JPH02239108A - Production of silicon nitride - Google Patents

Abstract

PURPOSE:To produce Si3N4 having a high content of beta type by wet-crushing metallic Si with a ball mill and nitriding the obtained powder using a gaseous reactant contg. N. CONSTITUTION:Metallic Si is wet-crushed with a ball mill. Water, hexane, etc., are preferably used as the medium, and steel balls, Si3N4 balls, etc., are appropriately used as the crushing media. The grain diameter of the treated Si is preferably controlled to about 1-2.5mum, the BET specific surface to about 5-20m<2>/g, the Fe content to about 0.05-0.2wt.% and the O content to about 3-6wt.%. The Si powder is nitrided in a reaction furnace using a gaseous reactant contg. N. Gaseous N2, a mixture of N2 and gaseous H2, gaseous NH3 and/or gaseous Ar, etc., can be used as the gaseous reactant. The nitridation temp. is preferably controlled to about 1200-1450 deg.C. By this method, beta-Si3N4 contg. about 20-90% or especially about 30-80% beta type is obtained.

Description

[Detailed description of the invention] The present invention has a high proportion of β type (for example, β-Si, N4 is 2
o to 90% by weight) relates to a method for producing silicon nitride.

In recent years, silicon nitride has been gaining attention for its properties such as excellent heat resistance, high strength, and corrosion resistance, and is being applied in the form of sintered bodies to various products. There are two crystal types of silicon nitride, α type and β type, which are used depending on the purpose. In this case, in order to obtain a sintered body with good dimensional accuracy, a compact with a high density before sintering is required, but silicon nitride powder has a higher ratio of β type than high α type. The higher the density of the compact, the higher the density of the compact, and for this reason a high β-type silicon nitride powder is desired.

Conventionally, to produce silicon nitride, a method has been adopted in which silicon metal is nitrided in a reaction furnace using nitrogen gas or a mixed gas of nitrogen gas and hydrogen gas, NH gas, or Ar gas as the reaction gas. However, in this case, if a combination of nitrogen gas and hydrogen gas is used as the reaction gas, α-type silicon nitride is likely to be formed. Therefore, in order to obtain silicon nitride with a high proportion of β-type, it is generally a method to use only nitrogen gas as the reaction gas. It is taken. In addition, a method of adding magnesium oxide (MgO) to metallic silicon in order to increase the ratio of β-type (Japanese Unexamined Patent Publication No. 54
-1200299 Public Relations) have also been proposed.

Here, reactors that use tungsten as a heater are widely used for the reaction of nitriding metal silicon, but when using a tungsten heater, nitrogen gas is used as a reaction gas to prevent oxidation. It is necessary to use hydrogen gas, which poses a problem in that it is difficult to obtain silicon nitride with a high β-type content.

The present invention has been made in view of the above circumstances, and silicon nitride with a high β-type ratio can be obtained whether only nitrogen gas or a combination of nitrogen gas and hydrogen gas is used as the reaction gas. It is an object of the present invention to provide a method for producing silicon nitride that can obtain silicon nitride with a high β-type ratio without being limited by the heater material or the like.

In order to achieve the above object, the inventors of the present invention conducted extensive studies and found that silicon metal is wet-pulverized in a wet ball mill using water, hexane, etc. as a medium, and preferably has a BET specific surface area of 5 to 20 po/ g t particle size 1-2.5/lm, further Fe
According to the method of adjusting the content to 0.05 to 0.2% by weight and the oxygen content to 3 to 6% by weight, and nitriding this in a reactor using nitrogen gas, the reaction using tungsten as a heater is performed. Even when hydrogen gas must be mixed, such as by using a furnace, for example, β-Si, N. The present invention was completed based on the finding that silicon nitride with a high β-type content of 20 to 90% by weight, particularly 30 to 80% by weight, can be obtained.

Accordingly, the present invention provides a method for producing β-type silicon nitride, which comprises wet-pulverizing metallic silicon in a ball mill and nitriding it using a nitrogen-containing reaction gas.

The present invention will be explained in more detail below.

The method for producing silicon nitride with a high β type ratio according to the present invention is as follows:
Metallic silicon as a raw material is wet-pulverized using a ball mill, and the silicon powder is nitrided in a reactor using a reaction gas containing nitrogen gas.

Here, the particle size of the raw material silicon metal is not limited, but those having a particle size of 0.01 to 2 ml are usually used. In addition, water and hexane are preferably used as the medium for wet pulverization, but the medium is not limited to these.

Furthermore, wet pulverization can be performed using a ball mill, etc.
What kind of grinding media should be used in this case? Cheel balls or Si,N4 balls are preferably used. Note that when steel balls are used as the media, it is preferable to perform a purification treatment with either hydrochloric acid, nitric acid, sulfuric acid, or aqua regia after pulverization.

The grinding conditions are not particularly limited, but the particle size after treatment is 1 to 2.5 rds, and the BET specific surface area is 5 to 20 rds.
/ g is preferable from the viewpoint of reactivity with nitrogen gas, and the Fs content is preferably pulverized so that the Fs content is O. OS~0.2
It is preferable that the oxygen content be 3 to 6% by weight.

The production method according to the present invention is one in which the metal silicon powder is reacted with a reaction gas containing nitrogen gas in a reaction furnace,
In this case, in the method of the present invention, only nitrogen gas can be used as the reaction gas, or hydrogen gas, NH gas, Ar gas, etc. can be used in a mixture of about 5 to 30% with nitrogen gas. Even in such a case, silicon nitride with a high proportion of β type can be obtained. Therefore, the reactor is not limited to the material of the heater, and various materials can be used, such as those made of tungsten.

Note that the nitriding temperature is not particularly limited, but 1. 2 0
0 to 1450'C is preferable, and other nitriding conditions can be set as usual.

Full 1L3. As explained above, according to the method of the present invention, silicon nitride with a high proportion of β type can be obtained whether only nitrogen gas or a combination of nitrogen gas and hydrogen gas is used as the reaction gas, and therefore the reaction furnace Silicon nitride with a high β-type ratio can be obtained without being limited by the material of the heater.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[Example, comparative example]

Metal silicon powder (particle size 0.03-0.5 mm, 02 content 0.15 wt%. Fe content 0.24 wt%) 400
Wet milling was carried out using a 5Q attrition mill using steel balls and water as the milling media to obtain the two types of silicon fine powders shown in Table 1. For comparison, the same raw materials as in the above example were used, and after being pulverized using a dry roller mill, the two types of silicon fine powders shown in Table 2 below were obtained by subjecting them to hydrochloric acid treatment. .

Next, the above-mentioned silicon fine powder was charged into a Milliconit furnace having a 50ay++φ alumina furnace core tube (layer height 10on).
, reaction gas (NZ only or N2 + 5% H2) 2Q/+
iin] and nitrided at 400° C. for 2 hours to obtain silicon nitride. Xa for the case of using only N2 gas as the reaction gas and the case of using N2 + 5% H gas
The ratio of α type and β type was calculated by diffraction (the ratio of α type and β type was determined from the peak heights of α (2 1 0) and β (2 1 0)). The results are shown in Table 3. Table 1: After finely pulverizing the silicon nitrides of Examples 1 and 2, the silicon nitrides were purified with acid and the amount of impurities was examined. 0
2% by weight or less, oxygen 1.5% by weight or less, and Si was not detected by X-ray diffraction.

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

Claims (1)

[Claims] 1. A method for producing silicon nitride, which comprises wet-pulverizing metallic silicon in a ball mill and nitriding it using a nitrogen-containing reaction gas.