JPS6186405A - Preparation of silicon nitride - Google Patents

Abstract

PURPOSE:To prepare fine Si3N4 having high alpha-phase content with high productivity by adding a specified dispersant and a specified nucleating material for the reaction to a slurry prepd. by adding water to silicon powder, carbon powder and/or resin powder, adjusting then the pH, drying, and nitriding by reduction. CONSTITUTION:A slurry is prepd. by adding water to silica powder (e.g. white carbon having <=3 micron particle size), carbon powder (e.g. carbon black having <=2 micron particle size), and/or resin powder (e.g. powdery phenol resin having <=30 micron particle size). Ammonium oxalate and nonionic surfactant are added as dispersant to the slurry, and at least one among Al2O3, sialon, oxide powder of the Group IIIA elements (e.g. Y2O3) as nucleating agent for reaction are also added. Then, the pH of the slurry is adjusted to 8-10, and the slurry is dried and nitrided by reduction. Thus, the productivity is improved remarkably, and Si3N4 having high content of alpha-phase and fine particle size is obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing silicon nitride by a silica reduction method, and more specifically, to a method for producing silicon nitride with a high content of α phase and a high yield. Regarding the manufacturing method.

[Conventional technology]

Silicon nitride ceramics are attracting attention as engineering ceramic materials for gas turbine plate materials, nozzle materials, etc. due to their high strength at high temperatures, and research and development is being conducted in various fields toward practical application.

Various methods have been proposed for producing silicon nitride powder, which is a raw material for silicon nitride ceramics.

It is manufactured by heating silica powder, carbon powder, or resin powder in a nitrogen or ammonia atmosphere.

The so-called silica reduction method is attracting attention as a method that can be mass-produced. However, since this silica reduction method has a low content of useful α phase, a method using reaction nuclei has been proposed as a method to improve this. In other words, silicon nitride is used as a reaction nucleus in the raw material.

A method of adding silicon carbide, silicon oxynitride, etc. (Japanese Patent Publication No. 54-23917) has been developed.

However, although the silicon nitride obtained by this method has a high alpha phase content, the amount of 2 reaction nuclei used ranges from 3θ to 40cm, so a part of the product obtained is used as reaction nuclei, resulting in a significant increase in productivity. low.

Therefore, in order to increase productivity, a method using a small amount of amorphous silicon nitride was developed (Japanese Patent Laid-Open No. 59-97508).

Although this method is excellent for mass production, it is impractical because the alpha phase content of the silicon nitride produced is as low as about 90 cm, and the grain size is coarse, several μm.

[Problem to be solved]

As described above, the conventional silica reduction method using silicon nitride as a reaction nucleus is a method that is unsatisfactory in either the α phase content or the productivity, and a manufacturing method that is excellent in both has not yet been developed. Therefore, the emergence of such an excellent manufacturing method has been strongly desired.

That is, the present invention provides a method for producing fine silicon nitride with a high alpha phase content and high productivity.

[Means for solving problems]

The inventors of the present invention have conducted intensive research on a manufacturing method using reaction nuclei in the silica reduction method, and have found that by using a specific oxide as a reaction nucleus and further using a dispersant, high productivity and high production of fine silicon nitride can be achieved. Obtained knowledge that alpha phase content can be obtained.

Based on this, the present invention was completed. That is, the present invention adds ammonium oxalate and a nonionic surfactant as a dispersant to a slurry made by adding water to silica powder and carbonaceous powder (collectively carbon powder and/or resin powder), which are the main raw materials, and Further, one or more of the oxide powders of aluminum oxide, sialon, and group I [[A of the periodic table] are added as reaction nuclei, and then the slurry p
This method of producing silicon nitride is characterized by adjusting H to 8 to 10, drying, and reducing and nitriding.

The substance used as a reaction nucleus in the present invention is oxidized Ttv
Miniram (A1203), +iT Roa (5i6
-2A1□02Ns-z) and oxides of group IIIA of the periodic table.

For example, yttrium neodymium oxide (YNdO3
).

