Method of manufacturing quartz glass

Abstract

The objective is to provide a method for manufacturing quartz glass that can transmit 222nm light while suppressing the transmission of 252nm light. [Solution] A method for producing quartz glass, comprising at least a preparation step of preparing tin-containing dry silica gel by drying tin-containing silica gel obtained by mixing silicon alkoxide, ethanol, tin(II) chloride, an alkali source, an acid source, and water; a first heat treatment step of heat-treating the glass raw material containing the tin-containing dry silica gel under a vacuum of 10 Pa or less at a temperature of 900°C to 1900°C; and a second heat treatment step of heat-treating the glass raw material heat-treated in the first heat treatment step in a nitrogen atmosphere at a temperature of 1400°C to 1900°C.

Description

[Technical Field]

[0001] This disclosure relates to a method for manufacturing quartz glass. [Background technology]

[0002] Ultraviolet light with a wavelength of around 222 nm (hereinafter also referred to as "222 nm UV light") has very little effect on living organisms, and sterilization and virus inactivation technologies using it are attracting attention. KrCl excimer lamps, which are widely used as a light source for 222 nm UV light, emit not only 222 nm UV light but also ultraviolet light with a wavelength of around 252 nm (hereinafter also referred to as "252 nm UV light"). Since 252 nm UV light is a concern because of its effect on living organisms, it is necessary to shield it when using KrCl excimer lamps for sterilization or virus inactivation targeting living organisms.

[0003] For example, Patent Documents 1 and 2 propose a sterilization device equipped with an optical filter that blocks 252 nm UV light. Non-Patent Document 1 discloses that tin-containing quartz glass manufactured by CVD or gas flame methods blocks 252 nm UV light. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Patent No. 6025756 [Patent Document 2] Patent No. 6973603 [Overview of the project] [Problems that the invention aims to solve]

[0005] Patent documents 1 and 2 disclose optical filters composed of a dielectric multilayer film in which multiple layers of HfO2 and SiO2 are alternately laminated on a glass plate. However, such optical filters require complicated manufacturing processes. Furthermore, dielectric multilayer films are not only difficult to form on curved surfaces, but the wavelength range they shield changes depending on the irradiation angle of light from a KrCl excimer lamp (hereinafter also referred to as "excimer light"). For this reason, excimer light equipped with optical filters such as those disclosed in Patent Documents 1 and 2 has a limited irradiation area that is effective for sterilization and virus inactivation.

[0006] The present disclosure aims to provide a method for manufacturing quartz glass that can transmit light at 222 nm while suppressing the transmission of light at 252 nm. [Means for solving the problem]

[0007] The present invention is as described in the claims, and the gist of this disclosure is as follows: [1] A method for producing quartz glass, comprising at least a preparation step of preparing tin-containing dry silica gel by drying tin-containing silica gel obtained by mixing silicon alkoxide, ethanol, tin(II) chloride, an alkali source, an acid source, and water; a first heat treatment step of heat-treating the glass raw material containing the tin-containing dry silica gel under a vacuum of 10 Pa or less at 900°C to 1900°C; and a second heat treatment step of heat-treating the glass raw material heat-treated in the first heat treatment step in a nitrogen atmosphere at 1400°C to 1900°C. [2] The method for producing quartz glass according to [1], wherein the tin-containing silica gel is obtained by mixing a first raw material comprising the silicon alkoxide, the ethanol, the acid source and the water with a second raw material comprising tin(II) chloride, and then mixing it with a third raw material comprising the alkali source. [3] The method for producing quartz glass according to [1] or [2], wherein the silicon alkoxide is tetraethoxysilane. [4] The method for producing quartz glass according to [1] or [2], wherein the alkali source is ammonia. [5] The method for producing quartz glass according to [1] or [2], wherein the acid source is hydrochloric acid. [6] The molar ratio of the hydrochloric acid to the silicon alkoxide is 5.0 × 10 -3 The above 3.0 × 10 -2 The method for manufacturing quartz glass described in [5] is as follows: [Effects of the Invention]

[0008] This disclosure provides a method for manufacturing quartz glass that can transmit light at 222 nm while suppressing the transmission of light at 252 nm. [Modes for carrying out the invention]

[0009] The method for manufacturing quartz glass according to this disclosure will be described below with reference to an example of an embodiment. Each component and parameter disclosed herein can be in any combination, and the upper and lower limits of the values ​​disclosed herein can also be in any combination.

[0010] The method for manufacturing quartz glass according to this embodiment (hereinafter also referred to as "the manufacturing method of this embodiment") includes at least a preparation step, a first heat treatment step, and a second heat treatment step.

[0011] First, the preparation step included in the manufacturing method of this embodiment will be described. The preparation step is a step of preparing tin-containing dry silica gel by drying tin-containing silica gel obtained by mixing at least silicon alkoxide, ethanol, tin(II) chloride, an alkali source, an acid source, and water.

[0012] The tin-containing silica gel to be dried in the preparation process is obtained by mixing at least silicon alkoxide, ethanol, tin(II) chloride, an alkali source, an acid source, and water (hereinafter also referred to as "starting materials"). Silicon alkoxide, one of the starting materials, undergoes a hydrolysis reaction when mixed with the other starting materials (ethanol, tin(II) chloride, alkali source, acid source, and water). When the hydrolysis reaction of silicon alkoxide occurs, the alkoxy groups bonded to the silicon in the silicon alkoxide are changed to hydroxyl groups, and these hydroxyl groups undergo a dehydration condensation reaction. As a result, the silicon derived from the silicon alkoxide is bonded via oxygen, and gel-like silica (silica gel) is produced via sol-like silica (silica sol). Similarly, tin(II) chloride, another of the starting materials, is also changed to hydroxyl groups and undergoes a hydrolysis reaction. Furthermore, during the silica gel production process, a condensation polymerization reaction occurs between silica and tin, so tin is incorporated into the silica, and the resulting silica gel contains tin (silica gel containing tin is obtained). The method of hydrolyzing silicon alkoxides to form silica sols or silica gels is generally called the sol-gel method.

