JP2018070397A - Silica powder, silica granulated powder with high fluidity, and method of producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an opaque quartz glass that is stably producible on an industrial scale and has a large size and a high quality.SOLUTION: Provided is a silica powder which is obtained from a silica slurry having a solid content concentration of 10 wt% subjected to separation using centrifugal sedimentation method (rotation: 5000 rpm, rotation duration: 15 minutes, the number of operations: one time), and which contains particulate silica that is present in the upper-layer liquid, which has 50% particle size (based on number) of 0.01 to 0.9 μm, and silica that is present in a concentrated layer, which has 50% particle size (based on volume) of 2 to 20 μm and 100% particle size (based on volume) of 200 μm or less, in which the particulate silica is contained in an amount of 0.8 wt% to 15 wt% with respect to a total amount of the silica. The silica powder is granulated to give a silica granulated powder having a repose angle of 40° or less and having an untamped density of 0.8 g/cm.SELECTED DRAWING: None

Description

  The present invention relates to a silica powder suitable for the production of opaque quartz glass, a high-fluidity silica granulated powder, and a method for producing the same.

  In recent years, there is a growing demand for high purity, high functionality, and large size in opaque quartz glass products used in the semiconductor field and the like. As a method for producing an opaque quartz glass, for example, a method in which fine high-purity amorphous silica powder is CIP-molded and sintered at a predetermined temperature (for example, see Patent Document 1) is known. The opaque quartz glass produced by such a method includes fine closed pores and thus has excellent heat shielding properties.

  However, fine amorphous silica powder is easy to agglomerate and has poor fluidity, so it is difficult to uniformly fill the mold when producing large products, and the density of the sintered body is lower than that of small products. In addition, there are quality problems such as easy cracking and uneven whiteness. Since such quality problems become more prominent as the size increases, a powder design with excellent moldability and sinterability is desired.

  In general, various granulation methods are known as methods for preparing ceramic powders used in the dry pressure molding method. For example, in the spray drying method, a raw material powder, a binder, a dispersant, a plasticizer and water are mixed to prepare a slurry, and by spray drying the slurry, spherical granules having relatively good fluidity are obtained, Uniform filling into the mold is easy to improve.

  However, since organic additives such as binders, dispersants, and plasticizers added to improve spray granulation are included in the granulated powder, a new degreasing process for heating and removing organic additives in the molded product is new. It is necessary for this, and productivity is inferior. Furthermore, in the degreasing step, gas is released inside the molded body due to decomposition of the organic additive, so that cracks are likely to occur in the molded body. Moreover, when the present inventors added the binder and produced granulated powder, it became clear that fluidity | liquidity is inferior compared with the silica granulated powder of this invention.

JP 2014-88286 A

  Until now, silica powder excellent in moldability and sinterability suitable for production of large-sized products has not been reported in the production of opaque quartz glass. The present invention has been made in view of the problems associated with powder for producing opaque quartz glass, and the object thereof is to provide a silica granulated powder having excellent moldability and sinterability. The object is to provide a large-sized and high-quality opaque quartz glass that can be stably produced on a global scale.

  As a result of diligent investigation focusing on the powder characteristics of the formability and sinterability of the opaque quartz glass, the inventors of the present invention blended predetermined fine silica as an auxiliary agent in the silica powder to be an aggregate, and wet-mixed. By preparing a uniform slurry and spray drying the slurry, a highly fluid silica granulated powder with significantly improved granulation properties can be produced, and a silica granulated powder with excellent moldability and sinterability can be obtained. As a result, the present invention has been completed.

  The present invention is described in detail below.

The present invention
[1] 50% particle size (number basis) of fine silica in the upper layer liquid obtained by separating a silica slurry having a solid content concentration of 10 wt% by centrifugal sedimentation (rotation speed: 5000 rpm, rotation time: 15 minutes, number of operations: 1) Is 0.01 to 0.9 μm, 50% particle size (volume basis) of silica in the concentrated layer is 2 to 20 μm, and 100% particle size (volume basis) is 200 μm or less. A silica powder comprising the fine silica in an amount of 0.8 wt% to 15 wt%.