Examples include oxide powders such as lanthanum oxide (La203) and ceria (CeO2). One or more of these oxide powders may be added to the slurry as appropriate, but it may also be added to the raw material before it is made into a slurry. The addition ratio is 0 to 100 parts by weight of silica powder.
The amount is 0.05 to 20 parts by weight, preferably 0.1 to 3 parts by weight.

If the amount added is less than 0.05 parts by weight, the effect of adding it as a reaction nucleus is small and fine silicon nitride cannot be obtained.On the other hand, even if it is added in excess of 20 parts by weight, there is no effect considering the amount added. It is small and uneconomical. The particle size of the reaction nucleus is preferably 5 μm or less; if the particle size is larger than that, the effect of promoting the nitriding reaction as a reaction nucleus becomes very small.

Next, ammonium oxalate ((NH
4) 2c204) and nonionic surfactants act as dispersants for raw material powders in slurry, and nonionic surfactants include commonly used ones such as alkylphenol ethylene oxide adducts and polypropylene glycol ethylene oxide. Examples include additives.

In the case of ammonium oxalate, the addition ratio is 0.1 part by weight or more, preferably 0.3 to 6.0 parts by weight, based on 100 parts by weight of silica powder. In addition, in the case of nonionic surfactant, 0.00% per 100 parts by weight of carbonaceous powder.
The amount is 2 parts by weight or more, preferably 0.3 to 2.0 parts by weight. If the above two types of dispersants are less than 0.1 part by weight or 0.2 parts by weight, respectively, the dispersion effect will be weak and the raw material powder will not be homogeneous, resulting in impurities such as silicon oxynitride in the product obtained by the reductive nitriding reaction. remains, which is not desirable. On the other hand, there is no particular technical problem in adding more than the preferable upper limit of 60 parts by weight or 2.0 parts by weight, but there is no effect corresponding to the amount added, so adding more than that is uneconomical. be.

After adjusting the raw materials and before drying, the pH of the slurry is adjusted, which is one of the features of the present invention. Ammonia water is used to adjust the pH of the slurry, and by adding and mixing the slurry to a pH of 8 to 10, it has the effect of further enhancing the dispersion effect and stabilizing the slurry.

In the present invention, the main raw materials used are those obtained by conventional methods,
For example, examples of silica powder include white carbon and silica gel with a particle size of 3 μm or less.

Carbon powder, coke powder, etc. with a particle size of 211 m or less are used as carphone powder, and carbon powder with a particle size of 30 m or less is used as resin powder.
Phenol resin powder of less than μm.

Urea resin powder, melamine resin powder, polycarbonate resin powder, etc. are used. These carbonaceous raw material powders, carbon powder and resin powder, may be used alone or in combination. If too much is mixed, the amount of these carbonaceous raw material powders is 40 parts by weight or more per 100 parts by weight of silica powder.

Next, an example of the manufacturing method according to the present invention will be explained.

Water in an amount of 2 to 10 times its weight is added to the blend of the above main raw materials to obtain a slurry. While forcibly stirring this slurry, a required amount of the oxide powder as a reaction nucleus, ammonium oxalate and a nonionic surfactant as a dispersant are added, and aqueous ammonia is added dropwise to adjust the pH. The order of these additions is not limited, as long as the final prepared slurry has the raw material powder and various additives sufficiently dispersed therein.

The prepared slurry thus obtained is optionally dehydrated and then dried using conventional equipment.

By heat-treating this dried product at 1850 to 1550°C for 0.5 hours or more in a nitrogen and/or ammonia atmosphere, silicon nitride containing a large amount of α phase and having a size of 1.2 μm or less can be obtained with high productivity. .

[For production]

The reaction nucleus used in the present invention constitutes a part of silicon nitride obtained by heat treatment. Therefore, whereas in the present invention the reaction nucleus is part of the raw material.

The reaction nucleus of the conventional method constantly cycles through 80 to 40 inches of silicon nitride, which reduces the effective capacity of the heat treatment furnace and other equipment by the amount that is recycled. Therefore, if a furnace or the like having the same effective volume is used for manufacturing, the productivity of the method of the present invention will be correspondingly higher.

However, in the present invention, the oxide used as a reaction nucleus promotes the nitriding reaction and increases the α phase content.

The reason why silicon nitride is made even finer is considered to be due to the following effect.