[0013] The silicon alkoxide used as a starting material is a compound represented as Si(OR)4, in which four alkoxy groups are bonded to a silicon atom. In Si(OR)4, each R independently represents an alkyl group having between 1 and 3 carbon atoms. From the viewpoint of controlling the hydrolysis rate, the silicon alkoxide used as a starting material is preferably one or more substances selected from the group consisting of tetramethoxysilane, tetraisopropoxysilane, and tetraethoxysilane, and more preferably tetraethoxysilane.

[0014] The ethanol used as a starting material functions as a solvent for dissolving the silicon alkoxide in water. From the viewpoint of further promoting the hydrolysis reaction of the silicon alkoxide, it is preferable that at least a portion of the ethanol used as a starting material is mixed with the silicon alkoxide before mixing it with the other starting materials. That is, it is preferable that the silicon alkoxide is mixed with the other starting materials as a silicon alkoxide-containing ethanol solution obtained by mixing it with ethanol.

[0015] The tin(II) chloride used as a starting material is a compound represented as SnCl2. By using tin(II) chloride as a starting material, the silica gel (tin-containing silica gel) obtained by mixing the starting materials can contain tin. The tin derived from tin(II) chloride contained in the tin-containing silica gel functions as a component in the manufactured quartz glass that transmits 222nm light while suppressing the transmission of 252nm light.

[0016] The water used as a starting material functions as a reaction substrate for the hydrolysis reaction of silicon alkoxide. Examples of water that can be used include distilled water, deionized water, pure water, or two or more of these. If other starting materials contain water, such as hydrates, structured water, or solvents, the water contained in those other starting materials can be considered as part of the starting material water.

[0017] The acid source used as a starting material functions as a catalyst to promote the hydrolysis reaction of silicon alkoxide. The acid source used as a starting material can be any substance that exhibits acidity in the mixture of starting materials (hereinafter also referred to as the "raw material mixture"), and for example, one or more substances selected from the group of hydrochloric acid, nitric acid, and sulfuric acid can be used. From the viewpoint of further promoting the hydrolysis reaction of silicon alkoxide, hydrochloric acid is preferred as the acid source used as a starting material.

[0018] The alkali source used as a starting material functions as a catalyst to promote the dehydration condensation reaction between hydroxyl groups (hydroxyl groups bonded to silicon derived from silicon alkoxide) produced by the hydrolysis of silicon alkoxide. The alkali source used as a starting material can be any substance that exhibits alkalinity in the raw material mixture, for example, one or more substances selected from the group consisting of ammonia, methylamine, and dimethylamine can be used. From the viewpoint of further promoting the dehydration condensation reaction between hydroxyl groups, ammonia is preferred as the alkali source used as a starting material.

[0019] The molar ratio of water to silicon alkoxide used as a starting material (hereinafter also referred to as the "H2O / Si(OR)4 molar ratio") is not particularly limited as long as the hydrolysis reaction of silicon alkoxide proceeds. However, from the viewpoint of further promoting the hydrolysis reaction of silicon alkoxide, it is preferable to have a ratio of 1.0 or higher, 1.5 or higher, or 2.0 or higher. The upper limit of the H2O / Si(OR)4 molar ratio is not particularly limited, but for example, it can be 17.0 or lower, or 25.0 or lower. The combination of the upper and lower limits of the H2O / Si(OR)4 molar ratio described above is arbitrary, but from the viewpoint of further promoting the hydrolysis reaction of silicon alkoxide, the H2O / Si(OR)4 molar ratio is preferably 1.0 or higher and 25.0 or lower, more preferably 1.5 or higher and 25.0 or lower, and even more preferably 2.0 or higher and 17.0 or lower.

[0020] The molar ratio of ethanol to silicon alkoxide used as the starting material (hereinafter, also referred to as "C2H6O / Si(OR)4 molar ratio") is not particularly limited as long as the hydrolysis reaction of the silicon alkoxide proceeds. However, from the perspective of further promoting the hydrolysis reaction of the silicon alkoxide, it is preferably 0.1 or more, 0.2 or more, or 0.5 or more, and preferably 3.0 or less, 4.0 or less, or 5.0 or less. The combination of the upper limit value and the lower limit value of the above-mentioned C2H6O / Si(OR)4 molar ratio is arbitrary. However, from the perspective of further promoting the hydrolysis reaction of the silicon alkoxide, the C2H6O / Si(OR)4 molar ratio is preferably 0.1 or more and 5.0 or less, more preferably 0.2 or more and 4.0 or less, and even more preferably 0.5 or more and 3.0 or less.

[0021] The molar ratio of the acid source to the silicon alkoxide used as the starting material (hereinafter, also referred to as "acid / Si(OR)4 molar ratio") can be appropriately set in consideration of the reaction rate of the hydrolysis reaction of the silicon alkoxide and is not particularly limited. However, from the perspective of further promoting the hydrolysis reaction of the silicon alkoxide, it is preferably 5.0×10 -4 or more, 2.5×10 -3 or more, or 4.0×10 -3 or more, and preferably 0.25 or less, 5.0×10 -2 or less, or 3.5×10 -2 or less. The combination of the upper limit value and the lower limit value of the above-mentioned acid / Si(OR)4 molar ratio is arbitrary. However, from the perspective of further promoting the hydrolysis reaction of the silicon alkoxide, the acid / Si(OR)4 molar ratio is preferably 5.0×10 -4 or more and 0.25 or less, more preferably 2.5×10 -3 or more and 5.0×10 -2 or less, and even more preferably 4.0×10 -3 or more and 3.5×10 -2The following is even more preferable. In particular, when hydrochloric acid is used as the acid source, the molar ratio of silicon alkoxide to hydrochloric acid (hereinafter also referred to as the "HCl / Si(OR)4 molar ratio") is 5.0 × 10⁻⁶, from the viewpoint of further promoting the hydrolysis reaction of silicon alkoxide. -3 The above 3.0 × 10 -2 The following is preferable:

