Method for preparing synthetic quartz glass

Abstract

To provide a production method and apparatus of synthetic quartz glass capable of bringing about excellent deposition efficiency of a silicon-containing starting material.SOLUTION: A production method of synthetic quartz glass includes a step for vaporizing a raw material containing at least one organic silicon starting compound to form raw material vapor and supplies the raw material vapor to a reaction unit, burns the raw material vapor in a flame in the presence of oxygen, and converts the raw material vapor to SiO2 soot particles by oxidation and / or hydrolysis. In the production method, the raw material gas containing the organic silicon starting compound is reacted using an optional flammable burner auxiliary gas, wherein the air number is 1.00 or less in a burner.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing synthetic quartz glass and a corresponding apparatus for carrying out the method according to the present invention.

Background Art

[0002] To produce synthetic quartz glass, SiO2 particles are generated by hydrolysis or oxidation from a starting material containing silicon by a CVD process and deposited on a moving carrier. It can be divided into an external deposition process and an internal deposition process. In the external deposition process, the SiO2 particles are deposited on the outside of the rotating carrier. Examples of such external deposition processes include the so-called OVD process (Out-side Vapour Phase Deposition), VAD process (Vapour Phase Axial Deposition), PECVD process (Plasma Enhanced Chemical Vapour Deposition), and the like. A well-known example of the internal deposition process is the MCVD (Modified Chemical Vapor Deposition) process in which SiO2 particles are deposited on the inner wall of a tube heated from the outside.

[0003] In the region of the carrier surface, at a sufficiently high temperature, the SiO2 particles directly vitrify, which is also called "direct vitrification". In contrast, in the so-called "soot process", since the temperature during the deposition of the SiO2 particles is very low, a porous SiO2 soot layer is obtained, which can be sintered in a separate process to obtain transparent quartz glass. Both the direct vitrification method and the soot method can obtain dense and transparent high-purity synthetic quartz glass.

[0004] In prior art processes for the production of synthetic quartz glass, methods are typically used to ensure sufficient deposition efficiency of SiO2 particles, where deposition efficiency is understood as the quotient between the weight of the resulting soot and the mathematically maximum amount of SiO2 that can be produced assuming complete conversion of silicon from the silicon-containing starting compound used. Such general conditions include, firstly, making the ratio of oxygen to fuel (= silicon-containing starting compound + fuel gas for ignition, for example) as stoichiometric as possible to ensure substantial complete conversion to the desired target product. Furthermore, a stoichiometric ratio of oxygen to oxidizable starting material, i.e., an air-to-air ratio of 1, results in a high conversion temperature, which is also considered favorable for process efficiency. In prior art, the silicon-containing starting material is usually burned in a turbulent flame, which ensures good mixing of the individual gases (especially oxygen and the silicon-containing starting compound) while simultaneously causing rapid conversion to the desired silicon dioxide. The formation of carbon soot in the flame is avoided as much as possible to prevent the deposition of carbon soot on the resulting soot. Finally, the prior art process is characterized by a minimum distance from the deposition surface of the burner used, so that the material converted to SiO2 can be collected as completely as possible on the soot body.

[0005] A process corresponding to the manufacture of synthetic quartz glass is described, for example, in WO90 / 10596A, in which an excess of oxygen, and therefore a number of air bubbles greater than 1, is used in conjunction with the above description.

[0006] EP3549921A discloses a method for manufacturing a porous glass matrix for optical fibers by depositing glass nanoparticles on a starting material, comprising the steps of: supplying a liquid organosilicon compound raw material and a carrier gas to a vaporizer; mixing and vaporizing the liquid organosilicon compound raw material and the carrier gas in the vaporizer to convert the organosilicon compound raw material and carrier gas into a raw material mixture gas; supplying the raw material mixture gas and a combustible gas to a burner; burning the raw material mixture gas and the combustible gas in the burner and ejecting the SiO nanoparticles generated by the combustion from the burner; and repeatedly moving the vaporizer and burner in synchronous and integrated manner parallel to the longitudinal direction of the starting material, thereby depositing the SiO nanoparticles ejected from the burner onto the starting material.

[0007] EP0622340A includes a method for preparing synthetic quartz glass components, using the general formula R n Si(OR) 4-n This method involves performing flame hydrolysis of a silane compound (where R is an aliphatic monovalent hydrocarbon group and the subscript n is an integer between 0 and 4) in an oxyhydrogen flame on a concentric multi-tubular burner nozzle consisting of a central nozzle and at least four ring nozzles: a first ring nozzle surrounding the central nozzle, a second ring nozzle surrounding the first ring nozzle, a third ring nozzle surrounding the second ring nozzle, and a fourth ring nozzle surrounding the third ring nozzle (in which vapor of the silane compound, oxygen gas, and hydrogen gas are introduced to form an oxyhydrogen flame, and the flame hydrolysis of the silane compound is carried out in the oxyhydrogen flame). The method comprises the following steps: (a) A step of introducing a mixture of silane compound vapor and oxygen into a central nozzle. (b) A step of introducing oxygen gas into at least two ring nozzles, including the first ring nozzle, and (c) The process includes introducing hydrogen gas into at least two ring nozzles, including a second ring nozzle. Furthermore, in this method, the total supply of oxygen gas is at least 50%, but not exceeding 90%, of the stoichiometric equivalent required for the complete combustion of hydrogen gas and the complete flame hydrolysis of the silane compound.

