JP3724084B2 - Method for producing synthetic quartz powder and quartz glass molded body - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing high-purity synthetic quartz powder and a method for producing a quartz glass molded body obtained by melt-molding the same.
[0002]
[Prior art]
In recent years, glass products used in the optical communication field, the semiconductor industry, and the like have been subjected to very strict management regarding the quality. As a method for producing such a high-purity glass, mainly, (1) a method of purifying and using natural quartz, (2) hydrolysis and thermal decomposition of gaseous silicon compounds such as silicon tetrachloride in an oxyhydrogen flame (3) A method using a synthetic quartz powder obtained by baking silica gel powder obtained by hydrolysis / gelation in a liquid phase such as silicon alkoxide, etc. Etc. are known.
Among these, the method (1) has a limit in reducing the content of trace impurities, and the method (2) has problems such as extremely high production costs. In addition, when the method of calcining the silica gel powder of (3) to obtain a synthetic quartz powder, the synthetic quartz powder obtained is considered to be derived from unburned carbon, OH, etc. there were.
[0003]
[Problems to be solved by the invention]
Such a problem is conventionally known, and various means have been proposed for solving the problem.
For example, the holding time at a temperature of 300 to 500 ° C. is lengthened to sufficiently reduce the remaining amount of carbon, or a gas having a low dew point is supplied at the maximum holding temperature (1000 to 1300 ° C.), and the residual OH concentration is reduced to several tens. There is a way to lower it down to the ppm level.
However, even when fired under such conditions, foaming may occur during melting.
[0004]
[Means for Solving the Problems]
Therefore, the present inventors have intensively studied to obtain the synthetic quartz powder with less foaming at the time of melt molding to solve the above-mentioned problems, and by setting the temperature rising process in a specific temperature range at a specific temperature range during firing. The present inventors have found that this problem can be solved and have reached the present invention. That is, the present invention resides in a method for producing synthetic quartz powder, characterized in that when silica gel powder is fired to obtain synthetic quartz powder, the temperature is raised to 800 to 1000 ° C. for 4 hours or more.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
First, the silica gel powder used in the present invention is not particularly limited. For example, fumed silica is dispersed in water to form a silica sol, which is a colloidal dispersion method using silica gel, hydrolysis of alkoxysilane, silicate, etc. Hydrolysis method for obtaining silica gel by hydrolyzing a silicon compound that can be used is mentioned, but the hydrolysis method is particularly suitable as a by-product due to the excellent physical properties of silica gel and the fact that it can be easily purified by purification of raw materials. Silica gel powder obtained by hydrolyzing alkoxysilane is preferred because it is only alcohol and does not cause corrosion of containers and the like and can be easily removed.
[0006]
Production of silica gel powder by hydrolysis of alkoxysilane is carried out by reacting alkoxysilane with water according to a method known as a so-called sol-gel method.
The tetraalkoxysilane used as a raw material is a C1-4 lower alkoxysilane such as tetramethoxysilane or tetraethoxysilane or an oligomer which is a low condensate thereof, and is easily hydrolyzed and carbon remains in the silica gel. Is preferable from the viewpoint of less.
The amount of water used is usually selected from the range of 1 to 10 times the amount of alkoxy groups in the alkoxysilane. At this time, if necessary, organic solvents such as alcohols and ethers compatible with water may be mixed and used. Representative examples of the alcohol used include lower aliphatic alcohols such as methanol and ethanol.
[0007]
In this hydrolysis reaction, an acid such as hydrochloric acid or acetic acid or an alkali such as ammonia may be used as a catalyst. As a matter of course, all the substances introduced into the reaction system such as water and catalyst used here have high purity.
Gelation of the hydrolysis product is carried out under heating or at room temperature. Since the gelation speed can be improved by heating, the gelation time can be adjusted by adjusting the degree of heating.
[0008]
In order to obtain silica gel, any of these known methods can be adopted without any particular limitation. Generally, the silica gel is generally formed as a single gel rather than formed as a precipitate, and this is pulverized by pulverization. The silica gel powder is preferably subjected to the following steps because the resulting quartz powder has particularly excellent physical properties, does not require extra steps such as separation from the supernatant, and has a good yield.
The silica gel thus obtained is subdivided by pulverization or the like as necessary to obtain silica gel powder. In general, the silica gel is dried prior to firing described later. In this case, the gel may be subdivided and then dried, or may be dried and subdivided. In any case, the particle size after drying is subdivided so as to be 10 to 1000 μm, preferably 100 to 600 μm, and the average particle size is 150 to 300 μm.
