JPS63256539A - Production of silica glass - Google Patents

Abstract

PURPOSE:To produce silica glass having a large-sized shape with good yield by previously hydrolyzing silicic acid ester partially with acid and water, and thereafter completely decomposing it and heat-treating it. CONSTITUTION:Silicic acid ester shown in a general formula Si(OCnH2n+1)4 [wherein (n) shows integer of 1-8] is previously hydrolyzed partially by using 0.5-1.5 molecule of water for 1 molecule of silicic acid ester and adding acid to the mixture. As the above-mentioned acid, acetic acid, formic acid, hydrochloric acid, nitric acid or sulfuric acid is used. Then stable silica gel is formed by furthermore adding water and completely hydrolyzing the mixture. Thereafter silica glass is obtained by heat-treating the silica gel.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an improved method for producing silica glass, and more specifically, to a method for producing large-sized silica glass with high yield and at low temperatures. The silica glass obtained by the present invention can be used as a material for optical communication fibers.

1.1 9. [Prior art] A method of melting 5iCI24, a method of oxidizing 5iCI24 to form fine particles, and then sintering it, and a method of sintering 5iCI24, which is called the sol-gel method.
There are three types of methods: silica gel is obtained using OC@Hzt+z)4 as a raw material, and silica glass is obtained by firing the silica gel. The method of the present invention belongs to the sol-gel method. The sol-gel method can produce extremely high-purity silica glass at a firing temperature of about 1200° C., which is much lower than the other two methods. however,
In the sol-gel method, the gel tends to break during the preparation or firing of the silica gel, making it extremely difficult to obtain large-sized products with good yield. In order to prevent gels from cracking, methods have been proposed that use special chemicals (for example, formamide) or create gels under supercritical conditions in solvents, but such methods do not contain substances that are harmful to the human body. New problems arise, such as the generation of waste as by-products and the need for large equipment.

:□ka’Ml&　Lyo, oh□, tsu.

! ,-2] An object of the present invention is to provide a method for efficiently producing large-sized silica glass by eliminating gel cracking during the production of silica glass in the sol-gel method.

[Means for solving problems]

As a result of extensive research to achieve the above object, the inventors of the present invention partially hydrolyzed the silicate ester represented by 5i (OC, H + 1), and then obtained further complete hydrolysis. The inventors discovered that strong silica glass without cracks can be obtained by polymerizing the silica glass, and that large-sized silica glass can be produced in good yield by heat-treating the same.Based on this knowledge, the present invention was developed. .

[Structure of the invention]

That is, the present invention provides general formula 5i (QC milk Hzl+x)
A silicate ester represented by * (where n is an integer from 1 to 8) is partially hydrolyzed in advance with acid and water,
The present invention provides a method for producing silica glass, which is characterized in that the silica gel is then completely hydrolyzed by adding water to form a strong silica gel, which is then heat-treated to obtain silica glass.

The substance represented by Si (QC%H+1)4 is a liquid called silicate ester, which undergoes hydrolysis as shown in equation (1) and polymerization as shown in equation (2). It becomes silica gel.

Silica glass is represented by Sin, and the reaction up to the final stage of the above equation is expressed as follows.

5i(oc,H,,,1),+2H,on 5iOz+
When the reactions of 4C++HzmtOH (3) (1) and (2) proceed to a certain extent, the silicate ester solidifies and becomes silica gel. By heat-treating this silica gel at a temperature of 1200° C. or lower, equations (1) and (2) proceed completely, the pores generated in the silica gel are also closed, and silica glass is formed.

In order to promote the progression of the formula (1), an acid having a number of about 1/10,000 to 1/10 of the number of molecules of the silicate ester is used. In this case, the acid is acetic acid or formic acid.

Hydrochloric acid, nitric acid, sulfuric acid, etc. are used. Further, since silicate ester and water do not mix, an alcohol having 1 to 8 carbon atoms is used as a co-solvent.

