JPH01275447A - Production of titania-silica glass by sol-gel process - Google Patents

Abstract

PURPOSE:To prevent the cracking of gel in drying and calcining stages by hydrolyzing silicon alkoxide and titanium alkoxide and adding a prescribed amt. of DMF to the resulting soln. before gelling. CONSTITUTION:Silicon alkoxide and titanium alkoxide are hydrolyzed by adding water to a soln. of the alkoxides in alcohol in 2-30 molar ratio of water to the alkoxides. The resulting soln. is converted into gel after 0.25-3 times as much DMF as the soln. is added to the soln. and the gel is dried and heated to obtain titania-silica glass.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for producing titania-silica glass, and more specifically, a dry gel is produced from a sol obtained by hydrolyzing silicon alkoxide and titanium alkoxide. , relates to a method of producing glass by firing this gel.

(Background of the Invention) Silica glass containing approximately 10% or less titania is known to have a lower coefficient of thermal expansion than pure silica glass, but it has a high melting point and is currently used for titanium tetrachloride and silicon tetrachloride. It is manufactured using a special furnace at a temperature of 1750°C or higher using the flame hytrolysis method as a raw material.

In response, attempts have recently been made to synthesize titania-silica glass by a sol-gel method using silicon alkoxide and titanium alkoxide as starting materials.

The advantages of the sol-gel method, compared to conventional glass manufacturing methods by melting, are that glass can be made by heating at low temperatures, crystallization can be prevented by heating at low temperatures, and the solution Since it is used as a starting material, it is possible to produce glass with excellent purity and uniformity, but on the other hand, it has the disadvantage that cracks and fractures easily occur during the drying process of the wet gel after gelation and the firing process of the dry gel. Until now, only small-sized glasses could be produced using methods using metal alkoxides as starting materials.

The cause of cracks in the gel body during the drying process of a wet gel is due to capillary stress based on the surface tension of the liquid filling the pores of the gel.

Since capillary stress is inversely proportional to pore diameter, this problem can be solved by increasing the pore diameter and reducing capillary stress.

Therefore, measures have been taken to expand the pore size, such as adding ammonia as a hydrolysis catalyst, increasing the drying temperature, and increasing the molar ratio of water to alkoxide.

However, there are limits to the method of enlarging the pore diameter, and it has not been possible to produce glass with a large capacity.

Another problem is that in the production of titania-silica glass by the sol-gel method, the rate of hydrolytic polycondensation of titanium alkoxide is much faster than that of silicon alkoxide, and titanium alkoxide is selective. Because titania tends to undergo hydrolysis and form fine particles of titania, it has been difficult to create transparent silica glass in which titania is uniformly dispersed.

The present invention has been made in view of the above background, and the first object is to prevent the occurrence of cracks in the drying process of a gel body and the occurrence of cracks and fractures in the firing process of a dried gel body, and to The object of the present invention is to provide a method for producing glass with a large diameter while avoiding an increase in the crystallization temperature, and as another object, to provide a method for producing titania-silica glass using a sol-gel method in which titania can be uniformly dispersed. be.

(Means for Solving the Problems) In order to achieve the above object, the present invention performs hydrolysis single polycondensation of an alcohol solution containing silicon alkoxide and titanium alkoxide in the presence of water to generate a gel body. It consists of a gelling step, a dry gel body forming step of drying the gel body, and a firing step of firing the dry gel body to make glass.

Here, in the gelation step, water is added in a molar ratio of 2 to 30 times the total amount of alkoxides of silicon alkoxide and titanium alkoxide, and silicon alkoxide and titanium alkoxide are added to the solution before gelation. 0.25 to 3.0 in molar ratio to the total amount of
It is desirable to add twice as much dimethylformamide (hereinafter abbreviated as DMF).

In addition, in order to prevent the precipitation of titania fine particles due to rapid hydrolysis of titanium alkoxide, titanium alkoxide is
A method in which a titanium chelate compound is formed in advance with a chelating agent and then hydrolyzed, or a silicon alkoxide is partially hydrolyzed by adding an amount of water that does not gel, and then a titanium alkoxide is added to form a silicone compound. A method in which titanium composite alkoxide is formed and then hydrolyzed by adding water, or a method in which a solvent that slows down the hydrolysis of titanium alkoxide is added and hydrolyzed is appropriately selected and used.

