JPS6346027B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing an alumina molded body. As conventional methods for manufacturing alumina molded products, the dry press method, the doctor blade method, and the Tyco method are known. However, the dry pressing method requires a pressurizing machine and has the disadvantage that it is difficult to mass produce.
On the other hand, the doctor blade method is suitable for mass production, but has the disadvantage that it is difficult to obtain thin micron thickness products. In addition, the Tyco method is a method in which a high-temperature melt exceeding approximately 2000°C is pulled through a slit into a plate shape, so it not only requires a large amount of heat, but also requires strict manufacturing conditions. Its manufacturing environment is also poor and has many drawbacks. The present invention eliminates the drawbacks of these conventional methods, does not require a large amount of heat, has few structural defects in the sintered body,
The object of the present invention is to provide a method by which a transparent sintered body can be easily produced. As a result of intensive research to achieve the above object, the present inventors have found that aluminum alkoxide is hydrolyzed in the presence of 80 to 100 moles of water per mole of aluminum alkoxide in an amount sufficient to peptize the aluminum alkoxide and make a sol. After that, when this is peptized to form an alumina monohydrate sol, it is highly pure and extremely uniform single fine particles without the contamination of large particles like those obtained by peptizing alumina trihydrate. A free-flowing sol is obtained, and by utilizing this free-flowing property, it is made into a film, for example, and dehydrated to form a gel-like molded product. When this is fired, the sintered body has few structural defects and becomes transparent. It has been found that a photosensitive sintered body can be obtained. The present invention was completed based on this knowledge. The gist of the present invention is to peptize aluminum alkoxide and hydrolyze it in the presence of a sufficient amount of water to form a sol, and then peptize the aluminum alkoxide to form an alumina monohydrate sol. A method for producing an alumina molded article, which is characterized by utilizing its free-flowing property to form a gel-like alumina molded article instead of molding and gel, and firing the gel-like alumina molded article. In the present invention, since aluminum alkoxide is used as a raw material for pseudo-boehmite, it has the advantage that a pure and stable sol can be obtained. As alcohol of aluminum alkoxide,
Methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol (including iso- and tertiary alcohols), etc. can be used. Next, a method for producing pseudo-boehmite using aluminum isopropoxide will be described. Production of Γ pseudo-boehmite (1) Hydrolysis method using aluminum isopropoxide powder. 100 moles of pH-adjusted ion-exchanged water was added to 1 mole of aluminum isopropoxide powder, and the mixture was hydrolyzed at room temperature with vigorous stirring using a magnetic stirrer. The results are shown in Table 1 below.

[Table] As shown in the above results, only pseudo-boehmite was produced during hydrolysis for up to 6 hours at pH 2.0 to 3.0. However, when the pH increases and the time for hydrolysis increases, alumina trihydrate is produced, resulting in a mixture of pseudoboehmite and trihydrate. Although not shown in this table, PH
When the pH is 1.0, the hydrolysis rate is slow and it takes 20 hours to completely hydrolyze, and the resulting hydrolyzate is not a powder like that obtained when the pH is 2.0 or higher, but a diameter of about 1 mm.
It contains a large amount of spherical particles. When the hydrolysis time is 15 to 30 minutes, only broad diffraction lines of pseudo-boehmite can be seen, but beyond that time, sharp diffraction lines of bayerite and gibbsite can be seen in addition to the diffraction lines of pseudo-boehmite. . Therefore, the hydrolysis time is 15 minutes ~
Preferably, the time is about 30 minutes. However, the hydrolysis time for obtaining pseudo-boehmite is also influenced by the amount of ion-exchanged water. The results of using 80 moles of ion-exchanged water per mole of aluminum isopropoxide are shown in Table 2 below.

[Table] As is clear from comparing Tables 1 and 2, even if water with the same PH is used, the higher the concentration of aluminum isopropoxide, the more trihydrate will be formed by hydrolysis in a shorter time. do. (2) A method of hydrolysis using aluminum isopropoxide solution. Dissolve 1 mole of aluminum isopropoxide in 800 c.c. of benzene to make a homogeneous solution, (1)
Hydrolysis was carried out in the same manner as when using the powder. The results were as shown in Table 3 below.

[Table] When used as a solution in this way, it is possible to slow down the formation of trihydrate even in neutral or alkaline solutions, where trihydrate is more likely to be formed than when used as a powder. Further, the short-time hydrolysis product is X-ray amorphous, and the particle size of the generated pseudoboehmite is extremely small. Pseudo-boehmite is produced by the method described above. If a trihydrate is mixed with this, a uniform sol will not be formed, it will become unstable, and moreover, it will not be possible to peptize it. A method for peptizing Γ pseudoboehmite and producing an alumina molded product. The production of a thin film will be explained below as a representative example. The pseudo-boehmite obtained by the above method is peptized by adding an acid, using a homogenizer, for example, and then poured into a fluororesin container, dried to form a boehmite gel thin film, and fired to produce an alumina thin film. Although the acid used for peptization is not limited, the amount of acid used for pseudoboehmite affects the properties of the resulting alumina thin film. Using hydrochloric acid, to describe the molar ratio of addition of hydrochloric acid,
When we created a sol by changing HCl/pseudo-boehmite and used it to create a gel film, we found that the above ratio was
0.1-0.6 gives a transparent gel film, 0.7
A transparent gel film can also be obtained when the value is ~0.9, but
It will be slightly moist. At 0.1, a thin film cannot be obtained. When the obtained gel thin film was fired at 800℃, those with a value of 0.1 to 0.5 became a transparent alumina thin film, and those with a value of 0.6 to 0.9 were opaque with a large number of fine cracks and peeling parallel to the film surface. . Therefore, it is necessary to adjust the amount of acid added during peptization. A thin film of boehmite sol can be easily produced by pouring it into a container made of fluororesin, for example, which has excellent releasability. It can also be formed by a film forming method using boehmite sol instead of the melt in the conventional pulling method, or by an extrusion method. Note that molded articles of other shapes than thin films can also be produced by the casting and pulling method. According to the method of the present invention, since a raw material sol obtained by hydrolyzing aluminum alkoxide is used, it is a pure frame, and since it is alumina monohydrate, it becomes stable and uniform, and this sol can be kept at room temperature. Because it can be molded with alumina, it not only does not require the heat required for conventional melting, but also can be molded with extremely simple equipment, and it has excellent properties such as being able to obtain alumina molded products with excellent transparency. have an effect. Example 1 Add 100 moles of ion-exchanged water adjusted to PH2 to 1 mole of aluminum isopropoxide powder, stir at room temperature for 20 minutes using a magnetic stirrer to hydrolyze it, and add hydrochloric acid to it. / alumina monohydrate (pseudo-boehmite) was added at a ratio of 0.1 to peptize the solution to turn it into an alumina monohydrate sol, which was poured into a fluororesin container to form a film. After dehydrating the obtained thin film, it was fired at 800°C to obtain a transparent alumina thin film. A plate-shaped body, a tubular body, etc. can be obtained by pulling up or extruding the sol into a plate-shaped body, a tube-shaped body, etc. Example 2 An alumina thin film was produced in the same manner as in Example 1, using a benzene solution instead of the aluminum isopropoxide powder. The obtained alumina thin film was transparent.

Claims (1)

[Claims] 1 After hydrolyzing the aluminum alkoxide in the presence of sufficient water to peptize and form a sol,
This is peptized to form an alumina monohydrate sol, and the sol is molded using its free-flowing properties to form a gel-like alumina molded product instead of a gel, which is then fired. How things are manufactured.