Opaque quartz glass and production method therefor

Abstract

The purpose of the present invention is to provide an opaque quartz glass containing voids of indefinite shapes, which has sufficient heat-ray-reflecting properties, heat-ray-shielding properties, and light-shielding properties, and to provide a method for producing the opaque quartz glass. This opaque quartz glass contains voids of indefinite shapes dispersed in the glass and gives a void diameter distribution in which D50 is 4-30 μm, the proportion of voids having a diameter of 5 μm or less is 1-50%, and the proportion of voids having a diameter of 15 μm or less is 30-90%. In a microscopic image of a section of the opaque quartz glass, the areal proportion of the voids is 5% or higher. This opaque quartz glass is obtained by mixing two or more kinds of specific silica powders differing in particle diameter distribution, in a given proportion, compacting this powder mixture, and sintering the compact.

Description

Opaque quartz glass and its manufacturing method

[0001] The present invention relates to opaque quartz glass that can be suitably used for, for example, members for semiconductor manufacturing equipment and parts for optical instruments, and to a method for producing the same.

[0002] Due to its excellent light transmittance, heat resistance, and chemical resistance, quartz glass is used in a variety of applications, including lighting equipment, optical equipment components, semiconductor industrial components, and laboratory equipment. Opaque quartz glass, which contains pores, has been used for flanges and furnace tubes in semiconductor heat treatment equipment due to its excellent heat ray reflectivity and heat ray blocking properties. Furthermore, due to its excellent light blocking properties, opaque quartz glass is also used for optical equipment components such as the reflector substrate for projector light source lamps.

[0003] Opaque quartz glass is whitened by the inclusion of pores inside, giving it heat reflective, heat insulating, and light blocking properties. Opaque quartz glass can be broadly classified according to whether the pores are spherical or irregular in shape.

[0004] Opaque quartz glass containing spherical pores can be produced, for example, by adding a foaming agent such as silicon nitride to silica powder and melting the mixture (see, for example, Patent Documents 1 and 2). This method involves vaporizing the foaming agent to form pores, which makes it difficult to prevent the pore size from increasing. The pores become too large, resulting in reduced density and mechanical strength. Another problem is that the glass's heat ray reflectivity, heat ray blocking properties, and light blocking properties are likely to be reduced.

[0005] On the other hand, opaque quartz glass containing irregular pores can be produced, for example, by sintering amorphous silica powder at or below its melting point without using a foaming agent (see, for example, Patent Documents 3 to 5). When the pores have an irregular shape, the area of ​​the interface between the pores and the glass increases, which has the advantage of making it easier to reflect and scatter light (general electromagnetic waves including visible light, infrared light, and ultraviolet light; the same applies hereinafter). For example, Patent Document 3 describes opaque quartz glass with a wall thickness of 1 mm that has a direct spectral transmittance that is substantially constant and less than 10% in the wavelength range from λ = 190 nm to λ = 2650 nm.

[0006] However, in the manufacturing methods described in Patent Documents 3 to 5, in order to form a molded body without generating cracks, it is necessary to form a slurry, and then solidify and dry the slurry in a mold, which poses a problem in that it takes a long time to solidify and dry the slurry.

[0007] To improve this, methods for producing opaque quartz glass have been proposed, in which a silica slurry is spray-dried and granulated, pressure-molded, and then fired (see, for example, Patent Documents 6 to 8). For example, Patent Document 6 describes opaque quartz glass having an infrared linear transmittance of 0.7% (wavelength: 2 μm, sample thickness: 1 mm). Patent Document 8 describes opaque quartz glass in which the shape of the pores in the quartz glass is controlled to be nearly spherical and the average pore size is controlled to be 1 μm or less, and which has a whiteness of 90% or more at a thickness of 10 mm and a reflectance of 85% or more at a thickness of 3 mm for light with a wavelength of 0.2 to 3 μm.

[0008] Patent Document 1: JP 4-065328 A Patent Document 2: JP 5-254882 A Patent Document 3: JP 7-267724 A (US 5497004A) Patent Document 4: JP 8-143329 A (US 5585173A) Patent Document 5: JP 9-506324 A (US 5736206A) Patent Document 6: JP 2014-088286 A Patent Document 7: JP 2018-070397 A Patent Document 8: Japanese Patent No. 6751822 A All descriptions in Patent Documents 1 to 8 are specifically incorporated herein by reference.

[0009] However, the opaque quartz glass described in Patent Documents 3 to 7 contains irregular pores, but does not have sufficient heat ray reflectivity, heat ray blocking properties, and light blocking properties. For example, Patent Documents 3 and 6 state that the linear transmittance of opaque quartz glass is low, as mentioned above, but much of the light is scattered by interaction with the pores and transmitted in directions other than the linear direction (the direction of travel of the incident light).

[0010] Furthermore, the opaque quartz glass of Patent Document 8 is manufactured by controlling the shape of the pores to be nearly spherical in a manufacturing method that usually results in irregular pore shapes. Because controlling the pore shape in this way is complicated, it is preferable to obtain sufficient heat ray reflectivity, heat ray blocking properties, and light blocking properties while leaving the pores in an irregular shape.

[0011] As described above, it is difficult to obtain opaque quartz glass containing irregular pores and having sufficient heat ray reflectivity, heat ray shielding properties, and light blocking properties using conventional methods.

[0012] An object of the present invention is to provide opaque quartz glass containing irregular pores, which has sufficient heat ray reflectivity, heat ray blocking properties, and light blocking properties. In another aspect, an object of the present invention is to provide a method for producing opaque quartz glass that enables the production of the opaque quartz glass.

[0013] As a result of intensive research into solving the above problems, the present inventors discovered that opaque quartz glass containing irregular pores and having sufficient heat ray reflectivity, heat ray blocking properties, and light blocking properties can be obtained by mixing, in a predetermined ratio, multiple types of specific silica powder and SiO powder having different particle size distributions, and sintering a pressure-molded product of this mixed powder, thereby completing the present invention.

[0014] The present invention is as follows: [1] An opaque quartz glass having irregular pores dispersed in a glass body, wherein the pore size distribution is D ５０ [2] Opaque quartz glass according to [1], in which the circularity of the pores is 0.62 or less. [3] D ５０ When the area ratio is 15% or more, ５０[4] The opaque quartz glass according to [1] or [2], wherein the area ratio is less than 15% when the area ratio is greater than 10 μm. ＊ a ＊ b ＊ Display system brightness L ＊ [5] The opaque quartz glass according to any one of [1] to [3], wherein L ＊ a ＊ b ＊ Display system saturation a ＊ The absolute value of is 2 or less and b ＊ [6] The opaque quartz glass according to any one of [1] to [5], wherein the absolute value of is 4 or less. [7] The opaque quartz glass according to any one of [1] to [5], wherein the content of each of metal impurities is 1 ppm or less. [8] The opaque quartz glass according to any one of [1] to [5], wherein the density is 2.10 to 2.18 g / cm ３ [8] The opaque quartz glass according to any one of [1] to [6], wherein the density distribution in the opaque quartz glass is 2% or less, and the lightness L ＊ [9] The opaque quartz glass according to any one of [1] to [7], wherein the distribution of particle size is 2% or less. ５０ A method for producing opaque quartz glass according to any one of [1] to [8], comprising: pressurizing and molding a mixed powder of silica powder, which is silica particles having a BET diameter of 5 to 100 μm, and fine silica particles, which are silica particles having a BET diameter of 10 to 50 nm, in which the fine silica content is 20 to 50 mass% relative to the total amount of silica material containing the silica powder and the fine silica, and sintering the pressurized molded product.

