Quartz glass

Abstract

Provided is at least one of: quartz glass having excellent heat-ray shielding properties and mechanical strength; and a method for producing the quartz glass.　The quartz glass has a porosity of 0.5% or more, an average pore diameter of 8.0 μm or less, and an average circularity of the pores of 0.70 or more. The method for producing the quartz glass comprises: a preparation step of mixing 2 parts by mass or more of graphite powder with 100 parts by mass of amorphous silica powder to obtain a raw material powder; a molding step of molding the raw material powder into a molded body; and a sintering step of sintering the molded body. The amorphous silica powder contains a first silica powder having an average particle diameter of 0.60-2.50 μm and a second silica powder having an average particle diameter of 0.001-0.060 μm, and the graphite powder has an average particle diameter of 0.50-10.00 μm.

Description

Quartz glass

[0001] This disclosure relates to quartz glass.

[0002] Quartz glass is used in a variety of applications, including lighting equipment, optical instrument components, semiconductor industrial materials, and scientific and chemical instruments, due to its excellent light transmission, heat resistance, and chemical resistance. Among these, quartz glass containing air bubbles is used for heat shielding applications such as flanges and furnace tubes in semiconductor heat treatment equipment due to its superior heat shielding properties.

[0003] As for the manufacturing method of quartz glass used for heat shielding applications, for example, a method of mixing a foaming agent (silicon nitride powder) with silica powder and melting the mixture (Patent Document 1), a method of mixing a pore-forming agent (graphite powder) with amorphous silica powder and sintering the mixture (Patent Document 2), a method of mixing silicon nitride powder produced by the wear of silicon nitride beads with silica powder as a foaming agent and melting the mixture (Patent Document 3), and a method of crushing and granulating silica powder under predetermined conditions and then firing the resulting granulated powder (Patent Document 4) are known.

[0004] U.S. Patent No. 5,972,488, U.S. Patent Application Publication No. 2017 / 174560, International Publication No. 2020 / 129174, U.S. Patent Application Publication No. 2022 / 250962.

[0005] However, the quartz glass produced by the methods described in Patent Documents 1 and 2 had low infrared light reflection performance due to the large average diameter of the pores, which allowed infrared light to pass through easily and resulted in poor heat shielding. Furthermore, the quartz glass produced by the method described in Patent Document 3 had fewer pores. As a result, infrared rays could easily pass through the areas without pores, resulting in poor heat shielding. In addition, the quartz glass produced by the method described in Patent Document 4 had irregularly shaped pores formed by the voids between the particles of amorphous silica powder, which easily caused stress concentration at the pore edges and resulted in low mechanical strength.

[0006] This disclosure aims to provide quartz glass with excellent heat shielding properties and mechanical strength, and at least one of the methods for manufacturing the same.

[0007] The inventors investigated methods to increase the infrared reflectivity of opaque quartz glass in order to improve its heat-shielding properties, and focused on the fact that infrared reflectivity correlates with multiple factors, including the diameter and amount of pores in the quartz glass. As a result, they found that by controlling the pores in quartz glass, while also focusing on the shape of the pores, it is possible to achieve both heat-shielding properties and mechanical strength.

[0008] In other words, the present invention is as described in the claims, and the gist of this disclosure is as follows: [1] A quartz glass having a porosity of 0.5% or more, an average pore diameter of 8.0 μm or less, and an average pore circularity of 0.70 or more. [2] An apparent density of 2.189 g / cm³ ３ The quartz glass described in [1] above, which is as follows: [3] The quartz glass described in [1] or [2] above, wherein the near-infrared reflectance at a wavelength of 2000 nm when the sample thickness is 3 ± 0.05 mm is 70.0% or more. [4] The quartz glass described in any one of [1] to [3] above, wherein the near-infrared linear transmittance at a wavelength of 2000 nm when the sample thickness is 3 ± 0.05 mm is 0.12% or less. [5] The quartz glass described in any one of [1] to [4] above, wherein the water absorption rate is 0.1% by mass or less. [6] A method for producing quartz glass according to any one of [1] to [5] above, comprising a preparation step of mixing 2 parts by mass or more of graphite powder with 100 parts by mass of amorphous silica powder to obtain a raw material powder, a molding step of molding the raw material powder to obtain a molded body, and a sintering step of sintering the molded body, wherein the amorphous silica powder comprises a first silica powder having an average particle diameter of 0.60 μm or more and 2.50 μm or less, and a second silica powder having an average particle diameter of 0.001 μm or more and 0.060 μm or less, and the average particle diameter of the graphite powder is 0.50 μm or more and 10.00 μm or less. [7] A method for producing quartz glass according to [6] above, further comprising a heat treatment step after the molding step and before the sintering step of heating the molded body in an atmospheric atmosphere at a temperature above which the graphite powder contained in the molded body burns off.

[0009] This disclosure provides at least one of the following: a quartz glass with excellent heat-shielding properties and mechanical strength, and a method for manufacturing the same.

[0010] This disclosure will be described in detail with reference to one embodiment. However, this disclosure is not limited to the following embodiment. Furthermore, this disclosure includes any combination of each configuration and parameter disclosed herein, and also includes any combination of upper and lower limits of the values ​​disclosed herein.

[0011] The definitions of terms in this embodiment are as follows:

[0012] In this embodiment, "quartz glass" refers to quartz (SiO₂). ２ It is an amorphous solid mainly composed of ) and may be an amorphous solid made of quartz. If the quartz glass contains metallic elements or metalloid elements other than silicon (Si), the content of each of those elements other than aluminum relative to the mass of the quartz glass is greater than 0 ppm by mass and 10 ppm by mass or less, and moreover than 0 ppm by mass and 5 ppm by mass or less. In addition, the content of aluminum relative to the mass of the quartz glass is greater than 0 ppm by mass and 20 ppm by mass or less.

[0013] In this embodiment, the "near-infrared reflectance at a wavelength of 2000 nm when the thickness is 3.0 ± 0.05 mm (hereinafter also simply referred to as "near-infrared reflectance")" and the "near-infrared linear transmittance at a wavelength of 2000 nm when the thickness is 3.0 ± 0.05 mm (hereinafter also simply referred to as "near-infrared linear transmittance")" are the total light reflectance and linear transmittance measured when a quartz glass with a thickness of 3.0 ± 0.05 mm is irradiated with incident light at a measurement wavelength of 2000 nm using a general spectrophotometer (for example, device name: V-770, manufactured by JASCO Corporation). The "near-infrared reflectance" is the ratio of total light reflected to the incident light [%] as described above, and the "near-infrared linear transmittance" is the ratio of linearly transmitted light to the incident light [%] as described above. "Incident light," "total reflected light," and "total transmitted light" are, respectively, the light irradiated onto the quartz glass, the light reflected by the quartz glass, and the light transmitted through the quartz glass. Furthermore, "total reflected light" consists of "specular reflected light," which is reflected at the same angle as the incident light, and "diffuse reflected light," which is reflected at a different angle than the incident light. "Total transmitted light" consists of "diffuse transmitted light," which is light that passes through the quartz glass while diffusing, and "linear transmitted light," which is light that passes through the quartz glass without diffusing.