[0008] WO99 / 20574A discloses a method for forming a layer of high-purity synthetic glassy silica on the surface of a glass substrate having different physical and / or chemical properties from the aforementioned high-purity layer. This is achieved by burning a silica precursor with a burner, depositing the resulting silica on the surface of a glass substrate at a sufficiently high temperature, and forming a coherent layer of porosity-free glassy silica without requiring subsequent firing.

[0009] US2019 / 0084866A describes a method for producing synthetic quartz glass by mixing a silicon-containing starting compound with oxygen and supplying it as a raw material to a burner. It states that the oxygen in the mixture with the silicon-containing starting compound is present in the raw material at a ratio lower than stoichiometric to avoid premature ignition of the mixture. However, this lower-than-stoichiometric ratio of oxygen to the silicon-containing starting compound refers only to the supply stream of the silicon-containing starting compound and oxygen mixture. The total amount of oxygen supplied, i.e., the amount of oxygen supplied to the burner both with and separately from the silicon-containing starting compound, is in a ratio higher than stoichiometric with respect to the silicon-containing starting compound.

[0010] DE 10 2011 121 153 A also describes a soot process for manufacturing synthetic quartz glass, in which raw materials containing carbon-containing silicon compounds are reacted with oxygen in a reaction chamber to form SiO2 particles, then the SiO2 particles are deposited on a deposition surface to form a porous SiO2 soot body containing carbon and hydroxyl groups, and finally the porous SiO2 soot body is dried to vitrify it. In this context, DE 10 2011 121 153 A states that the deposition efficiency of the silicon-containing starting material octamethylcyclotetrasiloxane (OMCTS) improves when the number of air is less than 1, i.e., when it operates as an oxygen shortage down to a number of air of 0.95 (number of air = the oxygen theoretically required for the complete conversion of all flammable gases / the oxygen actually actively supplied to the burner). However, based on DE 10 2011 121 153 A, if further oxygen is added to the carrier gas OMCTS fluid, it will inevitably lead to an increase in the number of air particles, and those skilled in the art will surmise that the advantages described in DE 10 2011 121 153 A will not be achieved. Furthermore, the higher growth rate in DE 10 2011 121 153 A is due to a decrease in the average gas velocity due to the less oxygen added, resulting in a longer residence time for SiO2 particles near the deposition surface.

[0011] Overall, prior art processes still need improvement in terms of the deposition efficiency of silicon-containing starting materials, and therefore, there is a need for a process for producing synthetic quartz glass that can improve the deposition efficiency of silicon-containing starting materials. Improving deposition efficiency is closely related to reducing the manufacturing cost of synthetic quartz glass. [Disclosure of the Invention]

[0012] According to the present invention, this problem is solved by the method for manufacturing synthetic quartz glass, and this process is characterized by the following steps. (1) A step of evaporating a raw material containing at least one organosilicon starting compound to form a raw material vapor, (2) A step of supplying the raw material vapor from step (1) to a reaction section, burning the raw material vapor in a flame in the presence of oxygen, and converting it into SiO2 soot particles by oxidation and / or hydrolysis. (3) A step of depositing the SiO2 soot particles generated in step (2) onto the deposition surface to form a soot body, and (4) If necessary, a step of drying and vitrifying the soot produced in step (3) to form synthetic quartz glass.

[0013] Furthermore, the present invention relates to a method for producing synthetic silica glass through the following steps. (1) A step of evaporating a raw material containing at least one organosilicon starting compound to form a raw material vapor, (2) A process in which the raw material vapor from step (1) is supplied to the reaction section of a concentric burner in which the raw material vapor is burned in the presence of oxygen in the presence of oxygen and converted into SiO2 soot particles by oxidation and / or hydrolysis, and in which the raw material vapor is introduced into the burner flame as a supply mixture together with oxygen within the concentric circular cross section, and the supply mixture is separated from the oxygen-containing fuel gas by a non-oxidizing separation gas. (3) A step of depositing the SiO2 soot particles generated in step (2) onto the deposition surface to form a soot body, and (4) If necessary, a step of drying and vitrifying the soot body produced in step (3) to form synthetic quartz glass. Furthermore, both of the above methods according to the present invention are characterized in that the conversion of the raw material steam in step (2) is carried out with the number of air in the burner being 1.00 or less.