[10] (a) The silica powder has a particle size distribution of D ５０ (b) the silica powder is a synthetic silica powder having a particle size distribution D of 30 to 100 μm; ５０ Synthetic silica powder with a particle size distribution of 30 to 100 μm and D ５０ and (c) the silica powder has a particle size distribution D of 5 to 50 μm. ５０

[11] A method for producing opaque quartz glass according to [9], wherein the content of the spherical silica powder is 1 to 20 mass% relative to the total amount of silica material in the case of (b) above.

[12] A method for producing opaque quartz glass according to

[10] , wherein the content of the spherical silica powder is 1 to 20 mass% relative to the total amount of silica material in the case of (b) above.

[13] A method for producing opaque quartz glass according to

[11] , wherein the content of the spherical silica powder is 1 to 20 mass% relative to the total amount of silica material in the case of (b) above.

[14] A method for producing opaque quartz glass according to

[14] , wherein the content of the spherical silica powder is 1 to 20 mass% relative to the total amount of silica material in the case of (b) above.

[15] A method for producing opaque quartz glass according to

[15] , wherein the content of the spherical silica powder is 1 to 20 mass% relative to the total amount of silica material in the case of (b) above.

[16] A method for producing opaque quartz glass according to

[16] , wherein the content of the spherical silica powder is 1 to 20 mass% relative to the total amount of silica material in the case of (b) above.

[17] A method for producing opaque quartz glass according to

[17] , wherein the content of the spherical silica powder is 1 to 20 mass% relative to the total amount of silica material in the case of (b) above.

[18] A method for producing opaque quartz glass according to

[18] , wherein the content of the spherical silica powder is 1 to 20 mass% relative to the total amount of silica material in the case of (b) above. １０ D ５０ More than 1 / 3 of ９０ D ５０ and the particle size distribution of the spherical silica powder is less than three times the D １０ D ５０ 1 / 5 or more, D ９０ D ５０

[13] The method for producing opaque quartz glass according to

[10] or

[11] , wherein the fine silica particles have (i) a tap bulk density of 0.03 to 0.10 g / cm or less. ３ (ii) a BET specific surface area of ​​50 to 100 m ２ / g, (iii) the OH group concentration is 0.5 to 1.0 mass%, and (iv) the content of metal impurities other than Si is 1 ppm or less.

[14] The method for producing opaque quartz glass according to any one of [9] to

[12] , wherein the mixed powder satisfies at least one of the following four requirements: (i) the D ５０ The method for producing opaque quartz glass according to any one of [9] to

[13] , further comprising SiO powder which is silicon monoxide particles having a size of 0.5 to 2 μm, and the content of the SiO powder is 0.1 to 1 mass % as an external addition relative to the total amount of silica material.

[15] １０ is 0.1 μm or more, D ９０

[16] The method for producing opaque quartz glass according to any one of [9] to

[15] , wherein the tapped bulk density of the mixed powder for pressure molding is 5 to 20 times the tapped bulk density of the particulate silica.

[0015] According to the present invention, it is possible to provide opaque quartz glass containing irregular pores, which has sufficient heat ray reflectivity, heat ray blocking properties, and light blocking properties. In another aspect, the present invention also provides a method for producing opaque quartz glass, which makes it possible to produce the opaque quartz glass.

[0016] Fig. 1 is an optical microscope photograph of a cross section of quartz glass in Example 3. Fig. 2 is an optical microscope photograph of a cross section of quartz glass in Example 4. Fig. 3 is an optical microscope photograph of a cross section of quartz glass in Example 5. Fig. 4 is an optical microscope photograph of a cross section of quartz glass in Example 6. Fig. 5 is an optical microscope photograph of a cross section of quartz glass in Example 7. Fig. 6 is an optical microscope photograph of a cross section of quartz glass in Example 9. Fig. 7 is an optical microscope photograph of a cross section of quartz glass in Comparative Example 3.

[0017] <Opaque quartz glass> The opaque quartz glass of the present invention is an opaque quartz glass having irregular pores dispersed in the glass body, and the pore size distribution is D ５０ The opaque quartz glass has a pore size of 4 to 30 μm, a ratio of pores having a pore size of 5 μm or less of 1 to 50%, and a ratio of pores having a pore size of 15 μm or less of 30 to 90%, and the area ratio of the pores in a microscopic image of the cross section is 5% or more.

[0018] The opaque quartz glass of the present invention has dispersed irregular pores. In the present invention and this specification, "irregular pores" refers to pores with a circularity of 0.7 or less. The method for measuring circularity will be described in detail in the Examples section. When a glass body has irregular pores, light reflection and scattering by the pores are more likely to occur compared to when the glass body has spherical pores. As a result, compared to opaque quartz glass containing spherical pores, it is possible to reduce the amount of pores required to achieve the same level of heat ray reflectivity, heat ray blocking, and light blocking properties, and the opaque quartz glass of the present invention has the advantage of easily improving density. From the viewpoint of facilitating light reflection and scattering by the pores, the circularity of the pores is preferably 0.65 or less, more preferably 0.63 or less, and even more preferably 0.62 or less. The lower limit of the circularity of the pores is not particularly limited, but can be 0.40, 0.45, 0.50, or 0.52.

[0019] In the pore size distribution of the opaque quartz glass of the present invention, the median diameter (area basis) D ５０ The pore size distribution is 4 to 30 μm, the proportion of pores with a pore size of 5 μm or less is 1 to 50%, and the proportion of pores with a pore size of 15 μm or less is 30 to 90%. When the pore size distribution satisfies the above requirements, light reflection and scattering occur easily over a wide wavelength range. ５０ By ensuring that the pore size distribution is 30 μm or less, the proportion of pores with a pore size of 5 μm or less is 50% or less, or the proportion of pores with a pore size of 15 μm or less is 90% or less, it is possible to ensure sufficient density of the opaque quartz glass and to easily prevent a decrease in strength. The method for measuring the pore size distribution will be described in detail in the Examples section.

[0020] In order to obtain more sufficient heat ray reflectivity, heat ray blocking and light blocking properties, D ５０ The upper limit of D is preferably 27 μm or less or 25 μm or less, and may be 15 μm or less or 10 μm or less. ５０ The lower limit of D is preferably 4.5 μm or more or 5 μm or more. ５０ can be, for example, 4 to 27 μm, 4 to 10 μm, 4.5 to 9.5 μm, or 5 to 9 μm.

[0021] From the viewpoint of obtaining more sufficient heat ray reflectivity, heat ray blocking properties, and light blocking properties, the upper limit of the proportion of pores having a pore size of 5 μm or less is preferably 47% or less or 45% or less, more preferably 43% or less, and particularly preferably 40% or less. The lower limit of the proportion of pores having a pore size of 5 μm or less is preferably 3% or more, more preferably 4% or more, particularly preferably 5% or more, and may be 10% or more, 15% or more, 20% or more, or 25% or more. The proportion of pores having a pore size of 5 μm or less can be, for example, 3 to 50%, 10 to 50%, 15 to 50%, 20 to 47%, or 25 to 45%.

