JPS61219761A - Manufacture of silicon nitride base 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 (Field of Industrial Application) The present invention relates to a method for producing a highly reliable silicon nitride sintered body.

(Prior art and its problems) Silicon nitride sintered bodies have excellent heat resistance and corrosion resistance, and are considered promising as next-generation structural materials. A typical method for producing a silicon nitride sintered body is to sinter a mixed powder of silicon nitride mixed with an oxide sintering aid such as yttrium oxide, aluminum oxide, or magnesium oxide. There is. For example, Japanese Patent Publication No. 49-21091 discloses a method of sintering a mixture of silicon nitride, yttrium oxide, and aluminum oxide.

Although the silicon nitride sintered body obtained by the above method has high strength, the Weibull coefficient, which is a measure of the reliability of the sintered body, is small, that is, the strength variation within the product is large, and it cannot be used as a structural material. It had the disadvantage of low reliability. When the variation within the above-mentioned products is expressed as a Weibull coefficient, it is 25 or more for metal materials currently in general use, whereas it is about 5 to 15 for silicon nitride sintered bodies. Therefore,
It is strongly desired that the Weibull coefficient of a silicon nitride sintered body be equal to or higher than that of a metal material.

Furthermore, JP-A-53-42208 describes a method in which a powder compact of a compound of silicon nitride and a rare earth element is temporarily sintered in boron nitride powder or in a boron nitride container, and then main sintered. There is. However, this method differs in structure from the present invention, and furthermore, the above-mentioned publication does not describe at all the purpose and effect of the present invention of increasing the Weibull coefficient of a silicon nitride sintered body.

(Means for Solving the Problems) The present invention satisfies the above-mentioned needs, and its gist is as follows: 100 parts by weight of silicon nitride, 1 to 20 parts by weight of an oxide sintering aid.
1 part of boron nitride and 0.1 to 10 frf of boron nitride are sintered.

The silicon nitride powder used in the present invention has an α phase content of 90
% or more, and the particle size is preferably 0.1 to 1 μm. Such silicon nitride can be produced by methods known per se, such as a direct nitriding method in which metallic silicon is reacted with nitrogen or ammonia at high temperatures, a reductive nitriding method in which a mixture of silica and carbon is reacted in a nitrogen or ammonia atmosphere, It can be obtained by the so-called imide decomposition method in which silicon diimide or silicon tetraamide is thermally decomposed.

As the oxide-based sintering aid, all oxides known as sintering aids for silicon nitride can be used, and specific examples thereof include magnesium oxide, yttrium oxide, aluminum oxide, cerium oxide, and beryllium oxide. , silicon oxide. These oxide-based sintering aids can be used alone or in combination of two or more. Examples of combinations include yttrium oxide/aluminum oxide, magnesium oxide/silicon oxide, magnesium oxide/aluminum oxide, magnesium oxide/yttrium oxide.

The amount of the oxide sintering aid used is 1 to 20 parts by weight, preferably 1 to 10 parts by weight, per 100 parts by weight of silicon nitride. If the amount used is too small, the sinterability of silicon nitride will be reduced, and if the amount used is too large, the strength of the obtained silicon nitride sintered body will be reduced.

The amount of boron nitride used is 0 per 100 parts by weight of silicon nitride.
．． The amount is 1 to 10 parts by weight, preferably 0.5 to 3 parts by weight. If the amount of boron nitride used is too low, it will not be possible to obtain a silicon nitride sintered body with a high Weibull coefficient, which is the objective of the present invention, and if the amount used is too large, the sinterability of silicon nitride will decrease,
As a result, the strength of the silicon nitride sintered body obtained becomes low.

In the present invention, aluminum nitride can be further blended with silicon nitride. Its blending amount is 100% silicon nitride.
Usually 5 parts by weight or less, preferably 0.5 to 3 parts by weight
Parts by weight. By incorporating aluminum nitride, the Weibull modulus and bending strength of the silicon nitride sintered body obtained are further improved.

