine (Ch) is particularly preferred.

[0274] The thermal drying of the soot body is preferably carried out in the presence of one or more inert gases. This prevents already cleaned areas of the soot body from being recontaminated. Preferably, the inert gas is selected from the group consisting of He, Ar, N2, and mixtures thereof.

[0275] A particularly preferred embodiment is one in which the soot body from process step c. is first dried in the presence of an inert gas and then in the presence of a chlorine-containing compound, the temperature being in a range of 700 to 1200 °C in each case.

[0276] Doped SiO2 soot body

[0277] In the present invention, a doped SiO2 soot body, which is obtainable according to the method described above, is passed through.

[0278] This doped SiO2 soot body has a first compaction layer of SiO2 particles having a density of 37% to 70%, more preferably 45% to 65%, and even more preferably 50% to 60%, each based on fully consolidated quartz glass. For further features of the doped SiCh soot body, reference is made to the above descriptions.

[0279] Method for producing a quartz glass body according to the invention

[0280] Following the doping, the doped soot body is vitrified in a further process step provided for according to the invention.

[0281] Therefore, the present invention relates to a method for producing a quartz glass body. The method according to the invention is characterized in that a doped SiO2 soot body, as described above, is provided with at least one densification layer and the subsequent process step is carried out.

[0282] e. Vitrification of the SiO2 soot body resulting from process step f., obtaining a quartz glass body.

[0283] In the final process step e., the doped soot body is vitrified, whereby the pressure inside the process chamber in which the vitrification takes place is lower than the pressure outside the process chamber.

[0284] Preferably, the vitrification temperature in process step e. is in the range of 1200 to 1500 °C, more preferably 1250 to 1350 °C. To avoid bubble formation in the subsequent quartz glass, it has proven advantageous if the pressure inside the process chamber is lower than outside the process chamber during vitrification, i.e., if the vitrification is carried out at reduced pressure. This also has the advantage that the material of the process chamber is not attacked by aggressive and corrosive gases and is therefore subject to reduced wear. Therefore, an embodiment is preferred in which the vitrification in process step e. preferably takes place at a pressure of less than 1 mbar. Consequently, the pressure inside the process chamber should preferably be less than 1 mbar. Another method of vitrification can be carried out in a fluorine-containing atmosphere at a reduced pressure of 10 to 200 mbar.

[0285] To optimize the manufacturing process of the quartz glass and to protect the materials, particularly the process chamber, it has proven advantageous to perform the doping of the soot body and the vitrification of the fluorinated intermediate in different process chambers. Therefore, according to the inventive method, the vitrification in process step e. typically takes place in a second process chamber, which differs from the first process chamber in which the doping is carried out according to process step d. In this way, each of the process chambers can be optimized for the corresponding process steps, and excessive stress on the materials, for example from aggressive and corrosive gases at high temperatures, is avoided. Therefore, an embodiment is preferred in which the vitrification in process step e. takes place in a second process chamber, which differs from the first process chamber, in which the doping in process step d.The process differs depending on the method used. The second process chamber can, for example, be a zone furnace in which the vitrification of the fluorinated soot body takes place zone by zone. Preferably, the second process chamber is not exposed to fluorine-containing gases. More preferably, the second process chamber is a vitrification furnace, preferably a zone sintering furnace. Such furnaces are known to those skilled in the art and can be used in the process according to the invention, depending on the specific requirements for the size and shape of the soot body. The vitrification can preferably be carried out in a vacuum, for example, under a vacuum. The vacuum during vitrification is preferably less than or equal to 10 mbar, more preferably less than or equal to 1 mbar, and even more preferably less than or equal to 0.1 mbar.

[0286] The process steps d. and / or e. according to the invention can also be carried out in a muffle furnace.

[0287] The process steps d. and / or e. according to the invention can also be carried out in a muffle furnace with a quartz glass crucible tube.

[0288] After obtaining the vitrified quartz glass body, the existing densification layers can be removed. This is preferably done by mechanically processing the quartz glass body or by chemically treating it. One way to remove the densification layers is by drilling the quartz glass body.

[0289] Quartz glass body according to the invention

[0290] The present invention further relates to a quartz glass body which is obtainable according to the method described above and which is obtained by vitrifying an optionally doped soot body according to the invention.

[0291] The quartz glass body according to the invention preferably has a doping of fluorine and / or chlorine.

[0292] The quartz glass body according to the invention preferably has a doping of fluorine and / or chlorine in an amount concentration of 1000 wt. ppm to 20000 wt. ppm, more preferably 1500 wt. ppm to 17000 wt. ppm, wherein the doping is homogeneously distributed over the quartz glass body.

[0293] Due to the special manufacturing process of the quartz glass body according to the invention, the variation in concentration and doping along the axis of rotation of the cylindrical hollow body is a maximum of + / - 10%, preferably + / - 5%.

