JPH068182B2 - Method for producing synthetic quartz powder - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing synthetic quartz powder, and more particularly to a method for industrially easily and inexpensively producing synthetic quartz powder having a desired particle size distribution. is there.

[Prior Art] For the production of synthetic quartz glass, a method of hydrolyzing a silicon compound such as silicon tetrachloride in an oxyhydrogen flame to form silica particles, and melting the silica particles to obtain quartz glass Known methods include a method of making a flame into a plasma flame, a so-called sol-gel method in which alkoxysilane is hydrolyzed in an alcohol solvent with an acid catalyst to produce silica, and the silica is sintered to obtain quartz glass.

However, in the method using this oxyhydrogen flame, 1,000 ppm of OH groups remain in the quartz glass, and the high temperature viscosity is low.
Although there is a problem that foaming occurs at high temperature in vacuum, the plasma method has the disadvantages of high cost and difficulty in mass production. Although silica glass can be obtained relatively inexpensively by the sol-gel method, It has the disadvantages that the base is likely to remain, the production requires a long time, and it is difficult to obtain a product having high temperature viscosity.

[Problems to be Solved by the Invention] Therefore, the inventors of the present invention proceeded with research on a method for producing synthetic quartz having high purity and high temperature viscosity by the sol-gel method, in which methyl silicate was dissolved in a methanol solvent. Hydrolyze in the presence of ammonia to make silica with a particle size of 200-3,000 nm, sinter and crush it at 1,700 ℃
Melting method (Japanese Patent Application No. Sho 63-229333)
No. 0329 gazette)), methyl silicate is hydrolyzed in the presence of ammonia to form silica having primary particles having a particle size of 100 to 500 nm, which are aggregated into particles having a particle size of 10 to 100 μm, and then solid-liquid separated, followed by firing A method of binding, crushing, sieving, and melt-molding at 1,700 ° C. or higher (Japanese Patent Application No. 63-335070 (JP-A-2-18072).
3)), and hydrolyze methyl silicate in the presence of ammonia to form silica, which is sintered at 1,500 to 1,700 ° C. under reduced pressure and then 1,800 to 2,000 ° C. under normal pressure or pressure. (See Japanese Patent Application No. 1-139619 (Japanese Patent Laid-Open No. 3-5329)).

However, although these methods provide synthetic quartz with high temperature and high viscosity, they all lack long-term productivity due to the long process, and have the disadvantage of high energy costs such as sintering, and they are not always satisfactory. Not kimono.

Therefore, the inventors of the present invention further dripped methyl silicate and aqueous ammonia into the reactor at the same time to collect the spherical silica particles produced by this continuous reaction, and then make an aqueous dispersion solution having a pH of 9 to 13 to the silica. After adding 5 to 20% by weight of methyl silicate (calculated as silica) to solidify, then heating, dehydration, desolvation and decarburization, sieving to a range of 30 to 100 mesh and 1,400 to 1,600 ℃ A method of sintering and crushing this has been proposed (see Japanese Patent Application No. 1-324637 (Japanese Patent Laid-Open No. 3-187936)), but with this method, the ideal particle size is 30 to 100 mesh. Therefore, it has been found that there is a disadvantage that a crushing loss occurs in order to obtain various particle sizes within a narrower range.

[Means for Solving the Problem] The present invention relates to a method for producing a synthetic quartz glass powder capable of solving such disadvantages, which comprises a) hydrolyzing methyl silicate with ammonia water having a pH of 13 or more. Prepared colloidal silica and b) methyl silicate
Characterized by mixing with silica sol prepared by hydrolysis with ammonia water of pH 8-13, granulating, heating in an oxidizing atmosphere, then sintering at 1,400-1,600 ° C, crushing and sieving It is what