[0022] From the viewpoint of obtaining more sufficient heat ray reflectivity, heat ray blocking properties, and light blocking properties, the upper limit of the proportion of pores having a pore diameter of 15 μm or less is preferably 88% or less or 87% or less, more preferably 86% or less, and particularly preferably 85% or less. The lower limit of the proportion of pores having a pore diameter of 15 μm or less is preferably 34% or more, more preferably 36% or more, particularly preferably 38% or more, and may be 40% or more, 45% or more, 50% or more, 55% or more, or 60% or more. The proportion of pores having a pore diameter of 15 μm or less can be, for example, 34 to 90%, 36 to 90%, 38 to 90%, 60 to 90%, 65 to 87%, or 70 to 86%.

[0023] In the opaque quartz glass of the present invention, the pore area ratio in a microscopic image of a cross section is 5% or more. An area ratio of 5% or more facilitates light reflection and scattering per unit space, achieving sufficient heat ray reflectivity, heat ray blocking, and light blocking properties. From the viewpoint of achieving more sufficient heat ray reflectivity, heat ray blocking, and light blocking properties, the pore area ratio is preferably 7% or more, and can be 9% or more, 10% or more, 15% or more, 18% or more, 19% or more, or 20% or more. From the viewpoint of ensuring the strength of the opaque quartz glass, the pore area ratio is preferably 45% or less, more preferably 40% or less, and even more preferably 37% or less. The method for measuring the pore area ratio will be described in detail in the Examples section.

[0024] In particular, D in the pore size distribution ５０When the area ratio of the pores is 10 μm or less, the area ratio of the pores is preferably 15% or more. ５０ When D in the pore size distribution is 10 μm or less, there are many relatively small pores, the surface area of ​​each pore is small, and the circularity of the pores is likely to increase (i.e., the shape of the pores approaches a circle), which increases the area ratio of the pores and increases the amount of interface between the pores and the glass. ５０ When the area ratio of the pores is more than 10 μm, the area ratio of the pores is preferably less than 15%. ５０ When the area ratio of the pores is greater than 10 μm, the opaque quartz glass tends to have a low density due to the large number of pores, and therefore the pore volume is reduced to ensure the strength of the opaque quartz glass. Since the circularity of the large pores tends to decrease, sufficient heat ray reflectivity, heat ray blocking properties, and light blocking properties can be ensured even if the pore area ratio is small.

[0025] The opaque quartz glass of the present invention has the above-mentioned constitution and therefore has sufficient heat ray reflectivity, heat ray blocking properties, and light blocking properties. In this specification, "having sufficient heat ray reflectivity and heat ray blocking properties" means that the infrared reflectance is 75% or more. Also, in this specification, "having sufficient light blocking properties" means that the SCE reflectance at wavelengths of 350 nm to 750 nm is 75% or more and that the L ＊ a ＊ b ＊ Display system brightness L ＊ is 85 or more.

[0026] That is, in the opaque quartz glass of the present invention, the infrared reflectance is 75% or more. By having a reflectance of 75% or more for infrared rays, which are heat rays, sufficient heat ray reflectivity and heat ray blocking properties can be obtained. From the viewpoint of improving heat ray reflectivity and heat ray blocking properties, it is preferable that the infrared reflectance is high, preferably 80% or more, more preferably 85% or more. The upper limit of the infrared reflectance is not particularly limited, but can be 99%. For example, it is possible to increase the infrared reflectance by adjusting the pore circularity, pore distribution, and pore area ratio within the above-mentioned preferred ranges.

[0027] In the opaque quartz glass of the present invention, the SCE reflectance at wavelengths of 350 nm to 750 nm is 75% or more. The SCE reflectance at wavelengths of 350 nm to 750 nm is measured in accordance with JIS Z 8722. From the viewpoint of enhancing light-blocking properties, a high SCE reflectance is preferred, preferably 78% or more, more preferably 80% or more. The upper limit of the SCE reflectance is not particularly limited, but can be 99%. For example, the SCE reflectance can be increased by adjusting the pore circularity, pore distribution, and pore area ratio within the aforementioned preferred ranges.

[0028] In the opaque quartz glass of the present invention, L ＊ a ＊ b ＊ Display system brightness L ＊ is 85 or more. ＊ When the lightness L is 85 or more, sufficient light blocking properties can be obtained, and color unevenness is less likely to occur, allowing the film to exhibit sufficient white color. ＊ is preferably 87.5 or more, and more preferably 90 or more. ＊ The upper limit of the lightness L is not particularly limited, but may be 99. For example, by adjusting the pore circularity, pore distribution, and pore area ratio within the above-mentioned preferred ranges, the lightness L ＊ It is possible to increase

[0029] In addition, in the opaque quartz glass of the present invention, L ＊ a ＊ b ＊ Display system saturation a ＊ The absolute value of is preferably 2 or less, and b ＊ The absolute value of saturation a is preferably 4 or less. ＊ and b ＊ When the chroma a is in the above range, the SCE reflectance is further improved, and the color tone of the opaque quartz glass of the present invention becomes whiter. ＊ The absolute value of saturation b is preferably 1 or less, and more preferably 0.5 or less. ＊ The absolute value of saturation a is preferably 3 or less, more preferably 2 or less, and particularly preferably 1 or less.＊ and b ＊ For example, by adjusting the pore circularity, pore distribution, and pore area ratio within the above-mentioned preferred ranges, the saturation a ＊ and b ＊ It is possible to lower

[0030] The content of each metal impurity in the opaque quartz glass of the present invention is preferably 1 ppm or less. By having the content of each metal impurity other than Si element be 1 ppm or less, it becomes easier to avoid the occurrence of process contamination in fields such as semiconductor manufacturing. Furthermore, in fields such as optical analysis, it becomes easier to avoid a decrease in measurement accuracy due to fluorescence generation, etc. The content of metal impurities can be analyzed, for example, by a method such as atomic absorption analysis.

[0031] The density of the opaque quartz glass of the present invention is 2.10 to 2.18 g / cm ３ It is preferable that the density is 2.10 g / cm ３ By setting the density to 2.18 g / cm or more, the strength of the opaque quartz glass is further improved. ３ By ensuring that the density is 2.14 to 2.17 g / cm or less, it becomes easier to ensure a sufficient amount of pores, and opaque quartz glass having more sufficient heat ray reflectivity, heat ray blocking properties, and light blocking properties can be obtained. ３ It is more preferable that:

[0032] The density distribution of the opaque quartz glass of the present invention is preferably 2% or less. By having a density distribution of 2% or less, the infrared reflectance, SCE reflectance and lightness L of the opaque quartz glass can be reduced. ＊ The density distribution is more preferably 1.7% or less, and even more preferably 1.5% or less.

[0033] The lightness L of the opaque quartz glass of the present invention ＊ The distribution is preferably 2% or less. ＊By keeping the distribution at 2% or less, it becomes easier to avoid a decrease in yield in the field of semiconductor manufacturing, etc., and it becomes easier to avoid a decrease in measurement accuracy due to the generation of fluorescence, etc. in the field of optical analysis, etc. ＊ The distribution is more preferably 1.7% or less, and even more preferably 1.5% or less.

[0034] As described above, the opaque quartz glass of the present invention has an infrared reflectance of 75% or more, an SCE reflectance of 75% or more at wavelengths of 350 nm to 750 nm, and an L ＊ a ＊ b ＊ Display system brightness L ＊ When the refractive index is 85 or more, sufficient heat ray reflectivity, heat ray blocking property and light blocking property are obtained.

