JPH02289407A - Production of alpha-silicon nitride - Google Patents

Abstract

PURPOSE:To obtain low carbon high alpha-silicon nitride by granulating at least one of metallic silicon powder and a mixture of silica powder with carbon powder and carrying out surface coating with silicon nitride, mixing and nitrifying under heating. CONSTITUTION:At least one of metallic silicon powder (a) and a mixture (b) of silica powder with carbon powder is granulated and the surfaces of the resulting granules are coated with silicon nitride. The granules are then mixed with the ungranulated component (a) or (b) and this mixture is nitrified under heating in a nitrifying atmosphere to obtain desired alpha silicon nitride. The pref. particle size of the metallic silicon powder used is <=10mum. When the powder contains a large amt. of particles of >10mum particle size, it is unfit to produce high purity silicon nitride because reaction time is prolonged and unreacted silicon remains. The pref. primary particle size of the silica powder and carbon powder is <=1mum from the view-point of reactivity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing α-type silicon nitride, that is, α-type-rich silicon nitride powder.

[Conventional technology]

Silicon nitride sintered bodies are considered to have a variety of uses as a high-temperature material with high mechanical strength (and excellent heat resistance).However, in order to make excellent sintered bodies, excellent raw material powder is required. In particular, in order to produce a sintered body with high heat resistance and high strength, the silicon nitride powder used as the raw material powder must not only have high purity but also contain α-type silicon nitride with a high crystal phase. Various methods have been proposed to obtain such silicon nitride, but these have advantages and disadvantages, and no fully satisfactory method has been found.

[Problem to be solved by the invention]

Among the conventional methods, the method of manufacturing α-rich silicon nitride powder by combining metal nitriding method and oxide reduction nitriding method, which is disclosed in JP-A No. 62-260704, yields high-quality powder. This is an industrially excellent method.

However, this method also has the disadvantage that the resulting silicon nitride powder contains a relatively large amount of carbon. This is an inherent drawback of the oxide reduction method, and although methods have been proposed to remove it by post-treatment, it is not always removed sufficiently and causes oxidation problems.

That is, there is amorphous silicon carbide that is not detected by X-ray diffraction, which causes a decrease in the purity of silicon nitride.

[Means to solve the problem]

As a result of various studies aimed at improving these problems, the inventors of the present invention granulated at least one of (a) metal silicon powder and (b) a mixture of silica powder and carbon powder, and further, at least The surface of one of the granules is coated with silicon nitride,
It has been found that the above-mentioned drawbacks can be significantly improved by subsequently mixing component (a) and component (b) and heating and nitriding the mixture in a nitriding atmosphere. Furthermore, the present inventors have found that by using component (c), which is a mixture of component (b) and silicon nitride, the - layer can be further improved.

The present invention has been completed based on such new knowledge, and the present application involves (a) granulating at least one of a metal silicon powder and a mixture of υ silica powder and carbon powder, and further granulating at least one of the granulated product. was surface coated with silicon nitride, and then the component (a
) and component (b) are mixed and heated and nitrided in a nitriding atmosphere.

Furthermore, the present application provides that instead of component b) in the first invention,
A second invention is provided, characterized in that component (c) is used, which is a mixture of component (b) and silicon nitride powder.

As the component (a) used in the present invention, that is, the metal silicon powder, those used in the case of ordinary metal direct nitriding can be used, and it is particularly preferable that the metal silicon powder has a particle size of 10 μm or less. . When a large amount of coarser particles of 10 μm are included, the reaction time becomes long and unreacted silicon remains, making it unsuitable for producing high-purity silicon nitride. In addition, in the conventional method, it was said that particles with a particle size of 1 μm or less cannot be used, but in the present invention, even fine powders with a particle size of 1 μm or less can be used because the temperature rise due to rapid reaction is significantly alleviated.

Component (b) is a mixture of silica powder and carbon powder, and those used in ordinary reductive nitriding methods can be used. For example, examples of silica include wet process silica powder, silica hume, rice husk silica, and finely powdered quartz, and examples of carbon powder include carbon black and petroleum coke powder. Further, as the carbon, an organic substance that carbonizes and gives carbon by heating may be used. These may be mixed either dry or wet, or may be mixed in a solution simultaneously with the production of silica.

From the viewpoint of reactivity, the primary particle size of silica powder and carbon powder is
Preferably, the thickness is 1 μm or less.

If the particles are coarser than that, unreacted substances tend to remain and are not suitable for producing high-purity silicon nitride. Further, in order to produce silicon nitride with a high α type ratio, the purity of both raw materials is preferably as high as possible, and those with a purity of 99% or more are particularly preferred.

The weight ratio of silica powder/carbon powder in component (b) is preferably 110.4 to 1/1.

If the blending ratio is less than 110.4, silicon oxynitride (StiONz) will be formed, which is undesirable, and if it exceeds 1/1, excess carbon will remain, causing problems in removal, economic efficiency, etc. This causes undesirable problems.