The above-mentioned methods for controlling the hydrolysis of titanium alkoxide are all used for the purpose of controlling the selective hydrolysis of titania, and the use of each method in combination is not prohibited.

As the silicon alkoxide in the present invention, silicon alkoxide and silicon tetraethoxide are suitable in consideration of availability and hydrolysis reactivity. As the titanium alkoxide, titanium tetraisopropoxide and titanium tetra-n-butoxide are suitable.

In addition, the amount of titanium alkoxide added to the total amount of zircon alkoxide and titanium alkoxide in the present invention is 1011111% by weight or less in terms of titania.
It is preferable from the viewpoint of obtaining a low expansion glass, and if it exceeds 10% by weight, it will no longer exhibit low expansion properties.

If the molar ratio of water to the total amount of silicon alkoxide and titanium alkoxide is 2 or less, a large amount of unreacted alkoxyl groups will remain in the dried gel, and the organic matter will be burned during the sintering process. It becomes an obstacle.

Moreover, if the molar ratio is 30 times or more, the strength of the gel body after gelation is low, so that cracks are likely to occur during the drying process. Therefore, it is desirable to add water at a molar ratio of 2 to 30 times that of the alkoxide.

As a result of analyzing the effect of DMF on the production of dry gel bodies without cracks, it was found that DMF controls the shrinkage of the pores of the gel bodies as drying progresses, and that DMF has a high boiling point of 153°C, and that it is difficult to finish drying. At some point, it replaces water with a high surface tension and remains in the gel pores, and its low surface tension is thought to minimize the capillary stress generated during the drying stage of the gel body and prevent cracks.

Furthermore, although DMF is almost neutral in an aqueous solution, it has the function of promoting the condensation reaction of alkoxides. Methods to control rapid titanium alkoxide hydrolysis must be used at the same time.

If the above method is not used, a crack-free dry gel body can be obtained, but titania fine particles will grow due to selective hydrolysis of titanium alkoxide, and a transparent glass will not be obtained.

Adding DMF to the solution at any time from before the addition of water to when the entire amount of water has been added is effective in preventing cracks in the gel body during the drying process. In order to avoid premature hydrolysis, it is desirable to add the water after the entire amount has been added.

Furthermore, if the molar ratio of DMF to the alkoxide is less than 0.25, it will not be effective in suppressing cracks in the gel body. On the other hand, if the molar ratio is 3 times or more, it will take a long time to dry the gel due to the high boiling point of DMF. Therefore, the amount of DMF added is desirably in a molar ratio of 0.25 to 3 with respect to the total amount of alkoxide.

Chelating agents for titanium alkoxides in operations to prevent selective hydrolysis of titanium alkoxides include acetic acid, acetic anhydride and acetic acid derivatives such as acetylacetone, oxalic acid, malonic acid.

Ethylene glycol etc. are effective. In addition, as a solvent to moderate the hydrolysis of titanium alkoxide, n-propatool,
n-butanol, 5ea-butanol, 3methyl-1
-butanol, 2methyl-1-butanol n-amyl alcohol are suitable.

For titanium tetra-n-butoxide, n-butanol, 5ee-butanol, 3-methyl-1-butanol, 2-methyl-1-butanol.

N-amyl alcohol is suitable.

The dried gel bodies obtained from the gelation and drying steps described above are both translucent and have a bulk density of approximately 0.8.
It was near g/air. The dried gel body was converted into transparent titania-silica glass without cracking or shattering during the firing process. The thermal expansion coefficients of the produced glasses were all smaller than that of silica glass (5.5×10° C.).

(Example) Hereinafter, the present invention will be explained in detail with reference to Examples.

Example 1 1.78 g (0.03 mol) of acetic acid was added to 6.74 g (0.02 mol) of titanium-n-butoxide,
A partially chelated titanium alkoxide was prepared by stirring at 40°C for 2 hours, and this was added to 74.4 mJl (0,5
mol) of silicon tetramethoxide and 84.3 mJ
(2,0 mol) of methanol is added to the mixed solution,
Mixed for several minutes at room temperature (20°C). The amount of titanium alkoxide added was 5% by weight in terms of titania. In this solution, 93.6 m! (5.2 mol) of water was slowly added dropwise over 1 hour with stirring, and stirring was continued for 1 hour. Finally, 40.1 mJ2 (0.52 mol) of DMF
was added and stirred for 20 minutes to obtain a homogeneous transparent sol.

