Method for producing titanium-containing silica glass

Abstract

Provided is a method for producing titanium-containing silica glass with high production efficiency.　The method for producing titanium-containing silica glass comprises preparing a slurry containing a silica component, a titanium component, and a solvent, obtaining raw material granules by spray freeze granulation drying using the slurry, pressure-molding the raw material granules to obtain a molded body, and heating the molded body to obtain titanium-containing silica glass.

Description

Method for producing titanium-containing silica glass

[0001] The present invention relates to a method for producing titanium-containing silica glass.

[0002] In recent years, EUV lithography using EUV light with a central wavelength around 13.5 nm as a light source has been studied for further miniaturization of semiconductor devices. In EUV lithography, a reflective optical system and a reflective mask are used due to the characteristics of EUV light.

[0003] A reflective mask used in EUV lithography is obtained by processing a reflective mask blank which is an original plate. As a substrate used for the reflective mask blank, a glass substrate having a low coefficient of thermal expansion is often used. As a glass substrate having a low coefficient of thermal expansion, for example, titanium-containing silica glass is known.

[0004] As a method for producing titanium-containing silica glass, a method (vapor phase method) is known in which glass raw materials are subjected to flame hydrolysis or thermal decomposition to generate fine particles of titanium-containing silica glass, the generated fine particles are deposited on a base material, and a heat treatment or the like is performed. In the above vapor phase method, titanium-containing silica glass having a structure (striae) in which the composition ratio of Ti and Si periodically varies is obtained. When the above striae are present, it is difficult to improve smoothness when the glass substrate is used for a reflective mask blank. Accordingly, Patent Document 1 discloses a method for producing titanium-containing silica glass by a method different from the above vapor phase method. Specifically, Patent Document 1 discloses a method for producing titanium-containing silica glass by a liquid phase method (sol-gel method). More specifically, in the liquid phase method described in Patent Document 1, a method is disclosed in which a slurry containing raw material powder is obtained, the raw material powder in the slurry is dispersed, solid-liquid separation is performed to obtain a wet cake, and drying and heat treatment are performed to obtain titanium-containing silica glass.

[0005] International Publication No. 2023 / 038036

[0006] As a result of studies on the production method described in Patent Document 1 by the present inventors, it has been found that the time required for drying the wet cake is long, and there is room for improvement in terms of production efficiency.

[0007] The present invention has been made in view of the above problems, and an object thereof is to provide a method for producing titanium-containing silica glass with high production efficiency.

[0008] As a result of intensive studies on the above problems, the present inventors have found that the above problems can be solved by obtaining a molded body using raw material granules obtained by a spray freeze granulation drying method and heating the molded body, thereby completing the present invention.

[0009] In other words, the inventors have found that the above problems can be solved by the following configurations: [1] A method for producing titanium-containing silica glass, comprising: preparing a slurry containing a silica component, a titanium component, and a solvent; obtaining raw material granules by spray freeze granulation drying using the slurry; obtaining a molded body by pressure molding the raw material granules; and heating the molded body to obtain titanium-containing silica glass. [2] The method for producing titanium-containing silica glass according to [1], wherein the titanium component comprises at least one selected from the group consisting of titania, titania-silica composites, titanium-containing silica, and organotitanium compounds. [3] The method for producing titanium-containing silica glass according to [1] or [2], wherein the slurry comprises silica and at least one selected from the group consisting of titania-silica composites, titania, and titanium-containing silica. [4] The method for producing titanium-containing silica glass according to any one of [1] to [3], wherein the slurry comprises silica and one or more selected from the group consisting of titania and titania-silica composites. [5] A method for producing titanium-containing silica glass according to any one of [1] to [4], wherein, in heating the molded body, the molded body is sintered to obtain a sintered body, and the sintered body is melted. [6] A method for producing titanium-containing silica glass according to any one of [1] to [5], wherein the pressure molding includes pressurization by isotropic press. [7] A method for producing titanium-containing silica glass according to any one of [1] to [6], wherein, when obtaining the molded body, the raw material granules are pressurized to form a layered molded body, the raw material granules are further arranged on at least one side of the obtained layered molded body, and pressurized to form an additional layered molded body, and one or more layers of the additional layered molded body are formed on the layered molded body to obtain the molded body. [8] A method for producing titanium-containing silica glass according to any one of [1] to [7], wherein the OH concentration of the obtained titanium-containing silica glass is less than 600 ppm by mass. [9] A method for producing titanium-containing silica glass according to any one of [1] to [8], wherein the heating of the molded body includes hot isostatic pressing.

[10] A method for producing titanium-containing silica glass according to any one of [1] to [9], wherein the average packing rate of the raw material granules is 12.0 to 45.0 by volume.

[11] A method for producing titanium-containing silica glass according to any one of [1] to

[10] , wherein the average collapse strength of the raw material granules is 0.10 to 1.00 MPa.

[12] A method for producing titanium-containing silica glass according to any one of [1] to

[11] , wherein the ratio of the diameter of intragranular defects in the raw material granules to the granular particle size of the raw material granules is 0.30 or less.

[13] A method for producing titanium-containing silica glass according to any one of [1] to

[12] , wherein the average particle size of the ceramic raw material powder among the silica component and the titanium component is 10 to 500 nm.

[14] A method for producing titanium-containing silica glass according to any one of [1] to

[13] , wherein the fluidity index of the raw material granules is 60 or more.

[15] The method for producing titanium-containing silica glass according to any one of [1] to

[14] , wherein the spray freeze granulation drying method is carried out in the order of spray freeze and vacuum drying, and after the vacuum drying, the drying is further carried out at 35 to 150°C under atmospheric pressure, and the amount of solvent remaining in the raw material granules is 2.0% by mass or less with respect to the total mass of the raw material granules.

[16] The method for producing titanium-containing silica glass according to any one of [1] to

[15] , wherein the slurry further comprises a binder, and after obtaining the molded body, a degreasing treatment is performed.

[17] The method for producing titanium-containing silica glass according to

[16] , wherein the binder comprises at least one selected from the group consisting of polyvinyl acetal, polyethylene glycol, paraffin wax, carnauba wax, and microcrystalline wax.

[18] The method for producing titanium-containing silica glass according to

[16] or

[17] , wherein the content of the binder in the slurry is 10.0 to 50.0% by mass of the silica component and the titanium component relative to the content of the ceramic raw material powder.

[19] The method for producing titanium-containing silica glass according to any one of [1] to

[18] , wherein the slurry further contains a pH adjusting agent, and the pH adjusting agent contains at least one selected from the group consisting of ammonia, quaternary ammonium hydroxide, and organic amine compounds.

[20] The method for producing titanium-containing silica glass according to

[19] , wherein the content of the pH adjusting agent in the slurry is 0.2 to 5.0% by mass of the silica component and the titanium component relative to the content of the ceramic raw material powder.

[21] The method for producing titanium-containing silica glass according to any one of [1] to

[20] , wherein the content of the ceramic raw material powder in the slurry is 12.0 to 68.0% by mass of the silica component and the titanium component relative to the total mass of the slurry.

[22] The method for producing titanium-containing silica glass according to any one of [1] to

[21] , wherein the viscosity of the slurry is 100 mPa·s or less.

[23] The method for producing titanium-containing silica glass according to any one of [1] to

[22] , wherein the solvent comprises at least one selected from the group consisting of water and tert-butyl alcohol.

[0010] According to the present invention, a method for producing titanium-containing silica glass with high production efficiency can be provided.

[0011] This is a schematic cross-sectional diagram illustrating a method for obtaining a molded body using a uniaxial press method (double-press method) comprising a first step and a second step.

[0012] The present invention will now be described in detail. The following descriptions of constituent elements may be based on representative embodiments of the present invention, but the present invention is not limited to such embodiments. In this specification, the term "~" indicating a numerical range is used to mean that the numbers described before and after it are included as the lower and upper limits. Unless otherwise specified, "~" will be used in the same sense hereafter in this disclosure. In numerical ranges described in steps in this specification, the upper or lower limit described in one numerical range may be replaced with the upper or lower limit of another numerical range described in steps. Also, in numerical ranges described in the specification, the upper or lower limit of that numerical range may be replaced with the values ​​shown in the examples. In this specification, unless otherwise specified, the units indicating physical properties apply to the entire numerical range. For example, "0.16 to 0.24 MPa" is synonymous with "0.16 MPa to 0.24 MPa".

[0013] In this specification, unless otherwise specified, the measurement environment for each physical property is a temperature of 23-25°C and a humidity of 40-50%.

[0014] In this specification, the term "process" includes not only processes that are independent of other processes, but also processes that cannot be clearly distinguished from other processes, provided that the purpose of the process is achieved.

[0015] <Method for producing titanium-containing silica glass> The present invention's method for producing titanium-containing silica glass involves preparing a slurry containing silica, titanium, and a solvent; obtaining raw material granules using the slurry by spray freeze granulation drying; obtaining a molded body by pressure molding the raw material granules; and obtaining titanium-containing silica glass by heating the molded body. The present invention's method for producing titanium-containing silica glass (hereinafter also simply referred to as "the present invention's method") uses raw material granules, obtains a molded body, and heats the molded body to obtain titanium-containing silica glass, thus eliminating the need for steps such as drying the wet cake, and allowing for efficient production of titanium-containing silica glass.

[0016] The manufacturing method of the present invention will be described in detail below. Hereinafter, the step of preparing a slurry containing silica, titanium, and a solvent will also be referred to as the "slurry preparation step." The step of obtaining raw material granules using the slurry by spray freeze granulation drying will also be referred to as the "granulation step." The step of obtaining a molded body by pressure molding the raw material granules will also be referred to as the "pressure molding step." The step of obtaining titanium-containing silica glass by heating the molded body will also be referred to as the "heating step." The following describes each step of the manufacturing method of the present invention.

[0017] [Slurry Preparation Step] In the slurry preparation step of the manufacturing method of the present invention, a slurry containing silica, titanium, and a solvent is prepared. The slurry preparation step will be described below.