[0014] The following conditions are used for measuring near-infrared reflectance and near-infrared linear transmittance. The direction of light transmission is the thickness direction of the quartz glass sample. Measurement wavelength: 2000 nm Data acquisition interval: 1 nm UV-Vis bandwidth: 5.0 nm Near-infrared bandwidth: 20.0 nm Response: 0.06 seconds Light source: Deuterium lamp, halogen lamp Light source switching wavelength: 340.0 nm Diffraction grating switching wavelength: 850.0 nm Scanning mode: Continuous Scanning speed: 1000 nm / min

[0015] For measurement of infrared linear transmittance, quartz glass obtained by mirror-polishing a measurement surface and a surface opposite to the measurement surface may be used. Examples of methods for obtaining a mirror-polished surface include a polishing method performed using diamond abrasive grains and / or ceria abrasive grains with a particle diameter of 1 μm or less, a urethane pad, or the like, and any generally known mirror-polishing method for quartz glass may be used.

[0016] The "water absorption rate" in the present embodiment is a value determined based on a change in mass when a measurement sample of quartz glass is immersed in water. Specifically, after drying a measurement sample of quartz glass at 110° C. for 24 hours, the temperature is returned to normal temperature by natural cooling, and the mass W1 of the measurement sample is measured. Next, after placing the measurement sample in water and boiling it for 1 hour, the temperature is returned to normal temperature by natural cooling, water droplets on the surface of the measurement sample taken out from the water are removed, and then the mass W2 of the measurement sample is measured. The water absorption rate is obtained from the following formula (1) based on W1 and W2. The removal of water droplets on the surface of the measurement sample may be performed by a method such that no water droplets can be confirmed on the surface of the measurement sample; for example, the surface of the measurement sample may be wiped with gauze. Water absorption rate (mass%) = ((W2-W1) / W1) × 100 (1)

[0017] The "average particle diameter" in the present embodiment is a particle diameter corresponding to a 50% frequency (hereinafter also referred to as "D50") in a volume particle diameter distribution obtained under the following conditions using a laser diffraction scattering type particle diameter distribution measuring apparatus (for example, SALD-2300, manufactured by Shimadzu Corporation), unless otherwise specified. The refractive index for measurement conditions may be automatically set by the above-described apparatus according to the particles to be measured. Measurement method : Dry method Pump speed : 5.0 Distribution function : No conversion Built-in ultrasonic irradiation time: 10 seconds Smoothing : 3 Data shift : 0

[0018] Provided, however, that in measurement performed with a laser diffraction scattering particle size distribution analyzer, there is a risk that measurement accuracy may decrease for particles having a particle size of less than 0.500 µm. For this reason, with respect to the "average particle size" of powder having D50 of less than 0.500 µm, a converted particle diameter calculated from the following formula (A) using the BET specific surface area S of the powder shall be used. Converted particle diameter [µm] = 6 / (S×2.2) (A) In the above formula (A), S is the specific surface area of the powder [m ２ / g].

[0019] S (specific surface area of the powder) in the above formula (A) may be calculated from the slope and intercept of a straight line fitted based on ISO9277, after preparing a BET plot using an adsorption isotherm obtained by measurement at a temperature of 77 K using nitrogen as the adsorption gas with a common BET specific surface area analyzer (e.g., BELSORP-mini II, manufactured by Microtrac MRB Belsorp Inc.). For a measurement sample to undergo nitrogen gas adsorption, powder that has been subjected to degassing treatment under vacuum at 350°C for 2 hours may be used.

[0020] [Quartz Glass] The present embodiment relates to quartz glass having a porosity of 0.5% or more, an average pore diameter of 8.0 µm or less, and an average circularity of pores of 0.70 or more. By satisfying such a configuration, the quartz glass of the present embodiment has heat ray shielding properties suitable for flanges and the like of semiconductor heat treatment apparatuses (hereinafter also referred to as "flange members and the like"), and is also excellent in mechanical strength.

[0021] The quartz glass of the present embodiment is quartz glass having high near-infrared reflectance and excellent heat ray shielding properties, that is, the property of blocking heat conduction caused by infrared rays, and in particular exhibits heat shielding properties suitable as a flange member or the like. The quartz glass of the present embodiment exhibits heat shielding properties due to the presence of pores. Therefore, the quartz glass of the present embodiment can also be regarded as quartz glass having pores, and further quartz glass having pores in a state of exhibiting heat shielding properties.

[0022] Furthermore, quartz glass is classified according to its manufacturing method, and one or more types are known, selected from the group consisting of quartz glass obtained by melting (hereinafter also called "fused quartz glass"), quartz glass obtained by chemical synthesis (hereinafter also called "synthetic quartz glass"), and quartz glass obtained by sintering (hereinafter also called "sintered quartz glass"). Sintered quartz glass is preferred for this embodiment because it offers a high degree of freedom in shape and is suitable for so-called near-net molding.

[0023] The quartz glass of this embodiment has a porosity of 0.5% or more. Having a porosity within the above-mentioned range, that is, having an appropriate amount of pores in the quartz glass, makes it easier for infrared rays incident on the quartz glass to be reflected and scattered by the pores, thereby improving the heat-shielding properties of the quartz glass. The lower limit of the porosity is preferably 1.0% or more, 1.5% or more, or 2.0% or more, and the upper limit is preferably 10.0% or less, 8.0% or less, 5.0% or less, or 4.0% or less, from the viewpoint of further improving the mechanical strength of the quartz glass. Examples of porosities for the quartz glass of this embodiment include 1.0% to 10.0%, 1.5% to 8.0%, 1.5% to 5.0%, or 1.5% to 4.0%.

[0024] In this embodiment, the "porosity" is calculated from the following formula (2) based on the apparent density ρ of the quartz glass, which is determined by the Archimedes method (JIS R 1634-1998) using an analytical balance (instrument name: XSR205DUV, manufactured by Mettler Toledo). Φ = (2.2 - ρ) / 2.2 × 100 (2)

[0025] In equation (2) above, Φ is the porosity [%] and ρ is the apparent density (g / cm³). ３Prior to measuring the apparent density ρ, the sample is pretreated by the boiling method described in JIS R 1634-1998. The porosity Φ is a value obtained from the apparent density ρ of the quartz glass, as described above, and indirectly represents the total volume of pores present in the quartz glass. The larger the total volume of pores in the quartz glass (the more pores there are, and the larger the average pore diameter), the smaller the apparent density of the quartz glass, and therefore the larger the porosity obtained from equation (2) above.

[0026] The quartz glass of this embodiment has an average pore size of 8.0 μm or less. The infrared reflectivity of quartz glass due to pores tends to decrease when the pore size is too large. In the quartz glass of this embodiment, because the average pore size is the value described above, small pores exist in the quartz glass. As a result, infrared rays incident on the quartz glass are more easily reflected by the pores, improving the heat shielding properties of the quartz glass. The lower limit of the average pore size is preferably 0.1 μm or more, 0.5 μm or more, or 1.0 μm or more, and the upper limit is preferably 7.0 μm or less, 6.0 μm or less, 5.0 μm or less, 4.0 μm or less, 3.0 μm or less, or 2.0 μm or less. Examples of the average pore size of the quartz glass in this embodiment include 0.1 μm to 7.0 μm, 0.5 μm to 6.0 μm, 1.0 μm to 5.0 μm, 1.0 μm to 4.0 μm, 1.0 μm to 3.0 μm, or 1.0 μm to 2.0 μm.