[0022] The molar ratio of the alkali source to the silicon alkoxide used as a starting material (hereinafter also referred to as the "alkali / Si(OR)4 molar ratio") can be appropriately set considering the reaction rate of the dehydration condensation reaction between hydroxyl groups (hydroxyl groups bonded to silicon derived from the silicon alkoxide) produced by the hydrolysis of the silicon alkoxide, and is not particularly limited, but from the viewpoint of further promoting the dehydration condensation reaction between hydroxyl groups, 1.0 × 10⁻⁶ is recommended. -3 The above is 5.0 x 10 -3 The above, or 1.0 × 10 -2 Preferably, it is 0.5 or less, 0.1 or less, or 6.0 × 10 -2 The following is preferable. The combination of the upper and lower limits of the alkali / Si(OR) 4 molar ratio mentioned above is arbitrary, but from the viewpoint of further promoting the dehydration condensation reaction between hydroxyl groups, the alkali / Si(OR) 4 molar ratio should be 1.0 × 10⁻⁶. -3 It is preferable that it is 0.5 or less, and 5.0 × 10 -3 It is more preferable that it be 0.1 or less, and 1.0 × 10 -2 The above 6.0 x 10 -2 The following is even more preferable:

[0023] The molar ratio of tin(II) chloride to silicon alkoxide used as a starting material (hereinafter also referred to as the "SnCl2 / Si(OR)4 molar ratio") is 1.0 × 10⁻⁶, as this ratio can more effectively suppress the transmission of 252 nm light and facilitate the production of quartz glass that transmits 222 nm light more easily. -4 The above is 2.0 × 10 -4 Above, or 5.0 × 10 -4 Preferably, it should be 3.0 × 10 -3Below, 5.0 × 10 -3 The following, or 1.0 × 10 -2 The following is preferable. The combination of the upper and lower limits of tin concentration mentioned above is arbitrary, but in order to further suppress the transmission of 252 nm light and to facilitate the production of quartz glass that transmits 222 nm light more easily, the tin concentration in the raw material mixture should be 1.0 × 10⁻⁶. -4 The above 1.0 × 10 -2 Preferably, it is 2.0 × 10 -4 The above 35.0 x 10 -3 It is more preferable that the following conditions apply: 5.0 × 10 -4 The above 3.0 × 10 -3 The following is even more preferable:

[0024] The molar ratio of the starting materials mentioned above can be calculated from the amount of starting materials used to be mixed.

[0025] The tin-containing silica gel to be dried in the preparation process may be obtained by mixing only the aforementioned starting materials (silicon alkoxide, ethanol, tin(II) chloride, alkali source, acid source, and water), but other components may also be mixed in addition to the aforementioned starting materials. Examples of such other components include unavoidable impurities that may be contained in each of the starting materials.

[0026] The tin-containing silica gel to be dried in the preparation step can be obtained by mixing the starting materials described above. The mixing order of the starting materials is not particularly limited; all starting materials may be mixed simultaneously, some may be mixed first and then the remaining starting materials, or they may be mixed in any order. In order that the tin derived from tin(II) chloride in the silica gel production process is more easily dispersed and incorporated, it is preferable to obtain the tin-containing silica gel to be dried in the preparation step by mixing a first raw material containing silicon alkoxide, ethanol, an acid source and water with a second raw material containing tin(II) chloride, and then mixing it with a third raw material containing an alkali source. Note that the mixing of the first and second raw materials only needs to involve mixing at least the first and second raw materials, and other starting materials may be further mixed in addition to the first and second raw materials. Similarly, the mixing of the mixture of the first and second raw materials (a mixture containing at least silicon alkoxide, ethanol, an acid source, water, and tin(II) chloride (hereinafter also referred to as "mixture A")) with the third raw material only requires that at least mixture A and the third raw material be mixed, and other starting materials may be further mixed in addition to mixture A and the third raw material.

[0027] The mixing conditions for the starting materials should be such that tin-containing silica gel is formed, and the mixing conditions used in conventionally known sol-gel methods can be used. For example, the mixing of the first and second materials can be carried out at a temperature of 10°C to 75°C for 10 minutes to 10 hours, and the mixing of mixture A and the third material can be carried out at a temperature of 10°C to 75°C for 10 minutes to 10 hours. The formation of tin-containing silica gel can be confirmed in the same way as in general sol-gel methods, for example, by the solidification (gelation) of the liquid starting material mixture (raw material mixture). The solidification of the raw material mixture can be confirmed by letting the mixture stand after mixing the starting materials to determine whether it has solidified.

[0028] In tin-containing silica gel obtained by mixing starting materials, tin may be chemically bonded to the atoms constituting the silica gel (oxygen atoms or silicon atoms), or it may be physically supported on the silica gel. Furthermore, the tin contained in the tin-containing silica gel may be in the form of a compound (e.g., an oxide), a metal (elemental), an ion, or two or more of these states.

[0029] In the preparation process, tin-containing silica gel is dried to prepare dried tin-containing silica gel. The drying method for tin-containing silica gel is not particularly limited, as long as at least a portion of the water and ethanol contained in the tin-containing silica gel is removed, but one example is a method of heat treatment of the tin-containing silica gel.

[0030] The heat treatment conditions for drying tin-containing silica gel are not particularly limited, as long as at least some of the water and ethanol contained in the tin-containing silica gel can be removed. However, it is preferable to dry it to the extent that the tin-containing silica gel does not adhere to the grinding device when it is placed in the grinding device described later. For example, possible heat treatment conditions for drying tin-containing silica gel include an air atmosphere, a temperature of 15°C to 100°C, and a duration of 12 hours to 96 hours. Preferably, the conditions are an air atmosphere, a temperature of 70°C to 90°C, and a duration of 24 hours to 48 hours.

[0031] Through the preparation process described above, tin-containing dried silica gel, which is a dried product of tin-containing silica gel, can be prepared. In tin-containing dried silica gel, tin may be chemically bonded to atoms (oxygen atoms or silicon atoms) constituting the dried silica gel, or it may be physically supported on the dried silica gel. Furthermore, the tin contained in the tin-containing dried silica gel may be in the form of a compound (e.g., an oxide), a metal (element), an ion, or two or more of these states.

[0032] The tin-containing dry silica gel prepared in the preparation step may be used as is in the first heat treatment step described later, or it may be used in the first heat treatment step described later after being subjected to at least one of the crushing and calcining treatments.

[0033] The grinding process is a procedure to adjust the particle size of the tin-containing dry silica gel. Conventional grinding equipment (e.g., jet mill, hammer mill, ball mill, vibration mill, bead mill) can be used for the grinding process. The particle size of the ground tin-containing dry silica gel can be set appropriately considering the characteristics of the quartz glass to be manufactured (e.g., color tone, amount of bubbles, filling rate during molding), but for example, it should be a particle size that can pass through a sieve with an opening of 10 μm to 150 μm.

