JP2001089125A - Porous silica granules, method for producing the same, and method for producing synthetic quartz glass powder using the porous silica granules - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nearly spherical porous silica granule having homogeneous texture, small pore diameter, pore volume and specific surface area, high bulk specific gravity and capable of forming a quartz glass without causing the shrinkage, provide its production process and provide a process for producing synthetic quartz glass powder by using the porous silica granule. SOLUTION: The porous silica granule is characterized by a nearly spherical form, a carbon concentration of <1 ppm, a pore volume of <=0.5 cm3/g per 1 g of the granule, an average pore diameter of <=50 nm, a specific surface area of <=100 m2/g and a bulk density of >=0.7 g/cm3. The invention further discloses its production process and a process for producing synthetic quartz glass powder by using the porous silica granule.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a high-purity porous silica granule and a method for producing the same, and a method for producing a high-purity synthetic quartz glass powder using the porous silica granule.

[0002]

2. Description of the Related Art Porous silica granules have been used as a raw material for synthetic quartz glass powder, as a catalyst carrier or as a filler in the semiconductor industry. In recent years, the high integration of semiconductors has led to the demand for high-purity quartz glass, and the purity and quality of quartz glass made from natural quartz and silica sand that have been used until now have reached their limits, Synthetic quartz glass is attracting attention. For the synthetic quartz glass, for example, a sol-gel method for pulverizing a gel obtained by hydrolyzing high-purity silicon alkoxide or the like, or silica fine particles obtained by flame hydrolysis of a high-purity silane-based gas are deposited (soot). Method) It is manufactured by firing to obtain a synthetic quartz glass and then pulverizing. However, in the conventional sol-gel method and soot method, both are once formed into a lump and then pulverized and refined to produce quartz glass powder. Was not enough. In particular, in the sol-gel method, a carbon-containing compound such as silicon alkoxide is used as a raw material. Therefore, a carbon component is mixed into the porous silica granules, and the concentration thereof becomes several percent, and remains as black foreign matter, or It is a cause of the generation of bubbles, and is not satisfactory as a synthetic quartz glass raw material for the semiconductor industry which requires high purity and high quality. In addition, since the sol-gel method contains a large amount of solvent and water, the gel obtained by evaporating these becomes extremely porous and has a large number of pores having a diameter of about 0.1 to 20 μm. Was trapped in the glass particles and expanded when the semiconductor was subjected to high-temperature decompression heat treatment. On the other hand, in the soot method, by using a carbon-free raw material, the carbon component does not remain and there is no contamination by the carbon component, but on the other hand, a large amount of by-products is generated during the production of the bulk body, and the production efficiency is lowered. There is a disadvantage that the cost is high. As a method for utilizing such a large amount of by-products, Japanese Patent Application Laid-Open Nos. 7-17706 and 11-130417 disclose a method in which silicate dust is dispersed in water and granulated. There is a process such as pulverization in the production of, and it is difficult to avoid the contamination of impurities, which is not a satisfactory method.

[0003]

However, the above-mentioned soot method has no residual carbon component, and has a small pore diameter and a high bulk density. Therefore, the soot method is further improved by further improving the soot method. Based on the belief that a synthetic quartz glass of high purity and high quality can be obtained, the present inventors have conducted intensive studies and as a result, dispersed fumed silica obtained by hydrolyzing a silicon compound raw material in pure water. After the slurry is formed, it is dried under specific conditions to obtain high-purity, high-quality porous silica granules without contamination by pulverization and purification. Was obtained. Further, the present inventors have also found that the silica granules can be obtained by using a large amount of silicate dust generated as a by-product during the production of synthetic quartz glass, thereby completing the present invention. That is,

An object of the present invention is to provide porous silica granules having high purity.

[0005] An object of the present invention is to provide a porous silica granule obtained by utilizing a large amount of by-product generated during the production of synthetic quartz glass.