[0027] In this embodiment, the quartz glass exhibits significantly improved heat shielding properties by controlling the porosity and average pore diameter to the ranges described above. Conventionally, in the manufacturing methods of quartz glass by melting (melting method) or by sintering (sintering method), techniques are known to form large pores in the quartz glass by mixing a foaming agent or a pore-forming agent with the silica powder raw material. However, if the pore diameter is large, the reflectivity of infrared rays by the pores decreases, reducing the heat shielding properties of the quartz glass. Alternatively, techniques are known to form small pores in the quartz glass by reducing the amount of foaming agent added to the silica powder. However, such techniques result in a decrease in the number of pores in the quartz glass, reducing the frequency with which infrared rays incident on the quartz glass come into contact with the pores, thereby reducing the heat shielding properties of the quartz glass. In contrast, the quartz glass of this embodiment has a certain number of pores with small diameters present within it, that is, the average pore diameter is small and the porosity is high, resulting in a large number of small pores that are excellent at reflecting infrared rays. This is considered to be one of the reasons why the heat-shielding properties of the quartz glass are significantly improved.

[0028] The quartz glass of this embodiment has an average pore circularity of 0.70 or higher. In the quartz glass of this embodiment, the mechanical strength of the quartz glass can be improved by controlling the average circularity to the range described above. Conventionally, when manufacturing quartz glass by sintering, a technique is known in which pores are formed in the quartz glass by the voids between the particles of amorphous silica powder, which is the raw material. However, because the voids between particles have an irregular, non-spherical shape, stress concentration tends to occur at the edges of the pores, and the mechanical strength tends to decrease. In particular, with such a technique, when trying to increase the number of pores in order to increase the infrared reflectivity of the quartz glass, the mechanical strength tends to decrease even more. In contrast, the quartz glass of this embodiment controls the average pore circularity to a high range as described above, that is, by making the shape of the pores close to a sphere, even if the number of pores is increased (even if the porosity is set to the high range described above), the occurrence of stress concentration at the edges of the pores is suppressed, and the quartz glass can be made to have excellent mechanical strength. Furthermore, the fact that the mechanical strength (breaking strength) increases as the pores in an object become closer to spherical is described, for example, in the publicly available document "Iron and Steel, Vol. 100, 2014, No. 2, pp. 140-147". The lower limit of the average circularity of the pores is preferably 0.72 or higher, 0.74 or higher, or 0.76 or higher, and the upper limit is 1.00 or lower, 0.90 or lower, 0.85 or lower, or 0.80 or lower. Examples of average circularity of pores in the quartz glass of this embodiment include 0.70 or higher and 1.00 or lower, 0.72 or higher and 1.00 or lower, 0.74 or higher and 1.00 or lower, 0.76 or higher and 1.00 or lower, 0.76 or higher and 0.90 or lower, 0.76 or higher and 0.85 or lower, or 0.76 or higher and 0.80 or lower.

[0029] In this embodiment, the "average pore size" is determined by analyzing the secondary electron image of the cross-section of quartz glass obtained by electron microscopy observation using a general scanning electron microscope (for example, instrument name: JSM-IT500LA, manufactured by JEOL Ltd.) under the following conditions: Magnification: 500x to 5000x Acceleration voltage: 10kV Std. PC: 30

[0030] For electron microscope observation, a cut surface inside quartz glass obtained by cutting quartz glass, which is subjected to mirror polishing performed using diamond abrasive grains and / or ceria abrasive grains with a particle diameter of 1 μm or less and a urethane pad or the like to remove defects (such as linear marks) generated by cutting and rough polishing, may be used as the observation surface.

[0031] For analysis of secondary electron images, general image analysis software (for example, software name: Image J) is used to obtain an image processed diagram, pores are detected, and the area of each pore is calculated based on the image processed diagram. Based on the calculated area of each pore, the diameter when each pore is circularly approximated is obtained as the pore diameter by the following formula (3), a pore diameter-area frequency distribution is prepared, and the pore diameter corresponding to a frequency of 50% in the distribution is taken as the average pore diameter. D=(4S / π) ０．５ (3)

[0032] In the above formula (3), D is the pore diameter of each pore [μm], and S is the area of each pore [μm ２ . Analysis of secondary electron images may be performed for 100 or more pores, and 2 or more (for example, 2 to 7) electron microscope observation diagrams may be used for image analysis.

[0033] The "average circularity of pores" in the present embodiment refers to an average value of the circularity of each pore obtained by obtaining the area of each white region (area of each pore) and the perimeter of the white region (perimeter of each pore) from the above-described image processed diagram and calculating by the following formula (4-1). For the "average circularity of pores", analysis of secondary electron images may be performed for 100 or more pores, and 2 or more (for example, 2 to 7) electron microscope observation diagrams may be used for image analysis. C ｐ =4πS ｐ / P ｐ ２ (4-1)

[0034] In the above formula (4-1), C ｐ is the circularity of each pore, S ｐ is the area of each pore [μm ２ , P ｐ is the perimeter of each pore [μm].

[0035] From the viewpoint of further improving mechanical strength, the apparent density of the quartz glass in this embodiment is 2.050 g / cm³. ３ Above, 2.060g / cm ３ The above, or 2.070 g / cm³ ３ The above points are cited. The upper limit of the apparent density is 2.189 g / cm³ in order to control the porosity within the range described above. ３ Below, 2.170g / cm ３ The following, or 2.165 g / cm³ ３ The following can be cited: The apparent density of the quartz glass in this embodiment is 2.050 g / cm³. ３ 2.189g / cm or more ３ Below, 2.060g / cm ３ 2.170g / cm or more ３ The following, or 2.070 g / cm³ ３ 2.165g / cm or more ３ The following are some examples:

[0036] The apparent density of the quartz glass in this embodiment can be determined using an analytical balance and the Archimedes method (JIS R 1634:1998), as described above.

[0037] The quartz glass of this embodiment may have any shape, for example, one or more shapes selected from the group consisting of plate-like, columnar, ring-like, substantially ring-like, spherical, substantially spherical, polyhedral, substantially polyhedral, conical, and substantially conical shapes, or various ingot shapes, semiconductor heat treatment device component shapes, and other shapes according to the application.

[0038] From the viewpoint of further improving heat shielding performance, the quartz glass of this embodiment preferably has a near-infrared reflectance of 70.0% or more, 80.0% or more, 83.0% or more, or 85.0% or more. The upper limit of the near-infrared reflectance is 100.0% or less, or 98.0% or less. The near-infrared reflectance of the quartz glass of this embodiment may be 70.0% or more and 100.0% or less, 80.0% or more and 100.0% or less, 83.0% or more and 100.0% or less, or 85.0% or more and 100.0% or less.

[0039] From the viewpoint of further improving heat shielding performance, the quartz glass of this embodiment preferably has a near-infrared linear transmittance of 0.12% or less, 0.10% or less, or 0.08% or less. The lower limit of the near-infrared linear transmittance is 0.00% or more, or 0.02% or more. The near-infrared linear transmittance of the quartz glass of this embodiment may be 0.00% or more and 0.12% or less, 0.00% or more and 0.10% or less, or 0.00% or more and 0.08% or less.

[0040] In this embodiment, it is preferable that the quartz glass contains a large proportion of closed pores (a small proportion of open pores). That is, it is preferable that the quartz glass of this embodiment has a water absorption rate of 0.10% by mass or less, 0.05% by mass or less, or 0.02% by mass or less. The lower limit of the water absorption rate is 0.00% by mass or more. The water absorption rate of the quartz glass of this embodiment can be 0.00% by mass or more and 0.10% by mass or less, 0.00% by mass or more and 0.05% by mass or less, or 0.00% by mass or more and 0.02% by mass or less.