[0034] The firing process is a treatment to remove impurities (e.g., water, carbon components derived from silicon alkoxide) contained in the tin-containing dry silica gel. The firing conditions only need to be sufficient to remove the impurities contained in the tin-containing dry silica gel, and can be set appropriately depending on the type and amount of impurities, but for example, conditions such as an air atmosphere, a temperature of 600°C to 1000°C, and a duration of 30 minutes to 24 hours can be used, and conditions of an air atmosphere, a temperature of 650°C to 900°C, and a duration of 1 hour to 24 hours are preferred.

[0035] Next, the first heat treatment step included in the manufacturing method of this embodiment will be described. The first heat treatment step is a step in which the glass raw material containing tin-containing dry silica gel prepared in the preparation step is heat-treated at a temperature of 900°C to 1900°C under a vacuum of 10 Pa or less.

[0036] The glass raw material heat-treated in the first heat treatment step includes tin-containing dried silica gel prepared in the preparation step. The glass raw material heat-treated in the first heat treatment step may consist only of tin-containing dried silica gel prepared in the preparation step, but silica powder (silica powder substantially free of tin) may be included in addition to the tin-containing dried silica gel to adjust the filling rate during molding, adjust the tin content in the quartz glass produced, or suppress the formation of bubbles in the quartz glass produced. The glass raw material containing tin-containing dried silica gel and silica powder can be obtained by mixing the tin-containing dried silica gel and silica powder.

[0037] For example, commercially available silica powder (e.g., product name: MKC Silica PS100, manufactured by Mitsubishi Chemical Corporation) can be used as the silica powder that can be included in the glass raw material. From the viewpoint of further suppressing the formation of bubbles in the quartz glass produced, it is preferable that the silica powder that can be included in the glass raw material has an average particle size D50 (median diameter) of 1 μm or more and 20 μm or less. The average particle size D50 is the particle size at which the cumulative volume from the smallest particle side in the volume particle size distribution accounts for 50%. The volume particle size distribution for determining the average particle size D50 can be determined using a general laser diffraction / scattering particle size distribution analyzer (e.g., Microtrac MT3300EXII, manufactured by Microtrac-Bell Corporation).

[0038] The amount of tin-containing dry silica gel in the glass raw material should be set appropriately considering the filling rate during molding and the tin content and amount of bubbles in the quartz glass to be manufactured. Examples include 0.5% by mass or more, 1.0% by mass or more, or 2.0% by mass or more, and 100% by mass or less, 50% by mass or less, or 10% by mass or less, based on 100% by mass of the glass raw material. The combination of the upper and lower limits of the tin-containing dry silica gel content mentioned above is arbitrary, but examples include 2.0% by mass or more and 10% by mass or less, 1.0% by mass or more and 50% by mass or less, or 0.5% by mass or more and 100% by mass or less.

[0039] The silica powder content in the glass raw material can be appropriately set considering the filling rate during molding and the tin content and bubble amount in the quartz glass to be manufactured. Examples include 0% by mass or more, 50% by mass or more, or 90% by mass or more, and 99.5% by mass or less, 99% by mass or less, or 98% by mass or less, relative to 100% by mass of the glass raw material. The combination of the upper and lower limits of the silica powder content mentioned above is arbitrary, but examples include 90% by mass or more and 98% by mass or less, 50% by mass or more and 99% by mass or less, or 0% by mass or more and 99.5% by mass or less. In this embodiment, a content of 0% by mass or 0 mol% means that the component is substantially absent, and substantially absent means that the component is not detectable (below the detection limit).

[0040] The glass raw material to be heat-treated in the first heat treatment step may be simply a collection of tin-containing dry silica gel and optionally contained silica powder, or it may be tin-containing dry silica gel and optionally contained silica powder molded into a predetermined shape. To mold the glass raw material, for example, a die press, a cold isostatic press (CIP), or both can be used.

[0041] In the first heat treatment step, the glass raw material is heat-treated at a temperature of 900°C to 1900°C. The heat treatment temperature of the glass raw material in the first heat treatment step may be 900°C to 1900°C, but from the viewpoint of suppressing the volatilization of silica and tin during heat treatment, it is preferable to be 1000°C or higher, or 1400°C or higher, and preferably 1700°C or lower, or 1800°C or lower. The combination of the upper and lower limits of the heat treatment temperature as described above is arbitrary, but from the viewpoint of suppressing the volatilization of silica and tin during heat treatment, the heat treatment temperature in the first heat treatment step is preferably 1000°C to 1900°C, more preferably 1000°C to 1800°C, even more preferably 1000°C to 1700°C, and particularly preferably 1400°C to 1700°C.

[0042] In the first heat treatment step, the heat treatment of the glass raw material is carried out under a vacuum of 10 Pa or less. The pressure during the heat treatment of the glass raw material in the first heat treatment step may be 10 Pa or less, but it is preferable to be between 0.1 Pa and 10 Pa. The pressure during heat treatment can be adjusted, for example, by degassing the air from the heat treatment container containing the glass raw material.

[0043] From the viewpoint of reducing the amount of bubbles, the heat treatment time for the glass raw material in the first heat treatment step is preferably 10 minutes or more, 30 minutes or more, or 60 minutes or more, and preferably 150 minutes or less, 200 minutes or less, or 300 minutes or less. The combination of the upper and lower limits of the heat treatment time as described above is arbitrary, but from the viewpoint of reducing the amount of bubbles, the heat treatment time in the first heat treatment step is preferably 10 minutes or more and 300 minutes or less, more preferably 30 minutes or more and 200 minutes or less, and even more preferably 60 minutes or more and 150 minutes or less.

[0044] Next, the second heat treatment step included in the manufacturing method of this embodiment will be described. The second heat treatment step is a step in which the glass raw material that has been heat-treated in the first heat treatment step is heat-treated in a nitrogen atmosphere at a temperature of 1400°C to 1900°C.

[0045] The second heat treatment step can be performed on the glass raw material that has been heat-treated in the first heat treatment step under the conditions described above, but it is preferable that it be performed immediately after the first heat treatment step. In other words, it is preferable that the heat treatment in the second heat treatment step be performed immediately after the heat treatment in the first heat treatment step is completed (before the glass raw material that has been heat-treated in the first heat treatment step is cooled).