[0035] Furthermore, the opaque quartz glass of the present invention has the advantage that its density can be easily improved compared to opaque quartz glass containing spherical pores. Therefore, the opaque quartz glass of the present invention can be easily made into a large-sized ingot while maintaining color uniformity, for example, 30 cm thick and 80 cm in diameter. Opaque quartz glass ingots can be processed using processing machines such as band saws, wire saws, and core drills that are used to manufacture quartz components to obtain opaque quartz glass products.

[0036] The opaque quartz glass of the present invention has sufficient color uniformity without color irregularities, exhibits a sufficient white color, and also has the effect of being able to be bonded to transparent quartz glass.

[0037] The opaque quartz glass of the present invention is useful in semiconductor applications and optical applications in general, and can be suitably used, for example, as quartz glass cells for optical analysis, light-shielding members and infrared-reflecting members for semiconductor manufacturing equipment and infrared heating equipment.

[0038] <Method for producing opaque quartz glass> The method for producing opaque quartz glass of the present invention is a method for producing opaque quartz glass by reducing the D ５０The method includes pressure-molding a mixed powder of silica powder, which is silica particles having a BET diameter of 5 to 100 μm, and fine silica, which is silica particles having a BET diameter of 10 to 50 nm, in which the fine silica content is 20 to 50 mass% relative to the total amount of silica material containing the silica powder and the fine silica, and sintering the pressure-molded product. As described above, the opaque quartz glass of the present invention is a sintered compact of a mixed powder obtained by mixing, in a predetermined ratio, several types of specific silica powders having different particle size distributions.

[0039] The silica powder has a particle size distribution of D ５０ It is preferable that the silica powder has a particle size of 5 to 100 μm and satisfies the following requirements (a) to (c). This makes it easier to achieve sufficient heat ray reflectivity, heat ray blocking properties, and light blocking properties in the opaque quartz glass. (a) The silica powder has a particle size distribution D ５０ (b) The silica powder is a synthetic silica powder having a particle size distribution D of 30 to 100 μm. ５０ Synthetic silica powder with a particle size distribution of 30 to 100 μm and D ５０ (c) The silica powder contains spherical silica powder having a particle size distribution D of 5 to 50 μm. ５０ It is a spherical silica powder with a particle size of 5 to 50 μm.

[0040] By adding fine silica to the above-mentioned synthetic silica powder or spherical silica powder, or a mixed silica powder of synthetic silica powder and spherical silica powder, the structure of the sintered body can be made more uniform and the heating time to the maximum temperature can be further shortened.

[0041] Synthetic silica powder is a highly pure powdered silica obtained by, for example, hydrolyzing, drying, pulverizing, and calcining chemically purified silicon alkoxide. ５０ In order to more easily achieve sufficient heat ray reflectivity, heat ray blocking properties, and light blocking properties, it is also possible to use commercially available synthetic silica powders if the particle size distribution of the synthetic silica powder is D ５０ From the same viewpoint, D in the particle size distribution of the synthetic silica powder is preferably 50 to 95 μm, and more preferably 60 to 90 μm. １０is D ５０ More than 1 / 3 of ９０ is D ５０ In particular, it is preferable that the silica powder has a particle size distribution D ５０ is 30 to 100 μm, D １０ D ５０ More than 1 / 3 of ９０ D ５０ The synthetic silica powder having a density of not more than three times that of the sintered body is preferable from the viewpoint of making the structure of the sintered body more uniform and shortening the heating time to the maximum temperature during sintering.

[0042] From the viewpoint of more easily achieving sufficient heat ray reflectivity, heat ray blocking properties, and light blocking properties, the content of the synthetic silica powder relative to the total amount of silica materials (synthetic silica powder, spherical silica powder, and fine silica) can be 1 to 80% by mass. The upper limit of this content is preferably 70% by mass or less, and more preferably 65% ​​by mass or less. The lower limit of this content may be 20% by mass or more, or 30% by mass or more. When the silica powder consists solely of synthetic silica powder (requirement a), the content of the synthetic silica powder relative to the total amount of silica materials can be 50 to 75% by mass or 60 to 70% by mass. When the silica powder includes both synthetic silica powder and spherical silica powder (requirement b), the content of the synthetic silica powder relative to the total amount of silica materials can be 20 to 70% by mass, 25 to 65% by mass, or 30 to 60% by mass.

[0043] Spherical silica powder is a high-purity synthetic fused silica obtained by reacting silicon tetrachloride gas or the like in the gas phase. ５０ In order to more easily achieve sufficient heat ray reflectivity, heat ray blocking properties, and light blocking properties, it is also possible to use commercially available spherical silica powders if the particle size distribution of the spherical silica powder is D ５０ From the same viewpoint, D in the particle size distribution of the spherical silica powder is preferably 7 to 40 μm, and more preferably 8 to 35 μm. １０ is D ５０ 1 / 5 or more, D ９０ is D ５０ It is preferable that the thickness is 5 times or less.

[0044] From the viewpoint of more easily achieving sufficient heat ray reflectivity, heat ray blocking properties, and light blocking properties, the content of spherical silica powder relative to the total amount of silica materials can be 1 to 80 mass%. The upper limit of this content is preferably 75 mass% or less, and more preferably 73 mass% or less. The lower limit of this content can be 3 mass% or more, or 4 mass% or more. When the silica powder consists solely of spherical silica powder (requirement c), the content of spherical silica powder relative to the total amount of silica materials can be 50 to 75 mass% or 55 to 73 mass%. When the silica powder contains both synthetic silica powder and spherical silica powder (requirement b), the content of spherical silica powder relative to the total amount of silica materials can be 1 to 50 mass%, 1 to 40 mass%, 1 to 30 mass%, 1 to 25 mass%, 1 to 20 mass%, 3 to 15 mass%, or 4 to 13 mass%. In the opaque quartz glass of the present invention, for example, the silica powder has a particle size distribution D ５０ Synthetic silica powder with a particle size distribution of 30 to 100 μm and D ５０ and spherical silica powder having a size of 5 to 50 μm, and the content of the spherical silica powder is 1 to 20 mass % based on the total amount of silica material.

[0045] In particular, the silica powder has a particle size distribution of D ５０ is 30 to 100 μm, D １０ D ５０ More than 1 / 3 of ９０ D ５０ Synthetic silica powder less than three times the particle size distribution D ５０ is 5 to 50 μm, D １０ D ５０ 1 / 5 or more, D ９０ D ５０and a spherical silica powder having a content of 1 to 50 mass%, 1 to 40 mass%, 1 to 30 mass%, or 1 to 20 mass% of the total amount of silica materials, from the viewpoints of making the structure of the sintered body more uniform and shortening the heating time to the maximum temperature during sintering. When the silica powder is a mixture of synthetic silica powder and spherical silica powder, it is preferable that the silica powder has two peaks in the particle size range of 5 to 100 μm in its particle size distribution, with the peak particle size ratio (peak particle size derived from synthetic silica powder / peak particle size derived from spherical silica powder) being 2 to 10 and the frequency ratio (peak frequency derived from synthetic silica powder / peak frequency derived from spherical silica powder) being 0.1 to 0.4.

