JPH0825757B2 - Silica glass manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing silica glass used for optics, semiconductor industry, electronic industry, physics and chemistry, and the like.

(Prior Art) In recent years, the sol-gel method has attracted attention as a new method for producing silica glass.

The method for producing silica glass by the sol-gel method is as follows.

A silicon alkoxide represented by the general formula Si (OR) ₄ (where R represents an alkyl group) and / or a polycondensate thereof,
For example, (RO) ₃ Si (OSi (OR)) nOSi (OR) ₃ (n = 0 to 8) is added with water (acid or alkali may be added in advance as a catalyst) and hydrolyzed to obtain a silica hydrosol. And At this time, an appropriate alcohol may be added as a solvent so that the silicon alkoxide and water become a uniform system.
This silica sol solution is allowed to gel by standing, heating, addition of a gelling agent, and the like. Then, the gel is dried to obtain silica gel. The dried gel is sintered in an appropriate atmosphere to obtain silica glass.

 This sol-gel method has the following features.

(1) Since it can be produced at a lower temperature than the conventional vapor-phase chemical vapor deposition method in which soot produced by flame hydrolysis or the like using SiCl ₄ or the like as a raw material is sintered and vitrified, energy saving and cost reduction can be achieved.

(2) Since it can be used as a raw material in a liquid state, it can be easily purified and highly purified.

(3) Since it can be mixed in liquid phase at room temperature, it can be homogeneous or glass even when mixed with other components.

Thus, there are still unsolved problems in the production of silica glass by the sol-gel method having various characteristics.

In particular, cracks and cracks are likely to occur in the gel during the process of drying the gel, and it is difficult to produce a large monolithic dry gel with a good yield. One of the causes of cracks and cracks is that stress occurs in the gel due to evaporation of water, alcohol, etc. during gel drying, and if this stress is greater than the strength of the gel, it is thought that the gel will crack or break. There is. Further, this stress increases as the surface tension increases and as the pore diameter decreases, as expressed by the following equation ΔP = γ cos θ / r (ΔP = stress, γ = surface tension, θ = wetting angle, r = pore diameter). Become.

Therefore, as a method of preventing such cracks and cracks, measures such as increasing the amount of water in the sol solution to increase the gel strength and increasing the hydrolysis temperature to increase the pore size have been taken. There is.

Further, JP-A-61-183129 proposes a method of adding a solvent having a boiling point higher than that of water, such as 1-butanol, 1-pentanol, 1-hexanol, or toluene, to a silicon alkoxide in order to prevent cracks and cracks. Has been done.

(Problems to be Solved by the Invention) However, in any of the above methods, it is difficult to obtain a sufficiently large dry gel body, and it is not possible to obtain a silica glass body having a very large size.

The present invention provides the production of silica glass that does not crack or split.

(Means for Solving the Problems) In the present invention, it is considered that the stress caused by evaporation of water, alcohol, etc. during gel drying contributes to cracks and cracks, and the occurrence of such a large stress is considered. To avoid
N, N-dimethylacetamide is used as a solvent for the silicon alkoxide.

The silicon alkoxide used in the present invention may be not only a silicon alkoxide monomer but also a polycondensate, for example, (CH ₃ O) ₃ Si (OSi (OCH ₃ ) ₂ ) nOSi (OCH ₃ ) ₃ (n = 0.
~ 8) can be mentioned. These may be used either alone or in combination. As the alkyl group of silicon alkoxide, a methyl group, an ethyl group, a propyl group and the like are preferable.

Water to be added for the hydrolysis may be previously added with a mineral acid such as hydrochloric acid or nitric acid as a catalyst, an organic acid such as formic acid or acetic acid, and not only ammonia but also an organic base such as ethylenediamine as a base.

The amount of diacetone alcohol added to the silicon alkoxide is preferably 0.1 to 5.0 times (molar ratio) that of the silicon alkoxide. Further, alcohol such as ethanol which is usually used can be used in combination.