That is, as a result of various studies by the inventors of the present invention on a method of obtaining a synthetic quartz powder having high purity and high temperature viscosity with an appropriate particle size, silica obtained by the sol-gel method proposed by the inventors has been described above. For production, alkoxysilane was specified as methyl silicate, which was hydrolyzed with aqueous ammonia, the resulting silica was granulated, then heated in an oxidizing atmosphere, and then sintered at high temperature for dissolution. If crushing and sieving reduce the OH groups, synthetic silica powder with high purity and high temperature viscosity can be obtained. However, in this case, it is difficult to control the particle size. Therefore, hydrolysis of this methyl silicate with ammonia water is required. A) a step of hydrolyzing with ammonia water having a pH of 13 or more to obtain colloidal silica having a relatively large particle size; and b) hydrolysis with ammonia water having a pH of 8 to 13 to give a relatively small particle size. The silica obtained in steps a) and b) is mixed at an arbitrary ratio, granulated and then heated in an oxidizing atmosphere, and then sintered at a high temperature, and then dissolved. It was found that synthetic quartz having a target particle size can be easily obtained by crushing and sieving, and the present invention was developed by conducting research on the operating method of each step, the mixing ratio of a) and b), and the like. Completed

This will be described in more detail below.

[Operation] In the present invention, a) colloidal silica prepared by hydrolyzing methyl silicate with ammonia water having a pH of 13 or more and b) silica sol prepared by hydrolyzing methyl silicate with ammonia water having a pH of 8 to 13 are mixed. The present invention relates to a method of obtaining synthetic quartz powder by granulating, heating in an oxidizing atmosphere, sintering at high temperature, crushing and sieving.

In step a), methyl silicate is hydrolyzed with ammonia water having a pH of 13 or more. However, since hydrolysis of methyl silicate with ammonia water is highly reactive, the hydrolysis and polycondensation are instantaneous. However, if the pH of this ammonia water is 13 or more, the hydrolysis of methyl silicate is further promoted and the silica grows.
The colloidal silica has a relatively large particle size of 00 nm.

In step b), methyl silicate is hydrolyzed with ammonia water having a pH of 8 to 13. In this case, however, since the pH of the ammonia water is lower than that in step a), the step a) is performed. Hydrolysis proceeds more slowly than that of silica, and silica having a relatively small particle size of 30 to 70 nm is obtained as a silica sol. However, in this case, the pH of the ammonia water should be 8
If the pH is below, the resulting silica will have low strength after granulation, and if the pH is 13 or above, the silica will become large colloidal silica and precipitate. Therefore, it is necessary to set the pH to 8-13. It

In the present invention, the colloidal silica obtained in this step a) and b)
The silica sol obtained in the step is mixed and granulated, but since the silica sol obtained in the step b) has a small particle size, this is the binder of the colloidal silica obtained in the step a). As it serves, this mixture can be easily granulated. This granulation may be carried out by any means, and usually rotary granulation may be carried out. According to this, silica particles having a particle size of 500 to 100 μm can be obtained. However, the particle size of this granulated silica is 1) the charged amount,
It is determined by 2) mixing ratio of sol, 3) diameter of rotating object, 4) number of rotations, 5) rotation time, and the larger the mixing ratio of sol and the longer the rotation time, the larger the particle size is obtained. So
For this, these conditions may be selected according to the particle size of the target silica, but the mixing ratio of the sol, in other words, the colloidal silica obtained in step a) and b)
The mixing ratio with the silica sol obtained in the step was obtained in the step b) to 100 parts by weight of the colloidal silica obtained in the step a) in order to obtain the desired silica particle size of 300 to 100 μm. To obtain 40 to 45 parts by weight of silica sol and a particle size of silica of 500 to 150 μm, 45 to 50 parts of silica sol obtained in step b) to 100 parts by weight of colloidal silica obtained in step a). The weight part may be set.