[2] The silica powder according to [1], wherein the BET specific surface area is 4.5 to 15 m ² / g.

[3] A silica granulated powder having an angle of repose after granulation of the silica powder of [1] or [2] of 40 ° or less and a light bulk density of 0.8 g / cm ³ or more.

  [4] Silica powder having a 50% particle size (volume basis) of 2 to 20 μm and a 100% particle size (volume basis) of 200 μm or less, and a fine particle having a 50% particle size (number basis) of 0.01 to 0.9 μm The method for producing a granulated silica powder according to the above [3], wherein the silica is wet-mixed at a ratio of 7 wt% to 40 wt% with respect to the total amount of silica to form a slurry, and the resulting slurry is spray-dried.

[5] An opaque quartz glass obtained by molding and sintering the silica granulated powder according to [3].
It is about.

  Here, as the silica powder having a 50% particle size (volume basis) of 2 to 20 μm and a 100% particle size (volume basis) of 200 μm or less, for example, an amorphous produced by a hydrolysis reaction of alkoxysilane, a so-called sol-gel method Silica powder, amorphous silica powder produced by flame reaction of silicon tetrachloride or siloxane compound, powder obtained by pulverizing quartz glass, and the like can be used. As the fine silica, commercially available high-purity amorphous silica can be used from the viewpoint of high purity. At this time, silica obtained by wet-mixing fine silica having a 50% particle size (number basis) of 0.01 to 0.9 μm with the silica powder at a ratio of 7 wt% to 40 wt% with respect to the total silica amount. By spray-drying the slurry, the cohesive force is increased by the fine particles interposed in the gaps between the particles of the silica powder, thereby increasing the granulation property and improving the fluidity of the obtained silica granulated powder. On the other hand, when the mixing ratio of the fine silica is less than 7 wt%, the granulating property of the silica powder is lowered. In addition, when the mixing ratio of the fine silica exceeds 40 wt%, the viscosity of the silica slurry obtained by wet-mixing the silica powder and the fine silica is increased, and the granulation operability is deteriorated. This is not preferable from the standpoint of homogeneity, for example, the strength increases and the crushability during molding deteriorates.

  The 50% particle size (number basis) of the fine silica is a space between the silica powder particles having a 50% particle size (volume basis) of 2 to 20 μm and a 100% particle size (volume basis) of 200 μm or less. In the present invention, it is 0.01 to 0.9 μm.

Furthermore, it is preferable that the BET specific surface area of the silica powder which mixed the silica powder and the fine particle silica is 4.5-15 m < ² > / g. When the BET specific surface area is less than 4.5 m ² / g, the granulation property of the silica powder is lowered. Moreover, when a BET specific surface area exceeds 15 m < ² > / g, the viscosity of the silica slurry obtained by wet-mixing a silica powder and a fine silica increases, and granulation operativity worsens. In the present invention, a desired silica granulated powder can be produced by using silica powder in which the silica particle size, the weight ratio of the fine silica, and the BET specific surface area are controlled.

The silica granulated powder of the present invention is characterized by an angle of repose of 40 ° or less and a light bulk density of 0.8 g / cm ³ or more. When the angle of repose exceeds 40 ° or the lightly packed bulk density is less than 0.8 g / cm ³ , the fluidity is inferior, so that uniform filling into the mold becomes difficult, and crack-free firing is produced when producing large products. It becomes difficult to obtain a knot.

  The content of each metal impurity of Na, Ca, Al, Fe, Cr, and Ni is 1 ppm or less in the silica granulated powder of the present invention.

  Next, the manufacturing method of the silica granulated powder of this invention is demonstrated.