The silicon alkoxide, diacetone alcohol and water are well mixed using a stirrer or the like in order to make the produced sol as uniform as possible. Also, ultrasonic waves may be applied. Fine particles of silica may be added during the preparation of the sol.

The produced sol solution is quickly transferred to another container for gelation. At the time of gelation, the container is preferably sealed in order to prevent the solvent from escaping from the generated gel, and the temperature at the time of gelation is preferably 0 ° C. or higher.

In the step of drying, a dry gel is prepared by shrinking and shrinking and solidifying under a suitable atmosphere instead of using a lid having holes. Then gel
Silica glass is manufactured by sintering by the sol method.

For the step of gelling, the step of drying and the step of sintering, generally used conditions are used. For example, 0 ° C
Leave at -100 ° C for several minutes to tens of days, room temperature to 100 ° C for several hours to several
Leave for 10 days, 1000 to 1300 ℃ in suitable atmosphere 50 to 200 ℃
/ Hour heating rate.

Example 1 Silicon tetramethoxide _{(Si (OCH 3) 4)} : N, N- dimethylacetamide _{(CH 3 CON (CH 3)} 2) = 1: adjusted to 1 molar ratio of methanol N, The same amount as N-dimethylacetamide was added and stirred to obtain a uniform solution. Aqueous ammonia having a concentration of 0.01 mol / mol was added to this solution in an amount of 4 mol with respect to 1 mol of Si (OCH ₃ ) _{4 and} sufficiently mixed to obtain a silica sol. The obtained sol was put into a Teflon-coated glass petri dish having a diameter of 150 mm to a depth of 10 mm, and the gel was sealed at room temperature. After gelling, it was dried at 60 ° C. for 10 days in place of the lid having holes, and then heated to 170 ° C. at 30 ° C./day and dried to obtain a dry gel without cracks or cracks. This dried gel in the air
By heating up to 1250 ° C. at a rate of 60 ° C./hour and heating, silica glass without cracks or foaming was obtained. This silica glass is of high quality without devitrification or bubbles. As a result of the analysis, this silica glass was in agreement with the properties of commercially available silica glass.

Example 2 silicon tetramethoxide _{(Si (OCH 3) 4:} N, N- dimethylacetamide _{(CH 3 CON (CH 3)} 2 = 2: adjusted to 1 molar ratio, ethanol N, N- Half the amount of dimethylacetamide was added and stirred to form a uniform solution.Ammonia water having a concentration of 0.01 mol / mol was added to this solution in an amount of 4 mol with respect to 1 mol of Si (OCH ₃ ) ₄ and sufficiently mixed to obtain a silica sol. The sol was placed in a Teflon-coated glass dish with a diameter of 150 mm to a depth of 10 mm, sealed, and gelled at room temperature.After gelling, replace the lid with a hole and dry at 60 ° C for 10 days, then to 170 ° C Drying was performed by heating at a rate of 30 ° C / day to obtain a dry gel without cracks or cracks.The dried gel was heated up to 1250 ° C in air at a rate of 60 ° C / hour to prevent cracks or foaming. A silica glass that does not have devitrification or bubbles is obtained. Is high of. The analysis results, the silica glass its properties were consistent with commercial silica glass.

(Effects of the Invention) According to the present invention, large-sized silica glass can be easily produced by the sol-gel method without generating cracks or cracks. The size is basically not limited, and the shape is not limited to the plate-shaped one, and rod-shaped or tubular-shaped ones can be manufactured, which can be manufactured at a lower cost than before.

In addition, since silica glass can be manufactured at a lower cost according to the present invention, it can be used not only in fields such as photomask base materials for IC manufacturing which have been conventionally used, but also in fields which have not been used because of its high price. Demand can be expanded.

Claims (1)

[Claims] 1. A process for preparing a sol solution in the production of silica glass, which comprises the steps of hydrolyzing a silicon alkoxide into a sol solution, gelling the sol, drying the gel, and firing the silica glass. A method for producing silica glass, characterized by adding N, N-dimethylacetamide.