[0046] The fine silica particles include, for example, fumed silica obtained by burning silicon tetrachloride gas or the like in the gas phase, and colloidal silica obtained by a precipitation method. Commercially available fine silica particles can be used as long as they have a BET diameter of 10 to 50 nm. From the viewpoint of more easily realizing sufficient heat ray reflectivity, heat ray blocking properties, and light blocking properties, the BET diameter of the fine silica particles is preferably 15 to 45 nm, and more preferably 20 to 40 nm. The BET diameter is determined by the specific surface area S (m ) measured by the BET method. ２ / g) and the true density ρ (g / cm ３ The particle diameter is calculated by the formula BET diameter (nm) = 6000 / (S × ρ) based on the silica particles (true density 2.2 g / cm ３ The BET diameter (nm) of the crystalline silicon nanoparticles is obtained by 2727 / S.

[0047] From the viewpoint of more easily realizing sufficient heat ray reflectivity, heat ray blocking properties, and light blocking properties, it is preferable to use particulate silica that satisfies at least one of the following four requirements (i) to (iv): (i) a tapped bulk density of 0.03 to 0.10 g / cm ３ (ii) BET specific surface area is 50 to 100 m ２ (iii) The OH group concentration is 0.5 to 1.0 mass %. (iv) The content of metal impurities other than Si is 1 ppm or less.

[0048] Furthermore, the particulate silica preferably satisfies at least two of the above four requirements, more preferably at least three, and most preferably all four.

[0049] From the viewpoint of more easily realizing sufficient heat ray reflectivity, heat ray blocking properties, and light blocking properties, the amount of finely divided silica is preferably 25 to 45 mass %, more preferably 30 to 40 mass %, of the total amount of silica materials.

[0050] In one embodiment, the mixed powder for pressure molding can contain silicon monoxide particles (SiO powder). When SiO powder is contained, the SiO powder can be in the range of D ５０ From the viewpoint of more easily realizing sufficient heat ray reflectivity, heat ray blocking property and light blocking property, it is preferable that the D in the particle size distribution of the SiO powder is 0.5 to 2 μm. ５０ From the same viewpoint, D in the particle size distribution of the SiO powder is preferably 0.6 to 1.5 μm, and more preferably 0.7 to 1.3 μm. １０ is 0.1 μm or more, D ９０ is preferably 5 μm or less, and D １０ is 0.2 μm or more, D ９０ It is more preferable that the thickness is 3 μm or less.

[0051] The SiO powder can be added externally in an amount of 0.1 to 1 mass % relative to the total amount of silica material. From the viewpoint of more easily achieving sufficient heat ray reflectivity, heat ray blocking properties, and light blocking properties, the SiO powder is added externally in an amount of preferably 0.15 to 0.7 mass %, and more preferably 0.2 to 0.5 mass %, relative to the total amount of silica material.

[0052] In a preferred embodiment, the mixed powder for compaction has a particle size distribution of D ５０ The silica material further contains SiO powder having a particle size of 0.5 to 2 μm, and the content of the SiO powder is 0.1 to 1 mass % added externally based on the total amount of the silica material.

[0053] The manufacturing method of the present invention includes a step of mixing dry powdered silica powder and fine silica particles in a predetermined ratio, or a step of mixing these powders together with a predetermined amount of SiO powder. When SiO powder is used, the SiO particles are uniformly mixed with the raw material powder in a substantially agglomerated state. Consolidation of the raw material powders proceeds simultaneously with mixing, resulting in a mixed powder for pressure molding with a uniform and suitable tapped bulk density. It is believed that fine silica particles with a small BET diameter also function as a sintering agent. The tapped bulk density of the mixed powder for pressure molding can be controlled by adjusting the ratio of fine silica and SiO powder particles in the mixed powder, as well as the powder mixing method and mixing time. The amount of porosity in the opaque quartz glass can also be controlled by adjusting the ratio of spherical silica powder in the silica material. In the present invention, since consolidation proceeds simultaneously with mixing, this operation is hereinafter also referred to as "mixed consolidation."

[0054] The mixing and compaction is preferably carried out so that the tapped bulk density of the mixed powder obtained by mixing and compaction is 5 to 20 times that of the particulate silica. When the tapped bulk density of the mixed powder for pressure molding is 5 times or more that of the particulate silica, the density of the sintered body tends to be high. When the tapped bulk density of the mixed powder for pressure molding is 20 times or less that of the particulate silica, the strength of the molded body is less likely to decrease. The tapped bulk density of the mixed powder for pressure molding is preferably 6 to 15 times, more preferably 7 to 10 times, that of the particulate silica. The mixing and compaction can be carried out using a general mixing device such as an agitator mixer, a ball mill, a rocking mixer, a cross mixer, or a V-type mixer.

[0055] The mixed and consolidated mixed powder can be molded into a desired shape. As a molding method, dry methods such as die press molding and cold isostatic pressing, which are commonly used in molding ceramics, can be used. A pressing pressure of, for example, 10 to 300 MPa is appropriate. If the pressing pressure is 10 MPa or more, the molded body will not collapse and the yield during molding can be maintained. If the pressing pressure is 300 MPa or less, no large-scale equipment is required, productivity is good, and production costs can be reduced, which is desirable.

[0056] Known methods can be used as sintering conditions. Sintering is preferably carried out in air, but is not limited thereto. The maximum sintering temperature is not particularly limited as long as it can sinter the mixed powder, but is, for example, 1200°C to 1400°C, preferably 1250°C to 1350°C, more preferably 1300°C to 1340°C, and even more preferably 1310°C to 1330°C. By setting the sintering temperature to 1400°C or less, it is possible to suppress a decrease in the amount of pores, and it is easier to achieve sufficient heat ray reflectivity, heat ray blocking properties, and light blocking properties. By setting the sintering temperature to 1200°C or more, a better sintered body can be obtained, and it is easier to achieve sufficient heat ray reflectivity, heat ray blocking properties, and light blocking properties.

[0057] In the heating and sintering steps, the sintering time at the maximum temperature in an atmospheric furnace can be appropriately adjusted taking into consideration the physical properties of the sintered body, and can be set in the range of 0.5 to 5 hours, for example. A sintering time of 0.5 hours or more tends to prevent a decrease in density and bending strength. A sintering time of 5 hours or less improves productivity and tends to reduce production costs.

[0058] Since the particle size of fine silica is as small as 10 to 50 nm, the bulk density of fine silica is very low, making fine silica unsuitable for granulation and molding. Therefore, the density of the sintered body obtained by sintering fine silica is usually low and is not satisfactory as quartz glass. For this reason, fine silica is generally not used as a sintering material for opaque quartz glass.

[0059] However, in the manufacturing method of the present invention, as described above, by mixing multiple types of specific silica powders with different particle size distributions in a predetermined ratio, or by adding a predetermined amount of SiO powder to a silica powder and mixing it, a mixed powder for pressure molding with a uniform and suitable tapped bulk density can be obtained, and by sintering this mixed powder, it is possible to produce a sintered body of opaque quartz glass containing irregular pores and having sufficient heat ray reflectivity, heat ray blocking properties, and light blocking properties. Such opaque quartz glass of the present invention can be suitably used for quartz glass cells for optical analysis, light blocking members and infrared reflecting members in semiconductor manufacturing equipment and infrared heating equipment.

[0060] In addition, the manufacturing method of the present invention has the effect of making the structure of the sintered body more uniform and shortening the heating time up to the maximum temperature during sintering.

[0061] In addition to the above effects, the opaque quartz glass of the present invention does not require the formation of a slurry of silica powder, and therefore is less susceptible to the problems associated with the formation of a slurry of silica powder in conventional methods. In other words, in conventional methods that involve the formation of a slurry of silica powder, the process leading up to pressure molding is complicated, involving the pulverization of the silica powder, the formation of a slurry of the silica powder, and the spray-drying and granulation of the slurry, which increases the production costs and the risk of contamination. However, in the present invention, since the formation of a slurry of silica powder is not required, opaque quartz glass can be produced with high productivity and the risk of contamination during production can be reduced.