[0041] [Method for Manufacturing Quartz Glass] The manufacturing method of the quartz glass of this embodiment is arbitrary as long as it has the above-described characteristics. The manufacturing method of the quartz glass of this embodiment is preferably a sintering method, and more preferably a method for manufacturing quartz glass that includes a molding step of molding raw material powder to obtain a molded body, and a sintering step of sintering the molded body. A preferred method for manufacturing quartz glass of this embodiment is a method for manufacturing quartz glass (hereinafter also referred to as "the manufacturing method of this embodiment") which includes a preparation step of mixing 2 parts by mass or more of graphite powder with 100 parts by mass of amorphous silica powder to obtain raw material powder, a molding step of molding the raw material powder to obtain a molded body, and a sintering step of sintering the molded body, wherein the amorphous silica powder comprises a first silica powder with an average particle diameter of 0.60 μm or more and 2.50 μm or less, and a second silica powder with an average particle diameter of 0.001 μm or more and 0.060 μm or less, and the average particle diameter of the graphite powder is 0.50 μm or more and 10.00 μm or less. The manufacturing method of this embodiment allows for the molding of raw material powder into a desired shape before firing, thereby obtaining quartz glass with complex shapes suitable for semiconductor manufacturing equipment components and the like. Furthermore, pores can be dispersed and formed within the quartz glass, improving the resulting heat-shielding properties. Specifically, according to the manufacturing method of this embodiment, graphite powder is included in the raw material powder, and a molded body obtained using such raw material powder is heat-treated to burn off the graphite powder, thereby obtaining a molded body with pores of an appropriate diameter and quantity formed inside. Then, by sintering such a molded body, quartz glass with pores that have excellent infrared reflectivity and excellent heat-shielding properties can be obtained.

[0042] The manufacturing method of this embodiment includes a preparation step of mixing 2 parts by mass or more of graphite powder with 100 parts by mass of amorphous silica powder to obtain a raw material powder.

[0043] The graphite powder contained in the raw material powder may be, for example, a powder composed of particles of one or more graphite materials selected from the group consisting of natural graphite, artificial graphite, carbon black, and pyrolytic graphite. From the viewpoint of having a low impurity content, artificial graphite, carbon black, and pyrolytic graphite are preferred.

[0044] The graphite powder content in the raw material powder is 2 parts by mass or more per 100 parts by mass of amorphous silica powder. Preferably, the graphite powder content in the raw material powder is 3 parts by mass or more, or 4 parts by mass or more, per 100 parts by mass of amorphous silica powder, and preferably the upper limit is 16 parts by mass or less, 12 parts by mass or less, or 8 parts by mass or less. Examples of graphite powder content in the raw material powder include 2 parts by mass or more and 16 parts by mass or less, 3 parts by mass or more and 16 parts by mass or less, 3 parts by mass or more and 12 parts by mass or less, or 4 parts by mass or more and 8 parts by mass or less per 100 parts by mass of amorphous silica powder. By setting the graphite powder content in the raw material powder within the above range, the molded body obtained using the raw material powder will have an appropriate amount of pores formed inside, and the quartz glass obtained using such a molded body will have pores with excellent infrared reflectivity and excellent heat shielding properties.

[0045] The average particle size of the graphite powder contained in the raw material powder is between 0.50 μm and 10.00 μm. This average particle size allows the average pore size of the manufactured quartz glass to be 8.0 μm or less. Conversely, if the average particle size of the graphite powder exceeds 10.00 μm, the average pore size of the manufactured quartz glass will exceed 8.0 μm. Furthermore, if the average particle size of the graphite powder is less than 0.50 μm, pores will not easily form in the manufactured quartz glass.

[0046] The average particle size of the graphite powder contained in the raw material powder is preferably 0.65 μm or larger, or 0.80 μm or larger, from the viewpoint of being able to form pores of a size that are excellent in reflecting infrared rays in the quartz glass, and the upper limit is preferably 8.00 μm or smaller, 6.00 μm or smaller, 5.00 μm or smaller, 4.00 μm or smaller, 3.00 μm or smaller, or 2.00 μm or smaller. The average particle size of the graphite powder is preferably 0.65 μm or larger and 8.00 μm or smaller, 0.80 μm or larger and 6.00 μm or smaller, 0.80 μm or larger and 5.00 μm or smaller, 0.80 μm or larger and 4.00 μm or smaller, 0.80 μm or larger and 3.00 μm or smaller, or 0.80 μm or larger and 2.00 μm or smaller.

[0047] When forming pores in quartz glass using graphite powder, the average pore size of the resulting quartz glass can be controlled according to the average particle size of the graphite powder. The average pore size of the resulting quartz glass tends to be smaller than the average particle size of the graphite powder used. This is because the pores formed by the burning of graphite powder shrink and deform in shape as the surrounding raw material powder sintersects. Therefore, it is preferable that the average particle size of the graphite powder used be greater than or equal to the target average pore size; for example, it should be between 1 and 2 times the target average pore size.

[0048] From the viewpoint of being able to form pores with high average circularity in quartz glass and improve the mechanical strength of the resulting quartz glass, the average circularity of the graphite powder contained in the raw material powder is preferably 0.70 or higher, 0.72 or higher, 0.74 or higher, 0.76 or higher, 0.80 or higher, or 0.85 or higher, and the upper limit is 1.00 or lower, or 0.95 or lower. Examples of average circularity of graphite powder include 0.70 or higher and 1.00 or lower, 0.72 or higher and 1.00 or lower, 0.74 or higher and 1.00 or lower, 0.76 or higher and 1.00 or lower, 0.80 or higher and 1.00 or lower, or 0.85 or higher and 1.00 or lower.

[0049] When forming pores in quartz glass using graphite powder, it is preferable to increase the average circularity of the graphite powder as the average particle size of the graphite powder decreases. Graphite particles with a small average particle size exhibit a larger difference between the original average circularity of the graphite particles and the average circularity of the pores formed by these graphite particles compared to graphite particles with a large average particle size. This is because the pores formed by the burning of graphite powder undergo deformation of their outer shape due to the sintering of the surrounding raw material powder, and the amount of change in circularity due to this deformation increases as the pore size decreases. Therefore, for example, graphite particles with an average particle size of 6.00 μm or less preferably have an average circularity of 0.82 to 1.00, 0.84 to 1.00, or 0.86 to 1.00.

[0050] The average circularity of graphite powder can be measured as follows. First, graphite powder is sprinkled onto a carbon tape commonly used for ensuring conductivity in scanning electron microscopes, cut to an appropriate length, and excess powder is removed with a blower to prepare the sample for measurement. A secondary electron image is obtained from this sample using a general scanning electron microscope (device name: JSM-IT500LA, manufactured by JEOL Ltd.), and the average circularity is determined by analyzing the secondary electron image. Observation magnification: 500x to 5000x Acceleration voltage: 10kV Std. PC: 30

[0051] The secondary electron image analysis is performed by obtaining an image processing diagram using general image analysis software (software name: Image J), ​​measuring the area of ​​each white region (area of ​​each particle of graphite powder) and the perimeter of each white region (perimeter of each particle of graphite powder) from the image processing diagram, and calculating the average circularity of each particle obtained using the following formula (4-2) to determine the average circularity of the graphite powder. The secondary electron image analysis is performed for 30 or more particles, and two or more electron microscope observation images may be used for image analysis. C ｃ = 4πS ｃ / P ｃ ２ (4-2)

[0052] In the above equation (4-2), C ｃ S is the circularity of each particle of graphite powder. ｃ The area of ​​each particle in the graphite powder [μm²] ２ ], P ｃ is the circumference [μm] of each particle of graphite powder.

