JPH0789703A - Production of crystalline silicon nitride powder - Google Patents

Abstract

PURPOSE:To control the oxygen content of crystalline silicon nitride powder and the distribution of oxygen in the particles and to produce crystalline silicon nitride powder excellent in sintering characteristics with high productivity in large quantities. CONSTITUTION:Amorphous silicon nitride powder and/or crystalline silicon nitride powder obtd. by firing a nitrogen-contg. silane compd. is milled in an atmosphere consisting of 5-40% oxygen and the balance inert. gas or further contg. 0.001-2.0% moisture.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a crystalline silicon nitride powder suitable as a raw material for producing a silicon nitride sintered material useful as a material for a high temperature structure.

[0002]

2. Description of the Related Art Conventionally, a method for producing a crystalline silicon nitride powder by firing an amorphous silicon nitride powder and / or a nitrogen-containing silane compound in an inert gas atmosphere is already known. . In order to improve the sinterability of this crystalline silicon nitride powder, it is necessary that the surface area of the powder and the oxygen content are within appropriate ranges. It is known that there is a close relationship between the surface area of crystalline silicon nitride powder and the oxygen content, that is, the higher the surface area, the higher the oxygen content, and the higher the oxygen content, the higher the surface area. This is because the oxide or oxynitride layer is formed on the particle surface of the crystalline silicon nitride powder. Therefore, controlling the oxygen content and the oxygen distribution in the silicon nitride powder is also important in controlling the surface area.

However, when producing the raw material amorphous silicon nitride powder by thermal decomposition of imide, it is necessary to eliminate oxygen as much as possible, so that the oxygen content of the amorphous silicon nitride powder is significantly changed. It was difficult. This is because imide has a high reactivity and easily reacts with oxygen to generate silicon dioxide, and this silicon dioxide remains as an impurity in the crystalline silicon nitride powder as it is.

On the other hand, in order to produce a good sintered body from the silicon nitride powder, it is desirable to mix the raw material silicon nitride powder and the sintering aid as uniformly as possible. for that reason,
A surface-modified silicon nitride powder capable of uniformly coating the surface of particles with a sintering aid is desired.

[0005]

The object of the present invention is to solve the above problems,
The present invention provides a method for producing a silicon nitride powder, which can control the oxygen content in the crystalline silicon nitride powder and the distribution of oxygen in the particles, and further can easily and uniformly coat the surface of the particles with a sintering aid. is there.

[0006]

According to the present invention, a crystalline silicon nitride powder obtained by firing an amorphous silicon nitride powder and / or a nitrogen-containing silane compound is mixed with oxygen in an amount of 5 to 40%, or further a moisture content. Of 0.001 to 2.0%, and the rest is milled in an atmosphere of an inert gas, to a method for producing crystalline silicon nitride powder.

In the present invention, first, the amorphous silicon nitride powder and / or the nitrogen-containing silane compound is fired in a nitrogen-containing inert gas atmosphere or a nitrogen-containing reducing gas atmosphere,
A crystalline silicon nitride powder is produced. As the nitrogen-containing silane compound, silicon diimide, silicon tetraamide, silicon nitrogen imide, silicon chlorimide or the like is used. These are known methods, for example, a method of reacting a silicon halide such as silicon tetrafluoride, silicon tetrachloride, silicon tetrabromide, and silicon tetraiodide with ammonia in a gas phase, a liquid silicon halide and a liquid. It is produced by a method of reacting with ammonia. The amorphous silicon nitride powder may be obtained by a known method, for example, by using the nitrogen-containing silane compound in a nitrogen or ammonia gas atmosphere in an amount of 600 to 1
Produced by a method of thermally decomposing at a temperature in the range of 200 ° C., a method of reacting silicon halide such as silicon tetrafluoride, silicon tetrachloride, silicon tetrabromide and silicon tetraiodide with ammonia at a high temperature. Is used. The average particle size of the amorphous silicon nitride powder and the nitrogen-containing silane compound is usually 0.002 to 0.05 μm.

