JPH03187936A - Production of synthetic quarts glass powder - Google Patents

Abstract

PURPOSE:To obtain synthetic quartz glass powder having high purity and increased high-temperature viscosity by adding methyl silicate to an aqueous dispersion containing spherical silica particles to solidify the dispersion, heating and dehydrating the solid, subjecting the product to solvent-removal process and decarbonation process, vitrifying to transparent glass and crushing the obtained glass. CONSTITUTION:Methyl silicate and ammonia water are supplied from tanks 1, 2 with metering pumps 3 to a reactor 4 and continuously reacted under stirring with a stirring motor 5. The produced spherical silica having particle diameter of 300-700nm are delivered through an outlet port 6 to a reservoir 7. The silica is dispersed in extra-pure water, the pH is adjusted to 9-13 with ammonia water and the dispersion is solidified by adding 5-20% (based on the silica) of methyl silicate. The solidified product is heated at 800-1000 deg.C to effect the dehydration, solvent-removal and decarbonation, sieved to collect particles of 30-100 mesh and sintered at 1400-1600 deg.C for 1-2hr. The obtained synthetic quartz glass is crushed to form the objective powder.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing synthetic quartz glass powder, and in particular to synthetic quartz glass, which is suitable for heat-resistant jigs for semiconductors due to its high purity and high viscosity at high temperatures. This invention relates to a method for producing powder.

[Prior art] Regarding the production of synthetic quartz glass, there are two methods: ■ A method of hydrolyzing silicon compounds such as silicon tetrachloride in an oxyhydrogen flame to create silica particles, and melting the particles to make quartz glass. Methods of converting oxyhydrogen flame into plasma flame include the so-called sol-gel method, in which silica is produced by hydrolyzing alkoxysilane with an acid catalyst in an alcohol solvent, and this is sintered to form quartz glass. There is.

However, this method using an oxyhydrogen flame has the problem that 1,000 pp of OH groups remain in the quartz glass, the viscosity at high temperatures is low, and foaming occurs at high temperatures in vacuum, and the plasma method is costly. The sol-gel method has the disadvantage of being expensive and difficult to mass produce.Although the sol-gel method can produce quartz glass at a relatively low cost, it tends to leave OH groups, takes a long time to manufacture, and is highly viscous at high temperatures. The disadvantage is that it is difficult to obtain.

[Problems to be Solved by the Invention] Therefore, the present inventors have conducted research on a method for producing synthetic quartz with high high temperature viscosity using a sol-gel method. When hydrolyzed in the presence of
OOnsan's silica is produced, sintered, crushed and then melted at 1,700°C (see Japanese Patent Application No. 63-229333). Methyl silicate is hydrolyzed in the presence of ammonia to reduce the particle size to the first order. A method in which silica of 100 to 500 nm in size is made from particles, agglomerated particles of 10 to 100 μl are separated, solid-liquid separated, sintered, pulverized, sieved, and melt-formed at 1,700°C or higher (Japanese Patent Application No. 1983- 335070), methyl silicate is hydrolyzed in the presence of anthonia to produce silica, which is then purified under reduced pressure to a
~1.Sintered at 700℃, then 1.
．． A method of sintering at 800 to 2,000°C (Patent Application Hei 1-1)
39619)).

However, although these methods yield synthetic quartz with high temperature and viscosity, they all require long processes and lack mass productivity, and the energy costs for sintering and other processes are high.
There is a disadvantage in that it is not always satisfactory.

[Means for Solving the Problems] The present invention relates to a method for producing synthetic quartz glass powder that can solve these disadvantages. After collecting the spherical silica particles generated by continuous reactions,
An aqueous dispersion solution with a pH of 9 to 13 is prepared, 5 to 20% by weight of methyl silicate (calculated as silica) is added to the silica to solidify it, and then heated to remove a water, solvent, and decarburize. Sieve into a range of 100 mesh, 1,40
It is characterized by sintering at 0 to IJOO°C and crushing it.

