JP2523693B2 - Ceramics manufacturing method - Google Patents

Description

The present invention relates to a method for producing ceramics, and more particularly to a method for producing ceramics by a sol-gel method using a metal alkoxide as a raw material.

[Prior art]

A so-called sol-gel method is known and used, in which a metal alkoxide is hydrodispersed, and the obtained gel is dried and sintered to produce a ceramic having high purity, such as glass or a sintered body. In this sol-gel method, a hydrolyzed solution is directly gelled in a container having a predetermined shape and dried to give a dry gel. Then, a manufacturing method for obtaining glass by firing it in an electric furnace or the like is performed particularly 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 0.5 to 2 months for drying, but also has a drawback that cracks and cracks easily occur as the volume decreases. Therefore, because of this, the finely divided silica is used in a molar ratio to the metal alkoxide.
It has been proposed to add 0.2 to 5 times the equivalent amount to make the gel structure porous so that cracks and cracks are less likely to occur during drying and firing.

However, this method also has a drawback that when the undried gel is left naked at room temperature, the surface thereof is rapidly dried to cause cracks or cracks in the gel. for that reason,
In the case of drying the gel, a method of covering the container with a lid having a small opening ratio and gradually drying it has been adopted. (JP-A-60-1318
33) [Problems to be Solved by the Invention] In the present invention, in order to shorten the production time (usually about 2 weeks to 2 months) of the dried gel and improve the dimensional accuracy, the undried gel is dehydrated under pressure in advance. Accordingly, it is to provide a method for producing ceramics by the sol-gel method, which is free from cracks and breaks.

[Means for solving problems]

The present invention relates to a method for producing a ceramic using at least one of starting materials as a metal alkoxide, wherein a hydrolyzing solution of the metal alkoxide is gelled, and the undried gel immediately after gelation is dehydrated under pressure. The above object is achieved by the method for producing ceramics.

Examples of the metal alkoxide as a raw material of the present invention include elements of Group III to V of the periodic table, for example, Al, B, Si, Ti,
Examples include P, Ge, Zr, Sb, Y and alkoxides of rare earth metals.

Examples of the alkoxy group of these metal alkoxides include a methoxy group, an ethoxy group, a propoxy group, a butoxy group and the like, and the number thereof is preferably 2 or more.

Specific examples of such metal alkoxides include trimethoxyaluminum, diethoxyaluminum chloride, tetramethoxysilane, trimethoxychlorosilane, dimethoxydimethylsilane, tetraethoxysilane, tetrapropoxytitanium and the like.

In the hydrolysis of the present invention, one kind or two or more kinds of the above metal alkoxides are used, but if necessary, the oxide powder, the metal salt or the metal complex of the element of Group III to V of the above periodic table, or the cycle Compounds other than groups III to V in the table can be present.

Examples of oxide powders of elements of Group III to V of the Periodic Table, metal salts or metal complexes include, for example, metal hydroxides or powders of metal oxides separately prepared by wet hydrolysis of metal alkoxides, Metal oxide powder produced by hydrolyzing or burning metal alkoxides and metal halides, inorganic acid salts of metals such as carbonates, hydrochlorides and nitrates, organic hydrochloric acid of metals such as oxalates, ethylenediamine tetra Examples thereof include complex salts with chelate compounds such as complex acids and cyclopentadienyl metal complexes.

In addition, as compounds other than groups III to V of the periodic table,
For example, alkali metals such as sodium and potassium, magnesium, calcium, barium, alkaline earth metals such as iron, cobalt, nickel, chromium, transition metal alkoxides such as manganese, hydroxides, oxides, inorganic acid salts,
Examples thereof include organic acid salts and metal complexes.

Hydrolysis of the metal alkoxide in the method of the present invention may be carried out by a conventional method, that is, with water, and if necessary, an organic solvent such as alcohol may be mixed, and the alcohol may be methanol, ethanol, propanol, butanol, etc. Is used. The amount of water or organic solvent is not limited, but if it is used in an excessively large amount, the amount of liquid removed during pressurized dehydration increases, which is not preferable.