Examples of the nitrogen-containing inert gas include nitrogen or a mixed gas of nitrogen and argon, helium or the like. Further, examples of the nitrogen-containing reducing gas include a gas that releases nitrogen gas by thermal decomposition of ammonia, hydrazine and the like at high temperature, or a mixed gas of nitrogen and hydrogen, carbon monoxide and the like. The firing temperature is in the range of 1400 to 1700 ° C. If the firing temperature is lower than 1400 ° C, crystallization of silicon nitride does not proceed sufficiently. Also, the firing temperature is 1700 ° C.
If it exceeds, crystalline silicon nitride powder composed of coarse crystals is likely to be generated, which is not preferable.

As a heating furnace used for heating the amorphous silicon nitride powder and / or the nitrogen-containing silane compound, a batch furnace by a high frequency induction heating method or a resistance heating method, a pusher furnace, a rotary kiln furnace, a shaft kiln furnace, a flow furnace A chemical firing furnace or the like is used. In particular, the continuous firing furnace is an effective means for efficiently dissipating the heat generated by the crystallization reaction of amorphous silicon nitride.

In the present invention, the crystalline silicon nitride powder obtained by the above-mentioned firing is milled in an atmosphere containing 5 to 40% oxygen and the balance being inert gas. The atmosphere gas may be an atmosphere containing oxygen in an amount of 5 to 40% and the balance being an inert gas such as nitrogen, helium, or argon. For example, an air atmosphere is preferably used. The milling method is not particularly limited, and a commonly used milling apparatus such as a vibration mill or an attritor may be used. This milling process can break the fusion and agglomeration between particles that occur during firing, and as a result, the surface oxygen amount of the silicon nitride powder increases, so that the surface area of the silicon nitride powder also increases and the sinterability remarkably increases. Can be improved. If the oxygen content in the milling atmosphere is less than 5%, the silicon nitride powder coats the inner wall of the mill, making milling difficult. Further, if the oxygen content is more than 40%, the mill material (resin such as monomer casting nylon) is worn, which is not preferable.

In the present invention, it is preferable that 0.001 to 2.0% of water is contained in the atmosphere of the mill treatment. At this time, the moisture contained in the atmosphere reacts with the surface of the silicon nitride particles, so that the particle surfaces are covered with silanol groups (Si—OH). Thereby, when the silicon nitride powder having an appropriate amount of silanol groups on the particle surface and the sintering additive are mixed, the surface of the silicon nitride particle can be uniformly coated with the sintering additive. The characteristics of the sintered body obtained by sintering can be improved. When the water content in the milling atmosphere is less than 0.001%, the effect of improving the characteristics of the sintered body is small, and when the water content exceeds 2.0%, silicon nitride is formed due to water condensation. The powder coats the inner wall of the mill, which makes milling difficult, which is not preferable.

[0012]

EXAMPLES The present invention will be described more specifically by showing Examples and Comparative Examples below. Example 1 Amorphous silicon nitride powder (oxygen content 0.55 wt%) obtained by thermally decomposing silicon diimide at 1000 ° C. in a nitrogen gas atmosphere was used to prepare an inner diameter of 280 mm and a height of 150 mm.
The carbon crucible of No. 1 was filled and set in a batch type electric furnace. Next, after degassing the inside of the electric furnace under vacuum to 0.1 torr or less, nitrogen gas was introduced and heating was started under the flow of nitrogen gas. The temperature was raised from room temperature to 1550 ° C. at 50 to 100 ° C./hr, and the temperature was maintained for 1 hour.

The obtained crystalline silicon nitride powder has an oxygen content of 0.75 wt%, of which the surface oxygen content is 0.10 wt.
%, The specific surface area was 8.0 m ² / g. The crystalline silicon nitride powder was placed in a vibration mill and milled for 30 minutes at room temperature in an air atmosphere containing 0.04% of water. The oxygen content of the crystalline silicon nitride powder after milling is 1.20.
wt%, of which the surface oxygen content was 0.55 wt% and the specific surface area was 9.5 m ² / g.

92 wt% of the obtained crystalline silicon nitride powder
The compounded powder obtained by adding 5 wt% of yttria (manufactured by Shin-Etsu Chemical Co., Ltd.) and 3 wt% of alumina (manufactured by Sumitomo Chemical Co., Ltd .: AKP-30) to ethanol was used as a medium, and 48
After wet mixing for an hour, it was dried under reduced pressure. The obtained mixture was preformed into a rectangular shape by using a mold having a cross section of 50 × 80 mm and then rubber-pressed at a pressure of 1.5 ton / cm ² . The obtained molded body was subjected to 1780 under an atmosphere of nitrogen gas using an electric furnace.
Sintered for 2 hours at ° C.