[0018] The method for preparing the slurry is not particularly limited, and known preparation methods can be applied. One method for preparing the slurry is to mix a composition containing a silica component, a titanium component, and a solvent. Methods for mixing the above composition include using a ball mill, bead mill, roll mill, homomixer, ultramixer, disperser mixer, attritor, jet mill, homogenizer, and through-type or impact-type high-pressure dispersion device. Among these, it is preferable to prepare the slurry by mixing the above composition using a ball mill or bead mill. If organic compounds such as binders, plasticizers, and lubricants are included, it is preferable to stir using a mechanical stirring method with a mill that does not contain media (balls, beads, etc.) and / or an agitator or stirring bar, in order to suppress foaming. Examples of agitators include, but are not limited to, propellers, paddle blades, ribbon blades, turbine blades, and anchor blades. The rotation speed of the mill and agitators is preferably a low rotation speed that does not cause foaming. When mixing the above composition, one or more of the following may occur: crushing, pulverization, dissolution, and elution of the silica component and the titanium component.

[0019] When using a mixing method that utilizes media, the media should be removed from the slurry before the granulation step described later. Furthermore, the slurry preparation step may include a step for removing coarse particles from the slurry. Methods for removing coarse particles include mesh passing and filter filtration.

[0020] The silica and titanium components used in the slurry preparation process are described below. The silica component refers to a component containing silica. In this specification, "silica" refers to SiO ２This refers to a compound represented by the composition formula. The silica component is preferably silica. The silica may be crystalline, amorphous, or a mixture of crystalline and amorphous forms, and if the silica contains crystalline silica, crystalline silica of different crystal structures may be mixed. Among these, amorphous silica is preferred. The titanium component is a component containing titanium. The titanium component preferably contains at least one selected from the group consisting of titania, titania-silica composites, titanium-containing silica, and organotitanium compounds, more preferably contains at least one selected from the group consisting of titania, titanium-containing silica, and titania-silica composites, and even more preferably contains titania-silica composites. In this specification, "titania" refers to TiO ２ This refers to a compound represented by the chemical formula .Titania may be crystalline, amorphous, or a mixture of crystalline and amorphous forms, and if titania is crystalline, the crystalline form may contain a mixture of different crystal structures. Among these, crystalline titania is preferred.When titania contains crystalline material, the crystal structure is preferably rutile or anatase.In this specification, a titania-silica composite refers to a composite having a portion mainly composed of titania and a portion mainly composed of silica.Examples of titania-silica composites include silica-coated titania particles.When the cross-section of a titania-silica composite is observed using scanning electron microscopy-energy-dispersive X-ray spectroscopy or transmission electron microscopy-energy-dispersive X-ray spectroscopy, a portion mainly containing titania and a portion mainly containing silica can be observed. Furthermore, in this specification, titanium-containing silica refers to a state in which titania is solid-dissolved in silica, or a state in which silica is solid-dissolved in titania. Examples of titanium-containing silica include titanium-containing silica glass.

[0021] The above-mentioned organotitanium compounds are preferably water-soluble and preferably used as aqueous solutions. Examples of organotitanium compounds include alkyl titanates (e.g., tetraisopropyl titanate, tetran-butyl titanate, butyl titanate dimer, tetraoctyl titanate), titanium acylates, titanium chelates (e.g., titanium lactate, titanium lactate ammonium salt, titanium triethanolamine, octylene glycol titanate), titanium citrate, titanium peroxocitrate complexes, amine-based water-soluble titanates, titanium oxycarboxylic acid chelates, titanium alkanolamine chelates, and titanium tetraacetate, as well as derivatives thereof.

[0022] From the viewpoint of homogeneously mixing the titanium component in the slurry, it is preferable that the titanium component also includes an organotitanium compound. That is, it is preferable that the slurry contains an organotitanium compound. Furthermore, from the viewpoint of the dispersion stability of the slurry, it is preferable that the titanium component includes at least one selected from the group consisting of titania, titania-silica composites, and titanium-containing silica. That is, it is preferable that the slurry contains at least one selected from the group consisting of titania, titania-silica composites, and titanium-containing silica. It is preferable that the silica component and titanium component include silica and at least one selected from the group consisting of titania, titania-silica composites, and titanium-containing silica. That is, it is preferable that the slurry contains silica and at least one selected from the group consisting of titania, titania-silica composites, and titanium-containing silica. Furthermore, it is more preferable that the silica component and titanium component include silica and one or more selected from the group consisting of titania and titania-silica composites. In other words, the slurry more preferably contains silica and one or more selected from the group consisting of titania and titania-silica composites. Alternatively, the slurry may contain only one or more selected from the group consisting of titania-silica composites and titanium-containing silica as the silica and titanium components. In other words, the slurry may contain only one or more selected from the group consisting of titania-silica composites and titanium-containing silica as the silica and titanium components. From the viewpoint of reducing manufacturing costs, it is also preferable to include silica and titania as the silica and titanium components. In other words, the slurry may also contain silica and titania. From the viewpoint of slurry dispersion stability, it is also preferable to include silica and titania-silica composites as the silica and titanium components. In other words, the slurry may also contain silica and titania-silica composites. It is more preferable that the titania-silica composites are silica-coated titania particles.

[0023] The silica, titania, titania-silica composites, and titanium-containing silica mentioned above are usually in powder form. It is also preferable that the silica and titanium components consist only of ceramic raw material powder. Ceramic raw material powder refers to powder composed of inorganic compounds that do not contain organic compounds such as organotitanium compounds. Specific examples of ceramic raw material powder include silica, titania, titania-silica composites, and titanium-containing silica.

[0024] The total content of silica and titania in the silica and titanium components is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more, expressed as an oxide-based mass percentage. The total content of silica and titania in the silica and titanium components may be 100% by mass or less. Here, "oxide-based" means the mass percentage of oxide when the silicon and metal in the silica and titanium components are converted to oxides and the total oxide is set to 100% by mass. The above oxide refers to silicon as SiO ２ In terms of form, titanium is TiO ２ It is in the form of...

[0025] In silica and titanium components, the titanium content is preferably 6.0% by mass or more, and more preferably 7.0% by mass or more, based on the total content of silica and titanium components, expressed as a mass percentage on an oxide basis. Furthermore, the titanium content is preferably 9.0% by mass or less, and more preferably 8.5% by mass or less, based on the total content of silica and titanium components, expressed as a mass percentage on an oxide basis. In silica and titanium components, the silica content is preferably 91.0% by mass or more, and more preferably 91.5% by mass or more, based on the total content of silica and titanium components, expressed as a mass percentage on an oxide basis. Furthermore, the silica content is preferably 94.0% by mass or less, and more preferably 93.0% by mass or less, based on the total content of silica and titanium components, expressed as a mass percentage on an oxide basis.

[0026] The solvent used in the slurry preparation process is not particularly limited, but it is preferable to include at least one of water and tert-butyl alcohol, and more preferably water, in order to easily obtain a frozen granule with a uniform structure and low distortion. The total content of water and tert-butyl alcohol is preferably 50% by mass or more, more preferably 80% by mass or more, and even more preferably 95% by mass or more, based on the total mass of the solvent used in the slurry preparation process. The total content of water and tert-butyl alcohol may be 100% by mass or less, based on the total mass of the solvent used in the slurry preparation process. In terms of the handling properties of the slurry, the water content is preferably 75% by mass or more, more preferably 90% by mass or more, and even more preferably 98% by mass or more, based on the total mass of the solvent used in the slurry preparation process. The ratio of water to the solvent used in the slurry preparation process may be 100% by mass or less. The solvent used in the slurry preparation process may also include solvents other than water and tert-butyl alcohol (other solvents). Other solvents mentioned above include dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone, N,N-dimethylformamide, acetone, tetrahydrofuran, methyl alcohol, ethyl alcohol, 1-propyl alcohol, isopropyl alcohol (2-propyl alcohol), triethanolamine, cyclohexane, xylene, toluene, ethyl acetate, methyl ethyl ketone (2-butanone), and methyl isobutyl ketone (4-methyl-2-pentanone). The solvent may also include solvents released by the hydrolysis of organotitanium compounds.

[0027] In the slurry obtained by the slurry preparation process, the content of the ceramic raw material powder relative to the total mass of the slurry is preferably 12.0% by mass or more, more preferably 16.0% by mass or more, even more preferably 20.0% by mass or more, particularly preferably 22.0% by mass or more, and most preferably 24.0% by mass or more. Furthermore, the content of the ceramic raw material powder relative to the total mass of the slurry is preferably 68.0% by mass or less, more preferably 63.0% by mass or less, even more preferably 55.0% by mass or less, particularly preferably 46.0% by mass or less, and most preferably 34.0% by mass or less.

[0028] Further, the average particle diameter of the ceramic raw material powder is preferably 10 nm or more, more preferably 12 nm or more, even more preferably 14 nm or more, particularly preferably 16 nm or more, and most preferably 18 nm or more, from the viewpoint of suppressing aggregation of the ceramic raw material powder and suppressing haze of the obtained titanium-containing silica glass. Further, the average particle diameter of the ceramic raw material powder is preferably 500 nm or less, more preferably 300 nm or less, even more preferably 100 nm or less, particularly preferably 80 nm or less, and most preferably 60 nm or less, from the viewpoint of uniformly dispersing the ceramic raw material powder in the slurry and suppressing haze of the obtained titanium-containing silica glass.

[0029] In the present specification, the average particle diameter of the ceramic raw material powder is a value calculated from the following formula (1). (1) a = (6 × 10 ３ ) / (ρ × S) a is the average particle diameter of the ceramic raw material powder, and the unit is nm. ρ is the theoretical density of the ceramic raw material powder, and the unit is g / cm ３ . S is the average specific surface area of the ceramic raw material powder, and the unit is m ２ / g. The average specific surface area of the ceramic raw material powder is measured in accordance with JIS Z8830:2013. The theoretical density ρ of the ceramic raw material powder is calculated from the following formula (2).