  In the method for producing a silica granulated powder of the present invention, a 50% particle size (volume basis) has a 50% particle size (volume basis) of 2 to 20 μm and a 100% particle size (volume basis) of 200 μm or less. It is characterized in that 0.01 to 0.9 μm fine silica is wet-mixed at a ratio of 7 wt% to 40 wt% with respect to the total amount of silica to form a slurry, and the resulting slurry is spray-dried.

  Hereinafter, the manufacturing method of the silica granulated powder of this invention is demonstrated in detail for every process.

(1) Selection of raw material powder In the present invention, the amorphous silica powder used as an aggregate has a 50% particle size (volume basis) of 2 to 20 μm and a 100% particle size (volume basis) of 200 μm or less. If there is no particular limitation, for example, hydrolyzing alkoxysilane, amorphous silica powder produced by so-called sol-gel method, amorphous silica powder produced by flame reaction of silicon tetrachloride or siloxane compound, quartz glass is crushed Used powder can be used.

  The particle size of the amorphous silica powder can be controlled by pulverizing with, for example, a jet mill, a ball mill, or a bead mill. At this time, if the 50% particle size (volume basis) of the pulverized amorphous silica powder is too small, the amount of metal impurities mixed from the material of the pulverizer increases, which is not preferable. Further, if the 50% particle size (volume basis) of the pulverized amorphous silica powder is increased by changing the pulverization conditions, the amount of metal impurities mixed from the pulverizer material decreases, but granulation, molding, and sintering are not possible. It becomes difficult. Therefore, in the present invention, the amorphous silica powder has a 50% particle size (volume basis) of 2 to 20 μm and a 100% particle size (volume basis) of 200 μm or less, and the amorphous silica powder is granulated, molded, and sintered. In order to improve each characteristic of the kneading, fine silica used as an auxiliary is wet mixed.

  Next, the fine silica used in the present invention is not particularly limited as long as the 50% particle size (number basis) is in the range of 0.01 to 0.9 μm. For example, hydrolysis reaction of alkoxysilane, so-called sol-gel method Silica fine particles produced by the flame reaction of silicon tetrachloride or siloxane compounds can be used.

(2) Mixing of raw material powder The amorphous silica powder selected in (1) and fine silica are wet mixed. The mixing ratio of the fine silica is 7 wt% or more and 40 wt% or less with respect to the total silica amount, but the preferable range can be appropriately set because it varies depending on the particle size distribution of the amorphous silica powder and fine silica used. As a method for mixing the amorphous silica powder and the fine silica, for example, a container rotating type rocking mixer, cross mixer, pot mill, ball mill, etc. are used, and ultrapure water is added to form a slurry having a solid content concentration of 30 to 80 wt%. The method of preparing and carrying out wet mixing uniformly in a rotation container is mentioned.

  In the present invention, a pore former powder used as a raw material for producing opaque quartz glass may be selected and wet mixed with amorphous silica powder and fine silica. For example, a silica powder having a 50% particle size (volume basis) of 2 to 20 μm and a 100% particle size (volume basis) of 200 μm or less and a fine silica having a 50% particle size (number basis) of 0.01 to 0.9 μm 7 wt% or more and 40 wt% or less with respect to the total amount of silica, and a graphite powder or amorphous carbon powder with a 50% particle size (volume basis) of 5 to 40 μm as the pore former powder is 4 wt% or more and 40 wt% with respect to the total silica amount. It can be set as the mixed silica powder containing below.

(3) Granulation Granulation is performed by a spray drying method using a slurry in which the amorphous silica powder obtained in (2) and the fine silica are uniformly mixed. Although the apparatus used by spray drying is not specifically limited, For example, a disk type (atomizer type), a pressure nozzle type, a two-fluid nozzle type etc. are mentioned. The spray drying conditions are appropriately set according to the specifications of the apparatus (type, drying chamber diameter, etc.). For example, in a spray dryer having a disk type and a drying chamber diameter of about 1.5 m, the slurry supply speed is 5 to 15 kg / hr, the disk rotation speed is 10,000 to 20000 rpm, the hot air inlet temperature is 100 to 170 ° C., and the outlet temperature is 60 to 120 ° C. .