[0014] Within the scope of the present invention, the raw material steam is optionally used in step (2) with the addition of one or more auxiliary gases.

[0015] According to the present invention, the gas flow in the burner of the apparatus according to the present invention, that is, the ratio of oxygen (including supplied oxygen) actively (i.e., pressurized) supplied from the burner to all combustible material actively (i.e., pressurized) supplied to the burner, is adjusted so that the number of air molecules relative to all gases actively (i.e., pressurized) supplied to the burner is 1 or less.

[0016] The air number λ is theoretically defined as the ratio of the amount of oxygen actually available to the minimum amount of oxygen required for complete combustion stoichiometrically.

[0017] Within the scope of this invention, the total amount of oxygen stoichiometrically (maximum) used for the reaction of the organosilicon starting compound with the auxiliary gas (H2) in the burner is understood to be the amount of oxygen actively supplied to the burner under pressurization. From this definition of total oxygen, it follows that the amount of oxygen passively (i.e., unpressurized) supplied to the burner is not added to the total amount of oxygen provided according to this invention. In particular, oxygen that diffuses into the flame from the atmosphere surrounding the burner during the combustion of the organosilicon starting compound is excluded.

[0018] Furthermore, the amount of oxygen used (at most) stoichiometrically in the burner to convert organosilicon starting compounds and, if necessary, flammable auxiliary gases is understood to be the total amount of oxygen supplied intensively to the burner.

[0019] In a concentric burner, the term "oxygen centrally supplied to the burner" refers to the total amount of oxygen actively exiting the burner in the flame-side surface region of the burner, which is formed by a substantially circular region with radius r. Here, radius r extends perpendicularly from the center of the material nozzle or the center of the material nozzle group (nozzles for supplying organosilicon starting compounds) in the direction of the bait rod rotation axis, and radius r corresponds to approximately 1 / 5 of the average distance between the material nozzles and the deposition surface of the formed soot body.

[0020] The term oxygen supplied intensively to the burner is understood, in the case of a linear burner, to mean the total amount of oxygen that actively leaves it at the flame side of the burner in the surface area, where the surface area is a surface, i.e., a surface having a perpendicular distance d from the center of a material nozzle or the center line of a group of material nozzles (nozzle(s) for supplying an organosilicon starting compound) in the direction of the bait rod rotation axis, and the distance d corresponds to approximately 1 / 5 of the average distance of the material nozzle(s) from the deposition surface of the formed soot body.

[0021] The (maximum) stoichiometric use of oxygen is preferably maintained during the complete growth time of the soot body, where the growth time is understood to be the time required to supply the organosilicon starting compound to the process according to the invention. t 成長時間 = t 開始-終了 ケイ素含有出発化合物の供給

[0022] Within the scope of the present invention, the deposition efficiency is given by the quotient of the weight of the produced soot body and the calculated maximum amount of SiO2 that could be produced assuming complete conversion of silicon from the used silicon-containing starting compound.

[0023] Within the scope of the present invention, by applying such that the air number becomes 1 or less during combustion, the following technical effects can be obtained.

[0024] The use of a high-concentration combustion mixture (accompanied by an air number of 1 or less) will cause ignition to occur more slowly and locally only in the peripheral part of the flame where the burner gas O2 has already sufficiently diffused from the outer nozzle. The central part of the flame becomes less prone to ignition because the mixture is too concentrated. As a result, a smaller amount of gas ignites simultaneously, and oxygen has to first diffuse inward. This prevents the hot combustion gas from expanding from the ignited region to other regions of the flame, reducing flame turbulence.

[0025] In the method according to the present invention, the gas volume containing the flammable mixture expands significantly upward and exhibits less lateral expansion. As a result, a more laminar flame is obtained. A related effect is that the narrower, more laminar flame adheres better to the soot, forming a more stable retention point directly beneath the soot. This shortens the diffusion pathway of SiO2 particles to the soot deposition surface and increases the residence time at the retention point, thus improving overall deposition efficiency.

[0026] Furthermore, using less oxygen than the stoichiometric amount additionally results in a yellow, glowing flame center of carbon black with oxygen deficiency at the center of the flame.

[0027] The methods according to the present invention are, in particular, the Outside Vapor Deposition Method (OVD) process, the Vapor Axial Deposition (VAD) process, or the Soot-Boule process. The corresponding OVD and VAD processes are well known to those skilled in the art, and the Soot-Boule process is known, for example, from US8,230,701. [Modes for carrying out the invention]

[0028] Each step of the method according to the present invention will be described in more detail below.

[0029] [Process (1) - Evaporation of supplied raw materials] In step (1), a raw material containing at least one organosilicon starting compound is vaporized to form a raw material vapor. The organosilicon starting compound is preferably a polyalkylsiloxane compound.

