JPH0196022A - Production of ceramics - Google Patents

Abstract

PURPOSE:To prevent cracking in a dry gel producing stage and to efficiently obtain large-sized ceramics by converting the hydrolyzate of a metal alkoxide into gel and dehydrating the gel under pressure. CONSTITUTION:An alkoxide of a metal, e.g., a group III, IV or V element of the periodic table is hydrolyzed. The resulting hydrolyzate is converted into gel and this gel is dehydrated, e.g., under 10-10000kg/cm<2> pressure for 10sec-1 hr. The dehydrated gel is dried and sintered to obtain ceramics.

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,
A 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 glass by firing it in an electric furnace or the like is particularly practiced in the field of quartz glass.

However, since the gel contains a large amount of water and alcohol due to hydrolysis, it not only requires a long time of 0-2 months to dry, but also has the disadvantage that it is prone to cracking as the volume decreases. Was. For this reason,
The molar ratio of finely powdered silica to metal alkoxide is 0.
It has been proposed that by adding 2 to j times the equivalent amount, the gel structure becomes porous, making it difficult to generate 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 has been used in which the container is covered with a lid with a small porosity and the gel is gradually dried. (Unexamined Japanese Patent Publication No. 1983-/3
/133) [Problems to be solved by the invention] In order to shorten the production time of dry gel (usually about 2 weeks to 1 month) and improve dimensional accuracy, the present invention dehydrates the undried gel under pressure in advance. By doing so, it is an object of the present invention to provide a method for manufacturing ceramics by a sol-gel method that is free from cracks and cracks.

[Means for solving problems]

The present invention is a method for producing ceramics using a metal alkoxide as at least one of the starting materials, which is characterized in that a hydrolyzed solution of the metal alkoxide is gelled, and the undried gel immediately after gelling is dehydrated under pressure. The above object is achieved by a method of manufacturing ceramics.

The metal alkoxide that is the raw material of the present invention includes elements of groups ① to ② of the periodic table, such as A1, B1Si, Ti,
Examples include alkoxides such as P, Ge, Zr%Sb%Y, and rare earth gold M.

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, one 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 1 to 2 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 powders of metal hydroxides or metal bonds produced by wet hydrolysis of metal alkoxides; Metal oxide powders produced by dry hydrolysis or combustion of metal alkoxides and metal halides; inorganic acid salts of metals such as carbonates, hydrochlorides, and nitrates;
Examples include organic acid salts of metals such as oxalate, complex salts with chelate compounds such as ethylenediaminetetralead acid, and cyclopentadienyl metal complexes.

In addition, examples of compounds other than Groups ■ to ■ of the periodic table include 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, cutam, and manganese.

Hydrolysis of the metal alkoxide in the method of the present invention is carried out by a conventional method, 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. is used. There is no limit to the amount of water or organic solvent, but if too large a quantity is used, the amount of liquid removed during pressurized dehydration will increase, which is not preferable.

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

At the time of pressurized dehydration, it is sufficient to prepare a hydrolyzed solution from the above-mentioned metal alkoxide as a starting material, place it in a container that can be pressurized and gel it, and pressurize dehydrate it while it is in a soft gel state immediately after gelation. .

In addition, 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. 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.

At room temperature, the gel usually hardens gradually in several hours to several days after gelation, and volumetric shrinkage is also observed. If a press dehydration operation is performed on such a hardened gel, cracks and cracks will occur.

Therefore, the gel should be dehydrated under pressure during the period from the time when the gel has almost lost its fluidity and can be considered to have become a gel, until the gel has hardened and volumetric shrinkage appears. The purpose can be achieved without creating cracks or cracks.

The pressure during pressurized dehydration of gel is /kf/crd or morej 00
00 AiF/crd or less, preferably jH/cd
It is more than 20,000 J4/d, more preferably more than 1O cape/cd and less than 10oooH/cm. pressure is /l
= 1/ If crA or less, the dehydration effect is small, and 5oo
o.

If it is I4/- or more, it becomes extremely expensive as an industrial device and is not practical.

The pressurization time is 1 io hour or less for sand removal, preferably 2 hours or less for j sand removal, more preferably 10 seconds or more and 1 hour or less. If the pressurization time is too short, the gel tends to be insufficiently dehydrated. Moreover, if the dehydration is carried out for a longer time than necessary, not only will the dehydration effect become saturated, but it will also be uneconomical.

On the other hand, the pressurization speed is also important; if the pressurization speed is too high, pressure and concentration distribution will occur inside the gel, causing cracks to occur, so it is preferable to keep the pressurization speed as low as possible. But usually more than 10kg/mM/000
kg/min or less can be adopted.