[0062] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0063] The sample properties were measured as follows: (1) The density of the sintered body was measured by the Archimedes method. (2) The SCE reflectance was measured by processing the sample to a thickness of 7 mm and using a spectrophotometer in accordance with JIS Z 8722. The lowest value in the wavelength range of 350 to 750 nm was used as the standard. (3) L ＊ a ＊ b ＊ Display system brightness L ＊ and saturation a ＊ , b ＊was measured using a spectrophotometer in accordance with JIS Z 8722. (4) Infrared reflectance is the reflectance of light with a wavelength of 2 μm for a 4 mm thick sample. (5) The pore size and pore size distribution were determined as follows: The sample was cut, the cut surface was polished, and the polished surface was observed using a scanning electron microscope and an optical microscope (observation magnification: approximately 500 to 3000 times) to obtain images (multiple images as necessary). The images were processed using the open-source, public domain image processing software "ImageJ," to measure the area A of each pore, and the pore size D was calculated by substituting it into the following formula (1). The pore size distribution was then calculated based on the pore sizes and frequency values ​​of a total of 3000 or more pores (generally 4000 or less). Pore size D = (4 × A / π) １／２ (1) (6) The circularity was determined by the following method. The image obtained in the measurement in (5) above was processed using the open-source, public domain image processing software "ImageJ," and the area A and circumferential length L of each pore were measured. These were then substituted into the following formula (2) to determine the circularity of a total of 3,000 or more pores (generally 4,000 or less), and the average value was used as the circularity in the present invention. Circularity = 4πA / L ２ (2) (7) The pore area ratio in the microscopic image of the cross section was determined by the following method. The optical microscope image obtained in the measurement in (5) above was processed using the open-source, public domain image processing software "ImageJ" to measure the total pore area S and the area TS of the entire processed image, and the area-based percentage obtained by substituting these into the following formula (3) was taken as the pore area ratio in the present invention. The area TS of the entire image is the area where the total number of measured pores is 3,000 or more (generally 4,000 or less) (multiple images were used as necessary). Pore area ratio = S / TS x 100 (3) (8) The density distribution was determined by cutting out 10 or more random locations from the sintered body, measuring the density, and then substituting these into the formula (maximum value - minimum value) / average value x 100. (9) Lightness L ＊ The distribution is the brightness L of 10 or more arbitrary points on the sintered body. ＊ After measuring, the value was calculated by substituting it into the formula (maximum value - minimum value) / average value x 100.

[0064] (Example 1) The following materials were used as raw materials for the mixed powder: Fine silica: BET diameter 32 nm, tap bulk density 0.06 g / cm ３ , BET specific surface area 85m ２ / g, OH group concentration 0.7 mass%, and the content of metal impurities other than Si is each 1 ppm or less. Synthetic silica powder: D ５０ is 80 μm, D １０ is 48 μm, D ９0 Silica particles having a particle size of 130 μm and a content of metal impurities other than Si of 1 ppm or less. SiO powder: D ５０ is 0.9 μm, D １０ is 0.4 μm, D ９０ Silicon monoxide particles having a particle size of 2.0 μm.

[0065] As shown in Table 1, 0.3% by mass of SiO powder was externally added to a mixture of silica particles prepared by mixing 37% by mass of fumed silica (fine silica) and 63% by mass of synthetic silica powder, and the mixture was mixed and consolidated in a ball mill without using a solvent to obtain a mixed powder for pressure molding. After mixing and consolidation, the tapped bulk density of the mixed powder was 0.70 g / cm. ３ This mixed powder for pressure molding was press-molded at 90 MPa, and sintered in the air for 3 hours while maintaining the temperature range of 1300 to 1350°C.

[0066] In the obtained opaque quartz glass, L ＊ a ＊ b ＊ Display system brightness L ＊ is 90.2, saturation a ＊ is -0.1, b ＊ The D in the pore size distribution was 1.8. ５０ The average diameter of the pores was 7.5 μm, the percentage of pores with a diameter of 5 μm or less was 32%, the percentage of pores with a diameter of 15 μm or less was 85%, and the circularity of the pores was 0.58. The density of the opaque quartz glass was 2.15 g / cm ３ , SCE reflectance is 75% or more, infrared reflectance is 80.6%, density distribution is 1.5%, brightness L ＊The distribution was 1.5%. This opaque quartz glass was free of color unevenness, exhibited a sufficient white color, was visually confirmed to be uniform, had a gloss, and had an excellent appearance. The pore area ratio in the microscopic image was 36%. The above results are summarized in Tables 2 and 3.

[0067] Example 2 In Example 2, in addition to the materials used in Example 1, the following spherical silica powder A was used. Spherical silica powder A: D ５０ is 10 μm, D １０ is 2 μm, D ９0 The spherical silica particles have a particle size of 31 μm and a content of metal impurities other than Si of 1 ppm or less.

[0068] A mixed powder for pressure molding was obtained by adding 0.3 mass% of SiO powder to a mixture of silica particles obtained by mixing 35 mass% of fumed silica (fine silica), 55 mass% of synthetic silica powder, and 10 mass% of spherical silica powder A. After mixing and compaction, the tapped bulk density of the mixed powder was 0.70 g / cm. ３ This mixed powder for pressure molding was sintered in the same manner as in Example 1.

[0069] In the obtained opaque quartz glass, L ＊ a ＊ b ＊ Display system brightness L ＊ is 90.5, saturation a ＊ is -0.1, b ＊ The D in the pore size distribution was 1.9. ５０ The average particle diameter was 8.1 μm, the percentage of pores with a diameter of 5 μm or less was 29%, the percentage of pores with a diameter of 15 μm or less was 77%, and the circularity of the pores was 0.61. The density of the opaque quartz glass was 2.15 g / cm ３ , SCE reflectance is 75% or more, infrared reflectance is 81.2%, density distribution is 1.5%, brightness L ＊ The distribution was 1.2%. This opaque quartz glass was free from color unevenness, exhibited a sufficient white color, and was visually confirmed to be uniform. It was glossy and had an excellent appearance. The pore area ratio in a microscopic image was 27%.

[0070] Example 3 In Example 3, in addition to the materials used in Example 1, the following spherical silica powder B was used. Spherical silica powder B: D ５０ is 20 μm, D １０ is 6 μm, D ９0 The spherical silica particles have a particle size of 42 μm and a content of metal impurities other than Si of 1 ppm or less.

[0071] A mixed powder for pressure molding was obtained by adding 0.3 mass% of SiO powder externally to a mixture of silica particles, which was a mixture of 37 mass% of fumed silica (fine silica), 57 mass% of synthetic silica powder, and 6 mass% of spherical silica powder B. By mixing and compacting, the tapped bulk density of the mixed powder was 0.70 g / cm. ３ This mixed powder for pressure molding was sintered in the same manner as in Example 1.