[0053] The amorphous silica powder contained in the raw material powder is mainly silica (silicon dioxide; SiO₂) ２ This is a silica powder composed of particles, consisting of a Si-O network structure and lacking a fixed crystalline structure.

[0054] The amorphous silica powder contained in the raw material powder should consist mainly of amorphous silica particles, and may include amorphous silica powder obtained by known manufacturing methods, as well as one or more selected from the group consisting of sol-gel silica, precipitated silica, gas-phase silica, and flame-fused silica.

[0055] The shape of the amorphous silica powder contained in the raw material powder can be arbitrary, and it is sufficient if it is one or more selected from the group consisting of polyhedral, spherical, and irregular shapes.

[0056] The amorphous silica powder contained in the raw material powder includes a first silica powder with an average particle diameter of 0.60 μm to 2.50 μm and a second silica powder with an average particle diameter of 0.001 μm to 0.060 μm. The inclusion of both the first and second silica powders in the amorphous silica powder allows the silica particles of the second silica powder to fill the voids between the silica particles of the first silica powder, thus reducing the likelihood of voids forming between the particles of the amorphous silica powder. This suppresses pore deformation caused by the connection of pores formed by the burning of graphite powder with the voids between silica particles, allowing the average circularity of the pores in the manufactured quartz glass to be 0.70 or higher. Furthermore, the inclusion of both the first and second silica powders in the amorphous silica powder allows the silica particles of the second silica powder to fill the voids between the silica particles of the first silica powder, thereby increasing the apparent density of the manufactured quartz glass. On the other hand, if the amorphous silica powder does not contain the first and second silica powders, voids are more likely to form between the silica particles. As a result, the pores formed by the burning of graphite powder tend to connect with the voids between the silica particles, and the average circularity of the pores in the manufactured quartz glass may be less than 0.70. In addition, the apparent density may decrease due to the voids between the silica particles.

[0057] The amorphous silica powder contained in the raw material powder may consist only of first silica powder and second silica powder, or it may further contain a third silica powder having a different average particle size from the first and second silica powders, but it is preferable that it consists only of first silica powder and second silica powder.

[0058] The average particle size of the first silica powder may be 0.60 μm or more and 2.50 μm or less, but from the viewpoint of further increasing the average circularity and apparent density of the pores of the manufactured quartz glass, it is preferable that it be 0.70 μm or more or 0.80 μm or more, and the upper limit is preferably 2.00 μm or less or 1.50 μm or less. The average particle size of the first silica powder is preferably 0.70 μm or more and 2.00 μm or less, 0.80 μm or more and 2.00 μm or less, or 0.80 μm or more and 1.50 μm or less. From the viewpoint of being able to easily control the average particle size within the above range, the first silica powder is preferably sol-gel silica.

[0059] The content of the first silica powder in the raw material powder is preferably 45% by mass or more, 50% by mass or more, or 55% by mass or more, relative to 100% by mass of amorphous silica powder contained in the raw material powder, and the upper limit is preferably 75% by mass or less, 70% by mass or less, or 65% by mass or less. Examples of the first silica powder content include 45% by mass or more and 75% by mass or less, 50% by mass or more and 70% by mass or less, or 55% by mass or more and 65% by mass or less, relative to 100% by mass of amorphous silica powder contained in the raw material powder. By setting the content of the first silica powder within the above range, the balance of the content of the first silica powder and the second silica powder makes it easier to fill the voids between the silica particles constituting each silica powder, thereby increasing the average circularity and apparent density of the pores of the resulting quartz glass, and further improving its mechanical strength.

[0060] The average particle size of the second silica powder may be 0.001 μm or more and 0.060 μm or less, but from the viewpoint of further increasing the average circularity and apparent density of the pores of the manufactured quartz glass, it is preferable that it be 0.010 μm or more, or 0.020 μm or more, and the upper limit is preferably 0.050 μm or less, 0.040 μm or less, or 0.030 μm or less. The average particle size of the second silica powder is preferably 0.010 μm or more and 0.050 μm or less, 0.010 μm or more and 0.040 μm or less, 0.020 μm or more and 0.040 μm or less, or 0.020 μm or more and 0.030 μm or less. From the viewpoint of being able to easily control the average particle size within the above range, the second silica powder is preferably vapor-phase silica.

[0061] The content of the second silica powder in the raw material powder is preferably 25% by mass or more, 30% by mass or more, or 35% by mass or more, relative to 100% by mass of amorphous silica powder contained in the raw material powder, and the upper limit is preferably 55% by mass or less, 50% by mass or less, or 45% by mass or less. The content of the first silica powder can be 25% by mass or more and 55% by mass or less, 30% by mass or more and 50% by mass or less, or 35% by mass or more and 45% by mass or less, relative to 100% by mass of amorphous silica powder contained in the raw material powder. By setting the content of the second silica powder in the raw material powder within the above range, the balance of the content of the first silica powder and the second silica powder makes it easier to fill the voids between the silica particles constituting each silica powder, thereby increasing the average circularity and apparent density of the pores of the resulting quartz glass, and further improving its mechanical strength.

[0062] The raw material powder can be prepared by mixing amorphous silica powder and graphite powder. The specific mixing method is dry mixing, and more preferably dry mixing using a bead mill or ball mill, and even more preferably dry mixing using a bead mill. As for the dry mixing method using a bead mill, from the viewpoint of easily suppressing changes in the average particle size of amorphous silica powder and graphite powder during mixing, one method is to put amorphous silica powder and graphite powder together with resin beads into a polyethylene container and apply vibration while rotating it.

[0063] In the molding process of this embodiment, the raw material powder is molded to obtain a molded body. It is believed that the molding process efficiently rearranges the silica particles constituting the raw material powder, resulting in a molded body with appropriately dispersed voids between the powder particles.

[0064] The molding method includes methods for obtaining a molded body (compacted body), and includes one or more selected from the group consisting of uniaxial pressing, cold isostatic pressing (hereinafter also referred to as "CIP"), slip casting, sheet molding, injection molding, and three-dimensional molding, and it is sufficient if at least one of uniaxial pressing and CIP is used. Since the pores tend to become more uniform, it is preferable that the molding process is performed using CIP.

[0065] When CIP treatment is selected, the molding pressure is preferably 270 MPa or less, 200 MPa or less, 150 MPa or less, or 140 MPa or less, and also preferably 95 MPa or more, 100 MPa or more, or 120 MPa or more. Examples of molding pressures include 95 MPa or more and 270 MPa or less, 95 MPa or more and 200 MPa or less, 100 MPa or more and 150 MPa or less, or 100 MPa or more and 140 MPa or less.

[0066] The manufacturing method of this embodiment includes a step of sintering the molded body (hereinafter also referred to as the "sintering step"). By going through the sintering step, the quartz glass of this embodiment is obtained as sintered quartz glass. In the sintering step, the molded body is heated to a temperature at which it sintersects, causing the graphite powder to burn off and the sintering of the molded body to proceed. In the manufacturing method of this embodiment, by burning off the graphite powder from the molded body and sintering the molded body which has pores derived from the graphite powder, pores can be dispersed and formed in the quartz glass, improving the heat-shielding properties of the resulting quartz glass.

