JPH0248407A - Production of silicon nitride powder - Google Patents

Abstract

PURPOSE:To obtain silicon nitride powder having high alpha-content in high yield and productivity by directly nitriding metallic Si in the presence of Ga2O3. CONSTITUTION:Ga2O3 is added to metallic Si powder, preferably fine powder of <=10mum in diameter. The Ga2O3 is preferably fine powder having specific surface area of >=2m<2>/g and its amount is preferably 0.03-5 pts.wt. per 100 pts.wt. of the metallic Si powder. The metallic Si powder added with the Ga2O3 is directly nitrided to obtain a silicon nitride powder having high ratio of alpha-silicon nitride content and containing little residue of unreacted metallic Si. The reaction can be carried out at a high temperature compared with conventional process. The thickness of the layer of the charged metallic Si can be increased and the objective powder can be produced in high yield and productivity.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for direct nitriding of metallic silicon powder, which can efficiently produce silicon nitride powder with a high α-type ratio.

In recent years, silicon nitride has attracted attention for its properties such as excellent heat resistance, high strength, and corrosion resistance. It is necessary to sinter the material and mold it into various shapes.

There are two crystal types of silicon nitride: α type and β type.
It is said that the sinterability of the mold is inferior to that of the α-type, and in order to sinter without impairing the properties of silicon nitride, it is desired that the ratio of the α-type be as high as possible.

Conventionally, known methods for producing silicon nitride powder include direct nitriding of metallic silicon, silica reduction, and imide thermal decomposition. Among these methods, silica reduction method and imide thermal decomposition method are easy to obtain α-type silicon nitride. However, since the silica reduction method uses carbon as a reducing agent, carbon is inevitably mixed in as an impurity, and the imide thermal decomposition method is not suitable for mass production.

In contrast to the silica reduction method and the imide thermal decomposition method described above, the direct nitridation method of metal silicon is suitable for mass production and has the advantage of not containing carbon. However, this direct nitriding method performs the reaction 38i + 2N2 → Si, N4 at high temperatures, but it involves a large reaction heat of 176 Kcal per 1 mole of silicon nitride, resulting in even higher temperatures, and β-type silicon nitride is a high-temperature stable type. The higher the temperature, the easier it is to form.
It has the disadvantage that the proportion of β-type silicon nitride increases.

For this reason, in the past, various additives were added as catalysts in order to increase the ratio of α type, and at 1300 to 1350'C
Although the reaction is carried out at a relatively low temperature, unreacted metal silicon tends to remain due to poor reactivity, which poses a problem in terms of yield. In this case, it is possible to achieve a certain degree of high α by reducing the amount of metal silicon charged, but reducing the amount of charged silicon poses a problem in terms of productivity and is not practical.

The present invention was made in view of the above circumstances, and an object of the present invention is to provide a method for producing silicon nitride powder having a high α-type ratio with good yield and productivity.

In order to achieve the above object, the present inventor conducted intensive studies and found that when Ga2O is added to the metal silicon powder when directly nitriding the metal silicon powder, the conventional 1300 to 135
Even if the nitriding reaction, which used to be carried out at 0°C, is carried out at a high temperature of 1,350 to 1,500°C, silicon nitride powder with a high ratio of α type can be obtained, and since the reaction can be carried out at high temperature, no unreacted metallic silicon will remain. It was discovered that the productivity can be improved because the height of the charging layer can be made thicker, and this led to the present invention.

In the past, many proposals have been made regarding methods of adding various additives to metal silicon powder to improve the α-type ratio. For example, magnesium oxide (JP-A-51-48
No. 800), metallic iron and iron compounds (JP-A-54-1)
5499), palladium oxide (JP-A-54-58)
No. 700), calcium compounds (Japanese Patent Application Laid-Open No. 1983-12)
0298 Publication), metal nets and copper compounds, vanadium and vanadium compounds (Japanese Unexamined Patent Publication No. 61-256906), manganese and manganese compounds (Japanese Unexamined Patent Publication No. 61-256
Although there have been proposals to add additives such as (No. 907 Publication), using Ga2O3 as an additive makes it possible to increase the amount charged as described above, and also enables high-temperature reaction, and is suitable for α-type silicon nitride. It was discovered for the first time by the present inventor that this can be obtained in high yield.

