JPS6136126A - Production of porous gel plate - Google Patents

Abstract

PURPOSE:To form a large-sized dry gel plate, in high reproducibility, by using a specific drying means in the preparation process of a porous dry gel plate comprising the gelation of the hydrolyzed sol liquid of a metal alkoxide followed by the drying of the gel. CONSTITUTION:A sol liquid 3 (e.g. a liquid mixture of silicon methoxide, ammonia water and methanol) is filled in a gel-forming vessel 5 made of glass, and the produced gel is dried in a manner to essentially equalize the rates of drying at both faces of the gel plate. A porous dry silica gel 4 suitable as a precursor for the preparation of an optical glass plate can be produced by this process.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for producing a plate-shaped porous dry gel, and particularly to a method for producing a porous silica gel suitable as a precursor for a plate-shaped optical glass.

[Background of the invention]

Conventionally, a plate-shaped porous dry gel has been produced by using a wide-mouthed flat-bottomed container such as a petri dish 1 for chemical experiments as shown in Fig. 1, and pouring a hydrolyzed sol solution of a metal alkoxide into it. The gel was obtained by sealing it with foil 2, etc., and then making a pinhole in the aluminum foil and gradually drying the gel. (b) However, when creating a large plate-like dry gel 4, cracks occur, making it difficult to create with good reproducibility.

Incidentally, as a prior art related to the present invention, for example, Japanese Patent Laid-Open No. 57-22126 can be found.

[Purpose of the invention]

Therefore, an object of the present invention is to provide a method for producing a large plate-shaped trigel with good reproducibility.

[Summary of the invention]

A sol solution obtained by hydrolyzing a metal alkoxide or halide is cast into a mold of a desired shape to create a plate-shaped wet gel. In the method of the present invention, a large plate-shaped gel can be produced by providing a means for making the drying rate on both sides of the plate substantially the same.

According to the experimental studies conducted by the present inventors, due to an imbalance in the drying speed on both sides of the gel, for example, in the case of the conventional method shown in FIG.
This caused the crack.

Various methods can be used to eliminate this difference in shrinkage. This will be explained in detail below using examples.

[Embodiments of the invention]

Example 1 In this example, silicon methoxide was used as the metal alkoxide. 1 per mole of silicon methoxide.
/ 4 moles of 100N ammonia water and 4 moles of methanol were added to prepare about 800 cc of a sol solution. Next, as a gel preparation container, a width of 10 cm as shown in Fig. 2,
Prepare 5 glass containers 5 with a height of 20 cm and a thickness of 0.8 cm (inside iJ), inject the above sol solution into each container so that the height is l0CII+, and cover the top with aluminum foil 2.
It was sealed and gelled. At the same time, for comparison,
Five petri dishes made of homogeneous glass with an inner diameter of approximately 8 cm and a height of 0
．． The sol solution was injected to a thickness of 8 cm, each sealed with aluminum foil, and gelatinized. After gelation (about 1 hour later), a pinhole was made in the aluminum foil for each container, and the sealed portion was inserted into a constant temperature bath at about 70° C. with the -L direction, and kept for about 1 week to dry. As a result, all of the gels in the petri dish were severely cracked, but up to 4 out of 5 gels in the glass container according to the example of the present invention were not cracked, and the remaining 1 gel was only slightly cracked. It was acceptable.

Then, the obtained dry gel was heated with oxygen in an electric furnace.
The temperature was raised to 800°C, then 1200° in helium.
The temperature was raised to C to make it non-porous. As a result, 4.2cmX4
A plate-like transparent quartz glass plate measuring 2 cm x 3 and 3 mm was obtained.

The essential difference between the method of the present invention and the conventional method is that in the conventional method, drying is performed in the vertical direction of the board, whereas in the method of the present invention, drying is performed in the in-plane direction of the board. It is in. In the case of the present invention, although non-uniformity in the drying state occurs in the direction within the board surface, there is no difference in the thickness direction of the board, so no cracks occur. Therefore, in order to avoid evaporation of the plate-shaped gel to be dried from the plate surface, it is preferable to keep the drying container and the surface of the wet gel as close as possible.

Further, although it is preferable to support the gel vertically during the drying process as in this example, the same effect can be obtained even if the gel is supported horizontally. Furthermore, although the present two examples relate to gels for producing quartz glass, it is obvious that similar effects can be obtained in the production of additive-type quartz glass or general metal oxide porous gels. Furthermore, by using a mold in which the inner surface of the gel preparation container has been processed by grating or the like, it is possible to create a replica of a diffraction grating or a Fresnel lens.

〔Effect of the invention〕

As explained below, according to the present invention, in the drying process of a plate-shaped wet gel obtained by hydrolyzing a metal alkoxide, the distortion applied to the plate in the thickness direction can be reduced, so that a large plate-shaped plate without cracks can be formed. Dry gel can be created with good reproducibility.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram of a drying process according to a conventional method, and FIG. 2 is a conceptual diagram of a drying process according to an embodiment of the present invention. 1... Petri dish, 2... Aluminum foil, 3. Wet lot 10 V2 diagram (0L) (4

Claims (1)

[Claims] 1. A method for producing a plate-shaped porous dry gel by gelling and drying a sol obtained by hydrolyzing a metal alkoxide, in which the drying rate from both sides of the plate-shaped gel is substantially 1. A method for producing a plate-shaped porous gel, characterized in that drying is carried out using drying means that are identical in terms of drying method. 2. The method for producing a plate-shaped porous gel according to item 1, wherein the drying means dries the plate-shaped gel from an end portion thereof in a direction including the plate surface. 3. The method for producing a plate-shaped porous gel according to items 1 and 2, characterized in that the gel is dried while being brought close to two surfaces having at least substantially parallel planes. 4. The method for producing a plate-shaped porous gel according to item 3, wherein the two substantially parallel surfaces are held substantially vertically.