JPH0196057A - Production of ceramics - Google Patents

Abstract

PURPOSE:To prevent cracking and crazing during the production of dry gel, to shorten the drying time and to enable the formation of largesized ceramics when ceramics is produced by a sol-gel process by carrying out conversion into gel in the presence of a water soluble polymer. CONSTITUTION:A metal alkoxide is hydrolyzed, the resulting hydrolyzate is converted into gel and this gel is dried and sintered to produce ceramics. At this time, the conversion into gel is carried out in the presence of a water soluble polymer. The polymer is preferably used by 0.1-10wt.% of the amt. of the metal alkoxide. The polymer may be PVA, sodium polyacrylate, polyethylene oxide, polyethylene glycol, starch, gelatin or gum arabic.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing ceramics.
Specifically, the present invention relates to a method for producing ceramics using a sol-gel method using metal alkoxide as a raw material.

[Prior art]

Hydrolyze the metal alkoxide, dry the resulting gel,
The so-called sol-gel method is known and used to produce highly pure ceramics, such as glass, and sintered bodies by sintering.

In this sol-gel method, a hydrolyzed solution is directly gelled in a container of a predetermined shape, and then dried to form a dry gel. A method of producing quartz glass by firing it in an electric furnace or the like is particularly practiced in the field of quartz glass.

However, since the above gel contains a large amount of water and alcohol due to hydrolysis, it not only requires a long period of time to dry, but also has the disadvantage that it is prone to cracking as the volume decreases. had. For this reason, the molar ratio of finely powdered silica to metal alkoxide is 0.
．． It has been proposed that by adding 2 to 5 times the amount, the structure of the shigeru becomes porous, making it less likely to cause cracks or cracks during drying and firing.

However, this method also has the disadvantage that if the undried gel is left naked at room temperature, the surface will rapidly dry, resulting in cracks and cracks in the gel. Therefore, when drying the gel, a method was used in which the container was covered with a lid with a small porosity and the gel was gradually dried. (Unexamined Japanese Patent Publication No. 6 o-ly/
g33) [Problems to be solved by the invention] In order to prevent cracks, cracks, etc. that occur during the manufacturing process of dry gel, the present invention adds a water-soluble organic polymer to strengthen the gel structure and The object of the present invention is to provide a method for manufacturing large-sized ceramics in a short time.

[Failure to solve the problem]

The present invention provides a method for producing ceramics using a metal alkoxide as at least one of the starting materials, in which a water-soluble polymer is added to the hydrolyzed solution of the metal alkoxide so that the polymer is uniformly dispersed. The above object is achieved by a method for manufacturing ceramics characterized by the following.

The metal alkoxide that is the raw material of the present invention includes elements of Groups 1 to V of the periodic table, such as Al.

B, Si, Ti, P, Ge, Zr, 5bX
Examples include alkoxides of Y, rare earth metals, and the like.

Examples of the alkoxy groups of these metal alkoxides include methoxy groups, ethoxy groups, propoxy groups, butoxy groups, and the number thereof is preferably two or more.

Specific examples of such metal alkoxides include trimethoxyaluminum, jetoxyaluminum chloride, tetramethoxysilane, trimethoxychlorosilane,
Examples include dimethoxydimethylsilane, tetraethoxysilane, and tetrapropoxytitanium.

In the hydrolysis of the present invention, seven or more of the above-mentioned metal alkoxides are used, but if necessary, oxide powders, metal salts or metal complexes of the elements of Groups 1 to V of the periodic table, or periodic Compounds other than Groups 1 to V of the Table of Contents may also be present.

Examples of oxide powders, metal salts, or metal complexes of elements in Groups Ⅰ to V of the periodic table include metal hydroxides or metal oxide powders produced by wet hydrolysis of metal alkoxides; Metal oxide powders produced by dry hydrolysis or combustion of metal alkoxides and metal halogenides, inorganic acid salts of metals such as carbonates, hydrochlorides, and nitrates, and organic acid salts of metals such as oxalates. , complex salts with chelate compounds such as ethylenediaminetetraacetic acid, cyclopentadienyl metal complexes, and the like.

Compounds other than Groups I to V of the periodic table include, for example, alkali metals such as sodium and potassium, alkaline earth metals such as magnesium, calcium, and barium, and transitions such as iron, cobalt, nickel, flume, and manganese. Examples include metal alkoxides, hydroxides, oxides, inorganic acid salts, organic acid salts, metal complexes, and the like.

Hydrolysis of the metal alkoxide in the method of the present invention is carried out in a conventional manner, ie, with water, and an organic solvent such as alcohol may be added if necessary. As the alcohol, methanol, ethanol, gropanol, butanol, etc. are usually used. Furthermore, known alkalis such as ammonia or acids such as hydrochloric acid may be added as metal alkoxide hydrolysis catalysts.

Water-soluble polymers added in the present invention include polyvinyl alcohol, sodium polyacrylate, polyethylene oxide, polyethylene glycol, polyphthylene gelicol, cellulose, starch, gelatin, casein, collagen, Niwa A1, and gum arabic. etc. are used.

The water-soluble polymer is added by dissolving it in water or a hydrophilic solvent in advance, and then adding it together with water as a metal alkoxide hydrolyzate.

■ Adding after hydrolysis of the metal alkoxide (but before gelation) can be done by any method;
It is sufficient if the polymer can be uniformly soluble.

The concentration of the water-soluble polymer added is 0.0% relative to the raw material components. /
It is preferably about 10 wt%, particularly preferably about 0.2 to 10 wt%. When the concentration of the water-soluble polymer is less than O,/wt% based on the raw material components, the reinforcing effect of the gel is small, and the effect of preventing cracks and cracks during drying is small. Furthermore, when the content is above /□vrt%, the effect of preventing cracks and cracks is saturated.