  The silica granulated powder obtained by the production method of the present invention can be used as a raw material for opaque quartz glass using a dry pressure molding method.

  The silica powder of the present invention has excellent characteristics in granulation, molding and sintering. Specifically, the granulated powder produced from the silica powder is a spherical granule that does not contain any organic additives, has a small amount of metal impurities, and has excellent fluidity. In addition, if the silica granulated powder of the present invention is used as a raw material for dry pressure molding and sintering, it is excellent in uniform filling and close-packing, so even if it is increased in size in industrial production, it has no cracks and density. An opaque quartz glass having a high purity and high heat shielding property can be provided, which can produce a high molded body and a sintered body with good yield.

The scanning electron micrograph of the silica granulated powder produced in Example 1 is shown. The scanning electron micrograph of the silica granulated powder produced in Example 2 is shown. The scanning electron micrograph of the silica granulated powder produced in Comparative Example 1 is shown. The scanning electron micrograph of the silica granulated powder produced in the comparative example 2 is shown.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

  For the fine particles in silica that affect the characteristics of granulation, molding and sintering, the weight ratio and particle size distribution of fine silica are determined by separating the fine silica using the centrifugal sedimentation method described in (a) below. did. In addition, when the particle size distribution of each silica slurry prepared in Examples and Comparative Examples was measured without using the centrifugal sedimentation method described later (a), no significant difference was observed in the particle size distribution, and the quantitative evaluation of the fine particles Was difficult.

(A) Centrifugal settling operation method After preparing a silica slurry with a solid content concentration (Cs ₁ ) of 10 wt%, 30 g of silica slurry is placed in a 50 ml centrifuge tube (resin, conical type, inner diameter of about 27 mm, height of about 113 mm). Prepared. The silica slurry was prepared with ultrapure water using silica powder dry-pulverized with various pulverizers. When using wet-pulverized silica slurry instead of dry-pulverized silica powder, after uniformly dispersing in a pot mill and drying at 130 ° C. to a constant weight, and measuring the solid content weight The solid content concentration (Cs ₁ ) is adjusted to 10 wt%.

Next, the silica slurry having a solid content concentration (Cs ₁ ) of 10 wt% was subjected to a dispersion treatment with an ultrasonic homogenizer (US-150T manufactured by Nippon Seiki Seisakusho, chip diameter φ12 mm, current value 150 μA, treatment time 5 minutes). The silica slurry was subjected to centrifugal sedimentation with a centrifuge (CN-1050 manufactured by ASONE, rotation speed 5000 rpm, rotation time 15 minutes, number of operations 1 time), and then the upper layer liquid was sampled in a 50 ml glass sample bottle using a 2 ml Pasteur. And separated from the concentrated layer (sedimentation layer and compression layer).

(B) Quantification of the weight ratio of fine silica in silica An appropriate amount (about 2 g) was collected from the concentrated layer after separation of the upper layer liquid described in (a) into a glass container with a Komagome pipette, and at 130 ° C. with a dryer. It dried until it became a constant weight, and the solid content weight of the concentration layer was measured. The weight ratio of fine silica to the total amount of silica was calculated from the following formula.

ここで、Ｗ_１は遠心沈降前のスラリー重量［ｇ］、Ｗ_２は遠心沈降後の濃縮層の重量［ｇ］、Ｃｓ_１は遠心沈降前のスラリーの固形分濃度［ｗｔ％］、Ｃｓ_２は遠心沈降後の濃縮層の固形分濃度［ｗｔ％］である。Ｗ_１，Ｗ_２は、精密天秤（天秤精度０．１ｍｇ）で秤量した値であり、Ｃｓ_１，Ｃｓ_２は、固形分重量／スラリー重量×１００で求めた値である。

Here, W ₁ is the slurry weight [g] before centrifugal sedimentation, W ₂ is the weight of the concentrated layer after centrifugal sedimentation [g], Cs ₁ is the solid content concentration [wt%] of the slurry before centrifugal sedimentation, and Cs _2. Is the solid content concentration [wt%] of the concentrated layer after centrifugal sedimentation. W ₁ and W ₂ are values weighed by a precision balance (balance accuracy 0.1 mg), and Cs ₁ and Cs ₂ are values obtained by solid content weight / slurry weight × 100.

