JPH013068A - Manufacturing method of alumina-silica sintered body - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention (aluminium oxide, etc., a mixture of silica and whiskers is sintered under pressure, or after sintered under pressure and further subjected to hot isostatic press treatment). This invention relates to a method for producing high-strength alumina-silica-based sintered bodies.

[Conventional technology]

The alumina-silica oxide substituted by mullite (3AJ203.25iOz) has many advantages such as a small coefficient of thermal expansion, low density, and excellent creep resistance, so it is being used in the field of engineering ceramics. Applications are being actively researched.

However, since the strength of alumina-based silica-based sintered bodies is relatively low, various methods have been devised to improve the strength, such as adding reinforcing materials to the raw materials or host press sintering.

For example, there is a method in which mullite powder is mixed with whiskers or ceramic fibers to make a slurry, the slurry is dried, pressure molded, and pressureless sintered, or
1-1974741, the method involves centrifugally molding the slurry, drying, and pressureless sintering.

[Problem that the invention seeks to solve]

However, no matter how high the pressure or centrifugal force is applied to create a compacted compact from the raw material mixture using the conventional method described above, if you look at the inside of the compact, you will notice that after the pressure is released, the forcibly twisted whiskers are restored. do. Therefore, voids are created between the light particles and the whiskers, and the contact area between the mullite particles is reduced. Even if such a compact is sintered under pressure for a long time, the voids in the sintered compact are completely filled.
The average porosity is as high as 1.01%. Therefore, the bending strength of the sintered body (
(hereinafter simply referred to as strength) is 15 to 25 Kgf/1+! 4
The improvement was not sufficient.

[Means for solving problems]

In order to increase the strength of the sintered body, the present inventors believe that it is necessary to make a dense sintered body. Focusing on this, they discovered that by utilizing the contraction driving force, voids can be significantly reduced and high strength can be developed, and the invention described below has been completed.

That is, the gist of the present invention is to add whiskers to a mixture containing 65 to 75% by weight of aluminum oxide and/or aluminum hydroxide (both collectively referred to as aluminum oxide, etc.) in terms of AlzOa and 25 to 35% by weight of silica powder. 15% by weight (external) is added, mixed wet to resemble a slurry, dried, pressure molded, and sintered under normal pressure to produce an alumina-silica sintered body (hereinafter referred to as the normal pressure method). The present invention provides a method for producing an alumina-silica sintered body (hereinafter referred to as the HIP method) by further subjecting the sintered body obtained by the above-mentioned pressureless sintering to hot isostatic pressing. .

The present invention will be explained in detail below.

The aluminum oxide ζ used in the present invention is γ-1δ
-1θ-1 includes -1α-alumina, and aluminum hydroxide includes gibbsite, bayerite, bauxite, boehmite, etc., and one or more of these are used in an appropriate combination.

In order to facilitate the formation of mullite and increase the amount of shrinkage, aluminum oxide or the like should be as fine as possible, preferably having an average particle diameter of 1 μm or less.

The silica powder may be crystalline, amorphous, naturally produced, or artificially produced, but especially silica powder produced artificially by the Aerosil method, alkoxide method, etc. Amorphous silica is preferred because it has high reactivity.

The silica powder should be as fine as possible, with an average particle diameter of at least 0.1 μm or less, in order to facilitate the reaction with the aluminum oxide, etc., and to make the molded product described later dense. is preferred.

Whiskers are commercially available AlN, Al2O3, B
, B4C1BN%MgO1SiC%Si3N4, Ti0
%TiN.

Any material such as carbon or graphite may be used, and the material of the whisker is not particularly limited in the present invention.

It is also possible to use a mixture of whiskers of different materials.

If the length of the whisker is too long, the restoring force will become large and abnormally large voids may be formed locally within the molded object, which may be undesirable.
It is desirable to use one with the following length. Furthermore, if the aspect ratio is too small or too thick, the reaction between the aluminum oxide, etc. and the silica is undesirable, and it is desirable to use whiskers in the range of about 5 to 40.

The blending ratio of aluminum oxide etc. and silica is 65-75% by weight of aluminum oxide etc. in terms of Al2O3 and 25-35% by weight of silica powder. If the content of aluminum oxide, etc. is less than 65% by weight, the sintered body will have a relatively high proportion of silica, so the sintered body will be heated (for example, 100% by weight).
0°C), which is undesirable because it limits its use in high temperature conditions, and conversely, AAhO
If the amount converted to s exceeds 75% by weight, not only the room temperature strength will be significantly lowered, but also the hot strength will be lowered to about 14 or less than that at room temperature, which is not preferable. The preferred blending ratio is 68 to 73% by weight of aluminum oxide etc. in Adz034A'J-, and 27 to 32% by weight of silica.