[0046] In the second heat treatment step, the glass raw material is heat-treated at a temperature between 1400°C and 1900°C. The heat treatment temperature of the glass raw material in the second heat treatment step may be between 1400°C and 1900°C, but from the viewpoint of suppressing the generation of bubbles in the glass and making it easier to transmit 222nm UV light, it is preferable to be between 1700°C and 1800°C. The combination of the upper and lower limits of the heat treatment temperature as described above is arbitrary, but from the viewpoint of suppressing the generation of bubbles in the glass and making it easier to transmit 222nm UV light, the heat treatment temperature in the second heat treatment step is preferably between 1700°C and 1900°C, and more preferably between 1700°C and 1800°C.

[0047] In the second heat treatment step, the heat treatment of the glass raw material is carried out in a nitrogen atmosphere. The nitrogen atmosphere is an atmosphere in which the excess space (space excluding the glass raw material) of the container containing the glass raw material is replaced with nitrogen gas, and does not exclude other gases other than nitrogen that may be unintentionally mixed in. For example, the nitrogen atmosphere for the second heat treatment step may be created by introducing nitrogen gas into a heat treatment container in the first heat treatment step, where the internal pressure has been set to 10 Pa or less.

[0048] The pressure during the heat treatment of the glass raw material in the second heat treatment step is not particularly limited, but from the viewpoint of suppressing the generation of air bubbles in the glass and facilitating the transmission of 222nm UV light, it is preferably 0.1 MPa or higher, 0.2 MPa or higher, or 0.3 MPa or higher, and preferably 0.98 MPa or lower, 0.5 MPa or lower, or 0.4 MPa or lower. The combination of the upper and lower limits of the heat treatment pressure as described above is arbitrary, but from the viewpoint of suppressing the generation of air bubbles in the glass and facilitating the transmission of 222nm UV light, the pressure during the heat treatment in the second heat treatment step is preferably 0.1 MPa or higher and 0.98 MPa or lower, more preferably 0.2 MPa or higher and 0.5 MPa or lower, and even more preferably 0.3 MPa or higher and 0.4 MPa or lower. The pressure during heat treatment can be adjusted, for example, by degassing air from the heat treatment container containing the glass raw material or by introducing nitrogen gas.

[0049] From the viewpoint of preventing deterioration of the heat treatment container, the heat treatment time for the glass raw material in the second heat treatment step is preferably 10 minutes or more, 20 minutes or more, or 30 minutes or more, and preferably 180 minutes or less, 120 minutes or less, or 90 minutes or less. The combination of the upper and lower limits of the heat treatment time as described above is arbitrary, but from the viewpoint of preventing deterioration of the heat treatment container, the heat treatment time in the second heat treatment step is preferably 10 minutes or more and 180 minutes or less, more preferably 20 minutes or more and 120 minutes or less, and even more preferably 30 minutes or more and 90 minutes or less.

[0050] In the second heat treatment step, the glass raw material is heat-treated to produce the quartz glass of this embodiment. In the second heat treatment step, the quartz glass obtained by heat treatment may be left to cool in a nitrogen atmosphere.

[0051] Quartz glass can be manufactured by the manufacturing method of this embodiment, which includes the adjustment step, the first heat treatment step, and the second heat treatment step described above. The quartz glass manufactured by the manufacturing method of this embodiment (hereinafter also referred to as "quartz glass according to this embodiment") can transmit 222 nm light and can suppress the transmission of 252 nm light compared to conventional quartz glass that does not contain tin. The reason why the quartz glass according to this embodiment can transmit 222 nm light while suppressing the transmission of 252 nm light is not clear, but it is presumed that in the quartz glass manufactured by the manufacturing method of this embodiment, the dispersion state of tin derived from tin(II) chloride and the state of the quartz are such that they can not only suppress the transmission of 252 nm UV light but also transmit 222 nm UV light, thus enabling the transmission of 222 nm light while suppressing the transmission of 252 nm light. Such quartz glass according to this embodiment can be applied, for example, to an excimer light optical filter.

[0052] The quartz glass according to this embodiment contains tin. From the viewpoint of further improving the balance between suppressing the transmission of light at a wavelength of 252 nm and transmitting light at a wavelength of 222 nm, the tin concentration in the quartz glass according to this embodiment is preferably 1 ppm or more, 3 ppm or more, or 5 ppm or more, and preferably 1000 ppm or less, 300 ppm or less, or 100 ppm or less. The combination of the upper and lower limits of the tin concentration described above is arbitrary, but from the viewpoint of further improving the balance between suppressing the transmission of light at a wavelength of 252 nm and transmitting light at a wavelength of 222 nm, the tin concentration in the quartz glass according to this embodiment is preferably 1 ppm or more and 1000 ppm or less, more preferably 3 ppm or more and 300 ppm or less, and even more preferably 5 ppm or more and 100 ppm or less. In this disclosure, ppm means mass ppm.

[0053] In the quartz glass according to this embodiment, the tin concentration can be measured by ICP emission spectroscopy using the following method. The quartz glass is crushed, dissolved in hydrofluoric acid, sulfuric acid is added, and the hydrofluoric acid is volatilized by heating to obtain a residue for measurement. The residue for measurement is dissolved in nitric acid to obtain a sample solution. The sample solution can be measured by inductively coupled plasma emission spectroscopy (ICP-AES) using a general ICP emission spectrometer (for example, product name: 5800 ICP-OES, manufactured by Agilent Technologies) under the following conditions. Frequency: 27MHz Output: 1.2kW Chrome mode: Axial Detector: CCD detector Scanning mode: Continuous Sample introduction: Cyclone nebulizer

[0054] In the quartz glass according to this embodiment, tin may be contained in any of the following states: as a compound (e.g., oxide), as a metal (element), as an ion, or in two or more of these states, but it is preferable that it be contained as an oxide (e.g., SnO2).

[0055] In this embodiment, the transmission of 252 nm light is more easily suppressed, so the linear transmittance of 252 nm light (hereinafter also referred to as "linear transmittance 252") when the thickness is 1.5 mm is preferably 60% or less, more preferably 50% or less, and even more preferably 40% or less. The lower limit of linear transmittance 252 is not particularly limited, but for example it can be 10% or more, or 15% or more. The combination of the upper and lower limits of linear transmittance 252 described above is arbitrary, but in order to more easily suppress the transmission of 252 nm light, the linear transmittance 252 is preferably 10% or more and 60% or less, more preferably 10% or more and 50% or less, and even more preferably 15% or more and 40% or less.