[0030] In principle, any polyalkylsiloxane compound suitable for the manufacture of synthetic quartz glass can be used in accordance with the present invention. Within the scope of the present invention, the term polyalkylsiloxane encompasses both linear (including branched) and cyclic molecular structures.

[0031] A particularly suitable representative cyclic product is the general empirical formula Si p O p (R) 2p This is a polyalkylsiloxane represented by , where p is an integer greater than or equal to 3, and the group "R" is an alkyl group, in its simplest case being a methyl group.

[0032] Polyalkylsiloxanes are characterized by their particularly high silicon content per unit weight, which contributes to their economic efficiency when used in the manufacture of synthetic quartz glass.

[0033] The polyalkylsiloxane compound is preferably selected from the group consisting of hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), dodecamethylcyclohexasiloxane (D6), tetradecamethylcycloheptasiloxane (D7), hexadecamethylcyclooctasiloxane (D8), their chain homologues, and any mixture of these compounds. The notations D3, D4, D6, D7, and D8 are adopted from the notation introduced by General Electric Inc., where "D" represents the group [(CH3)2Si]-O-.

[0034] Within the scope of the present invention, mixtures of the above polyalkylsiloxane compounds can also be used.

[0035] Currently, octamethylcyclotetrasiloxane (OMCTS) is preferred because it is readily available in high purity and in large quantities. Therefore, within the scope of the present invention, octamethylcyclotetrasiloxane (D4) is particularly preferred as the polyalkylsiloxane compound.

[0036] In principle, the raw materials can be subjected to purification before being introduced into step (1). Such purification processes are known to those skilled in the art. However, in a preferred embodiment, the raw materials are not subjected to an upstream purification process beforehand.

[0037] The evaporation of the raw materials can be carried out with or without the presence of a carrier gas component. Preferably, the evaporation of the raw materials is carried out in the presence of a carrier gas, as this allows evaporation to be performed at a temperature below the boiling point of the organosilicon starting compound. This means that the raw material vapor preferably also contains the carrier gas. This approach is preferred when the evaporation of the raw materials is performed below its boiling point. The inert gas is preferably chemically inert, and more preferably nitrogen or argon. In this case, the molar ratio of the organosilicon starting compound to the carrier gas is preferably in the range of 0.01 to 2, particularly preferably in the range of 0.02 to 1.5, and most preferably in the range of 0.05 to 1.25. In particular, it is preferable to use nitrogen with a water content of <40 vol ppm as the carrier gas and to use OMCTS as the organosilicon starting compound. Furthermore, it is preferable that the molecular ratio of OMCTS to nitrogen is in the range of 0.015 to 1.5.

[0038] The evaporation process is known to those skilled in the art. Depending on the selected molecular ratio of the organosilicon starting compound to the carrier gas, the organosilicon starting compound is converted to a vapor phase, preferably at a temperature of 120–200°C. The evaporation temperature in the evaporation chamber is always preferably at least several degrees higher than the dew point of the organosilicon starting compound. The dew point, likewise, depends on the selected molecular ratio of the organosilicon starting compound to the carrier gas. In a preferred embodiment, this is achieved by preheating the organosilicon starting compound to a temperature of 40–120°C before evaporation, and then spraying it into an evaporation chamber having a higher temperature than the preheating of the starting material. In a preferred embodiment, the inert carrier gas can further be preheated to a temperature of up to 250°C before being supplied to the evaporation chamber. It is advantageous that the temperature in the evaporation chamber is always, on average, higher than the dew point temperature of the mixture of the organosilicon starting compound and the carrier gas. Suitable evaporation processes are described, for example, in international applications WO2013 / 087751A and WO2014 / 187513A and German patent application DE 10 2013 209 673 A.

[0039] Within the scope of this invention, the term "dew point" describes the temperature at which equilibrium is reached between a condensing liquid and an evaporating liquid.

[0040] When using a temperature below the boiling point of the raw materials, evaporation preferably occurs together with an inert carrier gas.

[0041] Within the scope of the present invention, "evaporation" is understood as the process by which the raw materials are essentially converted from a liquid phase to a gaseous phase. This is preferably carried out by using a temperature that is above the dew point of the organosilicon starting compound as the main component of the raw materials, as described above. Those skilled in the art will recognize from a process engineering point of view that the possibility of small droplets of the raw materials being entrained cannot be ruled out. Therefore, in step (1), a raw material vapor is produced that preferably contains 97 mol% or more, preferably 98 mol% or more, particularly preferably 99 mol% or more, of gaseous components.

[0042] The vaporized organosilicon starting compound, or a mixture of the carrier gas and the vaporized organosilicon starting compound, is typically removed from the evaporation chamber and supplied to the burner. Before being supplied to the burner, the vaporizable substance or the mixture of the vaporizable substance and the carrier gas is preferably mixed with oxygen. In the flame, the organosilicon starting compound is oxidized to SiO2. Amorphous SiO2 particles (SiO2 soot) are formed, which are deposited in the form of porous masses, initially on the surface of the carrier and then on the surface of the soot body being formed.