Silica gel obtained by hydrolyzing and polymerizing a silicate ester is porous, sensitive to changes in temperature and humidity, and easily broken. Therefore, the destruction of the gel is different from that of the conventional sol.
This was a major problem with the gel method. However, as in the present invention, by controlling the hydrolysis and polymerization processes of silicate ester, it is possible to create a strong gel that is resistant to changes in temperature and humidity. In the conventional sol-gel method,
Because the amount of water required for complete hydrolysis was added at once, equations (1) and (2) proceeded simultaneously, and areas of high and low strength were irregularly distributed inside the gel. Ori,
This caused a decrease in the strength of the gel.

In the present invention, the silicate ester is not completely hydrolyzed first, but is partially hydrolyzed using an acid and 0.5 to 1.5 molecules of water per molecule of the silicate ester. do. At this time, the temperature is room temperature to 70°C. Through this operation, all molecules of the silicate ester undergo hydrolysis evenly, and because it is only partially hydrolyzed, it does not form a gel and maintains its original fluidity. By holding this for 6 hours to 3 days, equalization is promoted.

The holding time may be made shorter as the temperature is higher. This holding operation eliminates the internal strength distribution of the silica gel that will be obtained later, making the gel less likely to crack.

After holding, more water is added to ensure complete hydrolysis. The amount of water added at this time needs to be at least twice the number of molecules of the silicate ester, including the amount of water added initially. Furthermore, since water and silicate ester are immiscible, an appropriate amount of alcohol as a co-solvent is added. The amount of alcohol and the timing of addition are not particularly limited, but it is desirable to add at least the same number of molecules as the silicate ester at the beginning so that the solution does not become immiscible.

After adding water, the solution is left at a temperature ranging from room temperature to 70°C. At this time, a cover may be applied for the purpose of suppressing evaporation of the solution. The solution solidifies into a gel within a few days. Silica glass is obtained by heat-treating this gel at a heating rate of 5° C. or less per minute to a maximum temperature of 1200° C.

〔Example〕

Next, the present invention will be explained in more detail with reference to Examples.

Example 5i (OCH,), 30.4 g, water 3.6 g, acetic acid 0.01 mol, ethyl alcohol 40 m Q were mixed,
Partial hydrolysis was allowed to proceed by stirring at room temperature for 24 hours. 22.4 g of drained water, 20 mg of ethyl alcohol,
A mixed solution of 0.01 mol of acetic acid was added, and the container was covered with aluminum foil and maintained at 60°C. Then cover the aluminum foil 1
A hole was made with a needle at a rate of one per day. After 3 days, the solution became a gel. The gel was further dried at 60° C. for one week, and after cooling, it was heated to 900° C. in an electric furnace at a temperature increase rate of 10° C./hour. The shape of the gel is a cylinder similar to the container (
The resulting silica glass has a diameter of 8 mm and a height of 40 mm due to the disappearance of pores in the gel.
It was about 11, but it wasn't broken. The obtained silica glass was transparent and had the same density as normal silica glass, 2.20 g/a&.

For comparison, I added the same amount of the same ingredients all at once, and after 3 days I still got a gel, but it was broken into 8 pieces. Furthermore, when this was heat-treated in the same way, 6
It broke into pieces before reaching 50°C and no lump glass was obtained.

The experiments demonstrated the effectiveness of the method of the present invention.

Designated Agent: Director of Hokkaido Industrial Development Testing Institute, Agency of Industrial Science and Technology, Taibe Goto

Claims (4)

[Claims] (1) General formula Si(OC_nH_2_n_+_1)_4
(However, n is an integer from 1 to 8) After partially hydrolyzing the silicate ester with acid and water, water is added to completely hydrolyze it to form a strong silica gel. A method for producing silica glass, characterized in that silica glass is obtained by heat-treating the silica glass. (2) The method according to claim 1, in which 0.5 to 1.5 molecules of water are used per molecule of silicate ester in the partial hydrolysis. (3) The method according to claim 1 or 2, in which acetic acid, formic acid, hydrochloric acid, nitric acid, or sulfuric acid is used as the acid. (4) The method according to any one of claims 1 to 3, in which an alcohol having 1 to 8 carbon atoms is used as a solvent in the hydrolysis.