JPH038708A - Production of silica feedstock - Google Patents

Abstract

PURPOSE:To prepare silica feedstock which can inexpensively and efficiently produce quartz glass of high quality by mixing aggregated fine particles of amorphous SiO2 with crystalline particles of cristobalite and sintering the mixture. CONSTITUTION:Commercially and inexpensively available fine particles of amorphous silica is granulated into aggregated particles of 30 to 500mum particle sizes. The particles and crystalline particles of cristobalite are mixed so that the weight ratio becomes 20/1 to 1/10, heated over 1100 deg.C, sintered and crystallized to give the subject silica feedstock for quartz glass.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing a silica raw material used for producing quartz glass, and relates to a method for producing it inexpensively and easily.

[Conventional technology]

As is well known, transparent quartz glass is made by heating and melting natural silica raw materials such as crystal, silica stone, and silica sand. That is,
Usually, (1) the Bernoulli method is used, in which the silica raw material powder is gradually fed into an argon-oxygen plasma flame or an oxyhydrogen flame, melted and vitrified, and deposited on a table.

■ A vacuum melting method in which the above silica raw material powder is placed in a crucible, melted in a vacuum heating furnace, and vitrified.

It depends on one of the following.

[Problem to be solved by the invention]

As mentioned above, in order to make transparent quartz glass,
Natural silica is usually used as a raw material, but natural silica contains various impurities, and a purification process is required to industrially produce high-purity quartz glass. Therefore,
It is undeniable that the cost will be high, and the natural silica raw material also has the problem of resource depletion.

For this reason, iM has proposed a method of synthesizing high-purity quartz glass by oxidizing silicon tetrachloride, but this method has disadvantages of low production efficiency and high cost.

In addition, although commercially available amorphous silicon dioxide powder has a high purity, it has a particle size of 0.02 um or less, so even if you try to directly vitrify it, it will not be possible to produce it using the conventional method described above. It is also well known that it is not suitable for implementation on an industrial scale due to its inefficiency and high cost.

As a means to solve this problem, for example, Japanese Patent Laid-Open No. 61-588
No. 22, JP-A No. 61-58823, etc. disclose that amorphous silicon dioxide powder is heated to produce a porous sintered body having a cristobalite crystal phase, and this is heated under vacuum.
A method of melting and vitrifying it has been proposed. According to these methods, highly pure transparent quartz glass can be obtained without using natural silica raw materials, but a phase transition accelerator is required to obtain a porous sintered body with a cristobalite crystal phase. shall be. Furthermore, in order to obtain high-purity quartz glass, it is naturally necessary to remove the phase transition accelerator added to the raw materials. Therefore, we have no choice but to use the vacuum melting method,
It cannot be applied to glass manufacturing using other methods such as the Bernoulli method.

Therefore, the object of the present invention is to provide a method for producing silica raw material powder that can be used industrially, for example, in the Bernoulli method, using inexpensive amorphous silicon dioxide that is generally commercially available.

[Means to solve the problem]

In order to achieve the above object, the method for producing a silica raw material of the present invention involves granulating fine particles of amorphous silicon dioxide into agglomerated particles, and then granulating the particles with grease dopalite crystal particles, preferably amorphous silicon dioxide. The aggregated silicon dioxide particles and cristobalite crystal particles are mixed at a weight mixing ratio of 20:1 to 1:10, and sintered in the form of particles by heating to 1100°C or higher.

It is characterized by crystallization.

[For production]

This prevents necking between agglomerated particles of amorphous silicon dioxide, so that a sintered and crystalline material having a desired porous particle size can be obtained.

〔Example〕

Hereinafter, a method for producing a silica raw material according to the present invention will be explained based on one example.

Amorphous silicon dioxide powder is usually a fine powder with a particle size of 0.02 μm or less, but it is first granulated into aggregated particles of 30 μm to 500 μm, preferably 50 μm to 150 μm. The granulation means is arbitrary, but for example, using ion exchange water, silicon dioxide powder: ion exchange water - 1:10 (
After suspending the particles at a ratio of (weight ratio), spherical aggregated particles having a desired particle size can be obtained by sizing using a spray drying granulator or the like.

In principle, the cristobalite crystal powder obtained by the method of the present invention is reused, but this crystal powder must be prepared separately at first. The method for producing the crystalline powder is arbitrary, but for example, the above-mentioned amorphous silicon dioxide powder is heated to 1500°C or higher, sintered and crystallized, and then ground in a ball mill.
Cristobalite crystal particles of 0 to 100 μm can be used.