[0043] [Step (2) - The raw material vapor is supplied to the reaction section, and the raw material vapor is burned in a flame in the presence of oxygen, converting it into SiO2 soot particles by oxidation and / or hydrolysis.] In step (2), the gaseous raw material vapor obtained in step (1) is supplied to the reaction section, and the raw material vapor is converted into SiO2 particles by oxidation and / or hydrolysis.

[0044] This process corresponds in particular to a known suit process. Possible designs of this general process are known to those skilled in the art.

[0045] For the combustion of raw material vapor, a concentric burner is typically used, in which multiple gas outlet nozzles are arranged in a circle around the center of the burner opening.

[0046] According to the present invention, it has been found that reducing the number of air molecules is usually insufficient to achieve the desired deposition efficiency and, at the same time, to obtain a soot body substantially free of carbon deposits. For example, if the number of air molecules in the process according to DE 10 2011 121 153 A is lower than the number of air molecules applied in its embodiments, a soot body with an excess amount of carbon deposits is obtained. Therefore, the present invention (which differs fundamentally from the disclosure of DE 10 2011 121 153 A) preferably proposes at least one further process modification, which is described below.

[0047] In a burner preferably used according to the present invention, the central nozzle (inner nozzle) is typically used to supply raw material steam, which is generally pre-mixed with a carrier gas within the scope of the present invention. Furthermore, oxygen is preferably added to the raw material steam, resulting in a supply flow from the central nozzle of a concentric burner typically used that includes a carrier gas and oxygen in addition to the raw material steam.

[0048] In a preferred embodiment of the present invention, the organosilicon starting compound is supplied with oxygen and introduced into the burner.

[0049] This modified method, compared to the disclosure in DE 10 2011 121 153 A, makes it possible to reduce the number of air particles in the general-purpose process to below the range defined in the prior art, and thus improve yield efficiency without obtaining a soot body that simultaneously has an excess amount of carbon deposits.

[0050] Therefore, this preferred method according to the present invention differs considerably from the method described in DE 10 2011 121 153 A (a method that recommends using a high-concentration fuel mixture, i.e., an excess of SiO2 starting compound and the resulting oxygen shortage, but does not include any disclosure of a method for avoiding the simultaneous increase in carbon deposition on the soot body). Starting from the teachings of DE 10 2011 121 153 A, those skilled in the art who wish to improve the deposition efficiency of a general-purpose process would further reduce the burner oxygen, but would then fail due to an excess amount of unburned carbon in the soot body. Achieving a low air number according to the present invention is only possible by adding additional oxygen to the feed stream, with an overall reduced total amount of oxygen.

[0051] Within the scope of the present invention, burner shapes other than concentric burners can also be used. In these cases, it is preferable to supply the organosilicon starting compound to the burner chamber mixed with oxygen and optionally with a carrier gas, in accordance with the aforementioned new findings (the supply position of the organosilicon starting compound is not limited).

[0052] The central nozzle (inner nozzle) of the burner is typically surrounded by second nozzles (from which the separation gas is introduced into the burner), which are arranged concentrically around the central nozzle. This separation gas separates the oxygen-containing SiO2 starting compound from a further stream of oxygen entering the burner from another concentric nozzle arranged concentrically around the central nozzle and the separation gas nozzle.

[0053] Preferably, the gas used is one that generally contains more than 5 volume% hydrogen, particularly more than 10 volume% hydrogen, particularly more than 20 volume% hydrogen, particularly more than 30 volume% hydrogen, particularly more than 40 volume% hydrogen, and particularly more than 50 volume% hydrogen. In particular, it is used as a separation gas containing more than 60 volume% hydrogen, particularly more than 70 volume% hydrogen, particularly more than 80 volume% hydrogen, particularly more than 90 volume% hydrogen, particularly more than 95 volume% hydrogen, particularly more than 98 volume% hydrogen, and particularly more than 99 volume% hydrogen.

[0054] Preferably, essentially pure hydrogen is used as the separation gas.

[0055] Within the scope of the present invention, it may be specified that the distance between the burner and the surface of the soot body is adjusted during the deposition process. For this purpose, it is possible in principle to change the position of the burner and / or the soot body, thereby, in a preferred embodiment, moving the burner while keeping the rotation axis of the soot body stationary.

[0056] In the case of a deposition torch where the nozzle is coplanar with the torch mouth, the distance between the deposition torch and the deposition surface of soot particles is defined as the shortest distance between the torch mouth and the surface of the formed soot body. Alternatively, this distance is defined as the shortest distance between the nozzle mouth of the nozzle through which the quantitatively most important glass starting material passes and the surface of the formed soot body. This is typically a central nozzle (intermediate nozzle) with a concentric burner shape, which is usually preferred.

