JPH0345506A - High-oxygen high beta-type silicon nitride fine powder and production thereof - Google Patents

Abstract

PURPOSE:To enable sure production of high-oxygen and high beta-type silicon nitride fine powder excellent in calcinability by treating low-oxygen and high beta-type silicon nitride fine powder with a mixed acid of hydrofluoric acid and nitric acid. CONSTITUTION:High-oxygen high beta-type silicon nitride fine powder with >0.6 to <=4wt.% oxygen content, 50-100wt.% beta-type content and >=10m<2>/g BET specific surface area is obtained by the following method. That is silicon nitride fine powder with <=0.6wt.% oxygen content and 50-100wt.% beta-type content is treated with a mixed acid of hydrofluoric acid in an amount of >30 to <=70 pts.wt. based on 100 pts.wt. silicon nitride and nitric acid. The nitric acid is preferably used in an amount of 150-200 pts.wt. based on 100 pts.wt. silicon nitride. The treatment with the mixed acid is carried out at about 60-80 deg.C temperature for about 1-2hr.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fine silicon nitride powder having a high proportion of β type and a high oxygen content, and a method for producing the silicon nitride.

Previously, silicon nitride sintered bodies have mainly been produced using α-type silicon nitride powder from the viewpoint of sinterability and strength, but recently, when using β-type silicon nitride, α-type This is because good sinterability can be obtained at a lower sintering temperature than when using silicon nitride powder.

It is desired to obtain a silicon nitride sintered body using β-type silicon nitride. In addition, it is known that impurities in silicon nitride powder affect sinterability during sintering, and the oxygen content in silicon nitride has been found to have a particularly large effect, and α-type silicon nitride It is said that the oxygen content is preferably 1 to 3%.

Therefore, silicon nitride powder of β type and high oxygen content is desired in order to obtain a silicon nitride sintered body.

Conventionally, as a method for producing silicon nitride powder.

Direct nitriding method of metal silicon powder, silica reduction method.

Methods such as thermal decomposition of imide are known, but direct nitriding of metal silicon powder is easiest to obtain high β-type silicon nitride. In this direct nitriding method, metal silicon powder is generally subjected to a nitriding reaction at a temperature of 1350 to 1500°C in a nitrogen gas atmosphere mixed with hydrogen or ammonia gas to obtain silicon nitride powder.
In order to increase the mold content, attempts have been made to reduce the amount of hydrogen gas added, raise the nitriding temperature, or increase the amount charged. However, in such a method, β
It is difficult to increase the mold content to 50% or more, and when the amount charged is increased, the amount of unreacted metal silicon increases, resulting in a lower yield.

In order to solve this problem, the present inventor has developed a method of combining fine metal silicon powder with a BET specific surface area of ~3rd/g and an oxygen content of 0.6% by weight or less, hydrogen of 4.5% by volume or less, or ammonia gas of 5% by volume. % or less in a nitrogen gas atmosphere so that the unreacted metal silicon in the product is 5% by weight or less (Patent Application No. 1-76970) or β
- A method for producing high β-type silicon nitride powder, characterized by directly nitriding metal silicon powder to which silicon nitride powder containing 30% by weight or more of Si and N is added by a direct nitriding method (Patent Application No. -113269), and were able to obtain high β-type silicon nitride powder.

However, although the above proposal can achieve high β-type silicon nitride powder, the oxygen content is inevitably less than 0.6% by weight, making it difficult to obtain high-oxygen and high-β silicon nitride powder. Met.

The present invention was made in view of the above circumstances, and an object of the present invention is to provide a high-oxygen, high-β type silicon nitride fine powder and a method for producing the same.

As a result of intensive studies to achieve the above object, the inventors of the present invention have discovered a method for obtaining a high β type, for example, the above-mentioned patent application No.
-76970 or Japanese Patent Application No. 1-113269, the oxygen content is 0.6% (by weight).
, the same applies hereafter), silicon nitride fine powder with a β-type content of 50-100%, hydrofluoric acid, and 100 parts of silicon nitride (parts by weight,
(same hereinafter) is treated with a mixed acid of hydrofluoric acid and nitric acid containing more than 30 parts and less than 70 parts, even if the oxygen content of the silicon nitride fine powder used as the raw material is 0.6% or less. , the oxygen content of silicon nitride increases specifically in the above hydrofluoric acid amount range, has an oxygen content of more than 0.6% and 4% or less, and has a BET specific surface area of 1 On? The inventors have now discovered that it is possible to obtain a silicon nitride fine powder with a high oxygen content of at least 1/g, and therefore a silicon nitride powder that has both a high oxygen content and a high β type, and has thus arrived at the present invention.

Therefore, the present invention provides high-oxygen high-β type silicon nitride fine powder having an oxygen content of more than 0.6% and 4% or less, a β-type content of 50 to 100%, and a BET specific surface area of 10 m2/g or more. , and the oxygen content is 0.6% or less and the β type content is 50
The above-mentioned high oxygen concentration method is characterized in that ~100% silicon nitride fine powder is treated with a mixed acid of hydrofluoric acid and nitric acid containing hydrofluoric acid in an amount of more than 30 parts and less than 70 parts per 100 parts of silicon nitride. A method for producing β-type silicon nitride fine powder is provided.

The present invention will be explained in more detail below.

