JPH01257137A - Production of ceramic - Google Patents

Abstract

PURPOSE:To shorten the production time of dry gel and to prevent a crack and fracture by heat-treating the gel which has been obtained by hydrolyzing metal alkoxide, under pressure and thereafter drying and calcining it. CONSTITUTION:A gel is obtained by hydrolyzing one kind or two or more kinds of metal alkoxides selected from groups III-V elements in the periodic table in an organic solvent such as alcohol in accordance with necessity. Then this gel is heat-treated under pressure in a range within the temp. not lower than b.p. of the solvent at normal pressure and not higher than 250 deg.C and thereafter dried and calcined.

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 from metal alkoxides by a sol-gel method.

[Prior art]

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

[Problem that the invention seeks to solve]

In this sol-gel method, a hydrolyzed solution is directly gelled in a container of a predetermined shape and dried to form a dry gel. A method of producing 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 takes 0.0% to dry. ! - Not only does it require a long time of two months, but it also has the drawback of being susceptible to cracks as the volume decreases.

Therefore, by adding finely powdered silica in an amount of 0.2 to 5 times the molar equivalent of metal alkoxide, it is possible to make the gel structure porous and prevent it from cracking during drying and firing. Proposed.

However, this method also has the disadvantage that if the undried gel is left naked in the chamber (@), the surface will dry out violently, causing cracks and cracks in the gel. In some cases, the method used was to cover the container with a lid with a small porosity and gradually dry it (Japanese Patent Laid-Open No.
-/3/♂33) Naturally, this method still requires a long drying time.

The object of the present invention is to provide a method for producing ceramics by a sol-gel method that significantly shortens the production time of dry gel (usually about 2 weeks to λ months) and is free from cranks and cracks.

[Means for solving problems]

Therefore, the object of the present invention is to provide a method for producing ceramics by hydrolyzing a metal alkoxide to obtain a gel, drying and firing the gel, and heat-treating the gel under pressure before drying. This can be easily achieved by a method for manufacturing ceramics characterized by the following.

The present invention will be explained in more detail below.

The metal alkoxide that is the raw material of the present invention includes elements of the periodic table 1II to V6, such as AI, B, Si,
Examples include alkoxides of Ti, P, Ge, Zr%Sb, Y, and rare earth metals.

Examples of the alcohols of these metal alkoxides include methoxy groups, nidoxy 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 2 of the periodic table, or periodic Compounds other than groups m-V of the Table of Contents may also be present.

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

Compounds other than Groups 1 to 2 of the periodic table include, for example, alkali metals such as sodium and potassium, alkaline earth metals such as magnesium, calcium, and barium;
Examples include alkoxides, hydroxides, oxides, inorganic acid salts, organic acid salts, and metal complexes of transition metals such as iron, cobalt, nickel, chromium, and manganese.

Hydrolysis of the metal alkoxide in the method of the present invention is carried out in the usual manner, that is, with water, and if necessary, an organic solvent such as alcohol may be mixed. Examples of the alcohol include methanol, ethanol, propatool, butanol, etc. used.

There is no limit to the amount of water or organic solvent, but if too large a amount is included, the amount of liquid to be removed during drying in the subsequent step will increase, which is not preferable.

Further, known alkalis such as ammonia or acids such as hydrochloric acid may be added as metal alkoxide hydrolysis catalysts.

Next, the gel obtained by hydrolysis is heat-treated under pressure, and the temperature of the heat treatment under pressure is preferably higher than the boiling point of the solvent at normal pressure and lower than 300°C, more preferably the boiling point of the solvent. It is desirable that the temperature is above XSO°C or below. If this temperature is too low, the gel modification effect will not be sufficient and cracks or cracks will easily form during drying. On the other hand, even if the treatment is carried out at a high temperature of 300° C. or higher, no particular reforming effect can be expected, and the pressure will become abnormally high, increasing the danger, so it is not a good idea.

The pressure during gel heat treatment is determined by the substance with the highest vapor pressure among water and alcohols, and it is necessary to maintain the pressure higher than the vapor pressure of this substance to avoid boiling of the solvent. .

If the pressure in the system becomes lower than the vapor pressure of the substance with the highest vapor pressure in the system, a boiling phenomenon will occur and the gel will be damaged, so it is preferable to use a non-condensable gas as a preliminary pressure. . Non-condensable gases include air, nitrogen,
One dose of oxygen, helium, argon, etc. can be used.

In this way, by heating the gel under pressure in an airtight container such as an autoclave to a temperature above the boiling point of the solvent at normal pressure, the dehydration condensation reaction between hydroxyl groups proceeds in a much shorter time than in normal cases. It is believed that the gel network structure develops quickly. In addition, by maintaining the pressure in an airtight container at a pressure higher than the vapor pressure of the substance with the highest vapor pressure among water and alcohols, the hydrolysis reaction can proceed at high temperatures without drying the gel. . Therefore, by such a method, a strong gel can be obtained in a short time, and gel cracks will not occur even if the subsequent drying conditions are quite severe.

