JPH05163013A - Production of highly pure crystalline silica - Google Patents

Abstract

PURPOSE:To provide crystalline silica reduced in the content of silanol groups and useful as a raw material for highly pure quartz glass, and to provide a method for its production. CONSTITUTION:Highly pure amorphous silica fine powder and crystalline silica fine powder having a particle diameter of <=10mum in an amount of >=10wt.% are mixed with each other, granulated and heated to produce granular sintered crystalline silica. The crystalline silica granules thus produced are highly pure, contain a small amount of silanol groups and are useful as a raw material for highly pure and highly heat-resistant quartz glass.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a synthetic crystalline silica having a high purity and a low content of silanol groups.

[0002]

2. Description of the Related Art Although natural quartz powder has been used as a raw material for quartz glass by the melting method, in recent years, quartz glass has come to be used as a material for electronic parts and the like. Since it is necessary to obtain high-purity quartz glass, use of high-purity synthetic silica powder as a raw material thereof is being studied.

However, since synthetic silica is generally amorphous and contains several hundred ppm or more of silanol groups, the high temperature viscosity of fused silica products obtained by melting is higher than that of natural quartz powder. Has the drawback of being low.

As a method for solving this drawback, the present inventors have already been able to efficiently crystallize amorphous silica by crystallizing amorphous silica as a method for reducing the content of silanol groups in high-purity synthetic silica. A method for reducing the number of radicals has been proposed (Japanese Patent Application No. 2-418,013).

As a concrete means for crystallizing the amorphous silica, for example, in Japanese Patent Laid-Open No. 3-8708, after agglomerated amorphous silica fine particles are mixed with cristobalite crystal particles, A method has been proposed in which the particles are heated and sintered into cristobalite crystal particles. According to this method, the amorphous silica can be crystallized, but since the amorphous silica fine particles are granulated and then mixed with the crystalline silica, the granulated particles of the amorphous fine silica and the crystalline silica are mixed. The contact of silica is loose, the contact area is small, and the effect of mixing crystal particles is small. Therefore, in order to efficiently crystallize at a temperature of 1,200 ° C. or less at which necking due to sintering between the granulated particles of the amorphous silica particles is relatively difficult to occur, the mixing ratio of the crystalline silica is 50% by weight. More than required. When the mixing ratio of crystalline silica is low, heating at high temperature for a long time is required, which causes a problem in production efficiency.

[0006]

Therefore, the present invention is
It is an object of the present invention to provide a method for producing high-purity crystalline silica that efficiently crystallizes amorphous silica when the mixing ratio of crystalline silica is 0.01% by weight or more.

[0007]

[Means for Solving the Problems] That is, according to the present invention, fine particles of amorphous silica and fine particles of crystalline silica are mixed and then granulated and heated to be sintered into crystalline silica particles. This is a method for producing crystalline silica particles.

In the conventional method in which agglomerated amorphous silica fine particles are mixed with cristobalite crystal particles and then heated to sinter into granular cristobalite crystal particles, the amorphous granules are surrounded by In order to completely crystallize the amorphous granules because the crystals grow from the contact point with the crystalline silica, the crystal growth corresponding to at least the radius of the amorphous granules. Need.

However, before the amorphous silica fine particles are granulated into the agglomerated particles as in the present invention, if the mixed fine particles are granulated into the agglomerated particles after being uniformly mixed with the crystalline silica fine particles in advance, the granules Fine crystal particles can be included therein. Therefore, the crystal growth distance required for complete crystallization of the granules is less than or equal to the radius of the amorphous granules, the heating time required for crystal growth is greatly shortened, and crystallization is very efficient. It is thought to be something that can be done. In addition, since the amount of crystalline silica added may be small, it is advantageous in terms of production efficiency. If the particle size of the crystalline silica is further reduced, the addition amount can be further reduced.

The method for producing high-purity crystalline silica of the present invention will be specifically described below. The crystalline silica fine powder to be a crystal nucleus that can be used in the present invention, quartz,
There is no particular limitation as long as it is crystalline silica such as cristobalite or tridymite. The amount used can be reduced by reducing the particle size of the crystalline silica fine powder, but it is preferably substantially 0.01% by weight or more. If it is less than this range, crystallization does not proceed sufficiently substantially.

As the amorphous silica fine powder which can be used in the present invention, high-purity synthetic silica fine powder such as wet synthetic silica by the sodium silicate method and vapor phase synthetic silica made from silicon tetrachloride as a raw material may be used. However, those having a particle size of 1 μm or less and having excellent sinterability are preferable.

