JPH04209705A - Production of silicon nitride-based powder - Google Patents

Abstract

PURPOSE:To obtain powder reduced in production of whisker in a shortened production time by heating a mixture of silicon oxide particles and carbon particles respectively specified in particle diameters to a prescribed temperature in a rotating furnace under atmosphere containing nitrogen gas, etc. CONSTITUTION:Silicon oxide having <=50mum particle diameter and carbon black having <=5mum particle diameter are granulated to prepare a mixed particle having 50mum to 5mm particle diameter. The mixed particle is heated at 1200-1700 deg.C in a gas atmosphere containing nitrogen or ammonia while oscillating the mixed particle in a rotating furnace. Thereby silicon nitride-based powder reduced in formation of whisker is obtained, and further, production time thereof is shortened to half or below.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing silicon nitride powder using a rotary furnace.

(Prior art) The current industrial method for producing silicon nitride powder is to fill a carbon container with a mixture of silicon oxide powder and carbon, introduce a nitrogen-containing gas into the upper part of the raw material filling section, and heat the mixture to 1200°C
A common method is a tII oxide reduction method in which a silicon nitride powder is obtained by a heating reaction at 1700°C.

However, the above method ■Reaction formula s log + c - s t o + c.

3SiO+2N, +C→S l *Nm+ 3 CO, and if the 00 partial pressure is high, the reaction will be difficult to proceed, and as a side reaction, S I SN4+ 2 CO → 2SiC+510
m+2Nm reactions are likely to occur, and the SIC content in the resulting silicon nitride becomes high or non-uniform due to local variations in the 00 partial pressure. For this reason, it is necessary to make the generated 00 partial pressure uniform, but if the thickness of the filling layer is thick, it will be difficult to remove the CO generated inside, and the 00 partial pressure will become high inside. must be made thinner, which lowers productivity.

(2) The CO generated by the reaction must be removed along with the Nt flow, and an excessive amount of Nt, usually several tens of times the theoretical reaction amount, is required, which is uneconomical.

■ Easy to generate whiskers.

It has the following disadvantages.

(Plan R to be solved by the invention) In view of the above circumstances, the present inventors have developed a method that has higher productivity, lower SiC content, or uniform SiC content in the product compared to conventional methods. As a result of intensive studies to find a method for producing silicon nitride powder that also produces a small amount of whiskers, the present invention was finally completed.

(Means for Solving the Problems) That is, the present invention involves heating mixed grains of silicon oxide and carbon at 1200°C to 1700°C in a gas atmosphere containing nitrogen or ammonia while shaking them in a rotary furnace. The present invention provides a method for producing a characteristic silicon nitride powder.

The method of the present invention will be explained in further detail below.

When carrying out the method of the present invention, silicon oxide as a raw material is not particularly limited because this reaction is a gas phase reaction and the particle size of the silicon nitride powder does not depend on the silicon oxide raw material.
For ease of reaction, particles with a particle size of 100 μm or less are usually used.

During the reaction, it is also possible to mix ultrafine silicon nitride powder as a seed into the silicon oxide powder used as the raw material in order to obtain a silicon nitride powder that is finer and has a sharper particle size distribution.

Further, carbon as a raw material is usually preferably carbon black, with a particle size of 5 μm or less, preferably 3 μm or less.

If the particle size is large, it is difficult to react.

During the reaction, silicon oxide and alumina are mixed and granulated in advance.

The ratio of silicon oxide and carbon used during mixing is usually in the range of 40 to 140 parts by weight, preferably 45 to 120 parts by weight, per 100 parts by weight of silicon oxide. If there is less carbon than silicon oxide, the reaction will not be sufficient, and if there is too much carbon, it will take a long time to decarbonize.

The mixing time varies depending on the mixer used and the mixing amount.
Mixing may be performed in advance under the mixing conditions used, and a time may be set to allow uniform stirring of silicon oxide and carbon.

In the present invention, the mixed granules are used after being granulated into particles of 50 microns or more to 5 microns or less.

If the mixed grains are less than 50 μm, problems such as being easily scattered by air currents during reaction or easily adhering to the furnace wall occur.

In the method of the present invention, the mixed grains must be nitrided while being shaken in a rotary furnace.

The rotary furnace may be a known rotary furnace such as a kiln, and either a batch type or a continuous type can be used.

Nitriding is usually carried out at 120°C in a nitrogen or ammonia atmosphere.
At a temperature of 0°C to 1700°C for 1 hour or more, usually 2 hours to 8
All you have to do is take your time.

FIG. 1 shows a schematic cross-sectional view taken along a plane parallel to the longitudinal direction of a rotary furnace, as one embodiment of an apparatus used when carrying out continuous nitriding according to the method of the present invention.

In the figure, 1 is a raw material hopper, 2 is a mixed grain feeder, 3 is a rotary furnace, 4 is inside the shell, 5 is a heater, 6 is a nitride recovery container, 7
8 indicates a gas supply port, and 8 indicates a gas discharge port.

In the figure, mixed grains of silicon oxide and carbon in a raw material hopper 1 are fed into the shell 4 of a rotary furnace 3 by a feeder 2 such as a screw feeder.The rotary furnace is tilted so that the inlet side of the mixture is higher. However, in the case of a batch type furnace, it is not necessarily necessary to tilt the furnace.

The mixed grains supplied from the supply device 2 into the rotary furnace are heated by a heater while moving inside the shell, react with nitrogen, and undergo nitriding treatment.