[0009]
The temperature during drying varies depending on the conditions, but is usually 50 to 200 ° C. The operation can be performed either batchwise or continuously. The degree of drying is usually 5 to 30% by weight in terms of liquid content.
Next, the dried silica gel powder thus obtained is fired. That is, the silica gel powder is made nonporous by heating to form quartz glass powder.
In firing, it is preferable to perform heat treatment at a temperature of 300 to 500 ° C. in advance, lower the carbon concentration to some extent, and then raise the temperature to 1000 to 1300 ° C. to perform firing.
This is due to the following reason.
[0010]
In the dry silica gel powder obtained by the above method, an unreacted alkoxy group and a part of the by-produced alcohol remain even when the by-product alcohol is removed by drying. Actually, when the carbon concentration in the dried silica gel powder is measured, it is usually 1 to 3% by weight, although it varies depending on the drying conditions. When this silica gel powder is heated and calcined in an oxygen-containing gas at a temperature range of 1000 to 1300 ° C., most of the carbon is burned and removed in the temperature rising process, but a part of it is unburned carbon in the synthetic quartz powder. According to the study by the present inventors, the use of synthetic quartz powder containing unburned carbon may cause bubbles by forming CO ₂ or CO gas during melt molding. It is clear (Japanese Patent Application No. 7-280726). Therefore, it is necessary to remove substantially all of the unburned carbon in order to seal the silica gel.
[0011]
Here, as a result of further research by the present inventors, when the residual carbon in the dry silica gel powder comes into contact with an oxygen-containing gas in a temperature range of 300 ° C. or higher, CO and CO ₂ are generated while being reduced, and the processing temperature is reduced. It has been clarified that the rate of decrease increases as the temperature increases, and that the non-porous silica gel proceeds rapidly in the temperature range of 600 ° C. or higher. Therefore, it is desirable to subject the carbon concentration to 1000 ppm or less by heat treatment at a temperature of 300 to 500 ° C., and then to a firing step as described below.
Next, the heat-treated silica gel powder is heated to a temperature range of 1000 to 1300 ° C. and fired to obtain a synthetic quartz powder.
[0012]
In this invention, it is characterized by setting it as the specific temperature rising time in this case.
That is, the temperature raising step at 800 to 1000 ° C. is set to 4 hours or longer. Contrary to conventional knowledge, it has been clarified by the present inventors that the temperature raising step in this temperature range has a very important influence on foaming when the resultant synthetic quartz powder is melt-molded. Thus, it has been clarified by the present inventors that a remarkable effect for preventing foaming is exhibited by setting the temperature rising time at this temperature to 4 hours or more.
Preferably, the temperature increase rate at 800 to 1000 ° C. is set to 50 ° C./hr or less. By setting it as this temperature increase rate, there exists a remarkable effect in foaming suppression at the time of melt molding. Particularly preferably, the heating rate at 700 to 1100 ° C. is also set to 50 ° C./hr or less. More preferably, the heating rate at 700 to 1150 ° C. is also set to 50 ° C./hr or less.
[0013]
The time required for the temperature rise and the rate of temperature rise can be determined from actual measurement values obtained by actually inserting a thermocouple into the powder, for example.
The temperature is raised to 1000 to 1300 ° C. by the temperature raising step described above, and the final temperature of the temperature rise is not particularly limited as long as it is 1000 to 1300 ° C. However, for industrial implementation, it is desirable to raise the temperature to 1100 ° C. or higher, particularly 1150 ° C. or higher. This is because if it is less than 1100 ° C., it takes a very long time to achieve removal of silanol, particularly isolated silanol, to the extent preferable for a product.
Moreover, it is because it will become easy to raise | generate sintering between particle | grains when it exceeds 1300 degreeC.
[0014]
Thus, it is desirable that the temperature is once raised to 1000 to 1300 ° C. and then maintained in this temperature range for 10 to 100 hours.
The holding time is preferably maintained until the silanol concentration of the synthetic quartz powder is 100 ppm or less, preferably 60 ppm or less, depending on the degree of silanol removal up to the final temperature.
The temperature raising and firing steps described above may be performed either batchwise or continuously.
On the other hand, when firing at a high temperature, batch processing with a crucible having excellent heat resistance is suitable.
Of course, other requirements are not particularly limited as long as the predetermined temperature raising process of the present invention can be achieved.