An object of the present invention is to provide a method for producing the above-mentioned high-purity porous silica granules.

An object of the present invention is to provide a method for producing high-purity synthetic quartz glass powder using the above-mentioned porous silica granules.

[0008]

SUMMARY OF THE INVENTION The present invention, which achieves the above objects, is substantially spherical, has a carbon content of less than 1 ppm, a pore volume of 0.5 cm ³ or less per gram of granules, and an average pore diameter of 50 nm. Hereinafter, porous silica granules having a specific surface area of 100 m ² / g or less and a bulk density of 0.7 g / cm ³ or more, a method for producing the same, and a high-purity synthetic quartz glass using the porous silica granules The present invention relates to a method for producing powder.

As described above, the porous silica granules of the present invention can be prepared from compounds containing no carbon atom in the molecule, for example, silicon tetrachloride, disilicon hexachloride, silicon tetrabromide, silicon tetraiodide, hexadichlorosiloxane, Fumed silica obtained by hydrolyzing trichlorosilane, tribromosilane, trisilane and the like is used as a raw material, and is a silica granule having a carbon concentration of less than 1 ppm and having no trouble due to a carbon component. At the time of producing the silica granules, fumed silica is dispersed in pure water to form a slurry having a solid content concentration of 50 to 80% by weight, the pH value is adjusted to 1 to 4 by adding a mineral acid, and the slurry is stirred for 80 to 80% by weight. 150 ° C
It can be manufactured by supplying a heated clean gas to the substrate and drying. In the drying in the above-mentioned production method, the slurry gradually becomes paste-like, and further becomes spherical uniform granules by shearing force and rotation by stirring. The size of the granules varies depending on the stirring speed, the flow rate of the heating gas, the flow rate and the humidity, but the evaporation rate of water is preferably 50 g / h or less per kg of the initial slurry. If the evaporation rate of water exceeds the above range, the water inside the granules boils and the granules may be broken, which is not preferable. When the water content is reduced to 1% by weight or less by the drying, the particles are classified to form porous silica granules having a particle size of 50 to 800 μm. The fumed silica has an average particle size of 4 μm or less, preferably 1 μm, so that the slurry has sufficient viscosity.
m or less is good. The mineral acid to be added to the slurry is not particularly limited as long as it is a volatile acid, and examples thereof include hydrochloric acid and nitric acid. When silicon chloride is used as a raw material, hydrochloric acid is preferred because a small amount of hydrogen chloride, which is a by-product of hydrolysis, may dissolve in the slurry.

The porous silica granules obtained as described above have an average pore diameter of 50 nm or less, which is smaller than about one-twentieth of the silica granules obtained by the sol-gel method. It disappears from the inside of the granules without being closed as closed pores during firing during production. Further, the pore volume is 0.5 cm ³ or less per gram of granules, and the volume occupied by the pores is very small, and the specific surface area is 100 m ^2.
/ G or less and the bulk density is 0.7 g / cm ³ or more. Therefore, there is no shrinkage when producing bulk quartz glass, and since the silica granules are homogeneous and nearly spherical, they show almost similar firing and melting behavior, making firing and melt vitrification easy. It is possible to obtain a bulk transparent quartz glass by directly molding without firing to form a quartz glass powder. Further, the porous silica granules are high-purity and homogeneous granules, and thus are useful as a catalyst carrier and as a semiconductor filler.