[0030]

[0031] In formula (2), ρ ｉ is the theoretical density of each component contained in the ceramic raw material powder. In formula (2), φ ｉ is the volume fraction of each component contained in the ceramic raw material powder in the ceramic raw material powder. For example, when the ceramic raw material powder is composed of silica powder and titania powder, the theoretical density ρ of the ceramic raw material powder is calculated by the following formula (3). (3) ρ = ρ ＳｉＯ２ × φ ＳｉＯ２ + ρ ＴｉＯ２ × φ ＴｉＯ２ In formula (3), ρ ＳｉＯ２ is the theoretical density of the silica powder, and the unit is g / cm ３The theoretical density of silica powder differs between crystalline and amorphous forms, and within the crystalline form, the theoretical density varies depending on the crystal structure. Examples of the above crystal structures include cristobalite, tridymite, quartz, coesite, and stishovite. In this specification, ρ ＳｉＯ２ The following applies to each: Amorphous, cristobalite, and tridymite: 2.2 g / cm³ ３ Quartz is 2.5 g / cm³ ３ Cosite is 2.9 g / cm³ ３ And Stishobite is 4.4 g / cm³ ３ Let's assume that for silica powder containing the above structures, the sum of the values ​​obtained by multiplying the theoretical density and volume fraction of each structure is used, similar to equation (2). Note that there are high-temperature and low-temperature types of crystalline silica, but their theoretical densities are considered to be the same. φ ＳｉＯ２ ρ is the volume fraction of silica powder (greater than 0 and less than 1) and is unitless. In equation (3), ρ ＴｉＯ２ This is the theoretical density of titania powder, and its unit is g / cm³. ３ The theoretical density of titania powder differs between crystalline and amorphous forms, and within the crystalline form, the theoretical density varies depending on the crystal structure. Examples of the above crystal structures include rutile, anatase, and brookite. In this specification, ρ ＴｉＯ２ The following applies to each: Amorphous and anatase: 3.9 g / cm³ ３ Rutile contains 4.2 g / cm³. ３ And brookite is 4.1 g / cm³ ３ In the titania powder containing the above structures, the sum of the values ​​obtained by multiplying the theoretical density and volume fraction of each structure is used, similar to equation (2). φ ＴｉＯ２ is the volume fraction of titania powder (greater than 0 and less than 1), and is unitless.

[0032] The slurry obtained by the slurry preparation step may contain components other than the silica component, titanium component, and solvent mentioned above (hereinafter also referred to as "other components"). Examples of other components include at least one selected from the group consisting of binders, dispersants, pH adjusters, lubricants, and plasticizers, and it is preferable that it contains at least one selected from the group consisting of binders and pH adjusters. Other components will be described below.

[0033] The slurry obtained in the slurry preparation step may contain a binder. If the slurry contains a binder, it is preferable to perform a degreasing treatment after obtaining the molded product. The binder has the effect of increasing the strength of the molded product obtained in the pressure molding step described later. As the binder, an organic binder is preferred, and examples of organic binders include at least one selected from the group consisting of polyvinyl acetal, polyethylene glycol, polyacrylamine, polyethyleneimine, polyethylene oxide, paraffin wax, carnauba wax, microcrystalline wax, polyvinyl alcohol, cellulose derivatives, alginic acid, polyvinylpyrrolidone, acrylic resins, vinyl acetate, styrene resins, and polysaccharides. As the organic binder, at least one selected from the group consisting of polyvinyl acetal, polyethylene glycol, paraffin wax, carnauba wax, and microcrystalline wax is more preferred. One type of binder may be used alone, or two or more types may be used simultaneously. The binder may be added to the slurry in a dissolved or dispersed state in a solvent.

[0034] When the slurry contains a binder, the binder content is preferably 10.0% by mass or more, more preferably 15.0% by mass or more, even more preferably 17.5% by mass or more, particularly preferably 20.0% by mass or more, and most preferably 25.0% by mass or more, relative to the content of the ceramic raw material powder. When the slurry contains a binder, the binder content is preferably 50.0% by mass or less, more preferably 45.0% by mass or less, even more preferably 40.0% by mass or less, particularly preferably 35.0% by mass or less, and most preferably 30.0% by mass or less, relative to the content of the ceramic raw material powder, in order to obtain easily disintegrating granules. Easily disintegrating granules make it easier to obtain dense molded articles.

[0035] The slurry obtained by the slurry preparation process may contain a dispersant. If the slurry contains a dispersant, it is preferable to perform a degreasing treatment after obtaining the molded product. When the slurry contains a dispersant, it becomes easier to disperse the silica and titanium components (e.g., ceramic raw material powder) in the slurry. The dispersant is a compound different from the binder. Examples of dispersants include at least one selected from the group consisting of polycarboxylic acid polymers (e.g., polyacrylic acid, ammonium polyacrylate), condensed naphthalene sulfonates (e.g., ammonium condensed naphthalene sulfonate), polyacrylamide compounds, and alkyl sulfonic acid compounds (e.g., ammonium alkyl sulfonate). The dispersant may be added to the slurry in the form of a solution dissolved in a solvent or a dispersion in a solvent.

[0036] When the slurry contains a dispersant, the dispersant content is preferably 3.0% by mass or less, more preferably 2.0% by mass or less, even more preferably 1.5% by mass or less, and particularly preferably 1.0% by mass or less, relative to the content of the ceramic raw material powder. When the dispersant is used in solution or dispersion form, the dispersant content refers to the content excluding the solvent. When the dispersant content in the slurry is 3.0% by mass or less relative to the content of the ceramic raw material powder, the amount of dispersant is appropriate, the dispersion state of the primary particles is good, and the thickening of the slurry is easily suppressed. Raw material granules obtained from such a slurry tend to have a uniform granule structure and uniform granule size. Therefore, when the dispersant content in the slurry is 3.0% by mass or less relative to the content of the ceramic raw material powder, a dense molded body is easily obtained, and titanium-containing silica glass with fewer defects is easily obtained.

[0037] The slurry obtained by the slurry preparation process may contain a pH adjusting agent. When the slurry contains a pH adjusting agent, it becomes easier to disperse the ceramic raw material powder within the slurry. The pH adjusting agent is a compound different from the binder and dispersant mentioned above. Examples of the pH adjusting agent include acidic pH adjusting agents and basic pH adjusting agents, with basic pH adjusting agents being preferred. An acidic pH adjusting agent is a pH adjusting agent that causes the aqueous solution to be acidic. A basic pH adjusting agent is a pH adjusting agent that causes the aqueous solution to be basic.

[0038] As a basic pH adjusting agent, at least one selected from the group consisting of ammonia, quaternary ammonium hydroxides (e.g., tetraethylammonium hydroxide and tetramethylammonium hydroxide), and organic amine compounds (e.g., triethylamine and diazabicycloundecene) is preferred. Among these, quaternary ammonium hydroxide is preferred as the pH adjusting agent. The compound used as the pH adjusting agent may be added to the slurry in the form of a solution dissolved in a solvent.

[0039] When the slurry contains a pH adjusting agent, the content of the pH adjusting agent is preferably 0.2% by mass or more, more preferably 0.8% by mass or more, even more preferably 1.4% by mass or more, particularly preferably 2.1% by mass or more, and most preferably 2.5% by mass or more, relative to the content of the ceramic raw material powder. When the slurry contains a pH adjusting agent, the content of the pH adjusting agent is preferably 5.0% by mass or less, more preferably 4.5% by mass or less, even more preferably 4.0% by mass or less, particularly preferably 3.5% by mass or less, and most preferably 3.1% by mass or less, relative to the content of the ceramic raw material powder. When the pH adjusting agent content in the slurry is 0.2 to 5.0% by mass relative to the content of the ceramic raw material powder, the amount of pH adjusting agent is appropriate, the dispersion state of the primary particles is good, and the thickening of the slurry is easily suppressed. Granules obtained from such slurries tend to have a uniform granular structure and consistent granular size. Therefore, when the pH adjusting agent content in the slurry is within the range of 0.2 to 5.0% by mass relative to the ceramic raw material powder content, dense molded bodies are more easily obtained, and titanium-containing silica glass with fewer defects is more likely to be obtained.

[0040] The slurry obtained in the slurry preparation step may contain a lubricant. If the slurry contains a lubricant, it is preferable to perform a degreasing treatment after obtaining the molded body. The lubricant has the effect of providing slipperiness and release properties between the molded body and the member in contact with the molded body when pressure is applied in the pressure molding step described later. The lubricant is a compound different from the binder, dispersant, and pH adjuster mentioned above. Examples of lubricants include polyethylene glycol monostearate, fatty acids, fatty acid amides, fatty acid esters, and mineral oils. It is preferable that the lubricant contains at least one selected from the group consisting of polyethylene glycol monostearate, stearic acid, caprylic acid, lauric acid, palmitic acid, arachidic acid, oleic acid, stearic acid amide, oleic acid amide, erucic acid amide, methylenebisstearate amide, and ethylenebisstearate amide. One type of lubricant may be used alone, or two or more types may be used simultaneously. The lubricant may be added to the slurry in a dissolved or dispersed state in a solvent.

[0041] When the slurry contains a lubricant, the lubricant content is preferably 2.0% by mass or less, more preferably 1.5% by mass or less, even more preferably 1.0% by mass or less, and particularly preferably 0.8% by mass or less, relative to the content of the ceramic raw material powder. When the lubricant content in the slurry is 2.0% by mass or less relative to the content of the ceramic raw material powder, the amount of lubricant becomes appropriate, making it easier for the molded body to peel off the mold after molding during pressure molding, and tending to suppress the collapse of the molded body and the occurrence of internal cracks. Therefore, when the lubricant content in the slurry is within the range of 2.0% by mass or less relative to the content of the ceramic raw material powder, it is easier to obtain a dense molded body and titanium-containing silica glass with fewer defects.

[0042] The slurry obtained in the slurry preparation step may contain a plasticizer. The presence of a plasticizer in the slurry can impart flexibility to the raw material granules obtained in the granulation step, which will be described in detail later. The plasticizer is a compound different from the solvent, binder, dispersant, pH adjuster, and lubricant mentioned above. Any known plasticizer can be used as appropriate, such as ethylene glycol, diethylene glycol, triethylene glycol, polypropylene glycol, and polyglycerin. One plasticizer may be used alone, or two or more may be used simultaneously. The plasticizer may be added to the slurry in a dissolved or dispersed state in the solvent.

[0043] When the slurry contains a plasticizer, the plasticizer content is preferably 25.0% by mass or less, more preferably 15.0% by mass or less, even more preferably 12.5% ​​by mass or less, particularly preferably 10.0% by mass or less, and most preferably 7.5% by mass or less, relative to the content of the ceramic raw material powder.