There are no particular limitations on the method of blending silicon nitride with an oxide sintering aid and, if necessary, aluminum nitride.
A dry mixing method and a method of wet mixing using a lower alcohol such as methanol or ethanol as a dispersion medium and then removing the dispersion medium by evaporation can be appropriately employed.

There are no particular restrictions on the method for producing a sintered body from a mixed powder.
A known method can be adopted. Examples of such methods include a method in which a molded article is made by a mold press method, a rubber press method, a cast molding method and then sintered, and a hot press method in which molding and sintering are performed simultaneously. Sintering is
Generally, under an inert gas atmosphere such as nitrogen, ammonia, or a mixture of these gases with argon or helium,
It is carried out by holding at a temperature of 500 to 1800°C for a period of up to 10 hours.

(Example) Examples are shown below. In the following, all "parts" indicate "parts by weight."

Examples 1 and 2 Silicon nitride powder [manufactured by Ube Industries, Ltd., 5N-2101100
Yttrium oxide powder [manufactured by Shin-Etsu Chemical Co., Ltd.], aluminum oxide powder [manufactured by Sumitomo Chemical Co., Ltd., AR] in the amounts listed in Table 1.
P-30] and boron nitride powder [manufactured by Showa Denko, U H
P] were mixed in a ball mill for 64 hours using methanol as a dispersion medium, and then dried and granulated. Granules 40 x 80
After molding using a X 50 fin mold, press pressure 1
．． Rubber press was performed at 5 t/cut. The obtained molded product was heated in a high-frequency induction furnace at normal pressure in a nitrogen atmosphere at 175°C.
After raising the temperature to 0°C at a rate of 2°C/min, the temperature was maintained at the same temperature for 1 hour.

Test piece 4 of 3X4X35L was made from the obtained sintered body.
A piece was cut out and subjected to a three-point bending test with a span of 30 mm to determine its strength and Weibull coefficient. The results are shown in Table 1.

Comparative Example 1 The same method as Example 1 was repeated except that boron nitride was not used. The results are shown in Table 1.

Examples 3 and 4 The same method as in Example 1 was repeated, except that the amounts of yttrium oxide, aluminum oxide and boron nitride used were changed, and a predetermined amount of aluminum nitride powder (manufactured by Stark) was added. The results are shown in Table 1.

Comparative Example 2 The same method as Example 3 was repeated except that boron nitride was not used. The results are shown in Table 1.

Examples 5 to 7 The same procedure as in Example 1 was carried out except that a predetermined amount of the oxide sintering aid listed in Table 2 was mixed with 100 parts of silicon nitride powder [manufactured by Ube Industries 14ylJ, 5N-EIO]. A sintered body was manufactured. The results are shown in Table 2.

For magnesium oxide, a special grade reagent manufactured by Kishida Kagaku (■) was used, and for cerium oxide and beryllium oxide, special grade and chemical reagents manufactured by Wako Tsumugi Kogyo (■) were used.

Comparative Examples 3-5 Examples 5-7 were repeated except that no boron nitride was used. The results are shown in Table 2.

(Effects of the Invention) According to the present invention, a silicon nitride sintered body having a high Weibull coefficient can be obtained as seen from the results of Examples.

Since the silicon nitride sintered body obtained by the present invention has extremely high reliability, it can be suitably used as a structural material.

Table 1 Y2O3Aj! 203 BN Aj! N Weibull Bending strength-■-"LIL IL-Coefficient 1-1/
-Pair of crucian carp 11 8,9 2.2 2゜2 0 30 8
6〃2 8.9 2.2 1.1 0 40 93 Comparative example 1 8.9 2.2 0 0
10 94 force i + guri 3 5.5 3
．． 8 2.2 1.7 45
92〃4 5.5 3.8 0.6 1.7 28
97 Comparative Example 2 5.5 3.8 0
1.7 14 98 Table 2 Oxide-based sintering aids BN Weibull Bending strength type Quantity (iro
(kg/m) ■ Part L □

Claims (1)

[Claims] A method for producing a silicon nitride sintered body, which comprises sintering a mixed powder consisting of 100 parts by weight of silicon nitride, 1 to 20 parts by weight of an oxide sintering aid, and 0.1 to 10 parts by weight of boron nitride.