JPH0218307A - Production of alpha-silicon nitride powder - Google Patents

Abstract

PURPOSE:To improve the strength of a sintered body by adding specified beta-Si3N4 and alpha-Si3N4 to a silane compd. contg. nitrogen and/or amorphous Si3N4 and by heating them in a nonoxidizing atmosphere to carry out crystallization. CONSTITUTION:beta-Si3N4 and alpha-Si3N4 each having 10-20m<2>/g specific surface area and contg. <=1,000ppm, in total, of Fe, Al, Ca and Mg are added to a silane compd. contg. nitrogen and/or amorphous Si3N4 as starting material by 2-10wt.%, in total, of the amt. of Si3N4 theoretically produced from the starting material. The amt. of the beta-Si3N4 added is regulated to 0.3-3wt.%. They are heated to >=1,350 deg.C in a nonoxidizing atmosphere to carry out crystallization.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for producing α-silicon nitride powder.

Silicon nitride powder is used for jigs and tools that require high strength and wear resistance (cutting tools, dies, drawn plugs, etc.), industrial machine parts (mechanical seals, pump parts, etc.), and heat-resistant structural members (turbines, engine parts, etc.) ), etc.

[Conventional technology]

Conventionally, as a method for obtaining high-quality crystalline silicon nitride with a high pre-gelatinization rate, high purity, and constant crystal shape and size, a crystalline silicon nitride with a high pre-gelatinization rate has been added to a nitrogen-containing silane compound and/or amorphous silicon nitride. A technique of adding silicon nitride as a seed is known (Japanese Patent Publication No. 62-59050). According to this method, the gelatinization rate is 9, which does not contain needle crystals and has an appropriate specific surface area.
It is possible to synthesize silicon nitride powder of 0.01 or higher. - It is said that the higher the α-ization rate in the shell, the better for the formation of β-columnar crystals in sintering processes, but the high α-ization rate of silicon nitride and the high strength of silicon nitride sintered bodies It is not well understood about the relationship between the properties of
MPIL or higher has not been obtained.

[The problem that the invention aims to solve]

The present inventor investigated problems in the prior art, such as densification during sintering, α-β transition behavior, etc., by using various powdered metals obtained by variously changing the synthesis conditions of silicon nitride powder. As a result, controlling the β-columnar crystals in the structure of the sintered body plays an important role in improving the sintering properties and properties of the sintered body, and this is due to the fact that β-silicon nitride added in the synthesis process plays an important role. The present invention was completed based on the discovery that the present invention is based on a material consisting of .alpha.-silicon nitride and .alpha.-silicon nitride.

[Means to solve the problem]

Specifically, the present invention uses a nitrogen-containing silane compound and/or amorphous silicon nitride as a raw material, and this raw material has a specific surface area of 10
-2011="/!l in ple, ALs" and M
The total amount of g is 1 [100 ppm or less of β-silicon nitride and α-silicon nitride, and the total amount of β-silicon nitride is 2 to 10'N based on the theoretical silicon nitride produced from the above raw materials, and β-silicon nitride is 0.3 to This is a method for producing α-silicon nitride powder, in which the α-silicon nitride powder is added at a ratio of 5exs, and then heated and crystallized in a non-oxidizing atmosphere.

The present invention will be explained in more detail below.

First, a raw material obtained by reacting a nitrogen-containing silane compound and/or an amorphous silicon nitride raw material, such as silicon halide, monosilane, etc., with ammonia gas in the gas phase is reacted with the theoretical silicon nitride produced from the raw material. On the other hand, each has a specific surface area of 10 to 20 m”/El and F8.AL%Ca
and Mg (hereinafter referred to as metal impurities) is 1000
ppm or less β-silicon nitride, α-silicon nitride and t-S
In total, the inside weight range is 2 to 10, preferably 4 to 7, and the β-silicon nitride is 0.3 to 3, preferably 0.
．． It is added in a proportion of 4 to 1.2% by weight. The beta conversion rate of β-silicon nitride is desirably 80 or more, especially 901 or more, and the gelatinization rate of α-silicon nitride is preferably 801 or more, especially 90 or more.

Here, the reason why the specific surface area of β-silicon nitride and α-silicon nitride mixed as seeds is limited to t10 to 2011279 is that when it is less than 10 F16"/9, the particles of silicon nitride itself generated by thermal decomposition become larger. No improvement in the sintering properties or properties of the sintered body can be expected;
This is because if it exceeds the limit, the silicon nitride produced becomes too fine a powder, resulting in poor handling and moldability. Another metal impurity?
The reason for limiting the amount to 11,000 pp or less is 1,000 pp.
If m is exceeded, high-temperature strength deteriorates, which is presumed to be caused by concentration of metal impurities in the grain boundary phase.