[0044] The viscosity of the slurry obtained in the slurry preparation step is preferably 100 mPa·s or less, more preferably 50 mPa·s or less, and even more preferably 20 mPa·s or less, due to its ease of spraying in the granulation step described in detail later. The viscosity of the slurry is often 1 mPa·s or more. The viscosity of the slurry is measured by the following method and conditions: • Measuring device: Rheometer (MCR302, manufactured by Anton Paar) • Measuring jig: SUS cone-shaped plate (diameter 75 mm, angle 2°) • Shear rate: 2.2 s －１ ・Measurement temperature: 25℃

[0045] [Granulation Process] In the granulation process of the manufacturing method of the present invention, raw material granules are obtained using the slurry by spray freeze granulation drying. The raw material granules obtained in the granulation process contain the silica component and titanium component, as well as components other than the solvent contained in the slurry. The raw material granules contain at least the silica component and titanium component (e.g., ceramic raw material powder) as primary particles. Furthermore, in the spray freeze granulation drying method, the slurry is usually rapidly frozen immediately after spraying, so the dispersion state in the slurry is easily maintained, and segregation of components within the raw material granules is less likely to occur. More specifically, for example, when silica powder and titania powder are used as the silica component and titanium component, the distribution of silica particles and titania particles in the obtained raw material granules tends to be uniform. When the distribution of silica particles and titania particles is uniform in the raw material granules, it is thought that the haze in the obtained titanium-containing silica glass tends to be low. Furthermore, in the spray freeze-drying method, the solvent contained in the frozen granules typically sublimes from a frozen state to a gas without passing through a liquid state, thus minimizing shrinkage during the transformation from frozen granules to granules. Consequently, granules obtained by the spray freeze-drying method tend to have a lower packing density and are softer, with fewer internal defects. When such soft, uniformly packed granules are used for pressure molding, the granules tend to integrate easily, resulting in a homogeneous molded body. Titanium-containing silica glass obtained from such a homogeneous molded body is less prone to internal defects. In contrast, in the conventional spray-drying method, the evaporation of the solvent from the droplets is often not smooth, resulting in granules that are hollow inside and shell-shaped. Moreover, in these shell-shaped granules, the shell is often dense and hard. When a part of such a hard shell ruptures, it communicates with the hollow inside, easily forming a depressed sphere shape, which makes it prone to internal defects. When obtaining a molded body using such granules, and then obtaining titanium-containing silica glass from the molded body, it is considered that defects such as air bubbles are likely to occur.

[0046] Here, spray freeze granulation drying is a method in which a slurry is sprayed in droplet form, the sprayed slurry is frozen to form a frozen granule, and the solvent components are removed from the frozen granule to obtain raw material granules. For example, in spray freeze granulation drying, it is preferable to perform spray freezing and vacuum drying in that order. In addition, in spray freeze granulation drying, it is also preferable to perform drying under atmospheric pressure after vacuum drying. Drying under atmospheric pressure makes it easier to remove any remaining solvent components in the obtained raw material granules. The spray freeze granulation drying method will be described in detail below.

[0047] The above spray freezing can be carried out by spraying a slurry onto the cooling fluid. The cooling fluid may be a liquid or a gas. When the cooling fluid is a liquid, it is conveniently referred to as a "wet cooling method," and when the cooling fluid is a gas, it is conveniently referred to as a "dry cooling method." An example of a cooling fluid used in a wet cooling method is liquid nitrogen. The temperature of liquid nitrogen is usually below -196°C.

[0048] Examples of cooling fluids used in the dry cooling method include air and inert gases (e.g., nitrogen gas, argon gas). In the dry cooling method, the method of generating and supplying the cooling fluid is not particularly limited, but examples include cooling the spraying chamber with a cooling medium (e.g., liquid nitrogen) and supplying a gas cooled by contacting a heat exchanger to the spraying chamber. The temperature of the cooling fluid in the dry cooling method is preferably -15°C or lower, more preferably -25°C or lower, and even more preferably -35°C or lower. In addition, the temperature of the cooling fluid in the dry cooling method is often -85°C or higher, and preferably -65°C or higher. When the cooling temperature for spray freezing is -15°C or lower, freezing is likely to occur immediately after spraying, and ice crystals are less likely to grow. Therefore, the distortion of the shape of the resulting frozen granules tends to be small, and a homogeneous structure is likely to be obtained. Consequently, when the cooling temperature for spray freezing is -15°C or lower, a dense molded body is more likely to be obtained, and titanium-containing silica glass with fewer defects is more likely to be obtained. Furthermore, if the cooling temperature for spray freezing is -85°C or higher, the load on the spraying equipment is reduced.

[0049] In the above-described spray freezing, the spraying method is not particularly limited, but examples include a method of discharging slurry from a nozzle, and a method of supplying slurry to a rotating disk and generating droplets by scattering the slurry towards the outer circumference of the disk using centrifugal force (rotary atomizer method). The method of discharging slurry from a nozzle may be a one-fluid method or a two-fluid method. The above-described spraying method and conditions can be appropriately adjusted depending on the particle size and particle size distribution of the target raw material granules. The rotary atomizer method is preferred in terms of sharpening the particle size distribution of the raw material granules. Preferred particle sizes for raw material granules will be described later.

[0050] In the spray freeze granulation drying method, it is preferable to perform vacuum drying after spray freezing. Vacuum drying refers to drying under a pressure environment lower than atmospheric pressure. The vacuum level in vacuum drying is 6.1 × 10⁻⁶. ２ Preferably Pa or less, 1.0 × 10 ２ Pa or less is more preferable, and 5.0 × 10 １ A value of Pa or less is even more preferable, and 2.0 × 10 １ A pressure of Pa or less is particularly preferred. The lower limit of the vacuum in vacuum drying is not particularly limited, but 1.0 × 10⁻⁶ is preferable. ０ Pa is one example.

[0051] The temperature for vacuum drying is preferably -60°C or higher, more preferably -50°C or higher, and even more preferably -40°C or higher. Furthermore, the temperature for vacuum drying is preferably 50°C or lower, more preferably 25°C or lower, and even more preferably 10°C or lower. The duration of vacuum drying is preferably 12 hours or more, preferably 24 hours or more, and even more preferably 36 hours or more. In many cases, the duration of vacuum drying is 120 hours or less. When the vacuum drying temperature is 50°C or lower, the melting of ice crystals within the frozen granules is suppressed, liquefaction is reduced, and the distortion of the frozen granules' shape tends to be smaller. When vacuum drying is performed at a temperature of 50°C or lower and for a duration of 12 hours or more, ice crystals are less likely to remain within the frozen granules, liquefaction in subsequent processes is suppressed, the distortion of the frozen granules' shape is reduced, and a homogeneous structure tends to be achieved. Therefore, when vacuum drying is performed at a temperature of 50°C or lower and for a period of 12 hours or more, dense molded bodies are more likely to be obtained, and titanium-containing silica glass with fewer defects is more likely to be obtained. Furthermore, when the vacuum drying temperature is -60°C or higher, the load on the freeze-drying apparatus is reduced, which is preferable. Vacuum drying may be performed in multiple stages, and in the case of multi-stage vacuum drying, at least one of the temperature and pressure may be changed at each stage. Alternatively, vacuum drying may be performed while continuously changing at least one of the temperature and pressure.

[0052] The apparatus for performing the vacuum drying described above is not particularly limited, but examples include an apparatus having a chamber for containing the frozen granules and a means for setting the atmosphere (temperature and pressure) inside the chamber within the above range. It is also preferable that the chamber be equipped with a mechanism for stirring the frozen granules (for example, a chamber rotation mechanism).

[0053] As described above, in the spray freeze granulation drying method, it is also preferable to perform drying under atmospheric pressure after vacuum drying. The temperature when drying under atmospheric pressure is preferably 35°C or higher, more preferably 45°C or higher, even more preferably 55°C or higher, and particularly preferably 65°C or higher. Furthermore, the temperature when drying under atmospheric pressure is preferably 150°C or lower, more preferably 130°C or lower, even more preferably 120°C or lower, and particularly preferably 110°C or lower.

[0054] It is also preferable that the amount of solvent remaining in the raw material granules after drying under atmospheric pressure be 2.0% by mass or less. After drying under atmospheric pressure, the amount of solvent remaining in the raw material granules is more preferably 1.0% by mass or less, and even more preferably 0.5% by mass or less. In this specification, the amount of solvent remaining in the raw material granules is measured by the loss on drying method. Specifically, the amount of solvent remaining in the raw material granules is measured using a heating dryer moisture meter (e.g., MB45 halogen moisture meter, Ohaus Corporation). That is, the amount of solvent remaining may include components that volatilize when drying using the heating dryer moisture meter (e.g., pH adjusters). If it is known in advance that the only solvent contained in the raw material granules is water, the amount of solvent (water) remaining in the raw material granules may be measured by the Karl Fischer method. In the Karl Fischer titration method (coulometric titration method), the measurement is performed using a Karl Fischer moisture meter (e.g., MKC-710, Kyoto Electronics Manufacturing Co., Ltd.), and the heating temperature is 120°C. The measurement of the residual amount of solvent in the above raw material granules shall be in accordance with JIS K0068:2001.

[0055] The method for drying under atmospheric pressure described above is not particularly limited, but can be carried out using equipment such as a constant temperature bath, oven, or electric furnace. The drying time can be set appropriately according to the amount of solvent remaining in the raw material granules.

[0056] [Raw material granules] The raw material granules obtained by the granulation process described above will be explained below.

[0057] The average packing density of the raw material granules is preferably 12.0% by volume or more, more preferably 15.0% by volume or more, even more preferably 18.0% by volume or more, particularly preferably 21.0% by volume or more, and most preferably 24.0% by volume or more. Furthermore, the average packing density of the raw material granules is preferably 45.0% by volume or less, more preferably 42.0% by volume or less, even more preferably 39.0% by volume or less, particularly preferably 36.0% by volume or less, and most preferably 33.0% by volume or less. The average packing density of the raw material granules is defined by the following formula (i). F ａｖｅ = 100 - V ａｖｅ (i) In formula (i), F ａｖｅ This represents the average packing efficiency, and its unit is volume %.ａｖｅ V is the average space ratio, and its unit is volume %. ａｖｅ It is defined by the following equation (ii).

[0058]

[0059] In the above equation (ii), V ａｖｅ V is the average space ratio, and its unit is volume %. ｐｏｒｅ This is the pore volume, and its unit is mm. ３ / g. V ｐｏｒｅ ρ is determined from the pore distribution curve measured using the mercury intrusion method with raw material granules as a sample, and represents the pore volume corresponding to the interparticle voids of the primary particles constituting the raw material granules. In the above pore distribution curve, there are usually two peaks: one corresponding to the interparticle voids of the raw material granules and another corresponding to the interparticle voids of the primary particles constituting the raw material granules. Note that the pore diameter of the peak corresponding to the interparticle voids of the primary particles is smaller than the pore diameter of the peak corresponding to the interparticle voids of the raw material granules. ρ is the theoretical density of the substance constituting the raw material granules (e.g., the above ceramic raw material powder), and its unit is g / cm³. ３ Therefore, ρ is calculated from equation (3) above.