(C) Particle size distribution The particle size distribution of silica was measured by a laser diffraction / scattering method (sphere equivalent diameter). The measuring apparatus uses Microtrac (manufactured by Microtrac Bell Co., Ltd., MT3300EX). The measurement conditions are 1.46 for silica, water for solvent, 1.33 for water, and cumulative distribution. Under the sieve, the distribution format was based on the number or volume.

  In the present invention, the upper layer liquid and the concentrated layer separated by the centrifugal sedimentation method of (a) above are dispersed with an ultrasonic homogenizer for 2 minutes, and then the 50% particle size of fine silica in the upper layer liquid is evaluated on a number basis. Then, the 50% particle size and 100% particle size of silica in the concentrated layer were evaluated on a volume basis.

  Other measurements were performed by the following methods.

(D) BET specific surface area The BET specific surface area of silica was measured using a Flowsorb II2300 apparatus manufactured by Shimadzu Corporation. The degassing treatment was performed under a nitrogen gas flow with a heating temperature of 200 ° C. and a heating time of 30 minutes, and the adsorption gas was a mixed gas of 30% nitrogen and 70% helium (volume ratio) (BET one-point method). .

(E) Repose angle and light loading bulk density The repose angle and light loading bulk density of the silica granulated powder were measured using a multi-tester (manufactured by Seishin Enterprise Co., Ltd., MT-1001K).

(F) Metal impurity content The metal impurity content of the silica granulated powder was measured using an inductively coupled plasma emission spectrometer (ICP-AES).

Example 1
As the silica powder, an amorphous silica powder having a chemical purity of 99.9 wt% or more and a 50% particle size (volume basis) of 70 μm (product name “MKC Silica PS100” manufactured by Nippon Kasei Co., Ltd.) is used. The amorphous silica powder was pulverized at a supply rate of 5 kg / hr by a jet mill pulverizer (trade name “NJ-100”, manufactured by Aisin Nano Technologies Co., Ltd.), and the 50% particle size (volume basis) was changed to 4. The 9 μm and 100% particle size (volume basis) was 52 μm.

  As a fine silica used as an auxiliary agent, a fine spherical silica powder having a chemical purity of 99.9 wt% or more and a 50% particle size (number basis) of 0.1 μm (trade name “Sylfil NSS-3N” manufactured by Tokuyama Corporation) ) Was used.

  Next, 15.28 kg of jet silica-pulverized amorphous silica powder, 2.70 kg of fine spherical silica powder (15 wt% with respect to the total amount of silica), and 11.26 kg of ultrapure water were charged into a polyethylene pot. To prepare a slurry.

  The slurry was sprayed using a spray dryer (trade name “TR160” manufactured by Pris Co., Ltd., disk type, drying chamber diameter 1.6 m), slurry supply speed 8 kg / hr, disk rotation speed 18000 rpm, hot air inlet temperature 150 ° C., outlet About 18 kg of silica granulated powder was produced by spray drying at a temperature of 80 ° C.

Table 1 shows the silica preparation conditions, and Table 2 shows the silica physical properties and the silica granulated powder physical properties. The obtained silica granulated powder had an angle of repose of 30 ° and a light bulk density of 0.95 g / cm ³ .

  FIG. 1 shows an electron micrograph of the silica granulated powder. It is a spherical granule having a size of about 60 μm with good fluidity.