Furthermore, in the present invention, the reason why the amount of seeds added is 2 to 10''Nt in total of β-silicon nitride and α-silicon nitride is that if the amount is less than 2x, particles of silicon nitride itself will be generated by thermal decomposition. When K becomes large, the sintering properties and the properties of the sintered compact are improved by 1, but on the other hand, when K exceeds 10 times, the silicon nitride produced becomes too fine a powder, which deteriorates the handling and formability, and also makes it less economical. Furthermore, in this case, the β-silicon nitride amount t is set to be 0.5 to 5111. If the amount is less than 0.3x, β-columnar crystals will precipitate from the grain boundary phase. The number of nuclei is insufficient, resulting in non-uniform β-columnar crystals, making it impossible to improve the sintering properties and properties of the sintered compact.On the other hand, if the number exceeds !1″ - This is because the gelatinization rate of silicon nitride decreases, and furthermore, as the number of nuclei increases during sintering, the β-columnar crystals in the structure of the sintered body become finer, and the properties of the sintered body no longer improve.

Next, a mixture of a nitrogen-containing silane compound and/or amorphous silicon nitride with the above α- and β-silicon nitride powders is heated and crystallized in a non-oxidizing atmosphere, added, and then encapsulated on the surface of the silicon nitride powder. α-Silicon nitride is precipitated by crystal reaction. Here, the non-oxidizing atmosphere is an atmosphere containing nitrogen or ammonia.

The reason for heating in a non-oxidizing atmosphere is that raw materials obtained by gas-phase reactions are extremely unstable in an oxidizing atmosphere and easily react with oxygen, etc. to form oxides or oxynitrides. This is because the properties of α-silicon nitride are deteriorated. The heating crystallization temperature at this time is 1350°C or higher, especially 145°C.
The temperature is preferably 0°C or higher. At temperatures below 1650°C, amorphous portions remain and the resulting silicon nitride powder is oxidized and altered, making it impossible to obtain sufficient sintered properties.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Example t-6.

Comparative Examples 1 to 9 Comparative Examples 1 to 1O NH3 and 51cz4'1 reaction temperature 120°C, NHr5/
A nitrogen-containing gold compound was obtained by reacting in a gas phase at a 51dt4 molar ratio of 6.8. Next, β-
Each mixed powder of silicon nitride and α-silicon nitride was mixed with silicon nitride theoretically produced from the nitrogen compound at different amounts (inner side) as shown in Table 1, and then mixed in an N atmosphere. Heated at 1550℃ x 2h to crystallize α
- Obtain silicon nitride powder.

The α-silicon nitride powder obtained was measured for α-ization rate and specific surface area. The results are shown in Table 1.Next, Mgo was added to 90 ttl of this powder as a sintering aid.
33! m-superior, Al2O22N: Jtes, YJ1
035 weight residue was added, further 1,1,1-trichloroethane was added, wet-mixed in a ball mill for 4 hours, and after drying,
After molding into a 6 x 10 x 60 parrot shape with a molding pressure of 9/σ2 to 100, C was molded with a molding pressure of 2000 kg/aa".
IP molded.

These molded bodies were set in a carbon crucible and fired at 1700°C for 4 hours in a N2 gas atmosphere to obtain a sintered body.

After grinding the obtained sintered body, its relative density and strength at room temperature and high temperature (1200°G) were measured using a five-point bending method. The results are shown as sintered body A in Table 2.

In addition to the amount of α-silicon nitride powder 93X obtained above, the amount of Altos 2 il and y, o, as a sintering aid.

5] The test was carried out in the same manner except that R-11% was used and the sintering conditions for the CIP molded body were t-1850°C x 4 hours.The results are shown in sintered body B in Table 2.

Further, a quantity of 95"N of the α-silicon nitride powder obtained above was added as a sintering aid, AA, 031.5 weight II [% and y, o, 3.5 N image width, and CIP. The test was carried out in the same manner except that the sintering conditions for the molded body were t-1850°C for 4 hours.The results are shown in Sintered body C in Table 2.

The following method was used to determine the next-side constant value shown in the table.

(1) Pregelatinization rate: Gai manufactured by Rigaku Denki Co., Ltd.
Based on X-ray diffraction of flux RAD-IB type.

(2) Specific surface area: Based on the Cantarp Jr BET 1-point method manufactured by Yuasa Ionics.

(3) Metal impurities (Fe, At% CAL%
Mg) =, based on rxs-G-1322.

〔Effect of the invention〕

The α-silicon nitride powder of the present invention can be easily sintered and can produce a silicon nitride sintered body having excellent sintered body strength. By using a mixture of β-silicon nitride and α-silicon nitride, it is possible to control the precipitation of β-columnar crystals, so the size, aspect ratio, etc. of the precipitated β-columnar crystals can be changed. This is the result of being able to do so.

Patent applicant Denki Kagaku Kogyo Co., Ltd.

Claims (1)

[Claims] (1) Use a nitrogen-containing silane compound and/or amorphous silicon nitride as a raw material, and add a specific surface area of 10 to 20 m^2/
g and the total of Fe, Al, Ca and Mg is 1000 ppm
Adding the following β-silicon nitride and α-silicon nitride in a total proportion of 2 to 10% by weight and 0.3 to 3% by weight of β-silicon nitride based on the theoretical silicon nitride produced from the raw materials, A method for producing α-silicon nitride powder, which comprises then heating and crystallizing the powder in a non-oxidizing atmosphere.