[0060] The median diameter of the raw material granules is preferably 40 μm or more, more preferably 50 μm or more, even more preferably 60 μm or more, particularly preferably 70 μm or more, especially preferably 75 μm or more, and most preferably 80 μm or more. The median diameter of the raw material granules is preferably 500 μm or less, more preferably 400 μm or less, even more preferably 300 μm or less, particularly preferably 250 μm or less, especially preferably 200 μm or less, and most preferably 150 μm or less. The median diameter of the above raw material granules is determined by measuring 300 arbitrary raw material granules using an image analysis particle size distribution analyzer (e.g., Morphologi G3, Malvern Panalytical, etc.), and determining the median diameter (D) in the obtained volume-based distribution. ｇ５０ )

[0061] Furthermore, the ratio of the internal defect diameter of the raw material granules to the granule size of the raw material granules is preferably 0.30 or less, more preferably 0.25 or less, even more preferably 0.20 or less, particularly preferably 0.15 or less, especially preferably 0.10 or less, and most preferably 0.05 or less. The above ratio may be 0.00 or more. The above ratio is measured by the following method. First, the prepared raw material granules are filled into an alumina pipe (inner diameter 13 mm, outer diameter 15 mm, height 5 mm) placed on a glass slide, thermosetting resin is poured in, and the thermosetting resin is cured by heat treatment at 120°C for 5 hours. After that, the alumina pipe is polished to expose the cross-section of the granules and observed with an optical microscope (e.g., DM6, Leica Microsystems). In the above observation, raw material granules with an average structure and within ±10% of the median diameter of the raw material granules are selected. Using image analysis software, the diameter of the largest pores and depressions within the granules observed from the cross-sectional images is defined as the granular defect diameter, and the diameter of the observed raw material granules is defined as the granular particle size. The above ratio is then calculated. This measurement is performed on 10 raw material granules, and the above ratio is calculated for each. The ratio of the granular defect diameter of the raw material granules to the granular particle size is the arithmetic mean of the above ratios for the 10 raw material granules.

[0062] The average disintegration strength of the raw material granules is preferably 0.10 MPa or higher, more preferably 0.13 MPa or higher, even more preferably 0.16 MPa or higher, particularly preferably 0.20 MPa or higher, and most preferably 0.25 MPa or higher. Furthermore, the average disintegration strength of the raw material granules is preferably 1.00 MPa or lower, more preferably 0.80 MPa or lower, even more preferably 0.60 MPa or lower, particularly preferably 0.50 MPa or lower, and most preferably 0.35 MPa or lower. The average disintegration strength of the raw material granules is measured in accordance with JIS R1639-5:2007. The disintegration strength σ of a single raw material granule is calculated from the following formula (iv). As shown in the formula below, a coefficient of 2.8 is used. σ = 2.8 × P / (π × d ２) ...Equation (iv) In Equation (iv), σ is the collapse strength (unit: MPa), P is the crushing force (unit: N), and d is the raw material granule size (unit: mm). The crushing force P is measured using a microcompression tester (e.g., MCT series, Shimadzu Corporation). Specifically, raw material granules are dispersed on a glass slide so as not to overlap, and when viewed from above, raw material granules whose dimensions in both the X and Y directions are within ±10% of the median diameter of the raw material granule (for example, 90 to 110 μm if the median diameter is 100 μm) are selected and measured. More specifically, 12 raw material granules are measured, and the crushing force P and granule size d are calculated from the arithmetic mean of 10 values ​​excluding the lowest and highest values. The loading speed is 0.1 mN / s.

[0063] The fluidity index of the raw material granules is preferably 60 or higher, more preferably 70 or higher, and even more preferably 80 or higher. The upper limit of the fluidity index is 100. When the fluidity index of the raw material granules is within the above range, the fluidity of the raw material granules is high, they are uniformly filled into the mold in the pressure molding process, and the haze in the resulting titanium-containing silica glass tends to be reduced. The fluidity index of the raw material granules refers to the Carr fluidity index, which is the sum of the angle of repose index, compressibility index, uniformity index, and spatula angle index. Since the raw material granules do not easily aggregate, in this specification, uniformity is used instead of aggregation in the fluidity index of the raw material granules. Each index is assigned according to Table 1 below (Carr fluidity index table). For example, if the angle of repose of the raw material granules to be measured is 27°, the angle of repose index will be 24. Each parameter such as the angle of repose index is obtained by rounding the measured value to the first decimal place and referring to the table above. In the Carr fluidity index classification, a value of 60 or higher is considered "average" or better. The angle of repose, spatula angle, and compressibility of the raw material granules can be measured using a powder tester (e.g., Hosokawa Micron's PT-X). The angle of repose is the average value obtained from three measurements, while the spatula angle and compressibility are values ​​obtained from a single measurement. 200-300g of raw material granules are often used for each measurement. The measurement methods for each of the above parameters may be explained later.

[0064]

[0065] The angle of repose of the raw material granules is preferably 50° or less, more preferably 40° or less, even more preferably 35° or less, and particularly preferably 30° or less. When the angle of repose is within the above range, the fluidity of the raw material granules is good, making it easy to uniformly fill the mold used for pressure molding, and the resulting titanium-containing silica glass tends to have low haze. There is no particular lower limit to the angle of repose, and it may be 15° or more.

[0066] The degree of compression of the raw material granules is preferably 31% or less, more preferably 25% or less, even more preferably 20% or less, and particularly preferably 15% or less. When the degree of compression is within the above range, the ceramic granules tend to integrate easily when pressure-molded, and the resulting titanium-containing silica glass tends to have low haze. There is no particular lower limit to the degree of compression, and it may be 1% or more. The degree of compression of the raw material granules is measured by the following method. First, the raw material granules are filled into a predetermined jig, and the loose bulk density ρ of the raw material granules is calculated from the mass and volume of the raw material granules in a leveled state. Ａ Next, the bulk density ρ of the raw material granules is calculated from the mass and volume of the raw material granules in the leveled state after adding an appropriate amount of raw material granules and performing 180 tappings. Ｐ The compressibility C is calculated from equation (v). C = (ρ Ｐ -ρ Ａ ) / ρ Ｐ ×100...Formula (v)

[0067] Furthermore, the Hausner ratio of the raw material granules is preferably 1.34 or less, more preferably 1.25 or less, even more preferably 1.18 or less, and particularly preferably 1.11 or less. When the Hausner ratio is within the above range, the ceramic granules tend to integrate easily during pressure molding, and the resulting titanium-containing silica glass tends to have low haze. The lower limit of the Hausner ratio is usually 1.00 or higher. The Hausner ratio H is calculated from formula (vi): H = ρ Ｐ / ρ Ａ ...Formula (vi) In formula (vi), ρ Ａ ρ is the loose bulk density of the above raw material granules, Ｐ This is the bulk density of the above raw material granules.

[0068] The spatula angle of the raw material granules is preferably 60° or less, more preferably 55° or less, even more preferably 50° or less, and particularly preferably 45° or less. When the spatula angle is within the above range, the fluidity of the raw material granules is good, making it easy to uniformly fill the mold used for pressure molding, and the resulting titanium-containing silica glass tends to have low haze. There is no particular lower limit to the spatula angle, and it may be 10° or more.

[0069] The uniformity of the raw material granules is preferably 6.0 or less, more preferably 5.0 or less, even more preferably 4.0 or less, and particularly preferably 2.5 or less. There is no particular lower limit for uniformity, but it is usually 1.2 or higher. The uniformity U of the raw material granules is calculated from formula (vii): U = D ｇ６０ / D ｇ１０ ...Formula (vii) In formula (vii), D ｇ６０ This is the median diameter D based on the volume of the raw material granules. ｇ５０ In a volume-based distribution obtained by the same method, the granule size is such that the cumulative volume from the smaller diameter side accounts for 60%. Also, D ｇ１０ This is the median diameter D based on the volume of the raw material granules. ｇ５０ In a volume-based distribution obtained by the same method, this granule size is such that the cumulative volume from the smaller diameter side accounts for 10%.

[0070] [Pressure Molding Process] In the pressure molding process of the manufacturing method of the present invention, the raw material granules are pressure molded to obtain a molded body. The method of pressure molding is not particularly limited, but known molding methods such as the uniaxial press method, the die press method, and the isotropic press method can be applied. It is preferable to perform at least isotropic pressing in the pressure molding process. It is also preferable to combine multiple methods for the above pressure molding. More specifically, it is preferable to perform pressure molding using at least one method selected from the group consisting of the uniaxial press method and the die press method, and then pressurize using the isotropic press method. Since the raw material granules obtained by the spray freeze granulation drying method often have the above-mentioned average collapse strength, the granules tend to collapse during pressure molding (especially during pressure molding by the isotropic press method), and the density of the molded body tends to improve.

[0071] The above-mentioned unscrew press method includes methods such as the single-sided press method, the double-sided press method, the floating die method, and the with-drawal method. Furthermore, the above-mentioned isostatic press method includes the cold isostatic press (CIP) method and the warm isostatic press (WIP) method. These are also called the cold isostatic press method and the warm isostatic press method, respectively. Examples of the CIP method and WIP method include the wet method, which generates isostatic pressure using the isostatic pressure of a liquid pressure medium, and the dry method (also called the rubber press method), which fills a rubber mold with raw material granules and presses the rubber mold from all sides. From the viewpoint of obtaining a dense molded body, warm isostatic pressing is preferred, and the temperature of the pressure medium is preferably 40 to 100°C, more preferably 50 to 90°C, even more preferably 55 to 85°C, and particularly preferably 60 to 80°C.

[0072] Furthermore, when obtaining the above-mentioned molded body, it is also preferable to obtain a layered molded body by pressurizing the raw material granules to form layers, then to place the raw material granules on at least one side of the obtained layered molded body and pressurize to form an additional layered molded body, and to obtain the above-mentioned molded body by forming one or more layers of the additional layered molded body on the layered molded body. In other words, it is also preferable that the pressurizing process comprises a first step of obtaining a layered molded body by pressurizing the raw material granules to form layers, and a second step of placing the raw material granules on at least one side of the layered molded body and pressurizing to form an additional layered molded body, and that the second step be performed only once. It is also preferable that the second step be repeated two or more times. The above method can be carried out, for example, by a uniaxial press method. The specific method will be described with reference to the drawings.