[0294] Due to the special manufacturing process of the quartz glass body according to the invention, the variation in concentration and doping radially perpendicular to the axis of rotation of the cylindrical hollow body in a range of 0 to 70% of the wall thickness is a maximum of + / - 10%, preferably + / - 5%. BRIEF SUMMARY OF THE FIGURES

[0295] The following schematic drawings illustrate aspects of the invention for better understanding of the invention in conjunction with some exemplary figures, wherein Figure 1 shows an example of a radial density profile with a density jump; and Figure 2 shows typical refractive index profiles of a glass body resulting from the method according to the invention.

[0296] Figure 1:

[0297] Figure 1 shows an example of a radial density profile with a density jump.

[0298] Figure 2:

[0299] In Figure 2, the radial position “0%” denotes the outer surface of the hollow cylinder according to the invention, and the highest values ​​of the radial position denote the inner bore. The circular symbols (Version 1) are from a cylinder in which a conventional soot body with a constant density over the entire radius was used. After fluorination in the muffle furnace, the body was clear-sintered in a zone sintering furnace under vacuum (< 0.1 mbar). In the cylinder shown in green (Version 3), a radial soot density profile as shown in Figure 1 was used and again vitrified under vacuum. This results in a very small change in refractive index between the inner surface and the refractive index minimum. In the fluorine profile marked by squares (Version 2), in addition to the barrier, sintering was not carried out under vacuum, but in a sealed furnace, which was flooded with 50 mbar CF4 at the beginning of the process.This allows a flat refractive index profile to be achieved across the entire wall thickness. Alternatively, other fluorine-containing gases can also be used. According to the invention, a shut-off furnace is understood to be a furnace that is flooded with 50 mbar CF4 and then sealed (shut-off).

Claims

REQUIREMENTS 1. A method for producing a quartz glass body, characterized by the following process steps: a. Evaporation of a silicon-containing feed material to form a feed material vapor; b. Feeding the feedstock vapor resulting from process step a. to a reaction zone in which the feedstock is converted to SiO2 particles by pyrolysis or hydrolysis; and c. Deposition of the SiO2 particles resulting from process step b. on a depositional surface, forming a soot body as a tubular hollow body, d. Doping of the SiO2 soot body resulting from process step c.; e. Vitrification of the SiO2 soot body resulting from process step d. to obtain a quartz glass body. characterized by the fact that In process step c. the tubular hollow body of the SiO2 soot body is deposited in such a way that a first compaction layer of SiO2 particles is formed in the area of ​​the inside of the tubular hollow body, which has a density of 37% to 70%, more preferably 40% to 65%, and even more preferably 50% to 60%, each based on fully consolidated quartz glass, and The quartz glass body resulting from process step e. is processed in process step f. so that the densification layer(s) is / are removed from the quartz glass body.

2. Method according to claim 1, characterized in that in process step c. On the deposit surface, a first layer of soot consisting of SiO2 particles is built up, wherein the first soot layer has a density of 15 to 35%, more preferably 20 to 30%, in each case based on fully consolidated quartz glass, and the first compaction layer is built up on the first soot layer.

3. A method according to claim 1 or 2, characterized in that in process step c. a second layer of SiO2 particles is applied to the first compaction layer, wherein the second layer of SiO2 particles has a density of 15 to 35%, more preferably 20 to 32%, and even more preferably 25 to 29%, in each case based on fully consolidated quartz glass.

4. A method according to any one of claims 1 to 3, characterized in that the first compaction layer has a radial layer thickness a of 1 to 10 mm, more preferably 2 to 8 mm, and even more preferably 3 to 7 mm.

5. Method according to one of claims 1 to 4, characterized in that the SiC>2 soot body is exposed to a fluorine and / or chlorine-containing gas in process step d.

6. Method according to one of claims 2 to 5, characterized in that the thickness of the inner first soot layer is 0.5 to 10 mm and / or the thickness of the second soot layer is 100 to 190 mm.

7. Quartz glass body, obtainable by a method according to any one of claims 1 to 6.

8. A quartz glass body comprising a doping of fluorine and / or chlorine at a concentration of 1000 ppm by weight to 20000 ppm by weight, more preferably 1500 ppm by weight to 17000 ppm by weight, wherein the doping is homogeneously distributed over the quartz glass body.

9. A quartz glass body according to claim 8, characterized in that the quartz glass body exhibits a variation in the concentration of the doping along the axis of rotation of the cylindrical hollow body of a maximum of + / - 10%, preferably + / - 5%.

10. Quartz glass body according to claim 8 or 9, characterized in that the quartz glass body has a variation in the concentration of the doping radially perpendicular to the axis of rotation of the cylindrical hollow body in a range of 0 to 70% of the wall thickness of a maximum of + / - 10%, preferably + / - 5%.

11. Quartz glass body according to one of claims 8 to 10, characterized in that the quartz glass body has a variation in the concentration of the doping along the axis of rotation of the cylindrical hollow body of a maximum of + / - 10%, preferably + / - 5%.

12. Quartz glass body according to one of claims 8 to 11, obtainable by a method according to one of claims 1 to 6.

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