JPS63147832A - Production of glass - Google Patents

Abstract

PURPOSE:To increase the strength of gel for producing glass and to elevate the yield of the gel on the dry basis by drying the sol as a starting material for the production of glass by the sol-gel method after replacing the surface layer of the gel using aq. acid soln. having lower pH than the pH value for the gelling stage of the starting sol. CONSTITUTION:In the production of glass by the sol-gel method using metal alkoxide as a starting material, the surface layer of the gel is replaced using aq. soln. of acid or a mixture thereof with alcohol, having lower pH than the pH value for the gelling stage of the sol, then the gel is dried and glass is produced. In accordance with this method, a slower dehydration condensation reaction is caused in the surface layer of the gel than in the inner layer of the gel, so the contraction of the surface layer is smaller than that in the inner part of the gel. Therefore, even such gel having sufficiently large thickness is dried without causing cracking due to tensile stress exerted on the surface layer. This method is particularly effective for the drying of gel having large thickness.

Description

[Detailed description of the invention] [Application field with tumor] The present invention relates to a method for manufacturing glass.

[Praise for invention]

In the production of glass by the sol-gel method, the present invention has a pH lower than that of a wet gel whose surface layer is completely gelled.
The gel is replaced with a direct acid aqueous solution or an acid aqueous solution-alcohol mixture and dried. As a result, a dehydration condensation reaction occurs at the surface layer of the gel at a slower rate than the inside of the gel, and the contraction of the outside of the gel is slower than that inside the gel. . Therefore, the present invention is particularly effective in drying thick gels because tensile stress acts on the surface layer of the gel, and even sufficiently thick gels can be dried without cracking.

[Conventional technology]

Glass using the conventional sol-gel method! 2! In construction.

The wet gel drying method does not particularly control the reaction rate of the gel, and therefore shrinkage progresses from the gel surface where the solvent evaporates, and cracks are likely to occur on the surface. (α)Jo
urnal of non-CrystallinC
Bolids vol 63.1984 (2), Toki et al., Patent Application 1983- [Problems to be Solved by the Invention] However, in the above-mentioned prior art, the dehydration condensation reaction rate of the wet gel is not controlled, and the That's it.

The problem is that shrinkage progresses from the gel surface and cracks are easy to peel off from the surface.

The present invention solves these problems by replacing the wet gel surface with an acid aqueous solution or an acid aqueous solution-alcohol mixture having a pH value lower than that of the gelled pEl, thereby controlling the rate of dehydration condensation on one surface. and by applying compressive stress to the gel surface.

The gel strength can be increased and the drying yield within pt can be improved.

[Means for solving problems]

The present invention relates to the production of glass by the sol-gel method using metal alkoxide as a starting material.
After replacing the gel surface layer with an acid aqueous solution or an acid aqueous solution-alcohol mixture having a pH value lower than the H value, drying is performed.

[Effect]

According to the above configuration of the present invention, the drying yield of wet gel can be improved, and it is particularly effective for drying thick gel.

〔Example〕

Example 1 17.9 Kj' of tetraethoxysilane and 23.5 Kj' of 0.01N aqueous hydrochloric acid were mixed and vigorously stirred to obtain a colorless and transparent hydrolysis column at-. Ultrafine silica particles (Aerosil OX-50, manufactured by Degussa) were gradually added to the obtained hydrolyzed solution, and ultrasonic waves (26EIHz, 1.2 xw) were irradiated for 4 hours while stirring to obtain a uniform white color. It was made into a sol solution. Furthermore, the obtained sol solution was taken into a centrifuge and the total gravity of 3000G was 15 minutes.
After separating on coarse particles, 10/Am, 7 μm, 3 μm
, 1 μm filter to obtain a uniform sol solution.

0.0% to the obtained sol solution. OL Add normal ammonia water dropwise to raise the sol pHff1t from 2.2 to 4.5.

30cm x 30an x 10cm container (made of polypropylene) with thicknesses of 1cmM, 2cm,
When the sol was prepared into 4cm and 8m thick sheets and left in a sealed container for 3 days, it turned into a gel and had a shrinkage rate of 5%.
It shrunk.

Next, 4 pieces of 8α gel with thicknesses of 1 cm and 2 cm were immersed for 1 hour in a hydrochloric acid aqueous solution prepared to pHIi[2.0, and the gel surface layer was replaced with the hydrochloric acid aqueous solution until the porosity was reduced to 0. I attached a lid with a 5-inch hole and started drying it in a dryer with the temperature adjusted to 70 degrees Celsius.

The 13 thick one took about one week, the 2 cm thick one took about two weeks, the 4 cm thick one took about one month, and the 8 ar+ thickness took about two months to dry without cracking.

The obtained dried gel was placed in a dryer at an intercalary temperature of 1°C and forcedly dried.Then, the dried gel was placed in an electric furnace and heated at 300°C and 500°C.
℃ and 900℃ for 2 hours, respectively. The heating rate is ω
℃/hour. When this was left to cool in the furnace and taken out,
A white sintered gel (glass precursor) was obtained.

This was further heated to 1,750°C in a graphite full-heat furnace, held for an addition period, and then heated at 1,000°C/hour to 120-0°C.
Below that temperature, the temperature drops at 100℃/hour, and when taken out,
A colorless and transparent quartz glass was obtained.

Comparison row 1 In the same manner as in Example 11, the purified sol was adjusted to pH 1 and 4.5, and placed in a similar container, 1 crn, 2 cm.

4 art, the wet gel prepared to a thickness of 8 cm and left for 3 days was placed in a drying oven at 60'C without replacing with hydrochloric acid water and dried.
The α-thick one finished drying in about a week without cracking, but
The 2cIn, 4on, and acm thicknesses all cracked immediately after the start of drying.

Implementation row-2 A sol prepared and purified in the same manner as in Example 1 was used as pFi@
4.5 and charged into a similar container to a thickness of ioα.The resulting wet gel was left to stand for 3 days, and a mixture of water and ethanol prepared at a ratio of 55:45 was mixed with hydrochloric acid. pH @ 2. The surface layer was replaced with an OK-prepared water-soluble plate for 1 hour.

When I replaced the lid with a hole with an opening ratio of 0.4% and started drying it in a dryer at ω°C, it completed drying in about 2 months without cracking.

〔Effect of the invention〕

As explained above, according to one invention, the wet gel surface layer is gelatinized with pEIl! By substituting an acid aqueous solution or an acid aqueous solution-alcohol mixture with adjusted pH, the dehydration condensation reaction rate on the gel surface can be controlled, and the shrinkage on the gel surface can be made smaller than that inside the gel. This has the effect of generating compressive stress in the surface layer and increasing the gel strength during drying, thus increasing the drying yield.

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Claims (1)

[Claims] In the production of glass by the sol-gel method using metal alkoxide as a starting material, the gel surface layer is replaced with an acid aqueous solution or an acid aqueous solution-alcohol mixture having a pH lower than the pH value at which the sol is gelled, and then dried. A method of manufacturing glass characterized by the following.