[0073] Figure 1 is a schematic cross-sectional diagram illustrating a method for obtaining a molded body using a uniaxial press method (double-press method) and comprising the first and second steps described above. Figure 1 illustrates the procedure for obtaining a molded body using a press machine 10. The press machine 10 includes a die 12 having a hole into which raw material granules are filled, a lower punch 14 inserted into the hole of the die 12 and positioned on the lower side of the paper, and an upper punch 16 that can be inserted into the hole of the die 12 and is positioned opposite the lower punch 14. The lower punch 14 and the upper punch 16 can each be pressed in the direction of the die 12, and can compress a member placed between them. Although not shown in Figure 1, the lower punch 14 and the upper punch 16 are each connected to a mechanism for generating a pressing force.

[0074] First, as shown in Figure 1(a), raw material granules are filled into the space formed by the lower punch 14 and the die 12 to form a raw material granule layer 20. Next, as shown in Figure 1(b), the raw material granule layer 20 shown in Figure 1(a) is pressurized using the upper punch 16 and the lower punch 14 to form a layered molded body 22. Then, as shown in Figure 1(c), the pressurization by the upper punch 16 and the lower punch 14 is released, exposing the surface of the layered molded body 22 on the upper punch 16 side. Subsequently, as shown in Figure 1(d), raw material granules are filled into the space formed between the surface of the layered molded body 22 on the upper punch 16 side and the die 12 to form a second raw material granule layer 24. Next, as shown in Figure 1(e), the formed layered molded body 22 is pressurized using the upper punch 16 and the lower punch 14 to form an additional layered molded body 26. Next, in Figure 1(f), the pressure from the upper punch 16 and the lower punch 14 is released, exposing the surface of the additional layered molded body 26 on the upper punch 16 side. By following these steps, a molded body having the layered molded body 22 and the additional layered molded body 26 is obtained. Note that from the state shown in Figure 1(f), the molded body having the layered molded body 22 and the additional layered molded body 26 can be removed from the press machine 10 by pushing the die 12 downwards from the state shown in Figure 1(e) to release the pressure from the upper punch 16 and the lower punch 14. Alternatively, when removing the molded body having the layered molded body 22 and the additional layered molded body 26 from the press machine 10, the die 12 may be pushed downwards from the state shown in Figure 1(e) to release the pressure from the upper punch 16 and the lower punch 14 and remove it.

[0075] In the procedure described using Figure 1, only one additional layered molded body 26 was formed on the layered molded body 22, but two or more additional layered molded bodies may be formed. When forming the second and subsequent additional layered molded bodies, the procedures described in Figures 1(d), (e), and (f) should be repeated.

[0076] The press pressure is not particularly limited and can be selected as appropriate, but for example, 1 MPa or more is preferred, 3 MPa or more is more preferred, 5 MPa or more is even more preferred, and 7 MPa or more is particularly preferred. The upper limit of the press pressure is not particularly limited, but 100 MPa or less is preferred, 60 MPa or less is more preferred, 40 MPa or less is even more preferred, and 20 MPa or less is particularly preferred.

[0077] [Heating Process] In the heating process of the manufacturing method of the present invention, the molded body is heated to obtain titanium-containing silica glass. The heating process may be carried out in multiple stages. For example, the molded body may be sintered to obtain a sintered body, and the sintered body may be melted to obtain titanium-containing silica glass. That is, it is preferable to carry out the sintering treatment and the melting treatment in this order in the heating process. Furthermore, as described above, if at least one selected from the group consisting of binder, dispersant, lubricant, defoamer and plasticizer is used in the slurry preparation process, the above components will remain in the molded body, so it is preferable to carry out a degreasing treatment before performing the sintering. That is, it is preferable to carry out the degreasing treatment, sintering treatment and melting treatment in this order in the heating process. Furthermore, it is preferable to include hot isostatic pressing in the heating process. The heating process will be described below.

[0078] In the heating step described above, the molded body may be degreased. Degreasing removes organic components contained in the molded body. The degreasing may be carried out in either a non-oxidizing atmosphere or an oxidizing atmosphere. When degreasing in a non-oxidizing atmosphere, a temperature of 400 to 800°C is preferred, and when degreasing in an oxidizing atmosphere such as air, a temperature of 500 to 900°C is preferred. From the viewpoint of preventing cracking of the molded body, the degreasing may be carried out in two stages. For example, it is preferable to degrease by holding at 500°C for 3 hours in a non-oxidizing atmosphere, and then degrease by holding at 600°C for 2 hours in air. When degreasing in two stages, the atmosphere may be the same for both the first and second stages. For example, it may be preferable to degrease by holding at 600°C for 2 hours in air, and then degrease by holding at 800°C for 24 hours. The holding time for the degreasing is not particularly limited, but 1 to 48 hours is preferred, 1.5 to 24 hours is more preferred, and 2 to 12 hours is even more preferred.

[0079] In the heating step described above, it is preferable to perform a sintering treatment. The sintering treatment may be performed on the molded body or on the molded body that has undergone degreasing treatment. Through the sintering treatment, the silica and titanium components (titania) contained in the molded body are sintered, resulting in a sintered body with reduced voids and improved density. The atmosphere in which the sintering treatment is performed is not particularly limited, and the sintering treatment can be carried out in various atmospheres such as air, nitrogen gas, oxygen gas, carbon dioxide gas, inert gases (argon gas, helium gas), and reducing gases (hydrogen gas, carbon monoxide gas). When the sintering treatment is performed in the above atmosphere, the temperature is preferably 1100°C or higher, more preferably 1150°C or higher, and even more preferably 1200°C or higher. Furthermore, the temperature is often 1500°C or lower, preferably 1450°C or lower, and even more preferably 1400°C or lower. When the sintering treatment is performed in the above atmosphere, the duration is preferably 1 hour or more, more preferably 2 hours or more, and even more preferably 3 hours or more. Furthermore, the above time is often 48 hours or less, preferably 24 hours or less, more preferably 12 hours or less, and even more preferably 8 hours or less.

[0080] Furthermore, it is also preferable to perform the sintering process under vacuum. When performing the sintering process under vacuum, the vacuum level should be 1.0 × 10⁻⁶. ３ Examples include Pa or less, such as 2.0 × 10⁻⁶. ２ Preferably Pa or less, 1.0 × 10 ２ Pa or less is more preferable, and 1.0 × 10 １ A value of Pa or less is even more preferable, and 2.0 × 10 １ A pressure of Pa or less is particularly preferred. The lower limit of the above vacuum level is not particularly limited, but 1.0 × 10⁻⁶ is preferable. －２ Pa is one example. When sintering is performed under vacuum, the temperature is preferably above 900°C, more preferably above 1000°C, even more preferably above 1100°C, and particularly preferably above 1200°C. Furthermore, the temperature is preferably 1500°C or lower, and more preferably 1400°C or lower. When sintering is performed under vacuum, the time is preferably 1 hour or more, more preferably 3 hours or more, and even more preferably 5 hours or more. Furthermore, the time is often 72 hours or less, and preferably 48 hours or less.

[0081] In the heating step described above, a melting treatment is preferred. The melting treatment is usually performed on the sintered body. When the melting treatment is performed, the silica and titania contained in the sintered body melt, and titanium-containing silica glass is obtained. The atmosphere in which the melting treatment is performed is not particularly limited and includes air, nitrogen gas, oxygen gas, carbon dioxide gas, inert gas (argon gas, helium gas), and reducing gas (hydrogen gas, carbon monoxide gas), with an inert gas atmosphere being preferred. The melting treatment may also be performed under vacuum. The melting treatment temperature is often 1400°C or higher, preferably 1500°C or higher, and more preferably 1600°C or higher. The melting treatment temperature is often 2400°C or lower, preferably 2000°C or lower, and more preferably 1800°C or lower. The melting treatment time is preferably 10 minutes or more, more preferably 30 minutes or more, and even more preferably 1 hour or more. The above time is often 48 hours or less, preferably 24 hours or less, more preferably 12 hours or less, and even more preferably 6 hours or less. Furthermore, when performing melting under vacuum, the vacuum level should be 1.0 × 10⁻⁶. ３ Examples include Pa or less, such as 2.0 × 10⁻⁶. ２ Preferably Pa or less, 1.0 × 10 ２ Pa or less is more preferable, and 1.0 × 10 １ A value of Pa or less is even more preferable, and 2.0 × 10 １ A pressure of Pa or less is particularly preferred. The lower limit of the above vacuum level is not particularly limited, but 1.0 × 10⁻⁶ is preferable. －２ Pa is one example.

[0082] As described above, the heat treatment may preferably include hot isostatic pressing (HIP). Hot isostatic pressing refers to a method of heating while generating isostatic pressure using a medium such as a gas. Preferably, the medium is an inert gas (e.g., argon gas, helium gas). In other words, HIP is preferably performed in an inert gas atmosphere. When performing HIP, the temperature is preferably 1500 to 1800°C or higher, more preferably 1550 to 1750°C, and even more preferably 1600 to 1700°C. When performing HIP, the pressure is preferably 30 atmospheres or higher, more preferably 100 atmospheres or higher. The pressure is often 1000 atmospheres or lower. Note that HIP may be performed as one or more of the degreasing treatment, sintering treatment, and melting treatment. Also, HIP may be performed separately from the degreasing treatment, sintering treatment, and melting treatment. When HIP is performed separately from the above-mentioned degreasing treatment, sintering treatment, and melting treatment, it is also preferable to perform it after the melting treatment.

[0083] [Other steps] The manufacturing method of the present invention may include steps other than those described above. For example, a classification step may be included between the granulation step and the pressure molding step. Classification can be carried out by known methods. Examples of classification steps include a method of separating by the mesh opening of a sieve (mesh pass) and a method of utilizing interaction with a fluid such as air (gravity classification, inertial force classification, centrifugal force classification). From the viewpoint of suppressing the collapse of granules, the mesh pass method is preferred.