[0067] To avoid excessive porosity removal from the molded body, it is preferable that the sintering process be carried out at atmospheric pressure. In this embodiment, "atmospheric pressure sintering" refers to a method of sintering by heating the material to be sintered (molded body) without applying any external force during the sintering process.

[0068] The sintering atmosphere is not particularly limited if there is a heat treatment step before the sintering process in which the molded body is heated to a temperature above the temperature at which the graphite powder contained in the molded body burns off, and can be carried out in an atmospheric atmosphere. If there is no heat treatment step before the sintering process, any oxidizing atmosphere is acceptable, and an atmospheric atmosphere is preferred.

[0069] The holding temperature during sintering should be below the softening temperature of the raw material powder, preferably 1400°C or lower, or 1350°C or lower. The higher the holding temperature during sintering, the more easily the pores formed by the burning away of graphite powder tend to deform. That is, these pores are cavities surrounded by amorphous silica powder particles, and at the point when the graphite powder burns away, they are spherical, reflecting the shape of the graphite powder. However, the higher the holding temperature during sintering, the more fluid the amorphous silica powder becomes, and the more easily the pores deform from their spherical shape. If the holding temperature during sintering is 1400°C or lower, the pores formed by the burning away of graphite powder are less likely to deform, and the average circularity of the pores in the manufactured quartz glass can be increased. The holding temperature should be at a temperature at which densification progresses, preferably 1200°C or higher, or 1250°C or higher. The holding temperature during sintering is preferably 1200°C to 1400°C, or 1250°C to 1350°C.

[0070] Preferably, the heating rate to the holding temperature differs between the heating rate from the starting temperature to 1000°C (hereinafter also referred to as the "early heating rate") and the heating rate from 1000°C to the holding temperature (hereinafter referred to as the "later heating rate"), with the later heating rate being particularly slower than the early heating rate. In the production of quartz glass by sintering, sintering proceeds from the surface of the sintered material (molded body). By having a slower later heating rate in the temperature range where silica particle fusion and sintering proceed compared to the early heating rate in the temperature range where sintering progresses almost nonexistent, overheating of the surface of the sintered material (molded body) prior to sintering is suppressed, and the difference in the degree of sintering between the surface and the interior of the sintered material becomes smaller. As a result, the pore state of the resulting quartz glass as a whole is thought to become more uniform.

[0071] The initial heating rate is typically 300°C / hour or more and 700°C / hour or less, or 300°C / hour or more and 600°C / hour or less, while the later heating rate is typically 30°C / hour or more and 200°C / hour or less, or 50°C / hour or more and 200°C / hour or less.

[0072] The holding time at the holding temperature can be appropriately adjusted according to the size of the molded body subjected to the sintering process and the characteristics of the sintering furnace, but examples include 0.5 hours or more, 1 hour or more, and 5 hours or less, or 3 hours or less. Preferred holding times are less than 2 hours, 1.5 hours or less, or 1.0 hour or less. The longer the holding time in sintering, the more easily the pores formed by the burning away of graphite powder tend to deform. That is, these pores are cavities surrounded by amorphous silica powder particles, and at the time the graphite powder burns away they are spherical, reflecting the shape of the graphite powder. However, the longer the holding time in sintering, the more easily the amorphous silica powder flows, and the more easily the pores deform from their spherical shape. If the holding time in sintering is less than 2 hours, the pores formed by the burning away of graphite powder become less likely to deform, and the average circularity of the pores in the manufactured quartz glass can be increased. Examples of holding times at the holding temperature include 0.5 hours or more and 5 hours or less, or 1 hour or more and 3 hours or less. Preferred holding times include 0.5 hours or more but less than 2 hours, 0.5 hours or more but 1.5 hours or less, or 0.5 hours or more but 1.0 hour or less.

[0073] In the sintering process, particularly preferred sintering conditions include the following: Sintering method: atmospheric pressure sintering Sintering atmosphere: atmospheric atmosphere Holding temperature: 1250°C or higher and 1350°C or lower Heating rate: Early heating rate 100°C / hour or higher and 800°C / hour or lower Late heating rate 10°C / hour or higher and 80°C / hour or lower

[0074] The manufacturing method of this embodiment may include a heat treatment step before the sintering step in which the molded body is heated to a temperature above the temperature at which the graphite powder contained in the molded body is burned off. By burning off the graphite powder in the heat treatment step before the sintering step, the parts of the molded body where the graphite powder was present become pores with a shape closer to a sphere. In particular, when the size of the molded body is large, it is preferable to thoroughly burn off the graphite powder in the heat treatment step before the sintering step in order to suppress the sintering process from proceeding with graphite powder remaining inside the molded body.

[0075] To efficiently remove burnt graphite powder from the molded body, heating during the heat treatment process is preferably carried out under atmospheric pressure. The atmosphere during heating can be an oxidizing atmosphere, but an atmospheric atmosphere is preferred.

[0076] The heating temperature in the heat treatment process should be above the temperature at which the graphite powder inside the molded body burns off, depending on the shape and mass of the molded body, and is preferably 300°C or higher, 350°C or higher, or 400°C or higher. Furthermore, the upper limit of the heating temperature should preferably be below the temperature at which the molded body sintersects, so that the burnt graphite powder is efficiently removed from the molded body, and is preferably 1100°C or lower, 1000°C or lower, or 800°C or lower. Examples of heating temperatures include 300°C to 1100°C, 350°C to 1000°C, or 400°C to 800°C.

[0077] The heating time in the heat treatment process should be sufficient to remove the graphite powder from the molded body, and may be 0.5 hours or more, or 1 hour or more, and 500 hours or less, or 300 hours or less, with examples including 0.5 hours or more and 500 hours or 1 hour or more and 300 hours or less.

[0078] The present disclosure will be explained below with reference to examples. However, the present disclosure is not limited to these examples.

[0079] (Average Particle Size) The average particle size of each powder used as a raw material was determined using a laser diffraction scattering particle size distribution analyzer (SALD-2300, Shimadzu Corporation) and set to the particle size (D50) corresponding to the 50% frequency in the volume particle size distribution obtained under the following conditions. The refractive index of the setting conditions was automatically set by the above-mentioned device according to the particles to be measured. Specifically, for graphite powder in Example 1 and Comparative Example 3 (product name: Nikabeads (standard ICB-0120)), the refractive index was set to 3.00-0.00i, and for graphite powder in Example 2 and Comparative Examples 1 and 2 (product name: Nikabeads (standard ICB-0520, ICB-1020, ICB-2020)), the refractive index was set to 1.80-1.00i. In addition, for silica powder in each example and comparative example (product name: Sunseal (standard SS-10), product name: Rheoroseal (standard QS-09)), the refractive index was set to 1.45-0.00i. Measurement method: Dry method Pump speed: 5.0 Distribution function: No conversion Built-in ultrasonic irradiation time: 10 seconds Smoothing: 3 Data shift: 0

[0080] For each powder whose D50 was measured, the BET specific surface area S was determined for powders with a D50 of less than 0.500 μm. The BET specific surface area S was calculated by obtaining an adsorption isotherm using a BET specific surface area measuring device (device name: BELSORP-mini II, manufactured by Microtrac-Bell Co., Ltd.), creating a BET plot using the obtained adsorption isotherm, and calculating the BET specific surface area S from the slope and intercept of the fitted line according to ISO 9277. The calculated BET specific surface area S was substituted into the above formula (A) to determine the converted particle size. For each powder whose D50 was measured, the calculated converted particle size was used as the average particle size for powders with a D50 of less than 0.500 μm. The adsorption isotherm was obtained using nitrogen as the adsorption gas and measured at a temperature of 77 K. In addition, the measurement sample used for adsorption of nitrogen gas was a powder that had been degassed under vacuum at 350 °C for 2 hours.