The silica granules thus obtained are then subjected to heat treatment for dehydration, desolvation and decarburization. This heating may be carried out at 800 to 1,000 ° C. in an oxidizing atmosphere. It is preferable to raise the temperature from room temperature to 1,000 ° C. over 10 hours and then hold it at 1,000 ° C. for 1 hour or more. The silica powder is slightly solidified by this heating, but this powder is weakly crushed to particles of several tens to several hundreds of microns. Therefore, it is preferable to sieve the silica powder into particles having an appropriate particle size after crushing.

The silica thus sieved is then sintered to form a synthetic quartz ingot, which is compared with the conventional method in which the sintering was performed at a high temperature of 1,500 to 1,900 ° C. The silica of the present invention obtained by such a method may be sintered at a relatively low temperature of 1,400 to 1,600 ° C. for 1 to 2 hours. By this sintering, the particle size of the silica agglomerates is slightly reduced, but the particle size is almost 30 to 30 ° C. It becomes a transparent synthetic quartz glass block with 100 mesh.

This synthetic quartz glass lump is crushed and sieved to obtain the synthetic quartz glass powder of the present invention.
This synthetic quartz glass lump can be easily crushed with a roll mill or the like, so that it is easy to crush, and since there is no risk of impurities being mixed in each step described above, no purification step is required. Unlike conventional methods, glass powder has no loss (30-40%) due to crushing and sieving, and since it is manufactured at 100% yield, it has the advantage of being inexpensive. Also, since the particle shape is not a sharp shape like crushed powder, it becomes an aggregate of round particles and the filling state is uniform, so it is highly usable, and the synthetic quartz glass powder obtained here For example, if this is sintered at 1,950 ° C for 30 minutes and melt-molded, it can be made into a high-viscosity synthetic quartz glass body,
It is industrially advantageous that it is useful as a raw material for heat-resistant jigs for semiconductors such as crucibles.

[Examples] Next, examples of the present invention will be described.

Example 1 (Preparation of colloidal silica) 26.5 / hour of methyl silicate and 17.2 / hour of 20% by weight ammonia water so that the pH of the reaction solution would be 13 were simultaneously added dropwise to a continuous reaction flask of 5 to 40-50. React at ℃,
When the reaction was stopped after 5 hours, colloidal silica having a silica concentration of 25% was obtained. This was dehydrated, washed, and dried to obtain 42.5 kg of silica. Sifted with a polypropylene net 30 # to obtain a particle size of 5-40 μm 38.4 kg
made.

(Preparation of silica sol) 4.5 wt% ammonia water 3
Methyl silicate 13 was added dropwise to 7.5, and a hydrolysis reaction was carried out at 20 to 30 ° C. The silica concentration was 10.5% by weight.
As a result, 46.75 kg of a silica sol solution of was obtained.

(Production of Synthetic Quartz Powder) 5 kg of the colloidal silica obtained above was mixed with 40% by weight, 45% by weight and 50% by weight of the silica sol obtained above.
The mixture was put in a polyethylene bottle of 20 and rotated at 30 rpm for granulation, and the relationship between the rotation time and the granulated particle size (%) was examined, and the results shown in Table 1 were obtained. Was given.

From this result, 50 ~ 150 # which is suitable as a crucible raw material for pulling silicon single crystal can be obtained with the highest yield of 39.4% when the sol mixing ratio is 45% by weight after 20 minutes of rotary granulation. Since it was found that the granulated silica was made by this method, the granules with 150 # below were granulated again, and the granules with 50 ~ 150 # were collected. 25 kg of silica
In a quartz glass container, heated from room temperature to 1,000 ° C in air for 15 hours, then heated to 1,500 ° C under reduced pressure of 1 Torr for 2 hours, and held for 1 hour. Crush with quartz glass roll mill, 50 ~ 150 #
After sieving, 22 kg of synthetic quartz powder was obtained.

Regarding this synthetic quartz powder, when a crucible was molded using this using a known method, the obtained crucible did not change in appearance as compared with one made by melting natural quartz, and the amount of impurities was Al30ppb, Fe. , Ca35ppb, Na25ppb, K27ppb
With high purity, the viscosity (fiber elongation) at 1,400 ℃ was as high as log η = 10.89 poise.