S IO2 radical nitriding reaction is 5I02+C (or resin) → Si O+ Co
(1) SiO−+ C (or resin) + N2 (N in resin → Si s N4+ Co +2), but this reaction system also contains Si3 as a reaction nucleus.
When N powder is added, it is thought that Si3N crystals will gradually grow around it.

The speed is very slow and the α phase content is low.

Furthermore, when crystalline 513N4 is added, the α phase content is improved, but the crystal size is still not sufficiently fine.

Sialon as one reaction nucleus as in the present invention.

When oxides such as Y2O3 and YNd03 are added, the glass phase of Me -8i -0 (Me: a metal element constituting the reaction nucleus) generated at the initial stage of the reaction is generated and distributed throughout the system and activated, (1), +2 ) promotes the reaction of fine 8
By producing a large number of i 5 N 4 crystals,
In minute detail.

It is thought that 5L3N4 with a large amount of α phase can be produced.

In addition, the dispersant such as ammonium oxalate in the present invention is used not only to improve the mixing of raw materials, but also to uniformly disperse the reaction core material added in a small amount into a large amount of raw materials, and the pH adjustment further improves this. It is what makes it effective.

It is believed that by doing so, the nitriding reaction of the prepared raw material is promoted evenly, the α phase content of the product is increased, and the product is made fine.

Examples 1-12. Comparative Examples 1 to 8 Main raw materials below 1) Silica powder White carbon 100 parts by weight (average particle size 0.7 μm) 2) Carbon black 35 parts by weight (average particle size 1.I Jim, oil absorption 11 zrn)
4/i00, li') 3) Urea resin powder (20μ
m or less) 800 parts by weight of water was added to 100 parts by weight of the formulation in Table 1].

Add the oxide shown in (particle size 1 to 3 μm), 1 part by weight of ammonium oxalate, and 0.3 part by weight of polyethylene glycol alkyl ether into a forced stirrer, and adjust the pH to 9.0 by adding aqueous ammonia dropwise while mixing. A liquid slurry was produced.

The dried product obtained by spray drying this slurry was introduced into an electric furnace and heated at 1480'C in a nitrogen gas atmosphere.

The reductive nitriding reaction was carried out for 3 hours. This reaction product was heated at 720°C.
Decarbonization treatment was carried out in air, and the particle size of each product obtained was measured by X-ray diffraction and electron microscopic observation, and the results are listed in the same table.

Table 1 1) Amount added to Noriyoku powder (external ratio) Example 13.
Comparative Examples 4 to 6 After adding 0.5 parts by weight of Y2O3 to the main raw materials of Examples 1 to 12, 1 part of water and a dispersant and ammonia were added according to Table 2, and the mixture was put into a forced stirrer and mixed. Each slurry was spray-dried to obtain a prepared raw material. However, Comparative Example 4 is a powdered prepared raw material made of only the main raw material. The obtained raw materials were subjected to a reductive nitridation reaction in the same manner as in Examples 1 to 12, and the particle size of each product was measured by X-ray diffraction and electron microscopy, and the results are listed in the table.

〔Effect of the invention〕

The method for producing silicon nitride according to the present invention has significantly improved productivity as compared to the conventional method, and has been able to obtain silicon nitride with a high α phase content and a fine particle size of 1 particle. Therefore, the present invention eliminates all the drawbacks of the conventional methods and provides a highly effective method for producing silicon nitride.

Claims (2)

[Claims] (1) In a method of producing silicon nitride by drying a slurry obtained by adding water to silica powder, carbon powder and/or resin powder, and reducing and nitriding the slurry, ammonium oxalate and a nonionic compound are added to the slurry as a dispersant. A surfactant is added, and one or more of aluminum oxide, sialon, and oxide powder of group IIIA of the periodic table are added as reaction nuclei, and then the slurry is adjusted to pH 8 to 1.
1. A method for producing silicon nitride, which comprises adjusting the silicon nitride to 0, followed by drying and reducing and nitriding. (2) Claim No. 1, wherein the amount of reaction nuclei added is 0.05 to 20 parts by weight per 100 parts by weight of silica powder.
A method for producing silicon nitride as described in Section 1.