[0057] SiO2 soot particles produced by a deposition torch are typically deposited on a carrier tube rotating around its longitudinal axis, such that the soot body is constructed layer by layer. For this purpose, the deposition torch can be moved back and forth along the longitudinal axis of the carrier tube between two turning points. Furthermore, it is preferable to use a burner block in which a plurality of deposition burners, each having one flame, are arranged. When using a burner block, at least one, preferably all, of the burners are operated according to the present invention, i.e., the number of air according to the present invention is maintained for at least one, preferably all, of the burners, and the distance between each burner and the surface of the soot body is adjusted for at least one, preferably all, of the burners according to considerations according to the present invention.

[0058] As already mentioned at the beginning, within the scope of the present invention, we have found that a ratio of 1 or less of air, i.e., oxygen to the raw material, is advantageous for deposition. Therefore, according to the present invention, in step (2), it is even more preferable that oxygen is used in a ratio preferably less than stoichiometric amount relative to the raw material vapor and any combustible auxiliary gas to be hydrolyzed and / or polymerized.

[0059] In particular, the preferred number of air bubbles in the method according to the present invention is 0.95 or less, more preferably 0.90 or less, more preferably 0.85 or less, more preferably 0.80 or less, more preferably 0.78 or less, and still more preferably 0.76 or less.

[0060] In the method according to the present invention, it is desirable that the above number of air bubbles be maintained for at least 20%, more preferably at least 30%, even more preferably at least 40%, even more preferably at least 50%, even more preferably at least 60%, even more preferably at least 70%, even more preferably at least 80%, even more preferably at least 90%, even more preferably at least 95%, even more preferably at least 97%, even more preferably at least 98%, and even more preferably at least 99% of the previously defined growth time.

[0061] DE 10 2011 121 153 A discloses 0.952 as the minimum specific air number in the quartz glass manufacturing described herein. Therefore, those skilled in the art would not expect that a lower air number with significantly greater oxygen deficiency than that disclosed in DE 10 2011 121 153 A would lead to increased efficiency in the deposition of SiO2 particles according to the present invention, nor would they expect that increased efficiency could be achieved even if the flow of organosilicon starting compounds supplied to the burner were additionally oxygen-rich.

[0062] The overall decrease in ignition ability in a denser gas composition simultaneously reduces the average diameter of the igniting gas region (resulting in a smaller "smaller flame"). By suppressing the volume increase due to thermal expansion and molar increase due to decomposition (e.g., 1 mole of OMCTS gas produces x times the number of moles of combustion gas), smaller pressure waves are generated that make the flame less turbulent. As a result, the flame becomes more laminar, and the combustion length is increased, which has the advantages described above. In the burner and flame center of the method according to the present invention, only the feed flow and hydrogen are present, both of which are too highly concentrated to ignite quickly, and it must be considered that the oxygen from the outer nozzle, due to its lower turbulence, is dispersed over a longer distance and reaches the center more slowly.

[0063] Within the scope of the present invention, since the raw material is preferably released into the combustion chamber together with the carrier gas and oxygen from the central nozzle of a concentric burner, the amount of oxygen used in calculating the number of air bubbles must take into account that it results from the mixing of oxygen into the raw material flow and the mixing of additional oxygen used in the fuel gas.

[0064] Within the scope of the method according to the present invention, the number of air particles can be reduced significantly below the value defined in DE 10 2011 121 153 A, and at the same time, the deposition efficiency can be significantly improved.

[0065] At an exemplary number of air units of 0.85, the oxygen deficiency in the process according to the present invention is three times higher (15%) than in the process known from DE 10 2011 121 153 with an exemplary number of air units of 0.95 and an oxygen deficiency of only 5%, and at an exemplary number of air units of 0.75, it is five times higher (25%).

[0066] Furthermore, the method according to the present invention is preferably characterized by having a constant particle size distribution of excess soot, and thereby, preferably, can be used in secondary products.

[0067] [Process (3) - Deposition of SiO2 particles] In step (3), the SiO2 particles generated in step (2) are deposited on the deposition surface. The design of this step is within the scope of the skills and knowledge of a person skilled in the art.

[0068] For this purpose, the SiO2 particles formed in step (2) are deposited layer by layer onto a rotating carrier to form a porous soot body.

[0069] During the deposition of soot particles, the distance between the torch and the support is changed as needed to satisfy the aforementioned conditions.

[0070] [Step (4) - Drying and glass ] In step (4) , engineering By drying and vitrifying the SiO2 particles produced by step (3), synthetic quartz glass is formed. .child The design of the process is within the scope of the skills and knowledge of a person skilled in the art.

[0071] The method according to the present invention is suitable for the production of synthetic quartz glass carried out as an external or internal deposition process. When the method according to the present invention is carried out as an external deposition process, it is preferably an OVD process (external vapor deposition), a VAD process (vapor axial deposition), or a Sütboule process.