  Table 3 shows the results of metal impurity analysis of the silica granulated powder. From this table, it is clear that the content of each metal impurity of Na, Ca, Al, Fe, Cr, and Ni is 1 ppm or less in the silica granulated powder of the present invention.

Example 2
The same procedure as in Example 1 was performed, except that the same amorphous silica powder and fine spherical silica powder as in Example 1 were used, and the mixing ratio of the fine spherical silica powder to the total silica amount was 10 wt%.

Table 1 shows the silica preparation conditions, and Table 2 shows the silica physical properties and the silica granulated powder physical properties. The obtained silica granulated powder had an angle of repose of 34 ° and a light bulk density of 0.92 g / cm ³ .

Example 3
The same procedure as in Example 1 was performed, except that the same amorphous silica powder and fine spherical silica powder as in Example 1 were used, and the mixing ratio of the fine spherical silica powder to the total silica amount was 25 wt%.

Table 1 shows the silica preparation conditions, and Table 2 shows the silica physical properties and the silica granulated powder physical properties. The obtained silica granulated powder had an angle of repose of 30 ° and a light bulk density of 1.03 g / cm ³ .

Comparative Example 1
The same procedure as in Example 1 was performed, except that the same amorphous silica powder as in Example 1 was used and the fine spherical silica powder was not mixed.

Table 1 shows the silica preparation conditions, and Table 2 shows the silica physical properties and the silica granulated powder physical properties. Silica powder is difficult to granulate, is an amorphous fine powder similar to that before granulation, has an angle of repose as high as 47 °, and a light bulk density as low as 0.66 g / cm ^3. Granular powder was not obtained.

  In the upper layer liquid when the silica slurry having a solid content concentration of 10 wt% (ultrasonic homogenizer dispersion, treatment time 5 minutes) is separated by centrifugal sedimentation (rotation speed 5000 rpm, rotation time 15 minutes, number of operations 1 time), No fine silica having a 50% particle size (number basis) of 0.01 to 0.9 μm was detected.

Comparative Example 2
The same procedure as in Example 1 was performed except that the same amorphous silica powder and fine spherical silica powder as in Example 1 were used, and the mixing ratio of the fine spherical silica powder to the total silica amount was 5 wt%.

  Table 1 shows the silica preparation conditions, and Table 2 shows the silica physical properties and the silica granulated powder physical properties. Since the granulation property of the silica powder was inferior, the granulated powder collapsed, and the silica granulated powder according to the present invention was not obtained.

  In the upper layer liquid when the silica slurry having a solid content concentration of 10 wt% (ultrasonic homogenizer dispersion, treatment time 5 minutes) is separated by centrifugal sedimentation (rotation speed 5000 rpm, rotation time 15 minutes, number of operations 1 time), Fine silica having a 50% particle size (on a number basis) of 0.5 μm was detected, but the weight ratio of the fine silica to the total silica amount was 0.7 wt%, which is lower than the fine silica weight ratio of the present invention. Value.

Comparative Example 3
The same amorphous silica powder as in Example 1 was used, fine spherical silica powder was not mixed, and 1.0 wt% of an organic binder (manufactured by YUKEN INDUSTRY CO., LTD., CERANDER AP-5) was added (vs. amorphous silica). The procedure was the same as in Example 1 except that (powder).

Table 1 shows the silica preparation conditions, and Table 2 shows the silica physical properties and the silica granulated powder physical properties. The silica powder was slightly inferior in granulation property, the angle of repose was as high as 37 °, and the light bulk density was as low as 0.74 g / cm ³ , so that the silica granulated powder according to the present invention was not obtained.

  In the upper layer liquid when the silica slurry having a solid content concentration of 10 wt% (ultrasonic homogenizer dispersion, treatment time 5 minutes) is separated by centrifugal sedimentation (rotation speed 5000 rpm, rotation time 15 minutes, number of operations 1 time), No fine silica having a 50% particle size (number basis) of 0.01 to 0.9 μm was detected.