That is, the present inventors have conducted various studies on methods for more efficiently producing quartz glass with high high temperature viscosity using the sol-gel method.As a result, for silica synthesis by hydrolysis of methyl silicate, we have found that methyl silicate and ammonia are If the methyl silicate is added dropwise simultaneously into the reactor, the hydrolysis of methyl silicate will always occur continuously, streamlining this process.
When methyl silicate is added to an aqueous dispersion solution of No. 3, the resulting silica becomes densified, and the sintering temperature is increased from 1,500 to 1,900°C in the conventional method to 1.400 to 1.6°C.
The temperature can be lowered to 00°C, and this sintered body can be easily crushed with a roll mill, etc., and if it is sieved into a 30-100 mesh size before sintering, it can be used as it is as a sintering raw material. They discovered that this method eliminates the need for a refining process, making it possible to omit the process and reduce energy costs, and also confirmed that the silica glass made by this method has high high-temperature viscosity. The present invention has been completed.

This will be explained in further detail below.

[Function] The present invention relates to a method for producing quartz glass with high high temperature viscosity by an improved sol-gel method.

The synthesis of silica by hydrolysis of alkoxysilane in the present invention is carried out by dropping methyl silicate and aqueous ammonia into a reactor simultaneously. For example, as shown in FIG. 1, predetermined amounts of methyl silicate and ammonia water are taken out from a methyl silicate storage tank 1 and an ammonia water storage tank 2 using a metering pump 3, and these are simultaneously dropped into a reactor 4. Bye. The hydrolysis reaction of methyl silicate begins with this dropping, and this is carried out continuously as the reaction liquid is stirred by the stirring motor 5, and the silica generated in this reaction is discharged through the discharge port 6.
The silica is taken out from the silica storage tank 7.

The alkoxysilane used here has poor reactivity with ethyl silicate or methyl silicate trimer, and the resulting silica has small particles, and butyl silicate is hydrophobic and the reaction does not proceed, so this is different from methyl silicate. The ammonia water may have a concentration of 15 to 25% by weight, and the reaction temperature may be 20 to 45°C.

If this hydrolysis of methyl silicate is carried out by adding aqueous ammonia at the same time, the hydrolysis reaction of methyl silicate will always be carried out continuously, which will simplify this process. 300-700
Spherical silica particles with a relatively large particle size of nm are continuously obtained, and these particles are dehydrated to form silica with a water content of 20 to 30%.

This silica is then made into an aqueous dispersion solution, by first dispersing the silica in ultrapure water and then adding aqueous ammonia to the solution to adjust its pH to 9-13. This is because if this PO is neutral or acidic, it will not be strong, and if it is a strong alkali of 213 or higher, particles will be formed and the strength will not be improved.
~13. Methyl silicate is then added to this alkaline aqueous dispersion solution to solidify it. If too little methyl silicate is added, solidification will be insufficient and the strength will be increased; if too much methyl silicate is added, it will not solidify. Since the high-temperature viscosity of quartz glass decreases when silica glass is used as silica glass, this needs to be in the range of 5 to 20% with respect to the amount of silica present in the aqueous dispersion solution.

The silica lump obtained in this way is then heated to dehydrate, desolvent, decarburize, and then sinter. The heating for dehydration, desolvation, and decarburization is performed at 800 to 1,000°C. Preferably, the temperature is raised from room temperature to 1,000°C over 10 hours or more, and then maintained at 1,000°C for 1 hour or more. This heating causes the silica powder to solidify slightly, but this powder can be broken down by several degrees when it is weakly crushed.
Since it is from 0 to several hundred microns, this is 3
It is necessary to sieve into 0 to 100 meshes.

The silica sieved in this way is then sintered to form a synthetic quartz ring, but in the conventional method, this sintering was carried out at a high temperature of 1,500 to 1,900 degrees Celsius. On the other hand, the silica lump of the present invention obtained by the method described above may be sintered at a relatively low temperature of 1,400 to 1,600°C for 1 to 2 hours, and the silica lump is formed by this sintering. Although the particle size is slightly smaller, it is about 30~1
It becomes a transparent synthetic quartz glass block of 00 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, etc., so it is easy to crush, and there is no need for a refining process as there is no risk of contamination with impurities in each of the above steps. Silica glass powder has the advantage of being inexpensive because it can be manufactured with a 100% yield without any loss (30-40%) due to crushing and sieving as in conventional methods. Also, the particle shape is not a sharp shape like crushed powder, but an aggregate of round particles, and the filling state is uniform, making it highly usable, and the synthetic silica glass powder obtained here. For example, if this is sintered and melted at 1.950°C for 30 minutes, it can be made into a synthetic quartz glass body with high high temperature viscosity, making it useful as a raw material for heat-resistant semiconductor devices such as crucibles. It gives you a great advantage.