In the case of producing a synthetic quartz glass powder, which is a raw material of a synthetic quartz glass, using the above porous silica granules, the porous silica granules are mixed in an atmosphere containing oxygen for 150 minutes.
Heat treatment is performed at a temperature in the range of 300 ° C. to discharge fine powder adhering to the surface of the silica granules by the action of water to the outside of the system, and completely remove water remaining in the granules. The temperature is 3
If the temperature exceeds 00 ° C., the silica granules are undesirably cracked. Further, heat treatment is performed in a temperature range of 600 to 1100 ° C. to oxidize and remove organic substances and combustible substances mixed in the silica granules. If the temperature exceeds 1100 ° C., the pores are partially closed, which is not preferable. If the temperature is lower than 600 ° C., it is difficult to achieve the intended purpose. Finally, a heat treatment at 1100 to 1300 ° C. is performed in a flow atmosphere containing hydrogen chloride to remove contained trace metal impurities as chlorides. At this time, in order to increase the reaction rate, the temperature may be as high as about 1200 ° C. At this temperature, the pores begin to close, but there is no particular problem since impurities have been removed in the previous step. The purification treatment of the porous silica granules in the present invention refers to the heat treatment.

The high-purity porous silica granules obtained by the above heat treatment are fired in an electric furnace in a vacuum or in an atmosphere of hydrogen or helium at 1300 to 1500 ° C. and densified to obtain a transparent synthetic quartz glass powder. As the electric furnace, a furnace made of high-purity quartz glass or ceramics is preferable, and silica granules are put in the furnace, heated at a uniform temperature, and held for a predetermined time. In this sintering, the temperature is 1500 ° C
If it exceeds, fusion of the silica granules may occur, and it may be necessary to pulverize, which is not preferable.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described, but the present invention is not limited thereto.

The specific surface area, pore volume, average pore diameter and impurity concentration are values obtained by the following measuring methods. (A) Specific surface area: BET method (b) Pore volume: gas adsorption method (DH method) (c) Impurity concentration: IPC-AES method and infrared spectrophotometry

[0015]

Example 1 An oxyhydrogen flame was burned using a quartz glass burner in a reaction chamber made of quartz glass, and high-purity silicon tetrachloride was supplied therein to generate fumed silica.
Fumed silica in the gas exhausted from the exhaust port was collected by a bag filter to obtain 140 kg of fumed silica.

The inner and stirring blades are covered with polyurethane resin.
Prepare a covered stirrer, add 75 liters of pure water, and stir
Add fumed silica gradually while rotating the roots
A 65% by weight slurry was made. This slurry
Body grade hydrochloric acid 200cm ^ThreeAnd stir for about 30 minutes
Continued to stabilize. The slurry is filled with polyurethane
A container with a diameter of about 1 m covered with tin resin and made of quartz
Glass stirring jig and scraper are installed
Put into the container, rotate the stirring jig and the stirring container,
5m of dry clean air heated to 0 ℃^Three/ Min flow rate
Drying was continued for 30 hours while supplying with. The slurry is 8
It becomes pasty in time, and after 16 hours contains about 20% of water.
It became granular while watching. After 30 hours the water content
0.6% by weight. Then classify it 180-500μ
70 kg of granules of m were collected. The granules obtained are shown in FIG.
It is almost spherical and homogeneous, and its physical property value is
Is 55m^Two/ G, pore volume 0.307cm^Three/ G, average
The pore diameter was 11.2 nm. The impurity concentration is shown in the table.
No. 1. The unit of impurity concentration is ppm
It is.

[0017]

[Table 1]

Next, the granules are poured into a rotary kiln.
And oxygen flow 150cm at 200 ° C ^ThreeOxidation treatment per minute
Was done. The processing speed at this time is 12 kg / hour and the
The transit time was about 30 minutes. Set the temperature to 80 under the same conditions.
After heat treatment at 0 ° C, the temperature was raised to 1200 ° C.
Hydrogen chloride flow 150cm^Three/ Heat treatment
gave. The processing speed is 10 kg / hour and the passage time in the furnace is about
40 minutes. Granules after completion of this heat treatment
When the property value was measured, the specific surface area was 49 m.^Two/ G, stoma
The volume is 0.27cm^Three/ G, average pore diameter is 11.7 nm
Met. Table 2 shows the impurity concentrations.
The unit of the impurity concentration is ppb.