[0084] <Titanium-containing silica glass> According to the manufacturing method of the present invention, titanium-containing silica glass can be obtained. Hereinafter, for convenience, the titanium-containing silica glass obtained by the manufacturing method of the present invention will also be referred to as "the titanium-containing silica glass of the present invention." The titanium-containing silica glass of the present invention will be described below. TiO relative to the total oxide contained in the titanium-containing silica glass of the present invention ２The content of is preferably 6.0% by mass or more, more preferably 6.7% by mass or more, even more preferably 7.0% by mass or more, and particularly preferably 7.5% by mass, expressed as a mass percentage based on oxides. ２ The content is preferably 12.0% by mass or less, more preferably 11.0% by mass or less, and even more preferably 10.0% by mass or less, expressed as a mass percentage based on oxides. SiO2 in the total oxides contained in the titanium-containing silica glass of the present invention ２ The content of is preferably 88.0% by mass or more, more preferably 89.0% by mass or more, and even more preferably 90.0% by mass or more, expressed as a mass percentage based on oxides. ２ The content of is preferably 94.0% by mass or less, more preferably 93.3% by mass or less, even more preferably 93.0% by mass or less, and particularly preferably 92.5% by mass or less, expressed as a mass percentage based on oxides.

[0085] The OH concentration of the titanium-containing silica glass of the present invention is preferably less than 600 ppm by mass, more preferably 580 ppm by mass, and even more preferably 560 ppm by mass or less. The above OH concentration is often 100 ppm by mass or more, preferably 200 ppm by mass or more, and more preferably 300 ppm by mass or more. The OH concentration of the titanium-containing silica glass of the present invention can be measured using known methods. For example, the OH concentration can be determined from the absorption peak at a wavelength of 2.7 μm by measurement using an infrared spectrophotometer (J.P. Williams et al., American Ceramics Science Bulletin, 55(5), 524, 1976). The detection limit by this method is 0.1 ppm by mass.

[0086] The titanium-containing silica glass of the present invention does not have a structure (streaks) with fluctuating composition ratios and is suitable as a glass substrate for reflective mask blanks. Furthermore, since the molded body is formed using raw material granules obtained by spray freeze granulation drying, the composition is uniform and haze tends to be low. In addition, because the above raw material granules are used, there are few voids and few air bubbles in the titanium-containing silica glass. The titanium-containing silica glass of the present invention is usually obtained in block form. When using the titanium-containing silica glass of the present invention as a glass substrate as described above, the block-shaped titanium-containing silica glass is subjected to processes such as grinding, slicing, and polishing to obtain the glass substrate.

[0087] The present invention will be described in more detail below based on examples. The materials, amounts used, proportions, processing content, and processing procedures shown in the following examples can be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the following examples. Here, Examples 1, 2, 4, and 5 are examples, and Example 3 is a comparative example.

[0088] <Example 1> [Slurry Preparation Process] (Crushing of Titania Powder) 4800 g of 10 mm diameter iron-cored nylon balls and the following ingredients were added to a 175 mm diameter, 5 liter high-density polyethylene (HDPE) container. After covering the container, a ball milling process was carried out at a rotation speed of 60 rpm for 2 hours to obtain 654.9 g of primary slurry A1. ・Silica-coated titania powder (manufactured by Evonik, VP TiO ２ 1580 S, corresponding to the titania-silica composite mentioned above): 188.2 g pH adjuster (tetraethylammonium hydroxide, 35% by mass): 42.0 g Solvent (ion-exchanged water): 424.7 g

[0089] (Disintegration of silica powder) Next, the following components were added to slurry A1, and ball milling was performed at a rotation speed of 60 rpm for 48 hours to obtain 4626.1 g of secondary slurry B1. • Silica powder (Evonik, AEROSIL OX50): 1811.8 g • pH adjuster (tetraethylammonium hydroxide, 35% by mass): 194.3 g • Solvent (deionized water): 1965.1 g

[0090] (Binder Mixing) Next, the following components were added to the secondary slurry B1, and ball milling was performed at a rotation speed of 60 rpm for a rotation time of 6 hours to obtain 6960.4 g of tertiary slurry C1. • Binder (Chukyo Oil & Fat Co., Ltd., Celna P-222, concentration 39% by mass): 256.4 g • Lubricant (Chukyo Oil & Fat Co., Ltd., Celna Y-426, concentration 56% by mass): 17.9 g • pH adjuster (tetraethylammonium hydroxide, 35% by mass): 206.0 g • Solvent (ion-exchanged water): 1854.0 g

[0091] The content of the above ceramic raw material powder (silica-coated titania powder and silica powder) relative to the total mass of tertiary slurry C1 was 28.7% by mass, the viscosity was 12 mPa·s, and the pH was 11.8. Multiple batches of tertiary slurry C1 were prepared under the same conditions.

[0092] [Granulation Process] The above tertiary slurry C1 was used to obtain frozen granules D1 by spray freeze granulation drying using a CS220 freeze granulator manufactured by Pliss. The conditions for obtaining the frozen granules were as follows: • Disk rotation speed: 8000 rpm • Inlet temperature: -40°C • Outlet temperature: -35°C • Slurry supply rate: 1700 g / hour

[0093] Vacuum drying was performed on the obtained frozen granule D1. Vacuum drying was carried out in two stages by adjusting the final pressure and drying temperature. The conditions were as follows: The total drying time was 96 hours. (Vacuum drying) Stage 1: Final pressure: 10 Pa, Drying temperature: -10°C, Drying time: 72 hours (Vacuum drying) Stage 2: Final pressure: 10 Pa, Drying temperature: 40°C, Drying time: 12 hours After vacuum drying, drying was performed under atmospheric pressure to obtain raw material granules E1. The conditions were as follows: (Atmospheric pressure drying) Drying temperature: 85°C, Drying time: 12 hours

[0094] The obtained raw material granules E1 were measured using the method described above, and the following parameters were obtained: • Average packing density: 19.4% by volume • Average collapse strength: 0.44 MPa • Average granule size: 108.2 μm • Ratio of intragranular defect diameter to granule size: 0 • Residual solvent content: 0.4% by mass • Circularity: 0.99 • Aspect ratio: 0.98 • Angle of repose: 24.0° • Compressibility: 12.1% • Hausner ratio: 1.12 • Flowability index: 90.0

[0095] [Pressure Molding Process] Using the obtained raw material granules E1, a molded body was obtained using the method described in Figure 1. Six additional layered molded bodies were formed. The press pressure used to form the layered molded body was 3.4 MPa, and the press pressure used to form the additional layered molded bodies was 10 MPa each. Wet CIP was performed on the obtained molded body. For the wet CIP, water was used as the pressure medium, and the conditions were a pressure of 200 MPa and a pressurizing time of 5 minutes. The obtained molded body F1 was cylindrical with a diameter of 106 mm and a height of 20 mm.

[0096] [Heating Process] The molded body F1 was degreased in an air atmosphere at 600°C for 2 hours. After degreasing, a primary sintering process was performed in a metal furnace under vacuum (1 Pa), at a sintering temperature of 1150°C for 48 hours. After primary sintering, a secondary sintered body G1 was obtained by sintering in a carbon furnace under vacuum (10 Pa), at a temperature of 1288°C for 5 hours. The obtained secondary sintered body G1 was further melted in a carbon furnace under an argon atmosphere at a temperature of 1660°C for 30 hours to obtain titanium-containing silica glass H1.

[0097] [Physical Properties, etc.] When the OH concentration of the obtained titanium-containing silica glass H1 was measured under the conditions described above, it was found to be 550 ppm by mass.

[0098] <Example 2> In Example 1 (disintegration of silica powder), the same procedure was followed except that the silica powder was replaced with AEROSIL 90G manufactured by Evonik to obtain tertiary slurry C2. The content of the above ceramic raw material powder (silica-coated titania powder and silica powder) relative to the total mass of tertiary slurry C2 was 28.7% by mass, the viscosity was 20 mPa·s, and the pH was 11.8. Next, in the [granulation step] of Example 1, the same procedure was followed except that the tertiary slurry was replaced with tertiary slurry C2 to obtain raw material granules E2.

[0099] The obtained raw material granules E2 were measured using the method described above, and the following parameters were obtained: • Average packing density: 18.7% by volume • Average collapse strength: 0.37 MPa • Average granule size: 60.6 μm • Ratio of intragranular defect diameter to granule size: 0.04 • Residual solvent content: 0.4% by mass • Circularity: 0.97 • Aspect ratio: 0.93 • Angle of repose: 25.7° • Compressibility: 12.5% ​​• Hausner ratio: 1.14 • Flowability index: 89.0

[0100] In Example 1, titanium-containing silica glass H2 was obtained in the same manner as in the [pressure molding process] and [heating process], except that the raw material granules were changed to raw material granules E2.

[0101] <Example 3> In the [granulation process] of Example 1, raw material granules E3 were obtained in the same manner as in Example 1, except that granulation was performed using a spray dryer P260 manufactured by Pliss Corporation under the following conditions, instead of the spray freeze granulation drying method. Vacuum drying and atmospheric pressure drying were not performed. • Disk rotation speed: 4000 rpm • Inlet temperature: 180°C • Outlet temperature: 120°C • Slurry supply rate: 14000 g / h

[0102] The obtained raw material granules E3 were measured using the method described above, and the following parameters were obtained: • Average packing density: 23.0 volume% • Average collapse strength: 1.24 MPa • Average granule size: 93.9 μm • Ratio of intragranular defect diameter to granule size: 0.40 • Residual solvent content: 0.1 mass% • Circularity: 0.96 • Aspect ratio: 0.87 • Angle of repose: 28.8° • Compressibility: 12.3% • Hausner ratio: 1.14 • Flowability index: 93.0

[0103] In Example 1, titanium-containing silica glass H3 was obtained in the same manner as in the [pressure molding process] and [heating process], except that the raw material granules were changed to raw material granules E3.

