JPH0516375B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an improved method for producing silica glass. More specifically, the present invention relates to a fine gel powder obtained by hydrolyzing a silicate ester and a mixture thereof with desired additives;
Alternatively, the present invention relates to a method for economically producing silica glass of excellent quality without undergoing a molten state, containing no crystalline matter, and having no cracks or the like, using amorphous silica fine powder as a raw material.

[Conventional technology]

Conventionally, methods for manufacturing silica glass have been known, including a method that involves a molten state in the manufacturing process and a method that does not involve a molten state.

The former molten state method involves melting raw quartz and optional additives at a high temperature of 2,000°C or higher, and then cooling it to obtain glass. However, in this method,
(1) A large amount of heat is required for melting; (2) impurities may be mixed in during melting or certain components may evaporate; and (3) depending on the type of additive, melting may be significant. There are problems such as the production of glass becoming difficult or impossible due to crystal precipitation. All of these problems are associated with melting of the raw material powder.

On the other hand, as a method that does not require a molten state, a silicate ester or a mixture of a silicate ester and a metal alkoxide or a metal salt is hydrolyzed to obtain a gel, which is then dried and heated to obtain a gel. A method of obtaining glass by removing silica and water and extinguishing the pores in the gel, or a method of dispersing amorphous silica fine powder in water or alcohol, gelling it, and then heating this gel in the same manner as above. There is a way to get glass. These methods are generally called sol-gel methods, and since the raw materials do not go through a molten state, the above-mentioned problems can be avoided. However, even in such a sol-gel method, internal stress is generated due to the dissipation of moisture and solvent during drying and heating, which tends to cause cracks, and requires an extremely long heating time. It has its drawbacks.

[Problem that the invention seeks to solve]

The purpose of the present invention is to take advantage of the advantages of the sol-gel method and overcome its disadvantages, and to produce a fine gel powder obtained by hydrolyzing a silicate ester and a mixture thereof with desired additives. It is an object of the present invention to provide a method for economically producing silica glass of excellent quality, which does not contain crystalline substances and is free from cracks, using amorphous silica fine powder as a raw material, without going through a molten state.

[Means for solving problems]

As a result of intensive research to achieve the above object, the inventors of the present invention first calcined the gel fine powder or amorphous silica fine powder at a predetermined temperature to eliminate the moisture and solvent adsorbed on the raw material powder. This purpose is achieved by removing impurities such as, and reducing the active sites that re-adsorb moisture present in the raw powder, and then firing this calcined powder under predetermined hydrostatic pressure and temperature conditions. Based on this knowledge, the present invention was completed.

That is, the present invention provides a gel fine powder obtained by hydrolyzing a silicate ester or a mixture of a silicate ester and a metal alkoxide or a metal salt, or an amorphous silica fine powder at a temperature of 800 to 1200°C.
Provided is a method for producing silica glass, characterized in that the silica glass is calcined at a temperature of 100 to 1000 atm, and then fired at a temperature ranging from 900°C to the glass transition point of the silica glass produced. It is something.

The raw material used in the method of the present invention is a fine gel powder obtained by hydrolyzing a silicate ester or a mixture of a silicate ester and a metal alkoxide or a metal salt, or amorphous silica fine powder.

Examples of the silicate ester include methyl silicate, ethyl silicate, propyl silicate, butyl silicate, and examples of the metal alkoxide include:
Examples include metal methoxide, ethoxide, propoxide, butoxide, and the like. Examples of metal salts include those soluble in alcohol-water mixture solvents, such as carbonates, sulfates, sulfates, perchlorates, acetates, and oxalic acid.

These metal alkoxides and metal salts are used to adjust the physical and chemical properties of the target glass, and the amount added is usually 0 to 40 parts by weight per 100 parts by weight of silicate ester. selected within the range.

Hydrolysis of a silicate ester and a mixture of a silicate ester and a metal alkoxide or metal salt is usually carried out using a sufficient amount of alcohol to dissolve the silicate ester and a molar amount of 2 to 30 times the silicate ester, preferably The silicate ester or mixture is dissolved in a mixed solvent with 10 to 30 times the molar amount of water, and a mineral acid or ammonia is added thereto in a molar amount of 10 ^-5 to ^{10 -2} times the silicate ester. The alcohol is added as a catalyst and heated to a temperature in the range from room temperature to below the boiling point of the alcohol under normal pressure. The alcohol used in the solvent is preferably an alcohol having 1 to 8 carbon atoms.

A gel is produced by such hydrolysis, and this gel is crushed and used as a raw material powder.