[0015]
The synthetic quartz powder thus obtained can be melt-molded by various known methods to form a quartz glass molded body. For example, by using various forming methods such as arc melt method, Bernoulli method, fusion method, etc., ultrahigh high strength required for high temperature strength such as crucibles for pulling silicon single crystals, quartz glass members for semiconductor manufacturing such as diffusion furnace tubes and jigs, etc. It is particularly suitable as a purity quartz glass member. Of course, it may be used for applications other than the use at high temperatures, such as optical fibers and IC sealing materials.
Hereinafter, the present invention will be described more specifically with reference to examples. In addition, the apparatus used for baking in the Example is shown in FIG.
[0016]
(Example 1)
1 kg of silica gel powder having a particle size of 100 to 500 μm obtained by hydrolyzing, gelling, pulverizing, drying and classifying tetramethoxysilane was charged in a quartz glass crucible (1) of 200 mmφ × 200 mmH, and a 10 mmφ hole was formed in the center. The lid (2) was put on and set in the electric furnace. Next, the 6 mmφ quartz glass tube (3) inserted from the upper part of the electric furnace is inserted into the powder through the hole of the lid (2) to a position of 10 mm from the lower part of the crucible, and at a flow rate of 100 ml / min, the dew point −45. While supplying dehumidified air at a temperature of 200 ° C., the temperature was raised to 500 ° C. at 200 ° C./Hr, held at 500 ° C. for 5 hours, then from 800 ° C. to 200 ° C./Hr, from 800 to 1200 ° C. at 40 ° C./Hr The temperature was raised and held at 1200 ° C. for 45 hours for firing. The silanol concentration of the obtained synthetic quartz glass powder was measured by infrared absorption and found to be 48 ppm. Next, when quartz glass ingots of 15 mmφ × 50 mmL and 40 mmφ × 40 mmL were produced by two melting methods of an oxyhydrogen flame melting method (Bernui method) and a vacuum melting method, respectively, a level that can be detected visually. No bubbles were observed.
[0017]
(Comparative Example 1)
In Example 1, a synthetic quartz glass powder was produced in the same manner as in Example 1 except that the temperature was maintained at 500 ° C. for 5 hours and then increased to 1200 ° C. at 200 ° C./Hr.
When the silanol concentration of the obtained synthetic quartz glass powder was measured, it was 48 ppm. Next, quartz glass ingots of 15 mmφ × 50 mmL and 40 mmφ × 40 mmL were produced by two melting methods of oxyhydrogen flame melting method (Bernui method) and vacuum melting method, respectively. Dozens or more bubbles of 10 to several hundred μmφ were observed.
[0018]
(Comparative Example 2)
In Example 1, after holding at 500 ° C. for 5 hours, the temperature was raised to 800 ° C. at 30 ° C./Hr, and the temperature was raised from 800 to 1200 ° C. at 200 ° C./Hr, as in Example 1. A synthetic quartz glass powder was prepared by the method described above.
The silanol concentration of the obtained synthetic quartz glass powder was measured and found to be 50 ppm. Next, quartz glass ingots of 15 mmφ × 50 mmL and 40 mmφ × 40 mmL were produced by two melting methods of oxyhydrogen flame melting method (Bernui method) and vacuum melting method, respectively. Dozens or more bubbles of 10 to several hundred μmφ were observed.
[0019]
【The invention's effect】
According to the present invention, it is possible to obtain a high-purity synthetic quartz powder having a low silanol group concentration and a high-purity quartz glass molded body with less foaming during melt molding.
[Brief description of the drawings]
FIG. 1 is a diagram showing an apparatus used for firing in Examples.
1 quartz glass crucible 2 lid with hole 3 quartz glass tube

Claims (5)

  A method for producing synthetic quartz powder, characterized in that when silica gel powder is fired to obtain synthetic quartz powder, the temperature is raised to 800 to 1000 ° C. for 4 hours or more.   A method for producing a synthetic quartz powder, characterized in that when a silica gel powder is fired to obtain a synthetic quartz powder, the rate of temperature increase at 800 to 1000 ° C. is 50 ° C./hr or less.   A method for producing synthetic quartz powder, characterized in that when a silica gel powder is fired to obtain a synthetic quartz powder, the rate of temperature increase at 700 to 1100 ° C. is 50 ° C./hr or less.   A method for producing a synthetic quartz powder, characterized in that when a silica gel powder is fired to obtain a synthetic quartz powder, the rate of temperature rise at 700 to 1150 ° C is 50 ° C / hr or less.   The silica gel powder to be subjected to firing has a particle size of 10 to 1000 µm, an average particle size of 150 to 300 µm, and has undergone a drying step at 50 to 200 ° C. The manufacturing method of the synthetic quartz powder of description.

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