The above sol was poured into a Teflon cylinder with an inner diameter of 38mm and a depth of about 300mm, sealed with aluminum foil, and gelatinized in an oven at 30°C. After gelation, the temperature was maintained at 30°C for 24 hours, and then the temperature was raised continuously from 30°C to 70°C over 24 hours to sufficiently promote the gelation reaction. When the oven temperature reached 70° C., several pinholes of diameter 1 were formed in the aluminum foil and drying began. The temperature was raised continuously from 70° C. to 115° C. over 120 hours, the temperature was kept constant at 120° C. for 72 hours, and then the temperature was raised continuously again to 150° C. over 73 hours to complete drying. The dried gel body obtained was translucent and had a diameter of about 22 mm and a length of 138III11.

The dry gel body is placed in an electric furnace and heated at 20°C per hour from room temperature to 800°C, and at 10°C per hour from 800°C to 1000°C.
The temperature was raised from 1000°C to 1050°C at a rate of 5°C per hour, and the temperature was maintained constant at 1050°C for 2 hours to obtain a transparent fired body with a diameter of 15 mm and a length of 81 mm. In addition, during the temperature raising process from 150° C. to about 700° C., oxygen gas was flowed to promote the oxidation reaction of residual organic matter.

The obtained fired body was confirmed to be glass by X-ray diffraction measurement. The obtained titanium silicon glass has a thermal expansion coefficient of 0.6 x 10-7°C-1 and a density of 2.2.
g/cm.

Example 2゜124mj! (0,833 mol) of silicon tetramethoxide and 70.2 mβ (1,73 mol) of methanol were mixed with an alkoxide containing 8.4 x 10-4 mol of hydrochloric acid and 14°9 m of water of the same mol, 2 was slowly added dropwise at room temperature, and the mixture was stirred for 3 hours to partially hydrolyze the silicon alkoxide. Add 11.23g to this solution in advance.
(0,033 mol) of titanium tetra-n-butoxide and 64.7 mJ2 (0,867 mol) of isopropanol were slowly mixed dropwise over 1 hour to partially hydrolyze the solution. After condensation with silicon alkoxide to form a molecular species with a 5i-0-Ti bond, 1 containing 9.2X10-' moles of ammonia
41.7 ml (7.87 mol) of water was added dropwise over 1 hour, and the mixture was stirred to completely hydrolyze the mixture.

Finally, 66.8 m12 (0,867 mol) of DMF
was added and further stirred for 20 minutes to obtain a homogeneous transparent sol. This sol was poured into a Teflon cylinder with an inner diameter of 49 mm and sealed with aluminum foil. Thereafter, the same operations as in Example 1 were performed to obtain a transparent fired body with a diameter of 18 mm and a length of 94 mm. It was confirmed by X-ray diffraction that the fired body was glass.

Example 3 6.74 g (0.02 mol) of titanium tetra-n-butoxide was added to 23.9 mJ2 of 5eC-butanol (0.02 mol).
26 mol) and stirred at 50°C for 1 hour.
．． 4 mJ2 (0.5 mol) of silicon tetramethoxide and 84.3 mA (2.0 mol) of methanol were added and stirred for several minutes while cooling to 20°C. The amount of titanium alkoxide added was 5% by weight in terms of titania. Add 1 mol of water containing 5 x 10-5 mol of ammonia to this solution.
The mixture was slowly added dropwise over a period of time while stirring to carry out a hydrolytic polycondensation reaction. Finally, 40.1 m,e (0.52 mol) of DMF was added and stirred for 20 minutes to obtain a homogeneous transparent sol. Thereafter, gelation was performed in the same manner as in Example 1.

Drying and firing were performed and sintered at 1050°C to obtain a transparent fired body with a diameter of 15 mm and a length of 81 mm. It was confirmed by X-ray diffraction measurement that this fired body was glass. The coefficient of thermal expansion of the obtained titania-silica glass is 2
．． It was 0x10-7°C-1.