[0056] In this embodiment, the quartz glass is more easily transmitted with respect to 222nm light, so the linear transmittance of 222nm light (hereinafter also referred to as "linear transmittance 222") when the thickness is 1.5 mm is preferably 50% or more, more preferably 55% or more, and even more preferably 60% or more. The upper limit of linear transmittance 222 is not particularly limited, but for example, it can be 95% or less, or 90% or less. The combination of the upper and lower limits of linear transmittance 222 described above is arbitrary, but in order to more easily transmit 222nm light, the linear transmittance 222 is preferably 50% or more and 95% or less, more preferably 55% or more and 95% or less, and even more preferably 60% or more and 90% or less.

[0057] Linear transmittances of 252 and 222 can be measured using a general ultraviolet-visible spectrophotometer (for example, model name: V-770, manufactured by JASCO Corporation). The following conditions can be used for measurement with an ultraviolet-visible spectrophotometer. Note that in measurements with an ultraviolet-visible spectrophotometer, the direction of light transmission should be the thickness direction of the sample being measured. Data acquisition interval: 1nm Bandwidth: 5.0nm Response time: 0.06 seconds Light source: Deuterium lamp, halogen lamp Scanning mode: Continuous Scanning speed: 400 nm / min Measurement range: 200nm to 900nm

[0058] The sample used for measurement with the ultraviolet-visible spectrophotometer is a 1.5 mm thick quartz glass (quartz glass according to this embodiment) with a polished surface. The quartz glass sample can be obtained, for example, by cutting it to a thickness of 1.7 mm and then polishing the surface to a thickness of 1.5 mm. For polishing the surface of the quartz glass, a polishing machine commonly used in this art, such as the Labopole 30 manufactured by Struers, can be used. Surface polishing of the quartz glass only needs to be performed on at least two surfaces: the surface from which the light transmitted to the quartz glass is incident (hereinafter also called the "incident surface") and the surface from which the light transmitted to the quartz glass is emitted (hereinafter referred to as the "exit surface"). Furthermore, a general-purpose surface grinding machine (for example, product name: PSG-52SA1, manufactured by Okamoto Machine Tool Works, Ltd.) can be used to cut the quartz glass.

[0059] The quartz glass according to this embodiment is more easily able to suppress the transmission of light at 252 nm, and therefore the absorption coefficient at a wavelength of 252 nm (hereinafter referred to as "α") 252 (Also known as "...") but 3.0cm -1 Preferably, it should be 4.5 cm or more. -1 It is more preferable that the length be greater than or equal to 7.5 cm. -1 It is even more preferable that the above conditions are met. α 252 The upper limit is not particularly limited, but for example, 15.0 cm -1 The following, or 12.0 cm -1 The following is possible: α as mentioned above 252 The combination of the upper and lower limits is arbitrary, but since the transmission of 252nm light is more easily suppressed, α 252 It is 3.0cm -1 More than 15.0cm -1 Preferably, it is 4.5 cm. -1 More than 15.0cm-1 It is more preferable that the following conditions apply: 7.5 cm -1 More than 12.0cm -1 The following is even more preferable:

[0060] The quartz glass according to this embodiment transmits light at 222 nm more easily, and therefore has an absorption coefficient of 222 nm (hereinafter referred to as "α 222 (Also known as ) but 4.5cm -1 Preferably, the following: 4.0 cm -1 It is more preferable that the following conditions apply: 3.0 cm -1 It is even more preferable that the following occurs: α 222 The lower limit is not particularly limited, but for example, 0.5 cm -1 or more, or 1.0 cm -1 The above can be applied. α 222 The combination of the upper and lower limits is arbitrary, but since 222nm light is more easily transmitted, 0.5cm -1 More than 4.5cm -1 Preferably, it is 0.5 cm. -1 More than 4.0cm -1 It is more preferable that the following conditions apply: 1.0 cm -1 More than 3.0cm -1 The following is even more preferable:

[0061] In the quartz glass according to this embodiment, α 222 α for 252 The ratio (hereinafter referred to as "α") 252 / α 222 (Also known as ) is preferable to be 1.5 or higher, 2.0 or higher, or 2.5 or higher, as it improves the balance between suppressing the transmission of light with a wavelength of 252 nm and transmitting light with a wavelength of 222 nm. 252 / α 222 The upper limit is not particularly limited, but for example, it can be 10 or less, or 5.0 or less. 252 / α 222 The combination of the upper and lower limits is arbitrary, but the balance between suppressing the transmission of light at a wavelength of 252 nm and transmitting light at a wavelength of 222 nm is improved, so α252 / α 222 It is preferably 1.5 or more and 10 or less, more preferably 2.0 or more and 5.0 or less, and even more preferably 2.5 or more and 5.0 or less.

[0062] α 222 and α 252 This can be calculated from the following formula (1). Linear transmittance T in the following formula (1) w For this, either the linear transmittance of 252 (linear transmittance of light with a wavelength of 252 nm when the thickness is 1.5 mm) or the linear transmittance of 222 (linear transmittance of light with a wavelength of 222 nm when the thickness is 1.5 mm) can be used. When using these values, the thickness d of the measurement sample in equation (1) below is 0.15 [cm] (1.5 [mm]). α w ×d=-Ln(T w / 100)···(1) In the above equation (1), α w The absorption coefficient at wavelength W (nm) is [cm²] -1 ] represents the thickness of the sample [cm], and T represents the thickness of the sample [cm]. w This represents the linear transmittance [%] at wavelength W (nm).

[0063] α 252 / α 222 α can be obtained from equation (1) above. 252 α can be obtained from the above equation (1). 222 It can be calculated by dividing by . The absorption coefficient is a parameter that represents how much light a medium absorbs when light is incident on it, and a higher absorption coefficient means that less light is transmitted through the quartz glass. [Examples]

[0064] The present disclosure will be explained below with reference to examples. However, the present disclosure is not limited to these examples.

[0065] (Molar ratio of starting materials) The molar ratio of the starting materials was calculated from the amount of starting materials used.