As mentioned above, the high oxygen high β type silicon nitride fine powder of the present invention has an oxygen content of more than 0.6% and 4% or less, preferably 1 to 3%, and a BET specific surface area of 10 g / g or more, preferably 13~20rr? / g.

Further, the average particle diameter is preferably 1 μm or less, particularly 0.3 to 0.6 μm.

In order to obtain such a high-oxygen, high-β type silicon nitride fine powder, the low-oxygen, high-β type silicon nitride fine powder is treated with a mixed acid of hydrofluoric acid and nitric acid.

Here, the low-oxygen, high-β type silicon nitride is a nitride with an oxygen content of 0.6% or less, preferably 0.4% or less, and a β-type ratio of 50 to 100%, preferably 80 to 100%. Any silicon fine powder can be used as long as the amount of oxygen and the ratio of β type are within the above ranges. In order to obtain this low-oxygen, high-β type silicon nitride, the method previously proposed by the present inventor is effective.

That is, the BET specific surface area is 1 to 3 m2/g, and the oxygen content is 0.
Under a nitrogen gas atmosphere containing 6% or less of metallic silicon fine powder in an amount of hydrogen of 4.5% by volume or less or ammonia gas in an amount of 5% by volume or less, unreacted metallic silicon in the product becomes 5% or less. A method for producing low-oxygen, high-β-type silicon nitride fine powder that is nitrided to (Patent Application No. 1-076970),
8i3N, is a high-β nitriding method that uses a direct nitriding method to nitride metal silicon powder to which 1% or more of silicon nitride powder with 30% or more is added.
Method for manufacturing molded silicon nitride powder (Patent application No. 1-113269)
Silicon nitride powder having an oxygen content of 0.6% or less and a β type ratio of 50 to 100% can be obtained by a method such as No. 1).

In the present invention, the above-mentioned low-oxygen, high-β silicon nitride powder is treated with a mixed acid of hydrofluoric acid and nitric acid. Specifically, silicon nitride powder is mixed with iron ball media using an attritor, and this slurry is preferably treated with a mixed acid of hydrofluoric acid and nitric acid.

Next, the amount of hydrofluoric acid in the mixed acid exceeds 30 parts to 70 parts per 100 parts of silicon nitride powder. If the amount of hydrofluoric acid is outside the above range, the oxygen content of silicon nitride will be low. As the hydrofluoric acid, generally 55 parts of hydrofluoric acid is used.

The method of treating silicon nitride powder with a mixed acid of nitric acid and hydrofluoric acid is not limited, and any conventional method can be used.

For example, it can be carried out according to the acid treatment process for highly purifying silicon nitride powder after wet pulverization using iron media, and the amount of nitric acid is also according to this acid treatment process, although it is not particularly limited. The amount of nitric acid (specific gravity 1.38) used is at least 1.5 times the amount necessary to treat the amount of worn iron, preferably 150 to 200 parts per 100 parts of silicon nitride.

Note that the acid treatment is preferably carried out at a temperature of 60 to 80°C, for example. Also, the time is 1-2
This can be carried out with stirring for a period of time or while standing still.

As explained above, the present invention increases the oxygen content of low-oxygen, high-beta silicon nitride using a wet method using a specific mixed acid, thereby producing a high-oxygen, high-beta silicon nitride. The powder can be reliably produced, and the resulting high-oxygen, high-β type silicon nitride fine powder has excellent properties such as sinterability.

EXAMPLES Hereinafter, the present invention will be explained in more detail by showing examples and comparative examples, but the present invention is not limited to the following examples. In addition, in the following examples, the specific surface area is the specific surface area determined by the BET method, and % is weight %.

[Example 1, 2. Comparative Examples 1 and 2] Specific surface area is 2 to 3 rr? /g, metal silicon powder with a total particle size of 10μ or less and an oxygen content of 0.6% or less was nitrided in a nitrogen atmosphere at a maximum temperature of 1470°C for 2 hours to obtain the silicon nitride shown in Table 1. Ta.

After pulverizing 40 kg of the obtained silicon nitride with an attritor using iron media, it was immersed in hydrofluoric acid and nitric acid in the amounts shown in Table 2 at a temperature of 75° C. for 1 hour. Characteristics such as specific surface area and oxygen content of the silicon nitride fine powder after treatment were measured. The results are shown in Table 2.

The oxygen content was analyzed using EMGA2800 (manufactured by Iba Seisakusho).

From the results in Table 2, it is recognized that the oxygen content of silicon nitride can be specifically increased by using hydrofluoric acid in a range of more than 30 parts and less than 70 parts per 100 parts of silicon nitride according to the present invention. .

Claims (1)

[Claims] 1. Oxygen content is more than 0.6% by weight and less than 4% by weight,
A high-oxygen, high-β type silicon nitride fine powder having a β type content of 50 to 100% by weight and a BET specific surface area of 10 m^2/g or more. 2. Oxygen content is 0.6% by weight or less and β type content is 50%.
~100% by weight of silicon nitride fine powder is treated with a mixed acid of hydrofluoric acid and nitric acid containing hydrofluoric acid in an amount of more than 30 parts by weight and less than 70 parts by weight per 100 parts by weight of silicon nitride. A method for producing a high-oxygen, high-β type silicon nitride fine powder according to claim 1.