JPS61174125A - Production of quartz glass - Google Patents

Abstract

PURPOSE:To produce an optically homogeneous quarts glass having no bubble and good quality by constituting the sintering process with two stages, by carrying out the primary sintering in the quartz glass by a heat treatment at <=1,300 deg.C and then by carrying out the secondary sintering by a heat treatment at 1,000-1,600 deg.C. CONSTITUTION:The raw material is, at least, a metallic alkoxide and an ultrafine silica powder, a dried gel is sintered in the low-temp. synthesizing process of quartz glass by a sol-gel method by which the pH value of the gel is adjusted into 3-6, and the process obtaining transparent quartz glass is separated into two processes. In the 1st process the dried gel is subjected to a heat treatment at <=1,300 deg.C in the heat-resisting material of quartz glass, and in the 2nd process said gel is subjected to a heat treatment at 1,000-1,600 deg.C maximum temp.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing quartz glass by a sol-gel method using a metal alkoxide as a raw material, and more specifically to a method for sintering dry gel.

[Conventional technology]

In the manufacturing method of quartz glass by the sol-gel method using metal alphoxide as a raw material, the conventional dry gel sintering method involves the process of dephysically adsorbed water, decarbonization, etc., as shown in (POT application: written by Toki). The steps of 1 and 2 are performed continuously.

That is, during the stage where the dry gel was heat-treated in the furnace from room temperature to the nonporous temperature, the temperature was never lowered or the gel was taken out of the furnace.

[Problem that the invention seeks to solve]

However, the above-mentioned conventional technology has the following drawbacks.

There is a significant relationship between the quality of quartz glass after sintering and the atmosphere inside the sintering furnace. This is thought to be due to the impurities coming out of the heat-resistant material in the sintering furnace having a negative effect on the sintered sample. I know the quality will be better. Therefore, in order to prevent contamination from impurities in the furnace, it is necessary to use heat-resistant materials of high purity. In the present circumstances,
Quartz glass has the highest purity, is heat resistant, and is reasonable in terms of cost. When using quartz glass as a heat-resistant material, the heat-resistant temperature of quartz glass is normally around 1200°C, and at most 1300°C, so when dry gel is sintered and densified, it must be heated at temperatures above 1300°C. However, there is a problem in that quartz glass cannot be used when long-term heat treatment is required.

Therefore, the present invention aims to solve these problems.
The objective is to provide a method for obtaining high-quality quartz glass by sintering dry gel in a high-purity heat-resistant material.

[Means for solving problems]

The method for manufacturing quartz glass of the present invention is as follows. That is, in a low-temperature synthesis method of quartz glass using a sol-gel method in which metal alkoxide or fine powder silica is used as a raw material and the pH value of the sol is adjusted to 3 to 6, the step of sintering the dry gel to obtain transparent quartz glass is performed. Separate into two steps. In the first step, the dry gel is heated in a quartz glass heat-resistant material to a sintering temperature with a maximum temperature of 1300° C. or less using an appropriate heating program. (The gel after this step is hereinafter defined as a sintered gel). Next, the sintered gel is heat treated in a suitable furnace and a suitable heat-resistant material at a maximum sintering temperature of 1000°C to 1600°C to densify it. By going through this process, quartz glass with good transparency and quality can be obtained.

〔Example〕

Example 1゜Purified commercially available silicon ethoxide 208F (1 mol)
280 ml of normal hydrochloric acid was added to the mixture, and the mixture was vigorously stirred for hydrolysis. Next, add ultrafine powdered silica (Aerosil 0x50 with surface area saW?7t) to this solution 90 f (
1.5 mol) was added with stirring and ultrasonic vibration was applied. Further, clumps were removed by centrifugation. To this sol (L1 specified ammonia water was added dropwise and the pH value was 4).
I adjusted it so that it was 0. Next, this sol was placed in a polypropylene box-shaped container (W30xD30XE10e!11) so that the height was 1 cIII. Seal tightly and keep at 20℃
The mixture was left to gel at night, and then set up overnight. Next, change the lid of the container to one with an opening ratio (18%), raise the temperature from room temperature to 60°C,
When dried at this temperature for 10 days, a stable dry gel that did not crack even when left at room temperature was obtained.

The dry gel was then placed in a quartz container and placed in a box furnace.