[Example] Next, examples of the present invention will be given.

Examples 1-3. Comparative Examples 1 to 2 Using the reaction apparatus shown in Figure 1, methyl silicate 2
6.5it/hour and 17.2J of 20% by weight ammonia water
At the same time, 27 hours and 4 hours were added dropwise into a 5IL reaction flask.
When the reaction was carried out at 0 to 50°C and the reaction was stopped after 5 hours, a silica sol solution with a silica concentration of 23% was obtained.
This was dehydrated to produce silica with a water content of 25% by weight.

Next, 8kg of this silica was divided into 8β of ultrapure water, and 350kg of 29% by weight ammonia water was added to the solution to adjust its pH.
is 11, and 5% by weight in terms of silica for this silica,
After adding methyl silicate in amounts of 10 wt%, 20 wt%, 30 wt%, and 40 wt% and solidifying this, the mixture was heated from room temperature to 1.00 wt% in air.
Raise the temperature to 0℃ over 13 hours, then 1.000℃
The powder was sieved for 30~1 hour using a polypropylene 30 mesh sieve and a Teflon 100 mesh sieve.
It was sieved into 100-mesh sieves and placed in a quartz glass crucible with a diameter of 12 inches.

Next, this crucible was heated in an argon gas atmosphere for one hour.
, The temperature was raised to 500°C, held at this temperature for 2 hours to turn the silica into transparent vitrification, and after cooling, it was taken out and crushed with a quartz glass roller.
When sieved through a 00 mesh sieve, synthetic quartz glass powder was obtained with a yield of 95%.When this powder was photographed with an electron microscope, the powder shown in Figure 2 was obtained. The particles were confirmed to be round, transparent particles.

Furthermore, when a crucible was molded by a known method using the synthetic quartz glass powder, the resulting crucible was slightly more opaque than one made by melting natural quartz; As shown in , it was confirmed that the purity was high and the viscosity was also high.

Violet! [Effects of the Invention] The present invention relates to a method for producing synthetic quartz glass powder, which involves simultaneously dropping methyl silicate and aqueous ammonia into a reactor to form spherical silica particles, which are then collected. After making an aqueous dispersion solution with a pH of 9 to 13, methyl silicate was added to solidify it, and then heated.
After dehydration, solvent removal, and decarburization, the material is sieved into 300 to 100 mesh sieves, heated to high temperatures, sintered, turned into transparent vitrification, and then crushed. According to this method, silica production through hydrolysis is ensured. Moreover, it can be performed continuously, and sintering of silica salt solidified with methyl silicate can be performed at a lower temperature than in conventional methods, and furthermore, this pulverized product can be made into products without a refining process. Synthetic quartz glass obtained by sintering and melt-molding the quartz glass powder thus obtained has a high viscosity at high temperatures.

Therefore, according to the method of the present invention, 1) continuous reaction;
2) a reduction in sintering temperature; and 3) no refining process required. As a result, the advantages of mass production of synthetic quartz glass powder 3 4 , process omission, and energy saving are achieved.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view showing the hydrolysis process of methyl silicate according to the present invention, and FIG. 2 is a microscopic photograph of the synthetic quartz glass powder obtained in the example. 1... Methyl silicate storage tank

Claims (1)

[Claims] 1. Methyl silicate and aqueous ammonia are simultaneously dropped into a reactor, and the spherical silica particles produced in this continuous reaction are collected, and then made into an aqueous dispersion solution with a pH of 9 to 13. 5 to 20% by weight of methyl silicate (calculated as silica) is added and solidified, then heated, dehydrated, desolventized,
A method for producing synthetic quartz glass powder, which comprises decarburizing the powder, sieving it to a size of 30 to 100 mesh, heating it to a high temperature, sintering it, turning it into transparent glass, and then crushing it. 2. Synthetic quartz glass powder produced by the method of claim 1 contains 30
A synthetic quartz glass powder having a particle size in the range of ~100 mesh and used as a raw material for a synthetic quartz glass crucible.