[0066] (Tin concentration in quartz glass) Quartz glass was crushed, dissolved in hydrofluoric acid, sulfuric acid was added, and the hydrofluoric acid was volatilized by heating to obtain a residue for measurement. This residue was dissolved in nitric acid to prepare a sample solution. The sample solution was measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) under the following conditions using a general ICP emission spectrometer (product name: 5800 ICP-OES, manufactured by Agilent Technologies). Frequency: 27MHz Output: 1.2kW Chrome mode: Axial Detector: CCD detector Scanning mode: Continuous Sample introduction: Cyclone nebulizer

[0067] (Measurement sample) A disc-shaped quartz glass with a diameter of 23 mm and a thickness of 7 mm was prepared. While visually inspecting the prepared quartz glass, it was ground down to a thickness of 1.7 mm using a precision surface grinding machine (machine name: PSG-52SA1, manufactured by Okamoto Machine Tool Works, Ltd.). The areas of the ground quartz glass corresponding to the incident and exit surfaces were polished using a polishing machine (Labopol 30, manufactured by Struers) until the thickness of the quartz glass was 1.5 mm, and a measurement sample was obtained.

[0068] (Linear transmittance) Using a UV-Vis spectrophotometer (model: V-770, manufactured by JASCO Corporation), the sample was measured under the following conditions to determine the linear transmittance (linear transmittance 252) [%] for light at a wavelength of 252 nm when the sample was 1.5 mm thick, and the linear transmittance (linear transmittance 222) [%] for light at a wavelength of 222 nm when the sample was 1.5 mm thick. The direction of light transmission was defined as the thickness direction of the sample. Data acquisition interval: 1nm Bandwidth: 5.0nm Response time: 0.06 seconds Light source: Deuterium lamp, halogen lamp Scanning mode: Continuous Scanning speed: 400 nm / min Measurement range: 200 nm to 900 nm

[0069] (Absorption coefficient) Using the linear transmittance T in the above formula (1) as the linear transmittance 252 obtained by the method described above, and using 0.15 [cm] as the thickness d of the measurement sample in the above formula (1), α was obtained from the above formula (1). w Using the linear transmittance T in the above formula (1) as the linear transmittance 222 obtained by the method described above, and using 0.15 [cm] as the thickness d of the measurement sample in the above formula (1), α was obtained from the above formula (1). 252 Using the linear transmittance T in the above formula (1) as the linear transmittance 222 obtained by the method described above, and using 0.15 [cm] as the thickness d of the measurement sample in the above formula (1), α was obtained from the above formula (1). w Using the linear transmittance T in the above formula (1) as the linear transmittance 222 obtained by the method described above, and using 0.15 [cm] as the thickness d of the measurement sample in the above formula (1), α was obtained from the above formula (1). 222 Also, the obtained α 252 Dividing α by α 222 gives the ratio of the absorption coefficient at wavelength 252 nm to the absorption coefficient at wavelength 222 nm (α 252 / α 222 ).

[0070] Example 1 29 mL of ethanol (special grade, manufactured by Kanto Chemical Co., Inc.) and 112 mL of tetraethoxysilane (manufactured by Fujifilm Wako Pure Chemical Corporation) were mixed to obtain a tetraethoxysilane-containing ethanol solution. 36 mL of 0.1 mol / L hydrochloric acid (manufactured by Fujifilm Wako Pure Chemical Corporation) was added to the obtained tetraethoxysilane-containing ethanol solution, and the mixture was stirred for 1 hour to obtain the first raw material. 0.113 g of tin(II) chloride dihydrate (manufactured by Fujifilm Wako Pure Chemical Corporation) and 1.2 mL of ethanol were mixed to obtain the second raw material. Also, 9 mL of 0.1 mol / L hydrochloric acid and 29 mL of ethanol were mixed to obtain a hydrochloric acid-containing ethanol solution. The first raw material, the second raw material, and the hydrochloric acid-containing ethanol solution were mixed and stirred at 25 °C for 1 hour to obtain mixture A. 1.5 mL of 10% aqueous ammonia solution (manufactured by Fujifilm Wako Pure Chemical Corporation) and 18 mL of distilled water were mixed to obtain the third raw material. Mixture A and the third raw material were mixed at 25 °C for 1 hour. Then, it was allowed to stand, and it was confirmed that the mixture of mixture A and the third raw material solidified and tin-containing silica gel was formed.

[0071] The molar ratios of the starting materials used in this example were as follows. In the following compositions, the H2O / TEOS molar ratio indicates the molar ratio of water to tetraethoxysilane, the C2H6O / TEOS molar ratio indicates the molar ratio of ethanol to tetraethoxysilane, the HCl / TEOS molar ratio indicates the molar ratio of hydrochloric acid to tetraethoxysilane, the NH3 / TEOS indicates the molar ratio of ammonia to tetraethoxysilane, and the SnCl2 / TEOS molar ratio indicates the molar ratio of tin(II) chloride to tetraethoxysilane. H2O / TEOS molar ratio: 7.0 C2H6O / TEOS molar ratio: 2.04 HCl / TEOS molar ratio: 9.01×10 -3 NH3 / TEOS molar ratio: 1.80×10 -2 SnCl2 / TEOS molar ratio: 1.0×10 -3

[0072] The mixture of mixture A and the third raw material (tin-containing silica gel) was dried at 80 °C for 36 hours in an air atmosphere to obtain tin-containing dry silica gel. The tin-containing dry silica gel was pulverized and classified with a sieve having a mesh size of 125 μm, and then fired at 800 °C for 1 hour in an air atmosphere.

[0073] Commercially available silica powder (product name: MKC silica PS100, manufactured by Mitsubishi Chemical Corporation) was pulverized with a jet mill so that the average particle size D50 (median diameter) was 5 μm or less. 1 g of tin-containing dry silica gel was added to 39 g of the obtained silica powder and mixed for 60 minutes to obtain a glass raw material. After filling 6.0 g of the obtained glass raw material into a mold with a diameter of 30 mm, a pressure of 150 kgf / cm 2 was applied for 30 seconds to form it into a predetermined shape. The formed glass raw material was vacuum-packed in a nylon polyethylene bag and pressurized by applying a pressure of 200 MPaG for 3 minutes by a cold isostatic pressing method to obtain a molded body of the glass raw material.