1000 at a heating rate of 60℃/hr from room temperature
℃, and left at 1000°C for 20 hours, then roughly heated to 1250°C at a heating rate of 180°C/hr, left at that temperature for 30 minutes, and cooled. After cooling to room temperature, the sintered gel was taken out from the quartz container, put directly into a box furnace, heated to 1500° C., and left at that temperature for 1 hour. In this way, a transparent, bubble-free, optically homogeneous quartz glass was obtained. The physical properties of this quartz glass are as follows. Specific gravity 2.2. Vickers hardness 800.
The coefficient of thermal expansion was a 5 × 10 cm, which matched that of fused natural silica glass.

Example λ A dry gel prepared in the same manner as in Example 1 was placed in a quartz glass container and placed in a box furnace. From room temperature to 60℃/h
The temperature was raised to 1300°C at r2 and immediately cooled. The sintered gel was taken out from the quartz container, heated to 1550° C., and directly put into a box-shaped furnace. This resulted in a transparent and optically homogeneous quartz glass.

Examples & A dry gel prepared in the same manner as in Example 1 was placed in a quartz glass container and placed in a box furnace. From room temperature to 300℃/
After raising the temperature to 1100℃ for 10 hours, it was heated to 1150℃.
The temperature was increased to 3C) at 0 °C/hr. After being left at 1150° C. for 20 hours, it was cooled to room temperature, and the sintered gel was taken out from the quartz glass container. The sintered gel was placed in a box-shaped furnace at room temperature, heated to 1600°C at 300°C/hr, left for 10 minutes, and then cooled.

The quartz glass thus obtained was transparent and optically homogeneous.

Example 4 A dry gel prepared in the same manner as in Example 1 was placed in a quartz glass container and placed in a sintering furnace. From room temperature to 60℃/hr
The temperature was raised to 1000°C and left at 1000°C for 50 hours. After cooling to room temperature, remove from the quartz glass container.
The sintered gel was placed in a sintering furnace at room temperature and heated at 300℃/hr.
The temperature was raised to 1100°C and left for 30 hours. The quartz glass thus obtained was transparent and optically homogeneous. Example I A dry gel prepared in the same manner as in Example 1 was placed in a quartz glass container and placed in a box furnace. From room temperature to 60℃/h
The temperature was raised to 900°C at r2 and left for 100 hours. After cooling, the sintered gel was taken out of the quartz container and placed in a sintering furnace at room temperature. Raise the temperature to 1000℃ at 300℃/hr for 10
It was left to stand for 0 hours for densification. The quartz glass thus obtained was transparent and optically homogeneous.

As shown in the examples above, by performing the primary sintering in quartz glass, contamination from the furnace is prevented, and by sintering and making it densified to some extent, contamination from the furnace is prevented from contamination from the sintered gel during subsequent heat treatment. Since the inside of the quartz container is no longer affected, in-furnace heat treatment can be performed outside the quartz container, so secondary sintering can be performed directly in the furnace and densification can be achieved. In this way, the method of the present invention for obtaining optically high-quality silica glass is not limited to the sol-gel method using silicon ethoxide and finely powdered silica as raw materials as shown in this example. is clear.

〔Effect of the invention〕

As described above, according to the present invention, the sintering process is performed in two stages, and the primary sintering is heat-treated in quartz glass to a temperature of 1500°C or lower to cause some degree of shrinkage, and then the secondary sintering is performed at 100°C.
By heat-treating at a temperature of 0 to 1600° C. to make the quartz glass dense and transparent, it has the effect of producing optically homogeneous, bubble-free, high-quality quartz glass.

that's all

Claims (3)

[Claims] (1) A sol that uses at least metal alkoxide and ultrafine powder silica as raw materials and adjusts the pH value of the sol to 3 to 6.
A method for producing quartz glass characterized by separating the process of sintering dry gel into transparent quartz glass into two steps in a low-temperature synthesis method of quartz glass using a gel method, which includes primary sintering and secondary sintering. . (2) A method for producing quartz glass, characterized in that the maximum temperature of the primary sintering according to claim 1 is 1300°C or less. (3) A method for producing quartz glass as set forth in claim 1, characterized in that the maximum temperature of secondary sintering is between 1000°C and 1600°C.