[0072] The process according to the present invention can reduce the manufacturing cost of quartz glass.

[0073] A further object of the present invention is to provide an apparatus for manufacturing synthetic quartz glass, the apparatus according to the present invention comprising the following: (a) at least one evaporator section for evaporating at least one raw material comprising at least one organosilicon starting compound to form a raw material vapor, wherein the evaporator section comprises an evaporation unit, (b) At least one reaction section to which the raw material steam from step (a) is supplied and the raw material is converted into SiO2 particles by thermal decomposition or hydrolysis, the reaction section including a burner, (c) At least one deposition section, wherein the deposition section is made of a soot material, and the deposition section is made of a soot material, and the SiO2 particles generated by the reaction section (b) are deposited thereon to form synthetic quartz glass.

[0074] The apparatus according to the present invention is further characterized in that the burner has a nozzle designed as follows: • Supplying the raw material vapor together with oxygen from the nozzle to the reaction section, and, The apparatus is equipped with means for adjusting the amount of oxygen to the silicon-containing starting compound so that the reaction of the raw material vapor to be realized is carried out with an air number of 1.00 or less in the burner.

[0075] In accordance with the above description of the method according to the present invention, the gas flow in the burner of the apparatus according to the present invention, in particular the amount of oxygen and organosilicon starting compound as fuel, and optionally the amount of flammable auxiliary gas, is adjusted to preferably achieve an air number of 0.95 or less.

[0076] For the definition of the number of air bubbles, please refer to the explanation above.

[0077] Within the scope of the present invention, the raw material vapor may also be used together with a carrier gas.

[0078] In accordance with the above description of the method according to the present invention, the gas flow in the burner of the apparatus according to the present invention, in particular the amount of oxygen and organosilicon starting compound as fuel, and optionally the amount of flammable auxiliary gas, is adjusted to preferably achieve an air number of 0.90 or less.

[0079] In accordance with the above description of the method according to the present invention, the gas flow in the burner of the apparatus according to the present invention, in particular the amount of oxygen and organosilicon starting compound as fuel, and optionally the amount of flammable auxiliary gas, is adjusted to preferably achieve an air number of 0.85 or less.

[0080] In accordance with the above description of the method according to the present invention, the gas flow in the burner of the apparatus according to the present invention, in particular the amount of oxygen and organosilicon starting compound as fuel, and optionally the amount of flammable auxiliary gas, is adjusted to preferably achieve an air number of 0.80 or less.

[0081] In accordance with the above description of the method according to the present invention, the gas flow in the burner of the apparatus according to the present invention, in particular the amount of oxygen and organosilicon starting compound as fuel, and optionally the amount of flammable auxiliary gas, is adjusted to preferably achieve an air number of 0.78 or less.

[0082] In accordance with the above description of the method according to the present invention, the gas flow in the burner of the apparatus according to the present invention, in particular the amount of oxygen and organosilicon starting compound as fuel, and optionally the amount of flammable auxiliary gas, is adjusted to preferably achieve an air number of 0.76 or less.

[0083] Preferably, the apparatus according to the present invention is such that the number of air bubbles is maintained for at least 20%, more preferably at least 30%, even more preferably at least 40%, even more preferably at least 50%, even more preferably at least 60%, even more preferably at least 70%, even more preferably at least 80%, even more preferably at least 90%, even more preferably at least 95%, even more preferably at least 97%, even more preferably at least 98%, and even more preferably at least 99% of the previously defined growth time.

[0084] The burner of the apparatus according to the present invention preferably has a concentric cross-section, and within the concentric cross-section, raw material vapor is introduced into the burner flame as a supply mixture together with oxygen (and an inert gas as a carrier gas), and the supply mixture is separated from the oxygen-containing fuel gas by a separation gas.

[0085] Finally, the present invention relates to the use of this apparatus for the manufacture of synthetic quartz glass. [Examples]

[0086] The present invention will be described in more detail below with reference to the following embodiments and drawings.

[0087] Examples of the present invention

[0088] In an evaporator according to an embodiment of international patent application PCT / EP2012 / 075346, the liquid raw material OMCTS is vaporized at 170°C with nitrogen, which is preheated to 180°C as a carrier gas. The nitrogen-OMCTS vapor mixture is introduced into a concentric burner with oxygen (mixed O2), and the experiment is carried out under the following conditions.

[0089] In experiments 1-3, the same amount of OMCTS per hour was introduced into the burner, and the amount of mixed O2 and combustion O2 were adjusted to achieve the air volume shown in the table below. The amounts of H2 and N2 were also kept the same. Furthermore, the distance between the burner and the main body was kept the same in all experiments.