The whiskers are mixed in an amount of 5 to 15% by weight with respect to the mixture of aluminum oxide and the like and silica.

If the mixing ratio is less than 5% by weight, the effect of whiskers will not be achieved and the strength will not be improved.On the other hand, if it exceeds 15% by weight, the sinterability of the mixture will decrease and a dense sintered body will not be produced. It is not preferred because it cannot be manufactured.

Water or alcohol is added to the above-described composition containing a predetermined amount of silica and whiskers such as aluminum oxide, and the mixture is fed to a conventional mixer such as a hole mill or a sand mill and mixed. The obtained slurry is dried, for example, by a spray drying method. The dry mixture is molded by applying a required pressure using a mechanical press method or an isostatic press method.

The obtained compact is covered with a packing powder of a mixed powder of 5102 and BN, mullite powder, other silicate compound, or a powder of the same material as the whiskers used, and heated in air or an inert atmosphere, for example 1650 in N2 or Ar. ~
A pressureless sintered body is produced by sintering at 1750° C. for 0.5 hours or more.

This pressureless sintered body is further covered with a filling powder of mullite powder or other silicate compound powder, and then
1500-1800 °C in an inert atmosphere at r, 200
~250 oKqf/cr & hot isostatic pressing to produce the desired sintered body.

Next, the present invention will be explained by examples.

〔Example〕

Examples 1 to 12, Comparative Examples 1 to 5 A mixture of aluminum oxide (α-A1203), aluminum hydroxide (Al(OH) 3 ), silica (amorphous), and SiC whiskers shown in Table 1 was mixed with water. Pour into a pot mill (both the lining and medium are made of mullite), and
A slurry was prepared by mixing for 4 hours. The slurry was dried in a spray dryer at 200° C., and the resulting mixed powder was pressed by a hydrostatic press method (9/1000) to form a molded body of 5×÷X O, 6 cM.

The compact was sintered using the normal pressure method and the HIP method, and its strength and porosity were measured.

b) Normal pressure method The normal pressure sintering conditions for each compact are when aluminum oxide is used and when aluminum hydroxide is used (or when the compact is 5N
) 2 and BN, covered with a stuffing powder of equal total mixed powder and heated at 1740°
C. Sintered in N2 atmosphere for 2 hours, and when aluminum hydroxide was used, each compact was sintered under normal pressure under the same conditions as when aluminum oxide was used, except that the filling powder was SiC powder and the atmosphere was air. concluded.

In addition, for Example 9 in which aluminum oxide and aluminum hydroxide were used in combination, the compact was sintered under normal pressure under the same conditions as in the case where aluminum oxide was used alone.

For each of the produced sintered bodies, the three-point bending strength was measured according to JIS 1601, and the porosity was measured according to the Archimedes method, and the obtained results were also recorded in Cloth 1.

(1) HIP method Examples 1.8, 10111, and 12 were prepared into pressureless sintered bodies in the manner shown in the normal pressure method in (a) above, and then the sintered bodies were mixed with mullite powder (filling powder). A hot isostatic press treatment was performed under the conditions of 1650° C. and 1900 Kqf/ai+ for 1 hour in an Ar atmosphere to obtain each sintered body.

The bending strength and porosity of these sintered bodies were measured according to the method described in (a) above, and the obtained results are also listed in the same table.

〔Effect of the invention〕

In manufacturing an alumina-silica-whisker-based sintered body, the present invention utilizes the shrinkage of the raw material in the sintering process, so the voids are extremely reduced compared to sintered bodies manufactured by conventional methods. However, a sintered body with extremely high strength can be produced.

If this sintered body is further subjected to hot isostatic pressing treatment, a sintered body with higher strength can be produced.

Patent applicant: Nippon Cement Co., Ltd.

Claims (2)

[Claims] (1) A mixture of 65 to 75% by weight of aluminum oxide and/or aluminum hydroxide (calculated as Al_2O_3) and 25 to 35% by weight of silica powder, with the addition of 5 to 15% by weight of whiskers, is molded and molded under normal pressure. A method for producing an alumina-silica-based sintered body characterized by sintering. (2) A mixture of 65 to 75% by weight of aluminum oxide and/or aluminum hydroxide (calculated as Al_2O_3) and 25 to 35% by weight of silica powder, with the addition of 5 to 15% by weight of whiskers, is molded and molded under normal pressure. A method for producing an alumina-silica sintered body, which comprises subjecting the sintered body to hot isostatic pressing after sintering.