Further, an alkali such as ammonia or an acid such as hydrochloric acid which is known as a hydrolysis catalyst for metal alkoxide may be added.

The pressure dehydration may be performed by forming a hydrolyzed liquid from the above metal alkoxide as a starting material, putting it in a container capable of pressurization, gelation, and pressurizing dehydration in a soft gel state immediately after gelation. .

Also, when obtaining a gel from a hydrolysis product, it will gel immediately if heated, but it will gel in several 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 desirable that gelation is not performed during work such as putting in a mold, and thus the gelling time may be selected depending on the case in consideration of necessary work.

Usually, at room temperature, the gel gradually hardens within a few hours to a few days after gelation, and the volume shrinkage can be observed.
When a press dehydration operation is performed on such a cured gel, cracks or breaks occur.

Therefore, the pressure dehydration may be performed by subjecting the gel to pressure dehydration from the time when it is considered that the gel has almost lost its fluidity to the appearance of gelation until the curing proceeds and the volume contraction appears. The purpose can be achieved without causing cracks.

The pressure during pressure dehydration of the gel 1 kg / cm ² or more 50000kg / cm ² or less, preferably 5 kg / cm ² or more 20000 kg / cm ² or less, more preferably 10 kg / cm ² or more 10000 kg / cm ² or less. Pressure is 1kg
If it is less than / cm ² , the dehydration effect is small, and if it is more than 50000 kg / cm ^2, it is extremely expensive as an industrialized device and is not practical.

The pressurizing time is 1 second or more and 10 hours or less, preferably 5 seconds or more and 2 hours or less, and more preferably 10 seconds or more and 1 hour or less. If the pressing time is too short, dehydration of the gel will be insufficient. In addition, the dehydration effect is saturated even if it is performed for a longer time than necessary, and it is uneconomical.

On the other hand, the pressing speed is also important, and if the pressing speed is too high, the distribution of pressure and concentration occurs inside the gel, which causes cracks and cracks. Therefore, it is preferable that the pressing speed be as small as possible. , Usually 10kg / min or more and 1000kg / min or less can be adopted.

It is necessary to quickly remove water, alcohol, etc. flowing out from the gel during pressure dehydration, and a pressure machine with a structure with an upper surface on the wall surface is preferable, and not only a batch type press machine but also a continuous type extruder is used. it can. There is no particular limitation on the material of the upper surface, but a sintered metal or a perforated plate or a combination thereof with an agent such as cloth or paper is preferable from the viewpoint of strength due to pressurization. Also, if the applied pressure is released abruptly, the residual solvent in the gel will expand rapidly, causing cracks and cracks, so it is preferable that the decompression rate be low, but usually 500 kg / cm ² min or less. It is enough. The gel obtained by dehydration under pressure is dried and fired after release, but in the case of a batch method, there is no problem even if release is performed after release. Regarding the drying and firing of gel, it takes a very long time to dry and fire, such as shrinking the gel in a hermetically sealed state, drying it at 70 ° C for 2 weeks in a container with a porosity of about 1%, and then firing it. However, according to the method of the present invention, it is possible to dry without pressure after dehydration under pressure. For example, it is sufficient to dry at 70 ° C. for 2 hours and then at 120 ° C. for 1 to 2 hours. is there. Firing may be carried out in the usual manner, for example, by raising the temperature at 100 ° C./hr and then firing at 1200 ± 100 ° C. for several hours in an air atmosphere.

〔Example〕

Hereinafter, the method of the present invention will be described 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 1 10 g of ultrafine silica powder, Aerosil ^# 200 (manufactured by Nippon Aerosil Co., Ltd .; surface area 200 m ² / g) was uniformly dispersed in 200 ml of methanol and degassed on an ultrasonic disperser for 6 hours, followed by a water bath. Concentrate to 70 ml above.