Example 2 The amount of silica sol mixed with 5 kg of colloidal silica in Example 1 was set to 20% by weight, 25% by weight and 30% by weight, and rotation granulation was carried out in the same manner as in Example 1, and the rotation time and granulated particles at this time were set. When the relationship with the diameter (%) was examined, the results shown in Table 2 were obtained.

From this result, 100 to 200 suitable for vacuum sintering products
In order to obtain # #, it was found that the sol mixed ratio was 30 wt% and the granulation was carried out for 30 minutes by rotary granulation, and the highest yield was 61.7%, so this was repeated and the particle size was 100-200 #. Stuff for 29k
g, put in a quartz glass container, heated in air from room temperature to 1,000 ° C in 16 hours, then heated to 1,420 ° C under reduced pressure of 10 ^-2 torr over 2 hours and held for 1 hour After that, crush with a quartz glass roll mill and
After sieving to ~ 200 #, 27 kg of synthetic quartz powder was obtained.

The synthetic quartz powder thus obtained was again packed in a quartz glass tube and treated at 10 ⁻² torr at 1,700 ° C. to obtain a vacuum sintered product, which exhibited a viscosity of log η = 11.03. .

Example 3 From Table 1 in Example 1, in order to obtain 30 to 50 # silica suitable for making a filter, the sol mixing ratio is 5
It was found that the maximum yield was 53.1%, which was obtained by spin-granulating for 6 minutes at 0%.
Make ~ 50 # silica 35kg, put it in a quartz glass container, raise it in the air from room temperature to 1,000 ° C in 7 hours and hold it for 1 hour, then under reduced pressure of 1 Torr 1,580 ° C.
The temperature was raised for 2 hours and kept for 1 hour, then crushed with a quartz glass roll mill, and sieved to 30 to 50 # to obtain 30 kg of synthetic quartz powder.

The synthetic quartz powder obtained in this way was packed in a carbon case and processed at 1,500 ° C under atmospheric pressure to make a filter. This product has a maximum pore size of 150 μm and a minimum pore size of 75 μm.
It exhibited a physical property of μm.

[Effects of the Invention] The present invention relates to a method for producing synthetic quartz powder, which comprises: a) colloidal silica prepared by hydrolyzing methyl silicate with ammonia water having a pH of 13 or higher; and b) methyl silicate having a pH of 8 to 13 After mixing with silica sol prepared by hydrolyzing with ammonia water and granulating, heating in an oxidizing atmosphere, then sintering at 1,400-1,600 ℃, crushing and sieving Yes, but according to this a)
The silica obtained in the step is a colloidal silica having a relatively large particle diameter, and the silica obtained in the step b) is a silica sol having a small particle diameter. Since it is possible to easily obtain the granulated silica of, the synthetic quartz powder obtained by sintering, crushing and sieving it can be easily obtained as a powder having a predetermined particle size. Since the quartz powder has few OH groups and has high purity and high viscosity at high temperature, it is possible to easily produce synthetic quartz powder which is useful as a crucible material for pulling up semiconductor silicon, a vacuum sintered product, and a filter, for example. And the advantage that it can be obtained at low cost is given.

Claims (2)

[Claims] 1. A colloidal silica prepared by hydrolyzing a) methyl silicate with aqueous ammonia having a pH of 13 or more,
b) Mixing and granulating silica sol prepared by hydrolyzing methyl silicate with ammonia water having a pH of 8-13, heating in an oxidizing atmosphere, then sintering at 1,400-1,600 ° C, crushing and sieving And a method for producing synthetic quartz powder. 2. The adjustment of the particle size distribution of synthetic quartz glass powder is carried out by a),
The method for producing synthetic quartz glass powder according to claim 1, which is performed by adjusting the mixing ratio of the component (b).