JPS59207877A - Manufacture of high density silicon nitride reaction 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 The present invention relates to a method for producing a high-density silicon nitride reaction sintered body.

Among products of silicon nitride sr 3N4, those called reaction sintered bodies are usually molded bodies of Si powder or (Si
+Si 3N4) It is manufactured by applying nitrogen gas to a compact of a powder mixture to nitridize and sinter it.

This type of product has thermal shock resistance and hardness of 1. It has excellent electrical insulation and chemical stability at high temperatures, almost no shrinkage during reaction sintering, and high dimensional accuracy. It is widely used as an insulating material.

The drawback of conventional silicon nitride reaction sintered bodies is that they are mechanically weak, with a bending strength of only 20 K (about Jr/mm2,
The maximum temperature is only 30 K (l f /mm2), which is unsatisfactory as a heat-resistant structural material.
This is because even products obtained by completely nitriding silicon are only sintered bodies with a relatively low density and a porosity of 20 to 30%. If a reaction sintered body with higher density can be produced, it will be possible to improve the strength and other properties of opening from room temperature to high temperatures, so taking advantage of its characteristic of not losing strength even at high temperatures, it will be extremely useful as a material for heat-resistant structures. Become something.

The measures taken so far to increase the density of reaction sintered bodies are to increase the density of Sl or (St + Si 3N4) compacts. Specifically, the first step is to increase the powder compaction pressure, but even if a high pressure is applied to the practical limit, the density of the product after nitriding is only 2.39 g/c at most.
m3 (theoretical density (7), 75%). Attempts were made to adjust the particle size of the powder and blend powders with various particle sizes, but the density of the reaction sintered body was still 2.54 g.
/cm3 was considered to be the limit.

In order to further produce a high-density reaction sintered body, we introduced preliminary sintering of the S1 compact, that is, sintering in an inert atmosphere prior to nitriding, to produce a high-density sintered compact of the S1 compact. It was proposed to create one (Japanese Unexamined Patent Application Publication No. 121613, 1983).

The present inventor has conducted extensive research with collaborators with the intention of further increasing the density of 3i bottom molding using pre-sintering, and has achieved a maximum of 3.0.5CI/cm3 (96% of the theoretical density). We succeeded in obtaining a reaction sintered body with an extremely high density reaching
No. 65 and No. 57-188466). The method is
Adding a certain amount of boron to Si powder to improve sinterability or adding certain elements, i.e. Fe −, Q o S
N i 1C' zMo , Mn , W, Ti 1Zr
, Ta, Nb, V.

The gist of this method is to add a certain amount of one or more elements selected from M(1, Ca, Cu, Zn, and So, or a compound thereof) to promote nitriding.

Subsequent research revealed that nitriding promoters such as Fe have the effect of improving sinterability and are useful over a wide range of addition amounts. Of course, additives such as B and Fe may be used in combination, which is preferred.

However, in preliminary sintering, it has often been found that although the shrinkage rate due to sintering is high, the density may not increase. Unless the density of the pre-sintered body is increased, the density of the nitrided sintered body will not increase as intended.

As a result of research in search of a countermeasure for this problem, the present inventor found that this is due to the loss of Sl as SiO during sintering or due to the evaporation of Sl itself, and that the particle size of 3i powder is small and the 0 content is small. We found that the higher the value, the stronger this tendency. Among various attempts at countermeasures, one that was found to be effective was to suppress evaporation by allowing evaporation species to exist in the pre-sintering atmosphere.

Based on such knowledge, the method for producing a high-density silicon nitride reaction sintered body of the present invention includes boron or its compound as B of 0.15 to 5.0 weight percent, and (or) Fe,
, Co, Ni, Cr, Mo, Mn, W, Ti, Zr
XTa, Nb, VIM(], Ca, Cu, Zn
and 3n, one or more elements or compounds thereof as the above elements (in the case of two or more, the total amount) is 0.
Silicon powder containing 05 to 2.0% by weight is molded, and the molded body is heated to 1,100°C or higher in an inert gas atmosphere at 3i
N
In the method for producing a high-density silicon nitride reaction sintered body, which consists of nitriding by nitriding, silicon or a powder of silicon or its oxide, or a mixture thereof is placed around or near the molded body during preliminary sintering. It is characterized by heating. If preliminary sintering is performed under the above conditions, Si scum a5 and/or SiO gas will be generated from the silicon powder and/or silicon oxide powder, and their concentration will increase in the atmosphere surrounding the compact. As a result, evaporation from these molded bodies decreases.

As is easily understood, it is most preferable to embed the molded body in silicon powder, silicon oxide powder, or a mixture thereof and perform preliminary sintering by heating it.

As for the powder for suppressing weight loss, a mixture in which the molar ratio of Si:3i02 is 1:1 is highly effective. This is because most of the evaporation loss is due to evaporation as SiO, and when the above mixture is heated, Si +3i 02→2
This is thought to be because SiO is easily generated by the reaction of SiO↑, and this is effective in preventing evaporation by controlling the atmosphere.

The silicon powder, silicon oxide powder, or a mixture thereof placed around or in the vicinity of the molded body is preferably a fine powder, as can be understood from its effect.

The limits and reasons for the contents of the various substances having the effect of promoting sintering or nitriding are the same as in the invention disclosed above. That is, in order to expect the effect of boron, it is necessary to contain at least 0.15 m1%. However, boron generates nitrided 8-strand BN in the nitriding process, and when it becomes large, it inhibits reaction sintering. Therefore, 5.0
It must be kept within % by weight.

The content of Fe and other substances is 0.05 to Si powder.
If the amount is less than % by weight, no effect will be obtained.