Tetramethoxysilane (6.78 g) and distilled water (3.22 g) were stirred in a 50 ml beaker to form a transparent homogeneous phase, which was then mixed with the dispersion of the ultrafine silica powder. A square SUS mold (55 mm × 55 mm × 40 mm) with a total surface of this mixed sol liquid on the bottom (with a 40 μm sintered wire mesh and qualitative paper (5C) laid)
It was cast to a height of 26 mm and gelled. Immediately after gelation, the gel upper part was covered with paper impregnated with silicone oil, a square piston was inserted, and pressure dehydration was performed with an electric press machine.

Pressurization speed is 200kg / cm ² min, maximum pressure is 2ton / cm ²
Hold for 10 minutes. After that, depressurize at 200 kg / cm ² min to remove the dehydrated gel paper, and then leave the naked dehydrated gel at room temperature for 12 hours.
Drying was carried out at 90 ° C. for 1.5 hours, and further at 120 ° C. for 1.5 hours.

Next, the firing conditions for the dry gel are 200 ° C from room temperature to 800 ° C
The temperature was raised with / Hr, and when the temperature was 800 ° C or higher, the temperature was raised to 1170 ° C at 2 ° C / mm and then kept at 1170 ° C for 1.5 hours.

The dried gel has an apparent density of 48.6 x 48.6 x 5.3 mm.
It is 1.00 g / cm ³ , and the quartz glass after firing is 37.5 × 37.5 ×
A transparent quartz glass with 4.1 mm and an apparent density of 2.18 g / cm ³ was obtained. As a result of repeating this test 10 times, the dimensional error is ± 0.5.
%, And transparent quartz glass free from cracks or cracks was obtained.

Example 2 Ultrafine powder silica, brand name of Aerosil OX-50 (manufactured by Degussa, West Germany; surface area 50 m ² / g) and pressure dehydration conditions (maximum pressure)
The gel was dried and calcined in the same manner as in Example 1 except that 100 kg / cm ² was kept for 2 hours).
An opaque white glass with an apparent density of 2.16 was obtained.

Example 3 To 152 g of tetramethoxysilane, 72 g of distilled water was added and stirred vigorously for hydrolysis. After forming a transparent uniform phase,
23 g of the same ultrafine silica powder used in Example 1 was added, and the mixture was uniformly mixed and dispersed for 15 minutes with an ultrasonic disperser.

Using a part of this mixed solution, pressure dehydration, drying and baking were carried out in the same manner as in Example 1. As a result, translucent glass having an apparent density of 2.16 was obtained.

Comparative Example 1 In exactly the same manner as in Example 1, five mixed sol liquids were cast into a Sus rectangular container to have heights of 25 mm and 5 mm, respectively.
When the upper open surface was covered with Saran wrap and sealed and left at room temperature, it gelled in about 2 hours, and left for 1 day to shrink the gel. Then, about 10 minutes after the cover was opened and the upper part was opened, cracks of 1 to 3 lines were generated in all 10 materials.

〔The invention's effect〕

According to the present invention, it is possible to obtain a dry gel in an extremely short time without causing cracks, breakages, etc. in the dry gel manufacturing process, and therefore, a large-sized ceramic is temporally,
It is possible to make the yield extremely efficient.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Fumaya Ishikawa 1 2447 Fujita, Hachimansai-ku, Kitakyushu, Fukuoka Prefecture Mitsubishi Kasei Kogyo Co., Ltd. Kurosaki Plant (56) Reference JP-A 64-76922 (JP, Sho A) JP-A-63-256538 (JP, A)

Claims (1)

(57) [Claims] 1. A method for producing a ceramic by hydrolyzing a metal alkoxide, gelling a hydrolysis product, and drying and firing the obtained gel, wherein the gel is dehydrated under pressure prior to drying. A method for producing a characteristic ceramics.