As a method for mixing the amorphous silica fine powder and the crystalline silica fine powder, a method of dispersing them in pure water and wet mixing is preferable.

The method of granulating the agglomerated particles is arbitrary. For example, when the spray drying method is used, the wet-mixed slurry can be directly granulated and dried, and the granulated particle size can be controlled. It is also possible to

By mixing the fine particles of amorphous silica and the fine particles of crystalline silica in this manner and then heating the granulated material, sintering and crystallization occur, regardless of the kind of the added crystal. , Cristobalite is obtained,
The firing temperature is preferably 1,100 ° C. or higher. When the temperature is lower than this temperature, the crystallization speed is slow and it is not practical.

At this time, the crystallization by heating is carried out in a dry gas stream having a water content of 20 ppm or less, preferably 10 ppm or less, whereby the silanol groups can be further reduced.

The synthetic crystalline silica thus obtained is
It has a high purity and a silanol group content equivalent to that of natural quartz, and has the characteristics desired as a fused silica raw material.

[0017]

EXAMPLES The present invention will be described in detail below based on examples and comparative examples. Example 1 1 part by weight of cristobalite crushed to an average particle size of 3 μm with an agate ball mill and 100 parts by weight of fumed silica were mixed in 200 parts by weight of pure water, and then dried by a spray-dry method. Amorphous silica granulated particles having cristobalite crystal nuclei inside with an average particle size of 200 μm were obtained.

The granulated particles thus obtained were mixed with 1,3
By heating and firing at 00 ° C. for 10 hours, the amorphous phase could be sintered and crystallized into the cristobalite phase. Table 1 shows the OH group content and crystallinity of the obtained cristobalite.

The OH group content is 3,6 by FT-IR.
Lam by measuring the IR absorption around 60 cm ^-1
Calculated from Bert-Beer's law. The crystallinity was determined from the maximum peak relative area where 2θ was around 20 ° by the powder X-ray diffraction method. As a standard material, one having a true specific gravity of 2.33 was used as cristobalite having a crystallinity of 100%.

Example 2 In the same manner as in Example 1, the mixing ratio of cristobalite having an average particle size of 1 μm and fumed silica was 1: 1,000.
Granulated particles having an average particle diameter of 200 μm were obtained. this,
By heating at 1,300 ° C. for 10 hours, the amorphous phase could be sintered and crystallized into the cristobalite phase.
Table 1 shows the OH content and crystallinity of the obtained cristobalite.

Example 3 Cristobalite particles were obtained in the same manner as in Example 2, except that the heating for crystallization was performed while blowing a dry gas having a water content of 10 ppm into the casket through a quartz tube. Table 1 shows the OH content and crystallinity of the obtained cristobalite. Even with the same crystallinity as in Example 2, the amount of OH groups is further reduced.

Comparative Example 1 A mixture of 100 parts by weight of fumed silica and 200 parts by weight of pure water was dried by a spray drying method,
Amorphous silica granulated particles having an average particle diameter of 200 μm were obtained.
This was heated and baked at 1,300 ° C. for 10 hours to be sintered, but no crystal phase was obtained. Table 1 shows the OH group content and crystallinity of the obtained amorphous sintered body.

Comparative Example 2 Amorphous silica granulated particles 1 obtained in the same manner as Comparative Example 1
And an average particle size of 3 using 00 parts by weight of an agate ball mill
A mixture of 5 parts by weight of cristobalite pulverized to μm with a V-type mixer for 1 hour was mixed at 10 ° C. at 10 ° C. for 10 hours.
The material was heated and baked for an hour to crystallize the amorphous phase. Table 1 shows the OH group content and crystallinity of the obtained cristobalite.

[0024]

[Table 1]

[0025]

INDUSTRIAL APPLICABILITY According to the method of the present invention, silanol is highly purified.
A crystalline silica having a low ruthenium content is obtained. Such silica is particularly useful as a raw material for high purity, high heat resistant quartz glass products.

Claims (3)

[Claims] 1. Crystalline silica particles characterized by mixing amorphous silica fine particles and crystalline silica fine particles, and then granulating the mixture and heating it to sinter it into particulate crystalline silica. Manufacturing method. 2. The crystalline silica fine particles have a particle diameter of 10 μm.
The method for producing crystalline silica particles according to claim 1, wherein the content is less than or equal to 0.01% by weight with respect to the amorphous silica particles. 3. Crystallization by heating to a water content of 20
The method for producing crystalline silica according to claim 1, wherein the method is performed in a dry gas flow of ppm or less.