[0072] In the obtained opaque quartz glass, L ＊ a ＊ b ＊ Display system brightness L ＊ is 90.4, saturation a ＊ is -0.1, b ＊ The D in the pore size distribution was 1.3. ５０ The average diameter of the pores was 6.7 μm, the percentage of pores with a diameter of 5 μm or less was 39%, the percentage of pores with a diameter of 15 μm or less was 77%, and the circularity of the pores was 0.58. The density of the opaque quartz glass was 2.16 g / cm ３ , SCE reflectance is 75% or more, infrared reflectance is 80.9%, density distribution is 1.5%, brightness L ＊ The distribution was 1.3%. This opaque quartz glass was free from color unevenness, exhibited a sufficient white color, was visually confirmed to be uniform, was glossy, and had an excellent appearance. The pore area ratio in the microscopic image was 21%. Figure 1 shows an optical microscope photograph (observation magnification 1000 times) of the cross section of the quartz glass in Example 3.

[0073] Example 4 In Example 4, the above-mentioned fine silica, spherical silica A and SiO powder were used.

[0074] A mixed powder for pressure molding was obtained by externally adding 0.3% by mass of SiO powder to a mixture of silica particles obtained by mixing 30% by mass of fumed silica (fine silica) and 70% by mass of spherical silica powder A. After mixing and compaction, the tapped bulk density of the mixed powder was 0.82 g / cm. ３ This mixed powder for pressure molding was sintered in the same manner as in Example 1.

[0075] In the obtained opaque quartz glass, L ＊ a ＊ b ＊ Display system brightness L ＊ is 93.0, saturation a ＊ is 0.2, b ＊ The D in the pore size distribution was 1.0. ５０ The average particle diameter was 11.2 μm, the percentage of pores with a diameter of 5 μm or less was 17%, the percentage of pores with a diameter of 15 μm or less was 69%, and the circularity of the pores was 0.56. The density of the opaque quartz glass was 2.16 g / cm ３ , SCE reflectance is 75% or more, infrared reflectance is 85.0%, density distribution is 1.5%, brightness L ＊ The distribution was 1.5%. This opaque quartz glass was free from color unevenness, exhibited a sufficient white color, was visually confirmed to be uniform, was glossy, and had an excellent appearance. The pore area ratio in the microscopic image was 10.3%. Figure 2 shows an optical microscope photograph (observation magnification 1000 times) of the cross section of the quartz glass in Example 4.

[0076] Example 5 In Example 5, the above-mentioned fine silica, spherical silica B, and SiO powder were used.

[0077] A mixed powder for pressure molding was obtained by adding 0.3 mass% of SiO powder externally to a mixture of silica particles obtained by mixing 30 mass% of fumed silica (fine silica) and 70 mass% of spherical silica powder B. By mixing and compacting, the tapped bulk density of the mixed powder was 0.83 g / cm. ３This mixed powder for pressure molding was sintered in the same manner as in Example 1. The evaluation results are shown in Tables 2 and 3. This opaque quartz glass had no color unevenness, was sufficiently white, and was visually confirmed to be uniform. It was glossy and had an excellent appearance. Figure 3 shows an optical microscope photograph (1000x magnification) of the cross section of the quartz glass in Example 5.

[0078] Example 6 In Example 6, the above-mentioned fine silica, synthetic silica powder, spherical silica A, and SiO powder were used.

[0079] A mixed powder for pressure molding was obtained by adding 0.3 mass% of SiO powder to a mixture of silica particles obtained by mixing 34 mass% of fumed silica (fine silica), 33 mass% of synthetic silica powder, and 33 mass% of spherical silica powder A. After mixing and compaction, the tapped bulk density of the mixed powder was 0.74 g / cm. ３ This mixed powder for pressure molding was sintered in the same manner as in Example 1. The evaluation results are shown in Tables 2 and 3. This opaque quartz glass had no color unevenness, was sufficiently white, and was visually confirmed to be uniform. It was glossy and had an excellent appearance. Figure 4 shows an optical microscope photograph (1000x magnification) of the cross section of the quartz glass in Example 6.

[0080] Example 7 In Example 7, the above-mentioned fine silica, synthetic silica powder, spherical silica B, and SiO powder were used.

[0081] A mixed powder for pressure molding was obtained by adding 0.3 mass% of SiO powder externally to a mixture of silica particles obtained by mixing 34 mass% of fumed silica (fine silica), 33 mass% of synthetic silica powder, and 33 mass% of spherical silica powder B. By mixing and compacting, the tapped bulk density of the mixed powder was 0.75 g / cm. ３ This mixed powder for pressure molding was sintered in the same manner as in Example 1. The evaluation results are shown in Tables 2 and 3. This opaque quartz glass had no color unevenness, was sufficiently white, and was visually confirmed to be uniform. It was glossy and had an excellent appearance. Figure 5 shows an optical microscope photograph (1000x magnification) of the cross section of the quartz glass in Example 7.

[0082] Example 8 In Example 8, the above-mentioned fine silica and synthetic silica powder were used.

[0083] 37% by mass of fumed silica (fine silica) and 63% by mass of synthetic silica powder were mixed to obtain a mixed powder for pressure molding. After mixing and compaction, the tapped bulk density of the mixed powder was 0.71 g / cm ３ This mixed powder for pressure molding was sintered in the same manner as in Example 1. The evaluation results are shown in Tables 2 and 3. This opaque quartz glass had no color unevenness, was sufficiently white, and was confirmed to be uniform by visual inspection. It was glossy and had an excellent appearance.

[0084] Example 9 In Example 9, the above-mentioned fine silica and spherical silica A were used.

[0085] 30% by mass of fumed silica (fine silica) and 70% by mass of spherical silica powder A were mixed to obtain a mixed powder for pressure molding. After mixing and compaction, the tapped bulk density of the mixed powder was 0.83 g / cm ３ This mixed powder for pressure molding was sintered in the same manner as in Example 1. The evaluation results are shown in Tables 2 and 3. This opaque quartz glass had no color unevenness, exhibited a sufficient white color, was visually confirmed to be uniform, and was glossy and had an excellent appearance. Figure 6 shows an optical microscope photograph (1000x magnification) of the cross section of the quartz glass in Example 9.

[0086] Example 10 In Example 10, the above-mentioned fine silica, synthetic silica powder and spherical silica A were used.

[0087] 34% by mass of fumed silica (fine silica), 33% by mass of synthetic silica powder, and 33% by mass of spherical silica powder A were mixed to obtain a mixed powder for pressure molding. By mixing and compacting, the tapped bulk density of the mixed powder was 0.75 g / cm ３ This mixed powder for pressure molding was sintered in the same manner as in Example 1. The evaluation results are shown in Tables 2 and 3. This opaque quartz glass had no color unevenness, was sufficiently white, and was confirmed to be uniform by visual inspection. It was glossy and had an excellent appearance.

[0088] Comparative Example 1 In Comparative Example 1, unlike Example 1, no fumed silica (fine silica particles) was used.

[0089] 0.3 mass% of SiO powder was externally added to the synthetic silica powder to obtain a mixed powder for pressure molding. After mixing and compaction, the tapped bulk density of the mixed powder was 1.20 g / cm ３ This mixed powder for pressure molding was press-molded at 90 MPa in the same manner as in Example 1, but a molded body could not be obtained and the powder remained.

[0090] Comparative Example 2 In Comparative Example 2, unlike Example 1, synthetic silica powder and SiO powder were not used.

[0091] Fumed silica (fine particle silica) was press-molded at 90 MPa and sintered in air for 3 hours while maintaining the temperature range of 1300 to 1350° C. The obtained sintered body had many cracks and could not be evaluated.

[0092] Comparative Example 3 In Comparative Example 3, the amount of fumed silica (fine silica particles) was increased compared to Example 1.

