JPH03187934A - Production of quartz glass - Google Patents

Abstract

PURPOSE:To obtain a quartz glass free from crack and void by forming fine silica powder and heating the formed material in such a manner as to maintain a temperature gradient to slowly sinter the formed material from one end. CONSTITUTION:Fine silica powder produced by sol-gel process, thermal hydrolysis, etc., is formed by uniaxial compression molding, isostatic cold-press, wet- forming process, etc., to obtain a formed material. The formed material is heated to a temperature higher than the vitrification temperature in an atmosphere selected from He, H2, N2, O2, Cl2, Ar, SiF4 and NH3 at a heating rate of 1-80 deg.C/min while keeping a temperature gradient of 5-150 deg.C/cm to slowly sinter the formed material from one end.

Description

Detailed Description of the Invention The fine silica powder used as a raw material is not limited, but for example, fine silica powder manufactured by a sol-gel method using silicon alkoxide as a raw material, fine silica powder manufactured by thermal hydrolysis using silicon tetrachloride as a raw material, etc. An example is the fumed silica fine powder produced.

Further, fine silica powder to which other elements such as germanium and boron are added can be used. If the transparent quartz glass to be produced is required to have high purity or high light transmittance, it is desirable to use fine silica powder of high purity.

The silica fine powder is molded to ensure the filling properties of the particles necessary for sintering and vitrification, and to form and maintain the desired shape of the molded product, but the method is not particularly limited. For example, a dry pressure molding method or a wet molding method is used. Dry pressure molding methods include uniaxial pressure molding, in which powder is molded by applying pressure in a uniaxial direction using a mold, etc., and/or cold isostatic pressing, in which powder is placed in a rubber mold, etc., and pressure molded using hydrostatic pressure. can be given. The wet molding method uses fine silica powder as a raw material, suspends it in water or an organic solvent, filters this suspension to remove the water or organic solvent, and deposits fine silica particles.
A method of depositing the suspension to form a molded body, or a method of pouring the above-mentioned suspension into a desired container, evaporating off water or organic solvent, and molding can be used.

If the bulk density of the molded product obtained by the above method is small, the shrinkage during sintering is large and cracks are likely to occur.
The bulk density may be adjusted in advance by pre-curing sintering or the like so that it is 5%, more preferably 50 to 90%. In addition, when the bulk density is small, cracks can be prevented by reducing the rate of temperature increase during sintering to produce transparent glass.

In addition, if the raw material powder contains a large amount of carbon, heat treatment in an oxygen atmosphere is performed to remove carbon, and if a low concentration of OH groups is required in the manufactured glass body, treatment in an atmosphere such as chlorine gas is performed. The fine powder compact can be subjected to pretreatment as necessary.

The molded body obtained by the above method is heated and heated so as to have a temperature gradient, and is gradually sintered from one end of the molded body. The sintering atmosphere was He, H2.

NOCI Ar, SiF4. and 2°
It is preferable to use an atmosphere of one or more gases selected from 2° 2°N H3 depending on the characteristics of the quartz glass to be manufactured.

The method of heating and increasing the temperature so that the molded body has a temperature gradient is as follows.
This can be carried out by a method in which a heating zone with a temperature gradient is fixed and the molded body is sintered while moving from a low temperature side to a high temperature side. In addition, there are methods in which the molded body is fixed and sintered while moving through a heating zone with a temperature gradient, a method in which both the molded body and the heating zone with a temperature gradient are sintered while moving, and a method in which the molded body is sintered while moving in a heating zone with a temperature gradient. The same effect can be achieved by fixing the device in a heating zone and raising the temperature while maintaining the temperature gradient. The temperature gradient may be horizontal or vertical to the molded body. If the temperature gradient in the heating zone mentioned in item 2 is too small, the entire molded body will shrink and sinter, making it impossible to obtain a sufficient degassing effect and leaving bubbles.If it is too large, the difference in the degree of shrinkage will occur. Since cracks occur, which is thought to be due to too large a diameter, it is preferably 5 to b, more preferably 10 to b. The temperature range and temperature increase rate of heating and temperature increase are determined by the temperature at which the molded body shrinks, the shrinkage speed, and the sintering vitrification temperature, the properties of the raw silica fine powder, the molding method, the shape of the molded body, and the sintering process. Although it cannot be specifically limited because it varies depending on the type of atmospheric gas, it is desirable to set the temperature range so that the low temperature side is below the shrinkage temperature of the molded body and the high temperature side is set above the vitrification temperature of sintering, and the temperature increase rate is 1. ~b preferred.

Further, after vitrification is completed, heat treatment at a higher temperature may be performed, thereby improving the sinterability of the glass.

As described above, a bubble-free transparent quartz glass can be obtained. Preliminary sintering is performed to adjust the bulk density in order to prevent cracks during heating, and then, in the process of sintering this molded body into transparent glass, the molded body is heated so that it has a temperature gradient. A bubble-free quartz glass body can be easily obtained by raising the temperature and gradually turning the molded body into transparent glass from one end. In particular, the bubble-free effect is remarkable when sintering a large-sized molded body or sintering in an atmosphere containing a gas that has low solubility in a glass body or has a slow diffusion rate. This is thought to be because as the sintering progresses, the atmospheric gas and adsorbed gas contained within the molded body tend to escape to the outside of the molded body through the unsintered portion of the molded body.

[Example of implementation] The invention will be explained in detail by the following examples.

However, the present invention is not limited only to these examples.