The silicon dioxide agglomerated particles and cristobalite crystal particles thus obtained are uniformly mixed.

The mixing ratio at this time is agglomerated particles: crystal particles = 20:1 to 1: from the viewpoint of prevention of necking during heating and sintering and productivity.
A range of 10 is desirable. That is, if the mixing ratio of crystal particles is less than the above range, sintering between aggregated particles will proceed due to heating, necking will occur, and it will be difficult to obtain a particulate sintered product.
Moreover, if there are many crystal particles, the productivity will naturally be poor and it is not practical.

The mixture thus obtained is filled in, for example, a crucible and sintered into a cristobalite crystal phase using a heating furnace or the like.

The heating temperature at this time is preferably 1,100°C or higher.

This is because sintering and crystallization are difficult to proceed below this temperature.

Experimental Example 1 After suspending amorphous silicon dioxide powder with a particle size of 502 um or less in ion-exchanged water at a weight ratio of 1=10, the particles were sized using a spray drying granulator to form particles of 50 ham to 1100 um. Agglomerated particles having a spherical shape were obtained. Next, separately from this, i-star particle size 5
Cristobalite crystal particles of 0 J1 m to 1 m to 10 um were blended at a weight mixing ratio of 1=1, and mixed for 10 minutes using a V-shaped rotary mixer to homogenize.

After filling an alumina crucible with the mixed particles obtained above, the mixture was placed in a heating furnace and heat-treated at 1,200° C. for 24 hours to sinter the silicon dioxide powder into a cristobalite crystal phase. The obtained sintered product was porous in the form of particles, and using this as a raw material, high-quality quartz glass could be manufactured by the Bernoulli method.

Experimental Example 2 Agglomerated particles with a particle size of 50 Um to 100 μm obtained in the same manner as Experimental Example 1 and crystal particles of 1101 J to 30 μm obtained separately were mixed at a weight mixing ratio of 20:1 to form a V-shape. Mixed for 30 minutes using a mold rotary mixer.

After filling the obtained mixed particles into an alumina crucible, they are placed in a heating furnace and heated at 1,400°C for 40 hours to sinter the silicon dioxide powder into a cristobalite crystal phase, thereby obtaining porous crystal particles. I was able to do that. Next, when this was vitrified in the same manner as in Experimental Example 1, high quality quartz glass was obtained.

Experimental Example 3 The same agglomerated particles and crystal particles as in Experimental Example 1 were mixed at a weight mixing ratio of 1.
:10 and mixed for 10 minutes using a V-shaped rotary mixer. After filling the obtained mixed particles into an alumina crucible, the mixture is placed in a heating furnace and heat-treated at 1° 100°C for 240 hours to sinter the silicon dioxide powder into a cristobalite crystal phase, thereby obtaining porous crystal particles. was completed. When this was then vitrified in the same manner as in Experimental Example 1, high quality quartz glass was obtained.

〔Effect of the invention〕

As described above, according to the method for producing a silica raw material according to the present invention, since amorphous silicon dioxide, which is easy to handle, is used as a starting material without relying on natural resources, a stable supply of a silica raw material is possible. In addition, the silica raw material obtained by the method of the present invention has a higher purity than natural silica raw materials, and as a result, high-quality quartz glass can be manufactured.

Furthermore, the silica raw material obtained by the present invention can of course be applied to any gas sulfur production method, and has the advantage of high production efficiency and low cost.

This is because highly pure amorphous silicon dioxide is used, the particle size is desired, and the powder is cristobalite crystal t11.

Claims (1)

[Claims] 1. The method is characterized in that fine particles of amorphous silicon dioxide are granulated into agglomerated particles, mixed with cristobalite crystal particles, and then heated to sinter into a particulate cristobalite crystal phase. A method for producing silica raw materials. 2. Agglomerated particles of amorphous silicon dioxide have a particle size of 30 μm to 50 μm.
The method for producing a silica raw material according to claim 1, characterized in that the silica raw material is granulated to a size of 0 μm. 3. The method for producing a silica raw material according to claim 1, wherein the amorphous silicon dioxide aggregate particles and cristobalite crystal particles are mixed in a weight mixing ratio of 20:1 to 1:10. 4. The method for producing a silica raw material according to claim 1, characterized in that mixed particles of aggregated particles of amorphous silicon dioxide and crystalline cristobalite particles are heated to 1,100° C. or higher to sinter and crystallize them. .