[0090] [Table 1] meaning: -: Poor deposition efficiency +: Improved deposition efficiency ++: Significantly improved deposition efficiency +++: Greatly improved deposition efficiency

[0091] Tests 1-3 and the comparative examples demonstrate that the yield efficiency of general-purpose processes can be increased by reducing the number of air molecules, i.e., by using an increasingly lower stoichiometric ratio of oxygen to silicon-containing starting compounds and optionally flammable auxiliary gases. In particular, the air ratio is preferably significantly lower than the ratio of oxygen to silicon-containing starting compounds and optionally flammable auxiliary gases known from DE 10 2011 121 153 A.

[0092] In the experiment described above, a concentric burner is used, and the so-called raw material mixture is introduced into the burner area from the inner nozzle. The raw material mixture consists of polymerizable polyalkylsiloxane compound OMCTS, N2 carrier gas, and mixed O2. The inner nozzle of the burner is surrounded by a central nozzle concentric with it (from which H2 gas enters the burner area as a separated gas). Oxygen is introduced as a combustible agent (O2 combustible material) through the outer concentric nozzles. [Brief explanation of the drawing]

[0093] [Figure 1] This diagram shows the burner shapes used in the embodiments of Tests 1-3 and the comparative examples, with 1 representing the inner nozzle, 2 representing the intermediate nozzle, and 3 representing the outer nozzle.

[0094] [Comparative study] Starting with Test 4 according to Table 1 of DE 10 2011 121 153 A, the number of air molecules was reduced to a value lower than 0.952 in the comparative test. In this comparative test, oxygen was not supplied to the burner along with OMCTS at the central supply nozzle. The resulting soot material was unusable due to its excessively high carbon content.

Claims

1. (1) A step of evaporating a raw material containing at least one organosilicon starting compound to form a raw material vapor, (2) The raw material vapor is supplied to the reaction section, and the raw material vapor is burned in the flame of a burner in the presence of oxygen, and SiO is produced by oxidation and / or hydrolysis. ２ The process of converting into soot particles, (3) The SiO produced by step (2) ２ A process of depositing soot particles onto a deposition surface to form a soot body, (4) The SiO produced by step (3) ２ The process involves drying and vitrifying soot particles to form synthetic quartz glass. A method for manufacturing synthetic quartz glass having the following characteristics: The conversion of the raw material steam in step (2) is performed with the number of air bubbles in the burner set to 0.85 or less. The above step (2) is carried out by a burner having a concentric cross-section and comprising a supply flow nozzle, a separation gas nozzle, and an oxygen-containing fuel gas nozzle, wherein the raw material vapor is introduced into the burner flame as a supply mixture together with oxygen, the supply mixture is separated from the oxygen-containing fuel gas by a non-oxidizing separation gas, and the separated gas contains more than 5% by volume of hydrogen. A method for producing synthetic quartz glass, characterized in that the total amount of oxygen used to react the organosilicon starting compound and an optional flammable auxiliary gas in the burner is the amount of oxygen actively supplied to the burner.

2. The method according to claim 1, characterized in that the organosilicon starting compound is supplied to the burner together with oxygen.

3. The method according to claim 1 or 2, characterized in that the organosilicon starting compound is selected from hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), decamethylcyclohexasiloxane (D6), tetradecamethylcycloheptasiloxane (D7), hexadecamethylcyclooctasiloxane (D8), their chain homologs, and any mixture thereof.

4. (a) at least one evaporator section for evaporating at least one raw material containing at least one organosilicon starting compound to form a raw material vapor, wherein the evaporator section comprises an evaporation unit. (b) The raw material steam from step (a) is supplied, and the raw material is thermally decomposed or hydrolyzed to SiO ２ A reaction unit that converts particles, the reaction unit having a concentric cross-section and including a burner having a flame, (c) SiO produced by the reaction unit (b) ２ A deposition region comprising at least one deposition region that deposits particles to form a soot body, (d) at least one drying and vitrification section in which the SiO2 particles generated by the at least one deposition section (c) are dried and vitrified to form synthetic quartz glass A manufacturing apparatus for synthetic quartz glass, comprising: The burner having a concentric cross-section comprises a supply flow nozzle, a separation gas nozzle, and an oxygen-containing fuel gas nozzle, each equipped with a nozzle for introducing the raw material steam and oxygen as a supply mixture, the separation gas, and the oxygen-containing fuel gas into the reaction section, wherein the separation gas contains more than 5% by volume of hydrogen. The apparatus is equipped with means for adjusting the amount of oxygen to the organosilicon starting compound so that the reaction of the raw material vapor to be realized is carried out with an air number of 0.85 or less in the burner. A synthetic quartz glass manufacturing apparatus characterized in that the total amount of oxygen used to react the organosilicon starting compound and an optional flammable auxiliary gas in the burner is equal to the amount of oxygen actively supplied to the burner.

5. The apparatus according to claim 4, characterized in that the apparatus comprises a burner operated with an air number of 0.76 or less.

6. Use of the apparatus according to claim 4 or 5 for manufacturing synthetic quartz glass.

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