[0074] A molded body of glass raw material was placed in a carbon container and heat-treated at 1600°C for 120 minutes under a vacuum of 10 Pa or less (below the detection limit). After the 120 minutes of heat treatment, nitrogen was introduced into the vacuum atmosphere used for the heat treatment at 0.35 MPa, and the material was further heat-treated at 1800°C for 60 minutes in the nitrogen atmosphere. After the 60 minutes of heat treatment, the material was allowed to cool naturally overnight in a nitrogen atmosphere to obtain the quartz glass of this example.

[0075] Example 2 The quartz glass of this example was obtained in the same manner as in Example 1, except that the amount of 0.1 mol / L hydrochloric acid used to prepare the first raw material was changed from 36 mL to 72 mL, and the amount of 10% ammonia aqueous solution used to prepare the third raw material was changed from 1.5 mL to 2.8 mL. The molar ratios of the starting materials used in this example were as follows. H2O / TEOS molar ratio: 11.0 C2H6O / TEOS molar ratio: 2.04 HCl / TEOS molar ratio: 1.62 × 10⁻⁶ -2 NH3 / TEOS molar ratio: 3.24 × 10⁻⁶ -2 SnCl2 / TEOS molar ratio: 1.0 × 10⁻⁶ -3

[0076] Example 3 The quartz glass of this example was obtained in the same manner as in Example 1, except that the amount of 0.1 mol / L hydrochloric acid used to prepare the first raw material was changed from 36 mL to 108 mL, and the amount of 10% ammonia aqueous solution used to prepare the third raw material was changed from 1.5 mL to 4.0 mL. The molar ratios of the starting materials used in this example were as follows. H2O / TEOS molar ratio: 15.0 C2H6O / TEOS molar ratio: 2.04 HCl / TEOS molar ratio: 2.34 × 10⁻⁶ -2 NH3 / TEOS molar ratio: 4.69 × 10⁻⁶ -2 SnCl2 / TEOS molar ratio: 1.0 × 10⁻⁶ -3

[0077] Example 4 The quartz glass of this example was obtained in the same manner as in Example 1, except that the amount of tin(II) chloride dihydrate used in preparing the second raw material was changed from 0.113 g to 0.226 g. The molar ratios of the starting materials used in this example were as follows. H2O / TEOS molar ratio: 7.0 C2H6O / TEOS molar ratio: 2.04 HCl / TEOS molar ratio: 9.01 × 10⁻⁶ -3 NH3 / TEOS molar ratio: 1.80 × 10⁻⁶ -2 SnCl2 / TEOS molar ratio: 2.0 × 10⁻⁶ -3

[0078] Example 5 The quartz glass of this example was obtained in the same manner as in Example 1, except that the amount of tin(II) chloride dihydrate used in preparing the second raw material was changed from 0.113 g to 0.068 g. The molar ratios of the starting materials used in this example were as follows. H2O / TEOS molar ratio: 7.0 C2H6O / TEOS molar ratio: 2.04 HCl / TEOS molar ratio: 9.01 × 10⁻⁶ -3 NH3 / TEOS molar ratio: 1.80 × 10⁻⁶ -2 SnCl2 / TEOS molar ratio: 6.0 × 10⁻⁶ -4

[0079] Comparative Example 1 The quartz glass of this comparative example was obtained in the same manner as in Example 1, except that tin(II) chloride dihydrate was not added when preparing the second raw material. The molar ratios of the starting materials used in this comparative example were as follows. H2O / TEOS molar ratio: 5.0 C2H6O / TEOS molar ratio: 2.16 HCl / TEOS molar ratio: 5.41 × 10⁻⁶ -3 NH3 / TEOS molar ratio: 1.08 × 10⁻⁶ -2 SnCl2 / TEOS molar ratio: 0

[0080] For the quartz glass of the examples and comparative examples, the tin concentration, the linear transmittance of light at a wavelength of 252 nm at a thickness of 1.5 mm (linear transmittance 252), the linear transmittance of light at a wavelength of 222 nm at a thickness of 1.5 mm (linear transmittance 222), and the absorption coefficient at a wavelength of 252 nm (α 252 ), the absorption coefficient (α) at ​​a wavelength of 222 nm 222 ), and α 222 α for 252 The ratio (α 252 / α 222 The results are shown in Table 1 below. In Table 1 below, the tin concentration of Comparative Example 1 means that it is below the detection limit (0.7 ppm).

[0081] [Table 1]

[0082] As shown in Table 1 above, the quartz glass in each example had a lower linear transmittance of 252 nm than Comparative Example 1, which does not contain tin, indicating that the transmission of 252 nm light was suppressed. Furthermore, it was confirmed that the quartz glass in each example could transmit 222 nm light, as indicated by the linear transmittance of 222 nm. From these results, it was understood that the quartz glass in each example could transmit 222 nm light while suppressing the transmission of 252 nm light.

Claims

1. At a minimum, the preparation step involves mixing silicon alkoxide, ethanol, tin(II) chloride, an alkali source, an acid source, and water, and then drying the tin-containing silica gel to prepare tin-containing dry silica gel. A first heat treatment step involves heat-treating the glass raw material containing the aforementioned tin-containing dry silica gel at a temperature of 900°C to 1900°C under a vacuum of 10 Pa or less, A second heat treatment step in which the glass raw material heat-treated in the first heat treatment step is heat-treated in a nitrogen atmosphere at a temperature of 1400°C to 1900°C, A method for manufacturing quartz glass, including the method described above.

2. The method for producing quartz glass according to claim 1, wherein the tin-containing silica gel is obtained by mixing a first raw material comprising the silicon alkoxide, the ethanol, the acid source, and the water with a second raw material comprising tin(II) chloride, and then mixing it with a third raw material comprising the alkali source.

3. The method for producing quartz glass according to claim 1 or 2, wherein the silicon alkoxide is tetraethoxysilane.

4. The method for producing quartz glass according to claim 1 or 2, wherein the alkali source is ammonia.

5. The method for producing quartz glass according to claim 1 or 2, wherein the acid source is hydrochloric acid.

6. The molar ratio of the hydrochloric acid to the silicon alkoxide is 5.0 × 10 －３ The above 3.0 x 10 －２ The method for producing quartz glass according to claim 5 is as follows:

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