During pressurized dehydration, it is necessary to quickly remove water, alcohol, etc. that flow out from the gel, so a pressurizer with a structure with a filtration surface on the wall is preferable, and not only a batch-type press machine but also a continuous-type extruder can be used. can. There is no particular restriction on the material of the filter surface, but sintered metal, a perforated plate, or a combination thereof with a door-opening material such as P cloth or F paper is preferable from the viewpoint of strength problems caused by pressurization. In addition, if the applied pressure is released suddenly, the residual solvent in the gel will suddenly expand, causing cracks and cracks, so it is preferable to reduce the pressure at a low speed, but normally the speed is s o o kg/cr.
A value equal to or less than A-rttur is sufficient.

The gel obtained by pressurized dehydration is dried and fired after being released from the mold, but in the case of a batch method, there is no problem even if the gel is dried and then released from the mold. In addition, conventional methods for drying and firing gels include keeping the gel in a sealed state, shrinking the gel, drying it in a container with a porosity of about 1% for two weeks at 70°C, and then firing it, which takes a long time and causes cracks. Occurs at 70℃
It is sufficient to dry at 120° C. for 2 hours, followed by drying at 120° C. for about 2 hours. Also, the firing may be carried out in a conventional manner, for example at io0°C.
A method such as raising the temperature at 200±100° C. for several hours in an air atmosphere may be used.

〔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 to the same extent by the following Examples unless the gist thereof is exceeded.

Example 1 Ultrafine powder silica, Aerosil #200 (manufactured by Nippon Aerosil Co., Ltd.; surface area 200 m'/l) l0t
The mixture was uniformly dispersed in methanol of f: θOm/, degassed for 4 hours on an ultrasonic disperser, and then concentrated to 70% on a water path.

Tetramethoxysilane A, 7? and distilled water J, 22 t
The mixture was stirred in a 30.1 beaker to form a transparent homogeneous phase, and then mixed with the above dispersion of ultrafine powder silica. The entire amount of this mixed sol solution was poured into a square SUS mold (j jmm
I poured it all the way to the point where it turned into a gel. Immediately after gelation, the upper part of the gel was covered with paper impregnated with silicone oil, a square piston was inserted, and pressure dehydration was performed using an electric press.

Pressure was applied at a speed of 200 kf/-, with a maximum pressure of 2 tons.
It was held on/c4 for about io minutes. Then 200 kf
After removing the paper of the dehydrated gel by removing the pressure at /-・-, the bare dehydrated gel was heated at room temperature for 12 hours, then at 0°C for 1 hour, and then for another 72 hours.
Drying was carried out at 0° C. for 1.1 hours.

Next, the baking conditions for the dry gel are 20°C from room temperature to 100°C.
Raise the temperature at 0℃/Hr, and increase the temperature above 100℃ by 2℃/Hr.
After raising the temperature to 70°C/at 170°C/, it was held for 5 hours.

In addition, the gel after drying is ψr, A x a♂j X L31
@(The apparent density is /, 009/CrA, and the quartz glass after firing is 37.j X 37.!; X 4', /
g, the appearance is density,! , /rt/ad transparent quartz glass was obtained.

As a result of repeating this test io times, the dimensional error is ±08S
% or less, and transparent quartz glass without any cracks or breaks was obtained.

Example λ Ultrafine powder silica, Aerosil ox-! Gel was dried and dried in the same manner as in Example 1, except for changing the brand of 0 (manufactured by West German Degussa; surface area som2/l) and the pressurized dehydration conditions (maintained at maximum pressure/00 μ/c4 for 2 hours). As a result of the firing, an opaque white glass with an apparent density of 2.16 was obtained.

Example 3 Tetramethoxysilane/! Add 7 parts and 2 parts of distilled water to 29 and stir vigorously to hydrolyze. Then, after forming a transparent homogeneous phase, the same ultrafine powder silica 23 as used in Example/?
was added and uniformly mixed and dispersed for /j minutes using an ultrasonic disperser.

Pressure dehydration, drying, and calcination were carried out in the same manner as in Example 1 using a portion of this mixed liquid.

As a result, a translucent glass with an apparent density of 2.7 mm was obtained.

Comparative Example/In exactly the same manner as in Example/, the mixed sol solution was cast into square containers made by Sue, each having a height of 2j'm and 5m, respectively. The upper open surface was covered with Saran wrap and sealed and left at room temperature to gel in about 2 hours, and was left to stand for another day to shrink the gel. Next, New Testament 1 with the cover removed and the top open.
After 0 minutes, 7 to 3 cracks were generated in all the IO samples.

〔Effect of the invention〕

According to the present invention, cracks,
A dried gel can be obtained in an extremely short time without cracking, and therefore, it is possible to manufacture large ceramics extremely efficiently in terms of time and yield.

Claims (1)

[Claims] (1) A method for producing ceramics by hydrolyzing a metal alkoxide, gelling the hydrolysis product, drying and firing the resulting gel, which is characterized in that the gel is dehydrated under pressure. Production method.