[0093] To a mixture of silica particles, 60% by mass of fumed silica (fine silica) and 40% by mass of synthetic silica powder were added 0.3% by mass of SiO powder as an external additive, and the mixture was mixed and consolidated in a ball mill without using a solvent to obtain a mixed powder for pressure molding. After mixing and consolidation, the tapped bulk density of the mixed powder was 0.55 g / cm. ３ This mixed powder for pressure molding was sintered in the same manner as in Example 1.

[0094] In the obtained opaque quartz glass, L ＊ a ＊ b ＊ Display system brightness L ＊ is 73.3, saturation a ＊ is -0.1, b ＊ was 0.0. D in the pore size distribution ５０ The average particle diameter was 2.0 μm, the percentage of pores with a diameter of 5 μm or less was 88%, the percentage of pores with a diameter of 15 μm or less was 99%, and the circularity was 0.68. The density of the opaque quartz glass was 2.19 g / cm ３, SCE reflectance is less than 75%, infrared reflectance is 63.3%, density distribution is 0.5%, brightness L ＊ The distribution was 0.5%. This opaque quartz glass was free of color unevenness and appeared uniform to the naked eye, but did not exhibit a sufficient white color. The area ratio of pores in the microscopic image was 3%. Figure 7 shows an optical microscope photograph (observation magnification 1000 times) of the cross section of the quartz glass in Comparative Example 3.

[0095] (Comparative Example 4) Fused quartz glass having a purity of 99.99% was used to form a fused silica glass having a maximum particle size of 50 μm or less and a D ５０ The powder was wet-pulverized to a particle size of 7 μm, and water was added to the pulverized product to prepare a slurry with a solid content of 78 wt %, which was then cast into a hard plaster mold to obtain a molded product. The molded product was dried at 150° C. for 100 hours, heated at 1400° C. for 1 hour, and then cooled.

[0096] In the obtained opaque quartz glass, L ＊ a ＊ b ＊ Display system brightness L ＊ is 80.0, saturation a ＊ is -0.2, b ＊ The D in the pore size distribution was 0.4. ５０ The average diameter of the pores was 6.7 μm, the percentage of pores with a diameter of 5 μm or less was 36%, the percentage of pores with a diameter of 15 μm or less was 92%, and the circularity was 0.66. The density of the opaque quartz glass was 2.18 g / cm ３ , SCE reflectance is less than 75%, infrared reflectance is 68.5%, density distribution is 1.0%, brightness L ＊ The distribution was 1.0%. This opaque quartz glass was free of color unevenness and was uniform to the naked eye, but did not exhibit a sufficient white color. The area ratio of pores in a microscopic image was 15%.

[0097]

[0098]

[0099]

[0100] The present invention is useful in the field of opaque quartz glass. Because the opaque quartz glass of the present invention has sufficient heat ray reflectivity, heat ray shielding properties, and light blocking properties, it can be suitably used, for example, as a quartz glass cell for optical analysis, a light blocking member for semiconductor manufacturing equipment or infrared heating equipment, or an infrared reflecting member. According to the present invention, it is also possible to provide, with good productivity, large opaque quartz glass ingots that have sufficient heat ray reflectivity, heat ray shielding properties, and light blocking properties, as well as sufficient uniformity.

Claims

1. An opaque quartz glass having irregular pores dispersed in the glass body, wherein the pore size distribution is D ５０ The opaque quartz glass has a pore size of 4 to 30 μm, a ratio of pores having a pore size of 5 μm or less of 1 to 50%, and a ratio of pores having a pore size of 15 μm or less of 30 to 90%, and the area ratio of the pores in a microscopic image of the cross section is 5% or more.

2. 2. The opaque quartz glass according to claim 1, wherein the circularity of the pores is 0.62 or less.

3. The above D ５０ is 10 μm or less, the area ratio is 15% or more, The above D ５０ The opaque quartz glass according to claim 1 or 2, wherein the area ratio is less than 15% when the area ratio is greater than 10 μm.

4. The infrared reflectance is 75% or more, the SCE reflectance at wavelengths of 350 nm to 750 nm is 75% or more, and L ＊ a ＊ b ＊ Display system brightness L ＊ The opaque quartz glass according to claim 1 or 2, wherein the refractive index is 85 or more.

5. L ＊ a ＊ b ＊ Display system saturation a ＊ The absolute value of is 2 or less and b ＊ The opaque quartz glass according to claim 1 or 2, wherein the absolute value of

6. 3. The opaque quartz glass according to claim 1, wherein the content of each of the metal impurities is 1 ppm or less.

7. Density is 2.10 to 2.18 g / cm ３ The opaque quartz glass according to claim 1 or 2,

8. The density distribution in the opaque quartz glass is 2% or less, and the lightness L ＊ 3. The opaque quartz glass according to claim 1, wherein the distribution is 2% or less.

9. D in particle size distribution ５０ 2. A method for producing opaque quartz glass according to claim 1, comprising pressure-molding a mixed powder of silica powder, which is silica particles having a BET diameter of 5 to 100 μm, and fine silica, which is silica particles having a BET diameter of 10 to 50 nm, wherein the fine silica content is 20 to 50 mass% relative to the total amount of silica material containing the silica powder and the fine silica, and sintering the pressure-molded product.

10. (a) The silica powder has a particle size distribution of D ５０ is a synthetic silica powder having a particle size of 30 to 100 μm, or (b) The silica powder has a particle size distribution D ５０ Synthetic silica powder with a particle size distribution of 30 to 100 μm and D ５０ and a spherical silica powder having a size of 5 to 50 μm, or (c) The silica powder has a particle size distribution D ５０ The method for producing opaque quartz glass according to claim 9, wherein the silica powder is spherical silica powder having a size of 5 to 50 μm.

11. 11. The method for producing opaque quartz glass according to claim 10, wherein in the case of (b) above, the content of the spherical silica powder is 1 to 20 mass % relative to the total amount of the silica material.

12. When the synthetic silica powder and the spherical silica powder are present, D in the particle size distribution of the synthetic silica powder １０ D ５０ More than 1 / 3 of D ９０ D ５０ and D in the particle size distribution of the spherical silica powder is 3 times or less. １０ D ５０ 1 / 5 or more, D ９０ D ５０ The method for producing opaque quartz glass according to claim 10 or 11, wherein the thickness is 5 times or less.

13. The fine silica has (i) a tapped bulk density of 0.03 to 0.10 g / cm ３ (ii) a BET specific surface area of ​​50 to 100 m ２ / g, (iii) OH groups A method for producing opaque quartz glass according to any one of claims 9 to 11, which satisfies at least one of the following four requirements: (i) the concentration is 0.5 to 1.0 mass%; and (ii) the content of metal impurities other than Si is each 1 ppm or less.

14. The mixed powder has a particle size distribution of D ５０ The method for producing opaque quartz glass according to any one of claims 9 to 11, further comprising SiO powder, which is silicon monoxide particles of 0.5 to 2 μm, and the content of the SiO powder is 0.1 to 1 mass% externally added relative to the total amount of silica material.

15. D in the particle size distribution of the SiO powder １０ is 0.1 μm or more, D ９０ The method for producing opaque quartz glass according to claim 14, wherein the thickness is 5 μm or less.

16. 12. The method for producing opaque quartz glass according to claim 9, wherein the tapped bulk density of the mixed powder for pressure molding is 5 to 20 times the tapped bulk density of the fine silica particles.