It is also possible to obtain a composite powder of silicon nitride and silicon carbide with an arbitrary composition by controlling the partial pressure of CO in nitrogen in the reaction system during the nitriding treatment. The nitrided powder is collected in a nitride collection container 6.

Nitrogen or ammonium-containing gas is forcibly supplied into the shell from the gas supply lower in order to perform the nitriding process well.

It is preferable to flow these gases in a countercurrent direction to the mixed grains, since this is more efficient in nitriding and also more efficient in terms of heat recovery.

The rotation speed of the rotary furnace is not unique depending on the diameter of the rotary furnace used, and is not limited in some cases, but in order to carry out the reaction uniformly, it is preferably 0.1 to 10 rotations/min.

(Effects of the Invention) According to the method of the present invention detailed above, not only can the time required for nitriding be reduced to 1/2 or less compared to the conventional standing method, but also powder with less whisker formation can be obtained. Its industrial value is enormous.

(Examples) Hereinafter, the method of the present invention will be explained in more detail with reference to Examples, but the method of the present invention is not limited by these Examples.

In the present invention, a Sedigraph was used to measure the particle size of 40 μm or less, and a sieving method was used to measure the particle size of more than 40 μm.

The amount of whiskers was determined by wet sieving with a 10μ screen after decarbonization.

In the examples, parts are parts by weight unless otherwise specified.

Example 1 Silicon oxide powder 10 with an average particle size of 10μ and a purity of 99.8%
0 parts and 80 parts of carbon black with an average particle size of 1.5μ and ash content of 0.1% were put into a mixing granulator, and 435 parts of water in which 1 part of polyethylene glycol was dissolved were added. While adding a slurry in which 1 part of silicon nitride was dispersed, the mixture was stirred at high speed and mixed, granulated to form mixed granules, and then dried at 150° C. in a hot air dryer. The particle diameter of the obtained mixed particles was 0.1 to 3 mm.

The mixed grains were filled into the hopper shown in Fig. 1, and
The temperature inside the furnace was set at 1530°C, and the temperature was set at 99°C.
3 kg/Hr of nitrogen with a purity of 99% or higher is introduced into a rotary furnace in countercurrent flow to the mixed grains at 2ONrrr/Hr.
was supplied and nitrided.

Residual carbon in the silicon nitride powder thus obtained was removed by oxidation at 750°C.

The average particle size of the obtained powder was 0.6μ, and the amount of SIC produced was 0.
．． 5% or less, and the amount of whiskers produced was 0.5% or less.

Comparative Example-1 Mixed grains were prepared in the same manner as in Example 1, and the mixture was
Approximately 600 g was filled into an m square carbon container, and such containers were stacked in 5 layers (the filling height of the filling was 1.5
cm. ) A 5-tiered container is inserted into a pusher-type tunnel furnace at a rate of 1 unit/Hr, and the temperature inside the furnace is 15.
The nitriding reaction was carried out at 30°C (residence time in the furnace was 8 hours).The nitrogen had a purity of 99.99% or higher, and the gap between the filling and the bottom of the upper container was (1.5C11). introduced more.

The amount of nitrogen used was 25 μm''/Hr, and if it was less than this, the reaction would not be completed.

Residual carbon in the obtained silicon nitride powder was removed by oxidation at 750°C.

The average particle size of the obtained powder was 0.6μ, and the amount of SIC produced was 1
．． 7%, and the whisker production amount was 28%.

Example-2 Silicon oxide powder 10 with an average particle size of 10μ and a purity of 99.8%
0 parts and 80 parts of carbon black with an average particle size of 1.5μ and ash content of 0.1% were put into a mixing granulator, and 435 parts of water in which 1 part of polyethylene glycol was dissolved were added. While adding a slurry in which 1 part of silicon nitride was dispersed, the mixture was stirred at high speed and mixed, granulated to form mixed granules, and then dried at 150° C. in a hot air dryer. The particle diameter of the obtained mixed particles was 0.1 to 3 mm.

The mixed grains were filled into the hopper shown in Fig. 1, and
The furnace temperature was set at 1560"C and 99"
．． Nitrogen with a purity of 99% or higher was supplied at 3 kg/Hr into a rotary furnace in which 15Nnf/)Ir was introduced in countercurrent to the mixed grains, and nitriding was performed.

Residual carbon in the silicon nitride powder thus obtained was removed by oxidation at 750°C.

The average particle size of the obtained powder was 0.5p, and the SIC raw bottom was 3.
2%, and was a composite powder of 5isNa and SiC. Further, the amount of whiskers produced was 0.5% or less.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of an apparatus used for continuous nitriding in the method of the present invention, and in the figure, 1: raw material hopper, 2: mixed grain feeder, 3: rotary furnace, 4: inside shell, 5: heater ,6;
Nitride recovery container, 7; gas supply port; 8; gas discharge port is shown. Figure 1

Claims (1)

[Claims] 1) Mixed grains of silicon oxide and carbon are heated in a gas atmosphere containing nitrogen or ammonia while being shaken in a rotary furnace.
A method for producing silicon nitride powder, the method comprising heating at 200°C to 1700°C. 2) The mixed grains have a particle size of 50 μm to 5 mm, 50μ
2. The method for producing a silicon nitride powder according to claim 1, wherein the powder is a granulated product of silicon oxide having a particle diameter of 5 μm or less and carbon black having a particle size of 5 μm or less.