In the present invention, the gel fine powder or amorphous silica fine powder obtained as described above is used as the raw material powder. Since this raw material fine powder has impurities such as moisture and solvent adsorbed, in order to remove this and reduce the active sites that re-adsorb moisture, etc., it is heated in air or oxygen at a temperature of 800 to 1200℃. Calcined at temperature. At this time, the atmosphere may contain approximately several percent of chlorine. The temperature increase rate during calcination is 10°C/min or less, preferably 1°C/min to 5°C.
A range of °C/min is desirable. Also, the calcination time is usually 10
It takes about minutes to several hours. If the calcination time is too low,
If the heating rate is too fast, impurities and active sites will be incompletely removed, and if the calcination temperature is too high, the raw material powder will crystallize. The optimum calcination temperature varies depending on the type of additive, but in the case of pure silica, it is preferably selected in the range of 800 to 1200°C.

The powder calcined in this way is filled into a mold made of a high melting point metal such as platinum or gold, and the inside of the mold is vacuum degassed and then sealed, or the entire mold is filled with a low melting point metal such as a commercially available glass tube. Pack and vacuum seal. The metal mold is preferably as thin as possible. This is hydrostatically compressed and fired to obtain the desired silica glass. The reason for compaction and calcination is to facilitate sufficient mass transfer to occur to fill the voids between the powder particles. The reason for hydrostatic compression is to prevent stress from remaining in the resulting glass and to obtain a complex shape that is impossible with uniaxial compression.
If the pressure or temperature is too high or the firing time is too long, the raw material powder will crystallize. The optimal pressure, temperature, and time are determined by the composition of the raw material powder and the balance between these, but in the case of pure silica glass, the firing temperature is preferably selected in the range of 900 to 1200°C, and the firing time is several times. It takes about minutes to several hours.

〔Effect of the invention〕

The method of the present invention uses gel powder obtained by hydrolyzing a silicate ester or a mixture thereof with desired additives, or amorphous silica fine powder as a raw material, and produces silica glass without undergoing a molten state. According to this method, it is possible to economically obtain silica glass that does not contain crystalline materials and has excellent quality such as cracks.

〔Example〕

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

Example 1 Example of manufacturing pure silica glass from ethyl silicate Add 20 ml of ethyl silicate (commercially available special grade product), 40 ml of ethyl alcohol, 18 ml of water, and 0.003 mol of hydrochloric acid,
Hydrolysis was carried out at ℃ for 3 days to obtain a gel. This was ground to 200 mesh or less in an agate mortar and heated to 1000°C at a heating rate of 0.5°C/min in oxygen.
Holds time. The obtained powder was filled into a platinum foil container as shown in Figure 1, placed in a soft glass tube, kept at 0.1 Torr for 1 hour with a vacuum pump, and then sealed. Next, this was placed in a hydrostatic pressure device as shown in FIG. 2, and maintained at 300 atm and 1100° C. for 1 hour.
The pressure was applied using argon gas pressure. At a temperature of 1100 degrees Celsius, the soft glass melts, completely enveloping the platinum container and transmitting hydrostatic pressure. This results in a density of 2.20
A transparent, crystal-free pure silica glass of g/cm ³ was obtained.

Example 2 Example of adding ethyl silicate 6 additives Add 0.003 mol of hydrochloric acid to 20 ml of ethyl silicate, 2 ml of ethyl borate, 40 ml of ethyl alcohol, and 18 ml of water.
Hydrolysis was carried out at 60°C for 3 days to obtain a gel. The following procedure was carried out in the same manner as in Example 1, except that the firing conditions under hydrostatic pressure were
The temperature was 300 atm and 950°C. The reason is that glass can be obtained at a lower temperature than in Example 1 due to the addition of boric acid.

As a result, approximately 90 mol% transparent and crystal-free
A glass _{of SiO2-10} mol% _B2O3 was obtained.

Example 3 Example using amorphous silica fine powder Commercially available silica fine powder was used as a raw material. The average particle size was 10 nanometers. This was calcined in oxygen in the same manner as in Example 1, and then fired in the same manner.

As a result, transparent silica glass containing no crystals was obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of an ampoule filled with calcined raw material powder to be attached to a hydrostatic pressure device in an example, in which reference numeral 1 is soft glass, 2 is platinum foil,
3 is a calcined raw material powder. FIG. 2 is a schematic cross-sectional view of the hydrostatic device after heating with the ampoule attached thereto in the embodiment, and the symbols in the figure have the following meanings. 11: Furnace body, 12: Heating element, 13: Alumina protector, 14: Thermoelectric element, 15: Gas inlet, 1
6: Soft glass, 17: Alumina tube, 18: Silica glass.

Claims (1)

[Claims] 1 After calcining fine gel powder or amorphous silica powder obtained by hydrolyzing a silicate ester or a mixture of a silicate ester and a metal alkoxide or metal salt, at a temperature of 800 to 1200 °C,
A method for producing silica glass characterized by firing at a temperature ranging from 900°C to the glass transition point of the silica glass produced under hydrostatic pressure of 100 to 1000 atmospheres.