JPH0214833A - Production of silica glass - Google Patents

Abstract

PURPOSE:To produce large-sized silica glass without causing crackings and cracks in producing silica glass by sol-gel method, by adding morpholine and/or N-morpholine in a process of making a sol solution. CONSTITUTION:Morpholine and/or N-morpholine and water are added to a silicon alkoxide or a polycondensate thereof, which is hydrolyzed to give silica hydrosol. The sol solution is gelatinized, the gel is dried to give silica gel and the dried gel is sintered to give silica glass. By this method, occurrence of big stress made of evaporation of water, alcohol, etc., considered to be a cause of crackings and cracks during gel drying can be avoided.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for producing silica glass used for optics, semiconductor industry, electronic industry, physics and chemistry, etc.

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

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

Silicon alkoxide and/or its polycondensate represented by the general formula Si (OR) a (where R represents an alkyl group), such as (RO) *5i (O3i (OR)) nO5i (OR) +
Water (an acid or alkali may be added as a catalyst in advance) is added to (n-0 to 8) to hydrolyze it into silica hydrosil. At this time, an appropriate alcohol may be added as a solvent so that the silicon alkoxide and water form a homogeneous system. This silica sol solution is gelled by standing still, raising the temperature, adding a gelling agent, etc.

Thereafter, the gel is dried to obtain silica gel.

Silica glass is obtained by sintering this dried gel in a suitable atmosphere.

This sol-gel method has the following features.

(Since it can be produced at a lower temperature than the conventional vapor phase chemical vapor deposition method in which the soot produced by flame hydrolysis or the like using 113iCIa as a raw material is sintered and vitrified, it can save energy and reduce costs.

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

(3) Since liquid phase mixing is possible at room temperature, homogeneous glass can be produced even when mixed with other components.

There are still unresolved problems in the production of silica glass by the sol-gel method, which has various advantages as described above.

In particular, the problem is that the gel tends to crack or crack during the drying process, making it difficult to produce a large, monolithic dried gel with a high yield. One of the causes of cracks and cracks is that stress is generated in the gel as water, alcohol, etc. evaporate during gel drying, and it is thought that if this stress is greater than the strength of the gel, the gel will crack or crack. There is. Further, this stress increases as the surface tension increases and as the pore diameter decreases, as expressed by the following formula % (ΔP - stress, r - surface tension, θ = wetting angle, r - pore diameter).

Therefore, as a method to prevent such cracks and cracks, measures have been taken 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 diameter. There is.

In addition, JP-A-61-183129 discloses that a solvent with a boiling point higher than that of water, such as l-
A method has been proposed in which butanol, 1-pentanol, 1-hexanol, and toluene are added to silicon alkoxide.

(Problems to be Solved by the Invention) However, in all of the above methods, it was difficult to obtain a sufficiently large dry gel body, and it was not possible to obtain a silica glass body whose dimensions were very large.

The present invention provides the production of silica glass without cracking or cracking.

(Means for Solving the Problems) The present invention considers that stress generated due to evaporation of water, alcohol, etc. during gel drying is a cause of cracks and cracks, and the present invention aims to prevent the generation of such large stress. In order to avoid this, morpholine and/or N-morpholine is used as a solvent for silicon alkoxide.

As the silicon alkoxide used in the present invention, not only silicon alkoxide monomers but also polycondensates may be used. For example, (C1130) ssi (OSi (OC113)
z) nO5i (OC113) 2 (n = 0 to 8
) can be mentioned. One or more of these can be used. As the alkyl group of silicon alkoxide, methyl group, ethyl group, propyl group, butyl group, etc. are preferable.

To the water added for hydrolysis, mineral acids such as hydrochloric acid and nitric acid, organic acids such as formic acid and acetic acid as catalysts, and not only ammonia but also organic salts such as ethylenediamine as bases may be added in advance.

The amount of morpholine and/or N-morpholine added to silicon alkoxide is preferably 0.1 to 5.0 times (molar ratio) to the amount of silicon alkoxide. Moreover, commonly used alcohols such as ethanol can also be used together. Furthermore, ketones, esters, and esters can also be used in combination.

The silicon alkoxide, morpholine and/or N-morpholine, and water may be mixed using a starter or the like to make the resulting sol as uniform as possible. Ultrasonic waves may also be applied.

Fine silica particles may be added when preparing the sol.

The generated sol solution is quickly transferred to another container and allowed to gel. During gelation, it is preferable to seal the container to prevent the solvent from escaping from the generated gel, and the temperature during gelation is preferably 0° C. or higher.

In the drying process, instead of using a lid with holes, the gel is dried and shrunk and solidified in an appropriate atmosphere to form a dry gel.

Thereafter, silica glass is manufactured by sintering using a gel-sol method.

Generally used conditions are used for the gelling step, drying step, and sintering step. For example, each
Leave at 100℃ for a few minutes to several 10 days, leave at room temperature to 100℃ for several hours to several 10 days, 1000 to 130 in an appropriate atmosphere
Example 1 Morpholine and tetramethoxysilane in a weight ratio of 11:1
A homogeneous solution was prepared by mixing in the proportion of O, and further, 0.01 mol/11 aqueous solution of choline was added in a volume ratio of 0.64 times that of tetramethoxysilane, and the mixture was sufficiently mixed to obtain a silica sol. The obtained sol was placed in a Teflon-coated glass Petri dish with a diameter of 200 am to a depth of 10 cm, sealed, and allowed to gel at room temperature for 5 days. The gel was dried at -60°C for 7 days and further dried at 120°C for 1 day to obtain a dried gel with a diameter of about 160 squares. The bulk density of the dry gel thus obtained was 0.65 g/cd, with no cracks or breaks. This dried gel was heated in air to 1250° C. at a rate of 60° C./hour to obtain silica glass with a diameter of about 100 mm without cracks or foaming. This silica glass has no devitrification or bubbles and is of high quality. Further, as a result of analysis, the properties of this silica glass matched those of commercially available silica glass.

Example 2 A dry gel with a diameter of about 120 a+ was obtained in the same manner as in Example 1, except that a mixed solvent having a volume ratio of methanol:morpholine=7:3 was used.

The dry gel thus obtained was free of cracks and cracks. This dried gel was heated in the same manner as in Example 1 to obtain a silica glass having a diameter of about 8011 II m without cracks or foaming. This silica glass has no devitrification or bubbles and is of high quality. Further, as a result of analysis, the properties of this silica glass matched those of commercially available silica glass.

(Effects of the Invention) According to the present invention, large-sized silica glass can be easily manufactured by the sol-gel method without generating cracks or breaks. There are basically no restrictions on its size, and its shape is not limited to plate-like ones, but also rod-like and tubular ones, which can be manufactured at a lower cost than in the past.

Claims (1)

[Claims] 1. In the production of silica glass, which consists of the steps of hydrolyzing silicon alkoxide to form a sol solution, gelling the sol, drying the gel, and firing, morpholine and/or A method for producing silica glass, characterized by adding N-morpholine.