Table 2 shows the measurement results of the bulk density and bending strength of the obtained sintered body. The bulk density was measured by the Archimedes method. The bending strength is 3 × 4 from the produced sintered body.
Cut out a test piece of × 40mm and use it for outer span 3
The bending strength was measured at room temperature and 1200 ° C. by setting it in a 4-point bending test jig having 0 mm and an inner span of 10 mm.
The bending strength at room temperature is the average value of 40 test pieces,
The bending strength at 1200 ° C. was calculated as the average value of 10 test pieces.

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[Table 1]

[0017]

[Table 2]

Examples 2 to 3 Milling was performed in the same manner as in Example 1 except that the atmosphere during milling was changed to the atmosphere shown in Table 1. The results are shown in Table 1. A sintered body was manufactured in the same manner as in Example 1 using the obtained crystalline silicon nitride powder. Table 2 shows the measurement results of the bulk density and bending strength of the obtained sintered body.

Comparative Example 1 92 wt% of crystalline silicon nitride powder having an oxygen content of 0.75 wt% and a specific surface area of 8.0 m ² / g obtained in Example 1 and not subjected to milling was added to yttria (Shin-Etsu Chemical ( stock)
5 wt% and alumina (Sumitomo Chemical Co., Ltd .: AKP)
-30) The compounded powder to which 3 wt% was added was wet mixed using ethanol as a medium for 48 hours and then dried under reduced pressure. The obtained mixture was preformed into a rectangular shape by using a mold having a cross section of 50 × 80 mm and then rubber-pressed at a pressure of 1.5 ton / cm ² . The obtained molded body was sintered in an electric furnace in a nitrogen gas atmosphere at 1780 ° C. for 2 hours. Table 2 shows the measurement results of the bulk density and bending strength of the obtained sintered body.

Examples 4 to 6 Milling was carried out in the same manner as in Example 1 except that the water content at the time of milling was changed as shown in Table 1. The results are shown in Table 1. In Table 1, the peak intensity of the silanol group is the absorption (3750 cm ⁻¹ ) intensity of Si—OH in the FT-IR spectrum by the diffuse reflection method and the Si-
It is a value divided by the absorption (950 cm ^-1 ) intensity of N-Si. A sintered body was manufactured in the same manner as in Example 1 using the obtained crystalline silicon nitride powder. Table 2 shows the measurement results of the bulk density and bending strength of the obtained sintered body.

Comparative Example 2 The crystalline silicon nitride powder obtained in Example 1 was placed in a vibration mill and milled at room temperature in an air atmosphere containing 3.1% of water. Since the amount of water is large and the dew point is 25 ° C., the water is condensed and the silicon nitride powder is coated on the inner wall of the mill, which makes the milling process difficult.

[0022]

According to the present invention, the oxygen content in the crystalline silicon nitride powder and the distribution of oxygen inside the particles can be controlled, and furthermore, the sintering aid can be easily and uniformly coated on the surface of the particles. It is possible to mass-produce crystalline silicon nitride powder having excellent sintering characteristics and the like with high productivity.

Front page continuation (72) Inventor Toshihiro Fujita 10 Ube Kosan Co., Ltd., Ojikoshi, Ube, Ube City, Yamaguchi Prefecture (72) In Ube Kosan Co., Ltd.

Claims (2)

[Claims] 1. A crystalline silicon nitride powder obtained by firing an amorphous silicon nitride powder and / or a nitrogen-containing silane compound,
A method for producing a crystalline silicon nitride powder, which comprises milling in an atmosphere containing oxygen in an amount of 5 to 40% and the balance being an inert gas. 2. A crystalline silicon nitride powder obtained by firing an amorphous silicon nitride powder and / or a nitrogen-containing silane compound,
A process for producing a crystalline silicon nitride powder, which comprises milling in an atmosphere containing oxygen of 5 to 40% and water of 0.001 to 2.0% and the balance of inert gas.