If it is less than this lower limit, the density of the pre-sintered body may become high, and the time required to nitridize Si to a high degree becomes impractically long. On the other hand, if the content exceeds 2.0%, it must be avoided because it causes significant grain growth and prevents densification during pre-sintering.The preferred range varies depending on the elements used, but is usually 0.1・-0,
The amount is 6ffl%.

In the case of boron, the existing form may be metal boron, an amorphous substance, or a metal boride, and Fe and others may be in an elemental state or in a compound such as an oxide. , compounds between them are of course preferred.

When both are used together, it is preferable to select a compound of boron and these elements because both can be present at once.

The raw material Si powder should have an average particle size of 15 μm or less, and preferably a fine powder of 1 μm or less in order to facilitate high density during preliminary sintering.

The sintering accelerator and nitriding accelerator are also desirably fine particles with a particle size equal to or smaller than that of the Si powder.

The techniques for powder compaction and pre-sintering are the same as previously disclosed. That is, it goes without saying that the raw material powder or powder mixture can be molded by any means such as conventional die molding, isostatic pressure molding, slip cast and injection molding.

The density of the compact to be pre-sintered is set to 0.82 (J/cm3 (theoretical density of 185
%) or more. If the density is lower than this, it is difficult to obtain a sintered body having a uniform structure even if the density can be increased by preliminary sintering.

Pre-sintering is performed at a temperature of 1,100° C. or higher.

At such low temperatures, high density cannot be expected even if fine powder is used. The upper limit temperature is the melting point of Moraron Si. The atmosphere is preferably an inert gas such as argon, but may also be a vacuum.

The degree of densification at the preliminary sintering stage is determined by the shrinkage m associated with sintering. This does not depend on the density of the compact to be sintered, but in order to provide the high-density reaction sintered product that the present invention aims to achieve, the volumetric shrinkage rate must be at least 10%, and 20% or more. It is preferable that there be.

The density of the pre-sintered body varies greatly depending on the particle size of the raw material powder, molding conditions, and sintering conditions, but from the viewpoint of the density obtained in the reaction sintered body and the ease of nitriding, it is 1.8 to 2.
, 1 g/cm3.

In the present invention, the nitriding of the Si pre-sintered body can be carried out in the same manner as in the production of conventional silicon nitride reaction sintered wood.

That is, in general, under a nitrogen gas atmosphere at atmospheric pressure, 1
, to a temperature of 100 to 1,500°C.

The humidity can also be raised stepwise from a low temperature of 1,100 to 1,350°C. In order to adjust the reaction rate, the nitrogen pressure may be selected within the range from reduced pressure (up to about 1/100th of an atmosphere) to increased pressure (up to 2,000 atm).

In addition to pure nitrogen gas, hydrogen-mixed nitrogen gas and ammonia can also be used.

The time required for nitriding depends on the density of the presintered body, average grain size, nitriding temperature, and atmospheric conditions, as well as the allowable residual 3
Although it varies greatly depending on the amount of i, it ranges from several hours to about 200 hours.

As shown in the following examples, according to the method of the present invention,
The amount of unnitrided residual Si is set to 0, which is a practically preferable allowable limit.
A reaction sintered body having a high density of up to 94% of the theoretical density can be produced by suppressing the amount to 5% by weight or less.

Si fine powder with an average particle diameter of 0.13μ on the flow side and the middle side was filled with 80°4%.
N1) 203 (1.2%) was mixed uniformly and formed into a tablet with a diameter of 30 mm and a height of 10 mm using a rubber press. The density of the compact was 52% of the theoretical density.

This tablet was a) embedded in the same Si fine powder as above, b) embedded in S + O2 powder, c) embedded in a mixed powder of Si + Si 02 = 1 + 1, and 2) for comparison, under each of the same conditions, Preliminary sintering was performed by heating at 1345° C. for 2 hours in an Ar flow.

The density of the pre-sintered body is, respectively, b) 72% Mouth) 79% C) 86% 2) 67% Met.

Each of the above preliminary sintered bodies, (N2+5%1"2)
) In an atmosphere, nitriding was performed by heating at 1350°C for 20 hours, 1380°C for 60 hours, and 1410°C for 20 hours. The density and bending strength of the obtained reaction sintered bodies were as follows.

80% 47 K (If/mm2
0) 87 53 c) 94 60 2) 74 29 Patent applicant Daido Steel Co., Ltd. Agent Patent attorney Souo Suga

Claims (1)

[Claims] (1) Boron or its compound is 0°15 to B
5.0% by weight and/or Fe. Co, Ni1Cr, Mo, Mn5W1Ti. zr 1Ta 1Nb MV, Mg, Ca, Cu
. One or more elements of Zn and 3n or their compounds as the above elements (in the case of two or more types, the total amount)
Silicon powder containing 0.05 to 2.0% by weight is molded, and the molded body is heated in an inert gas atmosphere to a temperature of 1,100°C or higher but lower than the melting point of 3-i for preliminary sintering. In a method for manufacturing a high-density silicon nitride reaction sintered body, which involves heating the obtained pre-sintered body to a temperature of 1100 to 1500°C and nitriding it by applying N2, the molded body is heated during pre-sintering. A manufacturing method characterized by placing silicon or its oxide powder, or a mixture thereof, around or in the vicinity and heating it. (2) The manufacturing method according to claim 1, wherein the molded body is embedded in silicon or its oxide powder or a mixture thereof and heated during preliminary sintering. 3A As a mixture of silicon and its oxide, Si:5
The manufacturing method according to claim 1, which uses a mixture in which iQ2 has a molar ratio of 1=1. (4) The manufacturing method according to any one of claims 1 to 3, wherein the pre-sintered body has a volumetric shrinkage rate of 10% or more.