Further, the molecular weight of the water-soluble polymer is not particularly limited, but as the molecular weight increases, the solubility in water tends to decrease.

In that case, a water-soluble organic solvent such as acetone can be used in combination.

Next, when obtaining a gel from a hydrolysis product, it will gel immediately if heated, but it will gel in a few hours even if left at room temperature, so the easiest way is to adjust the degree of heating in this way. Yes, the gelation time can be adjusted appropriately.

For example, it is preferable that the product is not gelled during operations such as putting it into a mold, so the gelation time may be selected depending on the situation, taking into consideration the necessary operations.

The ceramic gel synthesized according to the present invention hardly cracks or breaks even when dried in an oven at room temperature. In addition, if the drying temperature is gradually increased when the volumetric shrinkage of the gel is no longer observed due to open drying at room temperature, there is no need for the conventional cumbersome management such as placing the gel in a sealed container and controlling the porosity. It is.

Further, during the gelation of the present invention, pressurized dehydration using a press or the like is effective as a sealing layer in terms of preventing cracks and crazing during drying.

Regarding drying and firing of the gel, conventionally the gel was kept in a sealed state and after shrinking the gel was heated to 70"C in a container with a porosity of about
However, according to the method of the present invention, drying can be done without problems even in an open state, for example, for one week at 10°C. Slight drying is sufficient. Further, the firing may be carried out by a conventional method, for example, after raising the temperature at ioo°C/hr,
A method such as firing at 200±100° C. for several hours in an air atmosphere can be used.

<Examples> Hereinafter, the method of the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples as long as the gist thereof is not exceeded.

Example/Tetramethoxysilane 2! ! (1 mol) to q distilled water
Add 2 g (ta mol) and stir vigorously to hydrolyze. Add to this solution a 2% aqueous solution of polyvinyl alcohol GH-:10 (manufactured by Nippon Gosei Kagaku Co., Ltd.)/! 2jp and 2rg of ultrafine powder silica Aerosil 200 (manufactured by Nippon Aerosil Co., Ltd.; surface area: t00rr 17g) were added under stirring.

This sol was poured into a Teflon circular container (Omφ×ism).
I installed IO pieces in H) so that the height was 5 pieces. The open upper surface of each container was covered with Saran wrap and sealed, and when left at 20° C., gelatinized after 2 hours and left for another day.

Next, even after the seals were broken and the samples were left at room temperature for 2 days, no cracks or cracks were found in any of the 10 samples, and it was confirmed that they had dried and shrunk in a dull manner.

Furthermore, after drying the above gel at 7θ℃ for 3 days, 5'C/Hr
Raise the temperature to 10℃ at a heating rate of
φ×3. com t) was obtained.

No cracks or breaks were observed in the dried gel obtained.

Next, put the dried gel in an electric furnace from room temperature to 2000C.
Raise the temperature at 7'C/hr, hold at 1200°C for 2 hours, and heat the transparent quartz glass in the order of za and o.
2. II) was obtained.

Example cotetramethoxysilane t t;ti (1 mol) containing O,
Add Tachi gelatin aqueous solution 2211fi and stir vigorously to hydrolyze. Add ultrafine powdered silica AerO5il to this solution.
Sugo (manufactured by Nippon Aerosil Co., Ltd.; surface area 5 ot
yr/11) Methanol liquid with 2-S dispersed in it 5-
was added and stirred uniformly. Place this sol in a Teflon circular container (50mmφ x 5w H) high! ;I prepared 10 pieces so that it would be ra.

When the mixture was sealed and left at 20° C. in the same manner as in Example 7, it turned into a gel after 3 hours, and was left to stand for another day.

Next, the seals were broken and the samples were left at room temperature for 2 days, but no cracks or breaks were found in any of the 10 samples, and it was confirmed that they were drying and shrinking smoothly.

After further drying the above gel at 70°C for 3 days, the temperature was raised to 0°C at a heating rate of 1°C/Hr, and the dried gel (/7Jvaaφ×
2.7 Wt) was obtained.

No cracks or breaks were observed in the dried gel obtained. Next, put the dried gel in an electric furnace and from room temperature /a00
The temperature was raised to 0G at 1oo0c7Hr and maintained at 1200℃ for 2H to form a transparent quartz glass (/LOrrmφX
2. /mst) was obtained.

Comparative Example 1 Distilled water t2 to tetramethoxysilane tr2E (1 mol)
1 cμmol) and stir vigorously to hydrolyze. Distilled water was added to this solution, and 2J and 25y of the same ultrafine powder silica as used in Example-7 were added under stirring. Place this sol in a Teflon circle container (RI0IIlllφX/RIlll1
IQ cells were prepared in order of increasing height. When the mixture was sealed and left at room temperature in the same manner as in Example 7, it gelled after about 2 hours, and was left for another day.

Next, after about 10 minutes, 1~
Three cracks occurred in all the IO samples.

A dried gel can be obtained in an extremely short period of time without causing scratches, cracks, etc., and therefore large-sized ceramics can be manufactured extremely efficiently in terms of time and yield.

Claims (2)

[Claims] (1) A method for producing ceramics by hydrolyzing a metal alkoxide, gelling the hydrolyzed product, drying and firing the resulting gel, characterized by the presence of a water-soluble polymer during gelling. A method for manufacturing ceramics. (2) 0.1 of the water-soluble polymer relative to the metal alkoxide
The method for producing a ceramic according to claim 1, characterized in that the ceramic is present in an amount of ~10 wt%.