[0019]

[Table 2]

After the heat treatment, 10 kg of the porous silica granules were placed in a quartz glass container, inserted into a vacuum furnace of a carbon resistance heater, once evacuated, and then helium gas was introduced to form a helium atmosphere. 2 up to 1200 ° C
The temperature was raised at 0 ° C./min, then slowly heated to 1380 ° C. at 1 ° C./min, kept at 1380 ° C. for 6 hours, and then cooled naturally. The quartz glass powder taken out of the furnace had almost no fusion between the powders, and was returned to a complete powder state by crushing by hand. No pores were detected in this transparent quartz glass powder, and the true specific gravity was 2.18.

The above synthetic quartz glass powder was melted under vacuum to produce a quartz glass rod and a block material. The obtained quartz glass rod and block material had no bubbles, foreign substances, and the like, and no expansion of the bubbles was observed even when vacuum heating was performed at 1600 ° C.

[0022]

Industrial Applicability The porous silica granules of the present invention are high-purity, homogeneous, small in pore diameter, pore volume, specific surface area, high in bulk density, and do not shrink during the production of quartz glass. . Further, it is useful as a semiconductor filler because of its high purity and large bulk density. The porous silica granules have high industrial value because by-products produced during the production of synthetic quartz glass can be used.

[Brief description of the drawings]

FIG. 1 is a micrograph of a porous silica granule of the present invention.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Reiner Kepler 63500, Zelligenstadt, Germany 83; Schutteinheimer Straße 83, 72 Inventor Klaus Anort Hanau, Germany 63457, Inden Hammersbysen 9F term (reference) 4G014 AH15 4G072 AA28 AA30 BB07 DD02 DD03 DD04 GG01 GG03 HH03 HH07 HH10 JJ01 JJ14 LL01 LL03 LL11 MM03 TT07 MM03 MM03 MM03 TT05 TT08 TT19 UU01 UU21

Claims (9)

[Claims] (1) a substantially spherical particle having a carbon concentration of less than 1 ppm, a pore volume of 0.5 cm ³ or less per gram of granules,
The average diameter of the pores is 50 nm or less, and the specific surface area is 100 m ² /
g, and a bulk density of 0.7 g / cm ³ or more. 2. The porous silica granules according to claim 1, wherein the water content is 1% by weight or less. 3. The porous silica granule has a particle size of 50 to 800 μm.
2. The porous silica granules according to claim 1, wherein m is in the range of m. 4. A high-purity synthetic quartz glass powder obtained by purifying and firing the porous silica granules according to claim 1. 5. A fumed silica obtained by hydrolyzing a silicon compound having no carbon atom is dispersed in pure water to form a slurry having a solid concentration of 50 to 80% by weight, and the pH value is adjusted to 1 to 4. Then, while stirring, a clean gas heated to 80 to 150 ° C. is supplied for 20 hours or more, and the water content is reduced to 1% by weight.
A method for producing porous silica granules, which is dried and classified as follows. 6. The method for producing porous silica granules according to claim 5, wherein the particle size of the fumed silica is 4 μm or less. . 7. The method for producing a high-purity synthetic quartz glass powder according to claim 5, wherein the water evaporation rate during drying with the heating gas is 50 g / h or less per kg of the initial slurry. 8. The method according to claim 5, wherein the porous silica granules obtained by the method according to claims 5 to 7 are further treated in an atmosphere containing oxygen at a temperature of 150-150.
Heat treatment at 300 ° C., then heat treatment at 600-1100 ° C., and in an atmosphere containing hydrogen chloride, 1100-13
A method for producing a high-purity synthetic quartz glass powder, comprising subjecting a heat treatment at 00 ° C. to firing in a vacuum or in a helium or hydrogen atmosphere. 9. A method for producing a high-purity synthetic quartz glass, which comprises vitrifying the high-purity synthetic quartz glass powder obtained by the production method according to claim 8.