In addition, when heating the gel, prepare a hydrolyzed solution from the above metal alkoxide as a starting material, add metal oxide fine powder or inorganic salt, etc. as necessary, and pour the solution into a container. This can be done at any time after gelation is observed.

To obtain a ceramic product from the heat-treated gel, it may be dried and fired in a conventional manner.

〔Example〕

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

Example/Si(OCH3)4/j2? (1 mol) ni0,0
/Add 2 rOml of specified hydrochloric acid and stir vigorously to hydrolyze. Ultrafine powdered silica ("Aerosil") is added to this solution.
OXjO”: Surface area of Nippon Aerosil!; 0m27?
(Ultrafine powdered silica) or (3 mol) was added under stirring, and ultrasonic vibration was applied. Add O0l specified ammonia water dropwise to this sol and adjust the pH! , adjusted to 3.

This sol was poured into a Teflon circular container (iooWInφX
/ j mmH) so that the height was 10 frrln.

When the mixture was sealed and left at 20°C, it turned into a gel after 75 minutes, and was further left overnight. Next, unseal the seal and place it in a Teflon mold.
01 capacity autoclave. In the autoclave, add a mixture of methanol:water =/:1wt ratio at 30% in advance.
0 ml was prepared. Apply a prepressure of 10 kg/crAG with N2 and heat the temperature to izo °C at a heating rate of ioo °C/h.
I raised it with r. After V hours at izo°C, cooling was started and the temperature was returned to room temperature in about 6 hours. Then gradually remove the pressure (about 7 hours)
I took out the gel. No cracks or breaks were observed in the gel treated in the autoclave, and it was confirmed that it had shrunk by about 70% compared to when it was cast.

This gel was open-dried at room temperature for 3 days and then dried at 70° C. for 3 days to obtain a dry gel of AAtrm+φ×twnH.

Next, the dried gel was placed in an electric furnace and heated to 1250°C from room temperature.
As a result of firing at 1250° C. for 2 hours, transparent quartz glass (!0ranφX j rranH) without cracks or cracks was obtained.

Example λ St (OC2H5)4 - 20gt (1 mol) with 0.
Add 2 Oml of 0/N hydrochloric acid and stir vigorously to hydrolyze. Ultrafine powdered silica ('Aeros
il #200” Nippon Aerosil Co., Ltd. surface area 20 om2
72 t (/l of ultrafine powder silica) (/l, 20 mol)
It was added under stirring and ultrasonic vibration was applied. 0.7N aqueous ammonia was added dropwise to this sol to adjust the pH to 0. Next, a glass circular container (100ranφX/j WInH) was coated with silicone oil as a mold release agent.
) was charged with the sol solution to a height of 10 THn.

When the container was sealed and left at 20° C., it turned into a gel after 30 minutes. Prepare a mixture of ethanol:water/:/wt ratio in advance at 3θ.
The gel was unsealed and placed in a 101-size tococlave containing θ-containing gel along with the glass container. 30~/cr for N2
d G was prepared and brought to room temperature for about an hour. Then, the pressure was gradually removed (about 3 hours) and the gel was removed. The gel after autoclaving had shrunk by about 70% compared to the original gel, but there were no cracks or breaks.

When this gel was open-dried at room temperature for 3 days and then dried at φ70°C for 3 days, A 3 WrInX lr
A dry gel of mmH was obtained.

Next, the gel was placed in an electric furnace and heated from room temperature to 200°C.
As a result of raising the temperature at SO℃/hr to 7200℃ and firing it for 5 hours, we obtained transparent quartz glass (≠Irrvn XJmm) with no cracks or cracks.
H) was obtained.

Comparative Example/A sol prepared under exactly the same conditions as Example/ was placed in a φ Teflon cylindrical container (10θ-X/!wnH)
The height was set to 10 mm. If g samples of this type are prepared and each sample is sealed and left at 20℃, /
It gelated in 5 minutes.

Therefore, as a result of unsealing two gels for each condition (immediately after gelation, after being left overnight, after being left for 3 days, and after being left for 7 days) and drying them in the open at room temperature, all samples had 7 to 2 gels. Cracks occurred in the rows.

Comparative Example 2 A sol prepared under exactly the same conditions as in Example 2 was placed in a glass circular φ container (/00wn . G samples were prepared,
All samples gelled after about 30 minutes when sealed and left at 20°C.

Therefore, as a result of unsealing two gels for each condition (immediately after gelation, after leaving overnight, after leaving for 3 days, and after leaving for 7 days) and drying them in the open at room temperature, all samples had 7 to 3 Cracks occurred in the rows.

〔Effect of the invention〕

When the method of the present invention is used, ceramics free of cracks and cracks can be produced in high yield with easy operations.

Sender: Mitsubishi Chemical Industries, Ltd. Representative Patent Attorney Hase - Others/Names

Claims (2)

[Claims] (1) A method for producing ceramics by hydrolyzing a metal alkoxide to obtain a gel, drying and firing the gel, characterized in that the gel is heat treated under pressure before drying. Ceramics manufacturing method (2) The temperature of the heat treatment is equal to or higher than the boiling point of the solvent at normal pressure25
A method for producing ceramics according to claim 1, wherein the temperature is below 0°C.