(Example 1) Fumed silica fine powder produced by thermal hydrolysis using silicon tetrachloride was used as the raw material powder, and this fine silica powder was uniaxially pressure molded using a mold with a diameter of 120 mm, and then put into a rubber mold. 500 K by cold isostatic pressing
Molded at a pressure of g/e-, weight 400g, diameter 10
Cylindrical shape, 2mm, height 70mm, bulk density approximately 0.7g/
A powder compact of cm3 (approximately 32%) was obtained. After dehydrating this powder molded body in a chlorine atmosphere at a temperature of 900°C,
When pre-sintered at 1050° C. in a helium atmosphere, a pre-sintered body with a bulk density of about 1.8 g/crn3 (about 82%) was obtained. This preliminary sintered body was heated in a helium gas atmosphere, with a temperature gradient of about 40°C/cm, and a temperature gradient of 10°C on the low temperature side.
00℃, the high temperature side is placed in a heating zone with a temperature gradient of 1480℃ in the radial direction, and 0.5c from the low temperature side to the high temperature side.
It moved at a speed of m/min to sinter and vitrify. As a result, silica glass without cracks and bubbles of 10 μm or more was obtained.

(Comparative Example 1) A molded body was produced in the same manner as in Example 1, and this molded body was placed in the soaking zone of a heating furnace, and heated to 105% in a helium gas atmosphere.
Sintering was carried out from 0°C to 1480°C at a heating rate of 5°C/min.

As a result, the obtained glass contained bubbles of 10 μm or more.

(Example 2) Using 10% germanium-added silica fine powder made by the sol-gel method as the raw material powder, this fine powder was
After uniaxial pressure molding using a mold of size m, put it into a rubber mold,
Molded using a cold isostatic press at a pressure of 1000 Kg/cJ, weighing 30g, diameter 36mm, height 26mm.
A cylindrical powder body having a bulk density of about 0.88 g/c+n3 (about 32%) was obtained. This powder molded body was placed in an oxygen atmosphere at a temperature of 700.
℃ to remove residual carbon, then heated to 900℃
, dehydrated in a chlorine atmosphere, then pre-sintered for 1 hour in an atmosphere of oxygen and helium mixed gas with an oxygen concentration of 40% at a temperature of 900°C to obtain a density of about 70%, followed by a temperature gradient of about 25%. °C/am.

It was placed in a heating zone with a temperature gradient in the radial direction, with the low temperature side being 900°C and the high temperature side being 1500°C, and moved from the low temperature side to the high temperature side at a rate of 1 cI11/min to sinter and vitrify it.

As a result, germanium-doped quartz glass without cracks and bubbles of 10 μm or more was obtained.

(Comparative Example 2) A powder compact was produced in the same manner as in Example 2, placed in the soaking zone of a heating furnace, and heated from 900°C to 1500°C in an atmosphere of oxygen and helium mixed gas with an oxygen concentration of 40%. Sintering was carried out at a heating rate of 4° C./min.

As a result, the molded body foamed and a transparent glass body could not be obtained.

1 (Example 3) Fine silica powder made by the sol-gel method was used as the raw material powder, this fine powder was mixed and suspended in water, the suspension was filtered to remove excess water, and the fine silica particles were removed. After being deposited and deposited, it dries to a diameter of 50+ am.

Length 110mm, bulk density 0.55g/cm3 (approximately 25
%) was obtained. This powder molded body is 1050
After pre-sintering in an oxygen atmosphere to a density of about 83%, the atmosphere was helium gas and the temperature gradient was about 40℃/8.
111% It was placed in a heating zone with a temperature gradient in the height direction of 1000° C. on the low temperature side and 1400° C. on the high temperature side, and moved from the low temperature side to the high temperature side at a speed of 1 cm/min to sinter and vitrify it. As a result, a cylindrical quartz glass with no cracks and bubbles of 10 μm or more was obtained.

[Effects of the Invention] As is clear from the above description, according to the present invention, fine silica powder is used as a raw material, and this fine powder is subjected to dry pressure molding,
Alternatively, the fine powder molded body is molded using a wet molding method, and if necessary, after performing preliminary sintering for the purpose of adjusting the bulk density to prevent cracking during sintering, the fine powder molded body is sintered. In the vitrification process, depending on the characteristics of the quartz glass to be manufactured, CI Ar.

He, H2, N 2. 02. 2゜SI
In an atmosphere of one or more 4' mixed gases selected from F N H3, the fine powder molded body is heated and heated so as to have a temperature gradient, and the molded body is gradually sintered from one end. , it is possible to produce transparent quartz glass without cracks and without bubbles. In particular, it is an effective manufacturing method for producing a large-sized molded body and for sintering and vitrifying in an atmosphere containing a gas that has a low solubility in the glass body or a slow diffusion rate.

Claims (6)

[Claims] (1) Fine silica powder is used as a raw material, it is molded, the molded body is then heated and heated to have a temperature gradient, and the molded body is gradually sintered from one end to become transparent glass. A method for producing quartz glass. (2) The method for producing quartz glass according to claim 1, wherein the bulk density of the molded body is 40 to 95% of the true density of the glass body. (3) In the quartz glass manufacturing method described in claim 1 or 2, the sintering atmosphere is He, H_
2, N_2, O_2, Cl_2, Ar, SiF_4, N
One or more methods selected from H_3. (4) A method for producing quartz glass according to any one of claims 1 to 3, wherein the molding is a dry pressure molding method or a wet molding method. (5) In the method for producing quartz glass according to claim 4, the dry pressure molding method is a uniaxial pressure molding method and/or a cold isostatic pressing method. (6) In the method for producing quartz glass as described in claim 4, the wet molding method involves suspending the silica fine powder raw material in water or an organic solvent, and filtering the suspension to form a water or organic solvent. A method in which the solvent is removed and fine silica powder is deposited and molded, or a method in which the suspension is poured into a container and the water or organic solvent is evaporated and molded.