[0081] (Average Circularity of Graphite Powder) The average circularity of graphite powder was measured as follows. Graphite powder was sprinkled onto carbon tape cut to an appropriate length, and excess powder was removed with a blower to prepare the sample for measurement. A general scanning electron microscope (device name: JSM-IT500LA, manufactured by JEOL Ltd.) was used to obtain secondary electron images of this sample under the following conditions. The average circularity was determined by analyzing these secondary electron images. Magnification: 500x to 5000x Acceleration voltage: 10kV Std. PC: 30

[0082] The secondary electron image analysis was performed using image analysis software (software name: Image J, version: 1.53t) to obtain an image processing diagram. From the image processing diagram, the area of ​​each white region (area of ​​each particle of graphite powder) and the perimeter of the white region (perimeter of each particle of graphite powder) were measured, and the average circularity of each particle obtained using the following formula (4-2) was calculated to determine the average circularity of the graphite powder. The secondary electron image analysis was performed for 39 particles of graphite powder in Example 1, 43 particles of graphite powder in Example 2, 63 particles of graphite powder in Comparative Example 1, and 60 particles of graphite powder in Comparative Example 2. The image processing diagrams were obtained in the same manner as the image processing diagrams used to determine the average circularity of pores, and the white regions in the image processing diagrams were considered to represent each particle of graphite powder. C ｃ = 4πS ｃ / P ｃ ２ (4-2)

[0083] In equation (4) above, C ｃ S is the circularity of each particle of graphite powder. ｃ The area of ​​each particle in the graphite powder [μm²] ２ ], P ｃ is the circumference [μm] of each particle of graphite powder.

[0084] (Porrosion) The porosity of the quartz glass was calculated using an analytical balance (instrument name: XSR205DUV, manufactured by Mettler-Toledo) based on the apparent density obtained by the Archimedes method (JIS R 1634-1998), using the following formula (2): Φ = (2.2 - ρ) / 2.2 × 100 (2)

[0085] In equation (2) above, Φ is the porosity [%] and ρ is the apparent density (g / cm³). ３ Prior to measuring the apparent density ρ, the sample was pretreated by boiling as described in JIS R 1634-1998. The obtained porosity was rounded to two decimal places.

[0086] (Average pore diameter and average pore circularity) In this embodiment, the average pore diameter was determined by analyzing the secondary electron image of the cross-section of the quartz glass obtained by electron microscopy observation using a scanning electron microscope (device name: JSM-IT500LA, manufactured by JEOL Ltd.) under the following conditions: Magnification: 500x to 5000x Acceleration voltage: 10kV Std. PC: 30

[0087] For electron microscope observation, the observation surface was the cross-section of the interior of quartz glass obtained by cutting the glass, after removing defects (such as linear marks) caused by cutting and rough polishing by mirror polishing with 1 μm diamond abrasive grains.

[0088] The secondary electron images were analyzed using image analysis software (software name: Image J, version: 1.53t) to obtain an image processing diagram, and then stomata were detected and the area of ​​each stomata was calculated based on the image processing diagram.

[0089] For the specific analysis of the secondary electron image, we first performed a binarization process on the secondary electron image. The binarization process involved background noise reduction (for example, using filters in Image J), ​​selecting Otsu as the binarization method, setting the lower limit of pixel values ​​to 135 ± 20 (i.e., 115 to 155) and the upper limit to 255, and performing binarization to obtain a binarized image in which pixel values ​​within this range were determined to be white (porous region). Next, the binarized image was subjected to concatenation (Close in Image J), ​​hole filling (Fill Holes in Image J), ​​and noise reduction (Open in Image J). Furthermore, three rounds of shrinkage (Erode in Image J) were performed, followed by noise reduction (Open in Image J) and smoothing (Smooth in Image J). Finally, the threshold was set to Auto, and the Otsu method was used to perform binarization again, resulting in the image processing diagram. In the obtained image processing diagram, the black areas were considered as quartz glass, and the white areas as pore areas. In this case, the white areas were continuous portions with an area of ​​0.01 μm². ２ Regions below a certain value were considered measurement noise and determined not to be pores. Secondary electron image analysis was performed for 104 pores in Example 1, 126 pores in Example 2, 105 pores in Example 3, 108 pores in Example 4, 117 pores in Comparative Example 1, 111 pores in Comparative Example 2, and 103 pores in Comparative Example 3.

[0090] The area of ​​each white region (the area of ​​each pore) was determined from the image processing diagram. The diameter of each pore, approximated as a circle using the following equation (3), was determined as the pore diameter. A pore diameter-area frequency distribution was created, and the pore diameter corresponding to 50% of the frequency in this distribution was taken as the average pore diameter. D = (4S / π) ０．５ (3)

[0091] In equation (3) above, D is the diameter of each pore [μm], and S is the area of ​​each pore [μm]. ２ ]

[0092] Furthermore, the area of ​​each white region (area of ​​each pore) and the perimeter of each white region (perimeter of each pore) were determined from the image processing diagram described above, and the average value of the circularity of each pore, calculated using the following formula (4-1), was taken as the average circularity of the pores. C ｐ = 4πS ｐ / P ｐ ２ (4-1)

[0093] In equation (4) above, C is the circularity of each pore, and S is the circularity of each pore. ｐ The area of ​​each pore [μm²] ２ ], P ｐ is the circumference of each stoma [μm].

[0094] (Near-infrared reflectance and near-infrared linear transmittance) Using a UV-Vis spectrophotometer (device name: V-770, manufactured by JASCO Corporation), a sample with a thickness of 3.0 ± 0.05 mm was measured under the following conditions. The reflectance was defined as the near-infrared reflectance and the linear transmittance as the near-infrared linear transmittance. The direction of light transmission was defined as the thickness direction of the sample. Measurement wavelength: 2000 nm Data acquisition interval: 1 nm UV-Vis bandwidth: 5.0 nm Near-infrared bandwidth: 20.0 nm Response: 0.06 seconds Light source: Deuterium lamp, halogen lamp Light source switching wavelength: 340.0 nm Diffraction grating switching wavelength: 850.0 nm Scanning mode: Continuous Scanning speed: 1000 nm / min

[0095] For near-infrared reflectance, a quartz glass sample was used, with the measurement surface and the opposing surface mirror-polished using 1 μm diamond abrasive grains.

[0096] (Apparent Density) For quartz glass, the apparent density was determined using the Archimedes method (JIS R 1634-1998) with an analytical balance (instrument name: XSR205DUV, manufactured by Mettler-Toledo). Prior to the measurement of apparent density, the sample was pretreated by the boiling method described in JIS R 1634-1998. The determined density was rounded to the third decimal place.