応用例
実施例１と実施例２のシリカ造粒粉末、及び比較例１のシリカ粉末を用いて、以下の方法により成形性、焼結性について評価した。

Application Example Using the silica granulated powder of Example 1 and Example 2 and the silica powder of Comparative Example 1, the moldability and sinterability were evaluated by the following methods.

  The density of the CIP compact was calculated from the weight and size, and the density of the sintered body was measured by Archimedes method according to JIS R 1634.

  After filling each powder of Example 1, Example 2, and Comparative Example 1 into a foam polystyrene mold, the entire foam polystyrene mold was sealed under reduced pressure in a polyethylene bag and CIP molded at a pressure of 280 MPa. Next, the CIP compact was sintered at a predetermined temperature in an air atmosphere to obtain an opaque quartz glass.

  Table 4 shows the density of the sintered body evaluated at each sintering temperature (holding time: 4 hours) in a compact size of 40 mm × 40 mm × 40 mm. From this table, it is clear that the silica granulated powder of the present invention has a high sintered body density and excellent sinterability.

表５に、大型サイズにおける成形性、焼結性の評価結果を示す。この表から、本発明のシリカ造粒粉末は、成形体密度が高く、１４２５℃（保持時間４時間）での焼結体密度も高く、クラックも発生していないことが明らかである。これに対し、５０％粒径（個数基準）が０．０１〜０．９μｍの微粒シリカが所定量含まれず、造粒困難であったシリカ粉末を用いた場合には、成形体密度も低く、１４２５℃（保持時間４時間）での焼結体にクラックが発生した。

Table 5 shows the evaluation results of formability and sinterability in large sizes. From this table, it is clear that the silica granulated powder of the present invention has a high molded body density, a high sintered body density at 1425 ° C. (holding time 4 hours), and no cracks. On the other hand, when a predetermined amount of fine silica having a 50% particle size (number basis) of 0.01 to 0.9 μm is not included and the silica powder that is difficult to granulate is used, the compact density is low, Cracks occurred in the sintered body at 1425 ° C. (holding time 4 hours).

  Accordingly, when the silica granulated powder prepared with the silica powder of the present invention is used, the uniform filling property, close-packing property, and sintering property at the time of CIP molding are improved. Opaque quartz glass can be produced.

  The silica granulated powder prepared with the silica powder of the present invention does not contain any organic additives, has high purity and high fluidity, and is excellent in moldability and sinterability. It is suitable as a raw material for producing opaque quartz glass used in, for example, and is extremely useful when producing large opaque quartz glass with high productivity on an industrial scale.

Claims (5)

The silica slurry having a solid content concentration of 10 wt% was separated by a centrifugal sedimentation method (rotation speed: 5000 rpm, rotation time: 15 minutes, number of operations: 1), and the 50% particle diameter (number basis) of the fine silica in the upper layer liquid was 0.00. The fine silica is from 01 to 0.9 μm, the 50% particle size (volume basis) of the silica in the concentrated layer is 2 to 20 μm, and the 100% particle size (volume basis) is 200 μm or less. A silica powder comprising 0.8 wt% or more and 15 wt% or less. The silica powder according to claim 1, wherein the BET specific surface area is 4.5 to 15 m ² / g. A silica granulated powder having an angle of repose after granulating the silica powder according to claim 1 or 2 and a light bulk density of 0.8 g / cm ³ or more. The silica powder having a 50% particle size (volume basis) of 2 to 20 [mu] m and a 100% particle size (volume basis) of 200 [mu] m or less is completely mixed with fine silica having a 50% particle size (number basis) of 0.01 to 0.9 [mu] m. The method for producing a granulated silica powder according to claim 3, wherein the mixture is wet-mixed at a ratio of 7 wt% to 40 wt% with respect to the amount of silica to form a slurry, and the resulting slurry is spray-dried. An opaque quartz glass obtained by molding and sintering the silica granulated powder according to claim 3.

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