[0104] <Example 4> [Slurry Preparation Process] (Crushing of Titania Powder) 3000 g of 10 mm diameter iron-cored nylon balls and the following ingredients were added to a 175 mm diameter, 5 liter high-density polyethylene (HDPE) container. After covering the container, a ball milling process was carried out at a rotation speed of 60 rpm for 2 hours to obtain 262.0 g of primary slurry A4. • Silica-coated titania powder (manufactured by Evonik, VP TiO ２ 1580 S (corresponding to the above titania-silica composite): 75.3 g pH adjuster (tetraethylammonium hydroxide, 35% by mass): 7.5 g Solvent (ion-exchanged water): 179.2 g

[0105] (Disintegration of silica powder) Next, the following components were added to slurry A4, and ball milling was performed at a rotation speed of 60 rpm for a rotation time of 48 hours to obtain 1850.5 g of secondary slurry B4. • Silica powder (Evonik, AEROSIL OX50): 724.7 g • pH adjuster (tetraethylammonium hydroxide, concentration 35% by mass): 34.6 g • Solvent (ion-exchanged water): 829.2 g

[0106] (Binder Mixing) Next, the following components were added to the secondary slurry B4 and stirred in a stainless steel container using a stainless steel stirring blade. The stainless steel container had a diameter of 180 mm and a height of 210 mm, the stirring blade had a diameter of 80 mm, the rotation speed was 60 rpm, and the rotation time was 2 hours, yielding 2205.3 g of tertiary slurry C4. • Binder (polyethylene glycol, average molecular weight 200): 240.0 g • pH adjuster (tetraethylammonium hydroxide, 35% by mass): 4.4 g • Solvent (ion-exchanged water): 110.4 g

[0107] The content of the above ceramic raw material powders (titania powder and silica powder) relative to the total mass of the tertiary slurry C4 was 36.3% by mass, the viscosity was 88 mPa·s, and the pH was 11.0. Multiple batches of tertiary slurry C4 were prepared under the same conditions.

[0108] In the granulation process of Example 1, raw material granules E4 were obtained in the same manner except that the tertiary slurry was replaced with tertiary slurry C4. The parameters of the obtained raw material granules E4 were measured using the method described above, and the results were as follows: • Average packing density: 19.6 volume% • Average collapse strength: 0.14 MPa • Average granule size: 91.0 μm • Ratio of intragranular defect diameter to granule size: 0.04 • Residual solvent amount: 0.4 mass% • Circularity: 0.90 • Aspect ratio: 0.93 • Angle of repose: 24.0° • Compressibility: 12.1% • Hausner ratio: 1.12 • Flowability index: 90.0

[0109] In Example 1, titanium-containing silica glass H4 was obtained in the same manner as in the [pressure molding process] and [heating process], except that the raw material granules were changed to raw material granules E4. When the OH concentration of the obtained titanium-containing silica glass H4 was measured under the above conditions, it was found to be 550 ppm by mass.

[0110] <Example 5> [Slurry Preparation Process] (Crushing of Titania Powder) 1450 g of 10 mm diameter iron-cored nylon balls and the following ingredients were added to a 92 mm diameter, 1 liter high-density polyethylene (HDPE) container. After covering the container, a ball milling process was carried out at a rotation speed of 90 rpm for 2 hours to obtain 65.5 g of primary slurry A5. ・Silica-coated titania powder (manufactured by Evonik, VP TiO ２ 1580 S (corresponding to the above titania-silica composite): 18.8 g pH adjuster (tetraethylammonium hydroxide, concentration 35% by mass): 1.9 g Solvent (ion-exchanged water): 44.8 g

[0111] (Disintegration of silica powder) Next, the following components were added to slurry A5, and ball milling was performed at a rotation speed of 90 rpm for a rotation time of 48 hours to obtain 462.6 g of secondary slurry B5. • Silica powder (Evonik, AEROSIL OX50): 181.2 g • pH adjuster (tetraethylammonium hydroxide, concentration 35% by mass): 8.6 g • Solvent (deionized water): 207.3 g

[0112] (Binder Mixing) Next, the following components were added to the secondary slurry B5 and stirred in a stainless steel container using a stainless steel stirring blade. The stainless steel container had a diameter of 135 mm and a height of 150 mm, the stirring blade had a diameter of 50 mm, the rotation speed was 60 rpm, and the rotation time was 2 hours, yielding 697.6 g of tertiary slurry C5. • Binder (Sekisui Chemical Co., Ltd., KW-3, polyvinyl acetal, concentration 20.5% by mass): 195.1 g • pH adjuster (tetraethylammonium hydroxide, 35% by mass): 1.6 g • Solvent (ion-exchanged water): 38.3 g

[0113] The content of the above ceramic raw material powders (titania powder and silica powder) relative to the total mass of the tertiary slurry C5 was 28.7% by mass, the viscosity was 88 mPa·s, and the pH was 11.2. Multiple batches of tertiary slurry C5 were prepared under the same conditions.

[0114] In the granulation process of Example 1, raw material granules E5 were obtained in the same manner except that the tertiary slurry was replaced with tertiary slurry C5. The parameters of the obtained raw material granules E5 were measured using the method described above, and the results were as follows: • Average packing density: 14.8 volume% • Average collapse strength: 0.92 MPa • Average granule size: 101.5 μm • Ratio of intragranular defect diameter to granule size: 0.03 • Residual solvent amount: 0.4 mass% • Circularity: 0.91 • Aspect ratio: 0.92 • Angle of repose: 27.0° • Compressibility: 12.1% • Hausner ratio: 1.16 • Flowability index: 88.0

[0115] In Example 1, titanium-containing silica glass H5 was obtained in the same manner as in the [pressure molding process] and [heating process], except that the raw material granules were changed to raw material granules E5. When the OH concentration of the obtained titanium-containing silica glass H5 was measured under the above conditions, it was found to be 550 ppm by mass.

[0116] When comparing the titanium-containing silica glasses obtained from Examples 1 to 5, titanium-containing silica glass H3 contained numerous large bubbles with a diameter of 10 μm or more, which were not observed in titanium-containing silica glasses H1, H2, H4, and H5.

[0117] Furthermore, the entire contents of the specification, claims, drawings, and abstract of Japanese Patent Application No. 2025-066614, filed on April 15, 2025, are incorporated herein by reference as disclosure of the present invention.

[0118] 10 Press machine 12 Die 14 Lower punch 16 Upper punch 20 Raw material granule layer 22 Layered molded body 24 Second raw material granule layer 26 Additional layered molded body

Claims

1. A method for producing titanium-containing silica glass, comprising: preparing a slurry containing silica, titanium, and a solvent; obtaining raw material granules using the slurry by spray freeze-drying; obtaining a molded body by pressure molding the raw material granules; and heating the molded body to obtain titanium-containing silica glass.

2. The method for producing titanium-containing silica glass according to claim 1, wherein the titanium component comprises at least one selected from the group consisting of titania, titania-silica composites, titanium-containing silica, and organotitanium compounds.

3. The method for producing titanium-containing silica glass according to claim 1, wherein the slurry comprises silica and at least one selected from the group consisting of titania-silica composites, titania, and titanium-containing silica.

4. The method for producing titanium-containing silica glass according to claim 1, wherein the slurry comprises silica and one or more selected from the group consisting of titania and titania-silica composites.

5. The method for producing titanium-containing silica glass according to claim 1, wherein, in heating the molded body, the molded body is sintered to obtain a sintered body, and the sintered body is melted.

6. The method for producing titanium-containing silica glass according to claim 1, wherein the pressure molding includes pressurization by isotropic pressing.

7. The method for producing titanium-containing silica glass according to claim 1, wherein when obtaining the molded body, the raw material granules are pressed to form a layered molded body, the raw material granules are further arranged on at least one side of the obtained layered molded body and pressed to form an additional layered molded body, and one or more layers of the additional layered molded body are formed on the layered molded body to obtain the molded body.

8. The method for producing titanium-containing silica glass according to claim 1, wherein the OH concentration of the obtained titanium-containing silica glass is less than 600 ppm by mass.

9. A method for producing titanium-containing silica glass according to claim 1, wherein the heating of the molded body includes hot isostatic pressing.

10. A method for producing titanium-containing silica glass according to any one of claims 1 to 9, wherein the average packing rate of the raw material granules is 12 to 45 volume percent.

11. A method for producing titanium-containing silica glass according to any one of claims 1 to 9, wherein the average disintegration strength of the raw material granules is 0.10 to 1.00 MPa.

12. A method for producing titanium-containing silica glass according to any one of claims 1 to 9, wherein the ratio of the diameter of intragranular defects in the raw material granules to the granular particle size of the raw material granules is 0.30 or less.

13. A method for producing titanium-containing silica glass according to any one of claims 1 to 9, wherein the average particle size of the ceramic raw material powder among the silica component and the titanium component is 10 to 500 nm.

14. A method for producing titanium-containing silica glass according to any one of claims 1 to 9, wherein the fluidity index of the raw material granules is 60 or higher.

15. A method for producing titanium-containing silica glass according to any one of claims 1 to 9, wherein the spray freeze granulation drying method is carried out in the order of spray freeze and vacuum drying, and after the vacuum drying, the drying is further carried out at 35 to 150°C under atmospheric pressure, and the amount of solvent remaining in the raw material granules is 2.0% by mass or less with respect to the total mass of the raw material granules.

16. The method for producing titanium-containing silica glass according to any one of claims 1 to 9, wherein the slurry further comprises a binder, and after obtaining the molded body, a degreasing treatment is performed.

17. The method for producing titanium-containing silica glass according to claim 16, wherein the binder comprises at least one selected from the group consisting of polyvinyl acetal, polyethylene glycol, paraffin wax, carnauba wax, and microcrystalline wax.

18. The method for producing titanium-containing silica glass according to claim 16, wherein the content of the binder in the slurry is 10.0 to 50.0% by mass of the silica component and the titanium component relative to the content of the ceramic raw material powder.

19. A method for producing titanium-containing silica glass according to any one of claims 1 to 9, wherein the slurry contains a pH adjusting agent, and the pH adjusting agent contains at least one selected from the group consisting of ammonia, quaternary ammonium hydroxide, and organic amine compounds.

20. The method for producing titanium-containing silica glass according to claim 19, wherein the content of the pH adjusting agent in the slurry is 0.2 to 5.0% by mass of the silica component and the titanium component relative to the content of the ceramic raw material powder.

21. A method for producing titanium-containing silica glass according to any one of claims 1 to 9, wherein the content of ceramic raw material powder among the silica component and the titanium component in the slurry is 12.0 to 68.0% by mass relative to the total mass of the slurry.

22. A method for producing titanium-containing silica glass according to any one of claims 1 to 9, wherein the viscosity of the slurry is 100 mPa·s or less.

23. The method for producing titanium-containing silica glass according to any one of claims 1 to 9, wherein the solvent comprises at least one of water and tert-butyl alcohol.

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