The mixing ratio of silicon nitride in component (c) is preferably 0.61 to 1 part by weight based on 1 part by weight of silica.

When it is less than 0.1, the improvement effect is not significant, and when it exceeds 1, the silicon nitride production efficiency decreases, impairing economic efficiency.

Considering the purity and α-type content of the final product, silicon nitride having high purity and high α-type content is preferable. Furthermore, the finer the particle size for both mixing and coating, the finer the product particle size can be obtained.

Components (a), (b) and/or (c) can be granulated by adding water or an organic solvent.

As the granulation method, any commonly used granulation method may be used, such as transfer granulation, extrusion molding, pressure molding, and crushing of dried slurry. Moreover, if the particle size of the powder is appropriately selected, pressure molding is also possible without adding a liquid component. If a coating operation is to be added later, it is preferable to use transfer granulation or the like to form a shape that is easy to coat.

The size of the granules is preferably about 0.5 to 20 am. 0
．． If it is finer than 5 fins, the coverage ratio becomes large and it is not efficient, and if it exceeds 20 fins, it is difficult to evenly cancel out the reaction heat of the two reactions, resulting in non-uniformity, resulting in a decrease in the α phase.

Granulation is performed on at least one of components (a), (b), and (c).

Next, after performing a coating operation on at least one of the granules,
Mix components (a) and (b) or (c).

In this case, component (a)/component (company) or component (a)
)/component (c) is the mixing ratio of component (b) or component (
When the silica in c) is 1, the weight ratio excluding the silicon nitride coating is preferably 0.1 to 3. If it is less than 0.1, it is almost the same as oxide reduction nitriding, and if it exceeds 3, the heat offset effect is not sufficient.

High quality α-type silicon nitride can be obtained by heating the obtained mixture in a nitriding atmosphere containing nitrogen or ammonia. The heating temperature is preferably in the range of 1400 to 1600°C.

〔Effect of the invention〕

In addition to separating reactions and offsetting heat by granulation as described in JP-A-62-260704, the present invention can avoid direct contact between metal silicon and carbon by coating the granules with silicon nitride. Furthermore, by quickly removing carbon monoxide generated by the addition of silicon nitride, it is possible to produce even lower carbon and higher α-type silicon nitride.

〔Example〕

Next, an example will be given and explained.

Examples 1 to 6 Wet process silica powder with a specific surface area of 180 m”/g (purity 99
．． 5% or more) and carbon black powder (purity 99.5%) with a specific surface area of 24 rn''/g, and a specific surface area of 7.6 m''/g.
Silicon nitride (purity 99.8%) was mixed in a ball mill in the proportions shown in Table 1 to obtain a mixture of component (b) or (c). Furthermore, metallic silicon powder (average particle size 1 μm 1 purity 99
．． 0%) was prepared. The granules shown in Table 1 have a diameter of 1.2 m.
It was granulated into particles of about 31I11 using a pan pelletizer. Furthermore, silicon nitride coating was also performed using the same pan pelletizer. The granules and the powder or the granules and the granules were mixed in the same proportions shown in Table 1. These mixtures are 1400-155
Heating and firing in a nitriding atmosphere with nitrogen at a temperature of 0°C,
Silicon nitride was obtained. The results of X-ray analysis and N analysis of the obtained silicon nitride are shown in Table 1. Comparative Example 1 is a case in which the granules are not coated with silicon nitride.

Examples 7 to 8 Aerosil (manufactured by Nippon Aerosil Co., Ltd.) was used as a silica raw material,
Acetylene black (manufactured by Denki Kagaku Co., Ltd.) as a carbon raw material,
Using semiconductor silicon (manufactured by Shin-Etsu Chemical Co., Ltd.) powder with an average particle size of 1 μm and the silicon nitride of Example 1, the particles were granulated to 6 g in the same manner as in Example 1, coated, and heated with N at 1500°C. ,
The sample was heated and nitrided for 2 hours in a 10% N113 gas stream. Table 1 shows the analytical values of the obtained silicon nitride. A case where the granules were not coated with silicon nitride was shown as Comparative Example 2.

Margin below

Claims (1)

[Claims] 1. At least one of (a) metal silicon powder and (b) a mixture of silica powder and carbon powder is granulated, at least one of the granules is surface-coated with silicon nitride, and then A method for producing α-type silicon nitride, which comprises mixing component (a) and component (b) and heating and nitriding the mixture in a nitriding atmosphere. 2. The manufacturing method according to claim 1, characterized in that component (c), which is a mixture of component (b) and silicon nitride powder, is used in place of component (b). 3. The manufacturing method according to claim 1 or 2, wherein the granules to be surface coated are component (a). 4. The manufacturing method according to any one of claims 1 to 3, wherein the granules to be surface coated are component (b) or component (c).