Therefore, the present invention provides a method for producing silicon nitride powder, which is a direct nitriding method of silicon metal, characterized in that Ga2O3 is added to silicon metal powder for nitriding.

The present invention will be explained in more detail below.

The method for producing silicon nitride powder according to the present invention uses metallic silicon powder as a raw material. The metal silicon powder is preferably a fine powder from the viewpoint of reactivity, and specifically, 10 Im or less, particularly preferably 2 to 7 Im. Further, the specific surface area is preferably 1 m/g or more, particularly 2 to 6 bo/g.

The Ga2O3 added to the metal silicon powder is preferably a fine powder like the metal silicon powder, specifically preferably 2d1g or more, particularly 3 to 6 m/g. The amount added is 0.0 parts by weight per 100 parts by weight of metal silicon powder.
3 to 5 parts by weight, particularly 0.1 to 0.5 parts by weight are preferred.

If the amount added is less than 0.03 parts by weight, the effect of the addition may not be sufficiently exhibited, and if it is added more than 5 parts by weight, it may have an adverse effect on sintering.

There is no particular restriction on the method of adding Ga2O, but from the viewpoint of workability, a method of simply mixing fine powder of Ga2O3 with metal silicon powder is preferably employed.

The method of the present invention involves directly nitriding the metal silicon powder added with Ga and 03 mentioned above, and a conventional method can be adopted as the direct nitriding method.

In this case, nitrogen gas, ammonia gas, or a mixture thereof can be used as the reaction gas, and in order to control the reaction, hydrogen or an inert gas such as argon can also be mixed therein.

Furthermore, a conventional nitriding furnace for carrying out the reaction can be used as is.

Note that the nitriding temperature is not particularly limited, but is 1350 to 15
00'C is preferred. If nitriding is carried out at a temperature lower than 1350°C, the reactivity will deteriorate and a large amount of unreacted metallic silicon will remain, and the height of the charged layer of metallic silicon powder cannot be made thicker, resulting in the inconvenience of reduced productivity. There is. On the other hand, when nitriding is carried out at a temperature higher than 1500°C,
The ratio of α type in the obtained silicon nitride powder may decrease.

As explained above, according to the method of the present invention, in the direct nitriding method of metallic silicon, the reaction can be carried out at a higher temperature than before, the amount of unreacted metallic silicon is small, and the ratio of α type is reduced. It is possible to obtain a silicon nitride powder with a high α-type, the height of the charged layer of metal silicon can be increased, and a high α-type silicon nitride powder can be obtained with good yield and productivity.

EXAMPLES Hereinafter, the present invention will be specifically explained by showing examples and comparative examples, but the present invention is not limited to the following examples.

[Example, comparative example]

Additives (powders) shown in Table 1 were added to metal silicon powder having a specific surface area of 2.6 ml/g by the BET method in the amounts shown in the table, and thoroughly mixed.

This mixture was placed in a tray made of 5i3N4-3iC with the layer height shown in Table 1, and heated in a nitriding furnace under a nitrogen atmosphere for 1 hour.
Nitriding was carried out at 400°C for 2 hours.

The amounts of unreacted Si, α-3i, and N4 in the obtained Si and N4 were analyzed. The results are also listed in Table 1.

Shin-Etsu Chemical Co., Ltd. Agent: Patent Attorney Takashi Kojima

Claims (1)

[Claims] 1. A method for producing silicon nitride powder, which comprises adding Ga_2O_3 to metal silicon powder and nitriding it in the direct nitriding method of metal silicon.