[0097] (Water Absorption Rate) A quartz glass sample was dried at 110°C for 24 hours, then allowed to cool to room temperature (22°C), and the mass W1 of the sample was measured. Next, the sample was boiled in water for 1 hour, then allowed to cool to room temperature, and after removing the sample from the water, the surface was quickly wiped with a damp gauze to remove water droplets, and the mass W2 of the sample was measured. The water absorption rate was calculated from W1 and W2 using the following formula (1): Water absorption rate (mass%) = ((W2 - W1) / W1) × 100 (1)

[0098] Example 1 As raw material silica powders, first silica powder (product name: Sunseal (standard SS-10), average particle size 1 μm, manufactured by Tokuyama Corporation) and second silica powder (product name: Rheoroseal (standard QS-09), average particle size 0.022 μm, manufactured by Tokuyama Corporation) were selected. As pore-forming agent powder, spheroidal graphite powder (product name: Nikabeads (standard ICB-0120), average particle size 1.327 μm, average circularity 0.90, manufactured by Nippon Carbon Co., Ltd.) was selected. Each silica powder was weighed so that the first silica powder accounted for 60% by mass and the second silica powder for 40%, totaling approximately 100 g. 5.26 g (5.26 parts by mass) of pore-forming agent powder was added to 100 g of these mixed powders, and the mixture was placed in a polyethylene container together with 2 kg of resin balls. The container was placed on the roller section of a ball mill rotating stand (Teraoka Co., Ltd., BKFD-203), and the powders were mixed and obtained a raw material powder by rotating it at a speed of 72 rpm for 2 hours while being struck with a hammer every 30 minutes.

[0099] After filling 4.5 g of the obtained raw material powder into a 30 mm diameter mold, a pressure of 126 kgf / cm² was applied. ２A compacted powder body was obtained by applying pressure for 30 seconds to form it. After vacuum-packing the compacted powder body, a CIP-molded body was obtained by applying a pressure of 100 MPa for 3 minutes in a CIP device. The diameter of the CIP-molded body was approximately 25 mm and the thickness was approximately 6 mm. The CIP-molded body was placed in an alumina container and treated under the following conditions: in an air atmosphere, a heating rate of 500°C / hour from room temperature to 1000°C, a heating rate of 60°C / hour from 1000°C to 1330°C, and a holding time of 1 hour at 1330°C. After this, it was allowed to cool naturally overnight to obtain the quartz glass of this embodiment.

[0100] Table 1 shows the porosity, average pore size, average circularity, near-infrared reflectance, near-infrared linear transmittance, apparent density, and water absorption rate of the quartz glass in this embodiment.

[0101] Example 2 The quartz glass of this example was obtained in the same manner as in Example 1, except that the pore-forming agent powder was spheroidal graphite powder (product name: Nikabeads (standard ICB-0520), average particle size 5.899 μm, average circularity 0.90, manufactured by Nippon Carbon Co., Ltd.).

[0102] Table 1 shows the porosity, average pore size, average circularity, near-infrared reflectance, near-infrared linear transmittance, apparent density, and water absorption rate of the quartz glass in this embodiment.

[0103] Example 3 A quartz glass of this example was obtained in the same manner as in Example 1, except that the amount of pore-forming agent powder added was 3 parts by mass per 100 parts by mass of raw silica powder.

[0104] Table 1 shows the porosity, average pore size, average circularity, near-infrared reflectance, near-infrared linear transmittance, apparent density, and water absorption rate of the quartz glass in this embodiment.

[0105] Example 4 A quartz glass of this example was obtained in the same manner as in Example 1, except that the amount of pore-forming agent powder added to 100 parts by mass of raw silica powder was 10 parts by mass.

[0106] Table 1 shows the porosity, average pore size, average circularity, near-infrared reflectance, near-infrared linear transmittance, apparent density, and water absorption rate of the quartz glass in this embodiment.

[0107] Comparative Example 1: The quartz glass of this example was obtained in the same manner as in Example 1, except that the pore-forming agent powder was spheroidal graphite powder (product name: Nikabeads (standard ICB-1020), average particle size 13.205 μm, average circularity 0.88, manufactured by Nippon Carbon Co., Ltd.).

[0108] Table 1 shows the porosity, average pore size, average circularity, near-infrared reflectance, near-infrared linear transmittance, apparent density, and water absorption rate of the quartz glass used in this comparative example.

[0109] Comparative Example 2: The quartz glass of this example was obtained in the same manner as in Example 1, except that the pore-forming agent powder was spheroidal graphite powder (product name: Nikabeads (standard ICB-2020), average particle size 19.486 μm, average circularity 0.85, manufactured by Nippon Carbon Co., Ltd.).

[0110] Table 1 shows the porosity, average pore size, average circularity, near-infrared reflectance, near-infrared linear transmittance, apparent density, and water absorption rate of the quartz glass used in this comparative example.

[0111] Comparative Example 3: The quartz glass of this example was obtained in the same manner as in Example 1, except that the amount of pore-forming agent powder added to the raw silica powder was 1% by mass.

[0112] Table 1 shows the porosity, average pore size, average circularity, near-infrared reflectance, near-infrared linear transmittance, apparent density, and water absorption rate of the quartz glass used in this comparative example.

[0113]

[0114] As can be seen from Table 1 above, it can be confirmed that the quartz glass in each example has an average circularity of 0.7 or higher, which suppresses stress concentration at the edges of pores that occur in irregularly shaped pores, and is considered to have excellent mechanical strength.

[0115] Furthermore, the quartz glass in each example had a smaller average pore size than the quartz glass in Comparative Examples 1 and 2. In addition, the porosity of the quartz glass in each example was higher than that of Comparative Example 3. As a result, it was confirmed that all examples exhibited high near-infrared reflectance and higher heat shielding performance.

[0116] The entire contents of the specification, claims, and abstract of Japanese Patent Application No. 2025-54112, filed on March 27, 2025, are incorporated herein by reference as part of the disclosure of the specification.

Claims

1. Quartz glass having a porosity of 0.5% or more, an average pore diameter of 8.0 μm or less, and an average pore circularity of 0.70 or more.

2. Apparent density is 2.189 g / cm³ ３ The quartz glass according to claim 1, which is as follows:

3. The quartz glass according to claim 1 or 2, wherein the near-infrared reflectance at a wavelength of 2000 nm is 70.0% or more when the sample thickness is 3 ± 0.05 mm.

4. The quartz glass according to any one of claims 1 to 3, wherein the near-infrared linear transmittance at a wavelength of 2000 nm is 0.12% or less when the sample thickness is 3 ± 0.05 mm.

5. A quartz glass according to any one of claims 1 to 4, wherein the water absorption rate is 0.1% by mass or less.

6. A method for producing quartz glass according to any one of claims 1 to 5, comprising: a preparation step of mixing 2 parts by mass or more of graphite powder with 100 parts by mass of amorphous silica powder to obtain a raw material powder; a molding step of molding the raw material powder to obtain a molded body; and a sintering step of sintering the molded body, wherein the amorphous silica powder comprises a first silica powder having an average particle diameter of 0.60 μm or more and 2.50 μm or less, and a second silica powder having an average particle diameter of 0.001 μm or more and 0.060 μm or less, and the average particle diameter of the graphite powder is 0.50 μm or more and 10.00 μm or less.

7. The method for producing quartz glass according to claim 6, further comprising a heat treatment step after the molding step and before the sintering step, in which the molded body is heated in an atmospheric atmosphere to a temperature above which the graphite powder contained in the molded body burns off.

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