In the above examples, the amount of water used for hydrolysis was 10 times the amount of alkoxide in terms of molar ratio. It is possible to manufacture uniform glass by increasing the amount of water by 2 to 10 times, or 20 times or 30 times, but the larger the amount of water, the larger the pores of the gel and the increase in capillary stress. On the other hand, if the amount of water increases, a large amount of alcohol as a solvent may be required, and taking these conditions into consideration, it is more preferable to use about 10 to 15 times as much water.

In addition, for adjustment to prevent selective hydrolysis of titanium,
We used a method using a chelating agent, a method in which silicon alkoxide was partially hydrolyzed and then added with titanium alkoxide for condensation, and a method in which a solvent was added to slow down the hydrolysis of titanium alkoxide. Since there are no strict boundaries, the use of each type of method is not limited, and their combined use is not prohibited.

Furthermore, although examples are shown in which hydrochloric acid is used as the acid or ammonia is used as the base, any catalyst may be used as long as it does not drastically change the hydrolysis reaction of the alkoxide, and there are no limitations on the type. isn't it.

(Effects of the Invention) As explained in detail in the examples above, in the method of the present invention, by adding titanium alkoxide and silicon alkoxide to a hydrolyzed solution, a dry gel body without cracks can be produced, and further It is possible to produce large titania-silica glass without cracking or fracturing.

Furthermore, according to the method of the present invention, since the rate of hydrolytic polycondensation of titanium alkoxide is controlled, transparent silica glass in which titania is uniformly dispersed can be obtained. Therefore, the method of the present invention is useful as a new method for producing titania-silica glass by the sol-gel method.

Patent applicant: Ube Nitto Kasei Co., Ltd.
Written by Masato Sueshiro
Patent Attorney - Kensuke Shiro Patent Attorney Masatoshi Matsumoto Procedural Amendment (Responsibility June 13, 1988 Director General of the Patent Office Kunio Ogawa 1, Indication of Case 1989 Patent Application No. 102389 2, Name of Invention Sol- Method for producing titania-silica glass by gel method 3, relationship with the amended case Patent applicant address: 2 Kanda Iwamoto-cho, Chiyoda-ku, Tokyo Name: Ube Nitto Kasei Co., Ltd. 4, Agent address: Port of Tokyo Rokin Shinbashi Building 7F, 2-12-7 Shinbashi, Ward Telephone 508-0338 (Main) 5, Subject of amendment (1) Column 6 of "Detailed explanation of the invention" of the specification, Contents of amendment (1) Specification On page 7, line 19, "silicon alkoxide" is corrected to "silicon tetramethoxide."

Claims (7)

[Claims] (1) A method for producing titania-silica glass by adding water to a solution of silicon alkoxide, titanium alkoxide, and alcohol, drying the gel formed by hydrolysis, and then heating the dried gel. A method for producing titania-silica glass by a sol-gel method, characterized in that dimethylformamide is added to the previous solution. (2) The amounts of water and dimethylformamide added are 2 to 30 times and 0.25 to 3 times, respectively, in molar ratio to the total amount of silicon alkoxide and titanium alkoxide.
The sol according to claim 1, characterized in that the sol has a double range.
A method for producing titania-silica glass using a gel method. (3) The sol-gel method according to claim 1, wherein in the hydrolysis, the titanium alkoxide is reacted with a chelating agent in advance to form a titanium chelate, and then the titanium alkoxide is hydrolyzed together with the silicon alkoxide. Method for producing titania-silica glass. (4) In the hydrolysis of the silicon alkoxide and titanium alkoxide, the titanium alkoxide is added after the silicon alkoxide is partially hydrolyzed with water in an amount that does not cause gelation. - A method for producing titania-silica glass using a gel method. (5) The sol-gel method according to claim 1, wherein in the hydrolysis of the silicon alkoxide and titanium alkoxide, the hydrolysis is carried out together with the silicon alkoxide after adding a solvent that slows down the hydrolysis of the titanium alkoxide. A method for producing titania-silica glass. (6) The chelating agent for the titanium alkoxide is acetic acid,
4. The method for producing titania-silica glass by a sol-gel method according to claim 3, wherein the acetic acid derivatives, dicarboxylic acids, and glycols are used. (7) The method for producing titania-silica glass by a sol-gel method according to claim 5, wherein the solvent that slows down the hydrolysis of the titanium alkoxide is an alcohol having 3 or more carbon atoms.