JPS61256906A - Preparation of alpha type silicon nitride - Google Patents

Abstract

PURPOSE:To obtain alpha-type silicon nitride having high purity by nitriding a mixture consisting of powdery metallic Si and a specified proportion of a V compd. at a specified temp. CONSTITUTION:Powdery metallic Si is mixed with 0.01-10wt% V and/or V compd. The mixture is nitrided at below the m.p. of the metallic Si. Thus, alpha-type silicon nitride having >=90wt% content is obtd. at relatively low temp. with improved productivity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for producing α-type silicon nitride by nitriding metallic silicon.

[Background of the invention]

The silicon nitride sintered sheath has a heat resistance of 1I compared to conventional ceramic materials.
It has excellent thermal properties, high-temperature properties, and chemical stability, and its use as high-temperature gas turbine components is being attempted.

In general, α-type crystal powder has excellent sinterability as a raw material powder for silicon nitride sintered sheath bodies. It is said that the higher the α rate of the raw material silicon nitride, the easier it is to sinter, and the greater the strength of the obtained sintered body. The reason for this is said to be due to crystal growth when α-type silicon nitride transforms into β-type silicon nitride due to heating during sintering.

Conventional methods for producing α-type silicon nitride include (1) direct nitriding of metal silicon powder, (2) method of nitridation reduction by heating a mixture of silicon oxide powder and carbon in nitrogen gas, and (3) A known method is to synthesize silicon imide from chlorinated silicon and ammonia gas and then thermally decompose it.

Among these methods, method (2) tends to leave oxygen and carbon <, (
In method 3), silicon imide easily absorbs oxygen from the air and is handled by rotation. Therefore, method (1) is the easiest, and many industrially produced powders are manufactured using this method. 51-48800
JP-A-54-15499 proposes metallic iron and iron compounds, JP-A-54-120298 proposes calcium compounds, and JP-A-59-92906 proposes copper compounds. However, in the method of directly nitriding metal silicon powder bundles, the problem is how to increase the powder content of α-type crystals, and when metal silicon powder bundles are nitrided at high temperatures, β-type crystals tend to form particles. Since silicon nitride also becomes coarse, the issue of how to produce silicon nitride at low temperatures has become an important topic.

[Purpose of the invention]

The present invention improves the conventional method for producing α-type silicon nitride, and involves nitriding a metallic silicon powder bundle with vanadium and a vanadium compound to produce high-purity α-type silicon nitride. [Summary of the Invention] The inventors of the present invention conducted further trials of the technology described in the above-mentioned published patent application, and further investigated various substances as additives. It was discovered that by adding vanadium or a vanadium compound, highly pure α-type silicon nitride, which is not available in conventional products, can be obtained.

The present invention improves the conventional method for producing α-type silicon nitride, and involves adding a mixture of 0.01 to 10 parts by weight of at least one of vanadium and vanadium compounds to a bundle of silicon metal powder. It is characterized by nitriding at a temperature below the melting point.

The nitriding reaction of the metal silicon powder bundle is performed based on the following equation.

3 S x + 2 N z → Si, N4 This reaction is exothermic and involves a large amount of heat generation.

If temperature control during the reaction is impaired, α-type silicon nitride transforms into β-type silicon nitride, making it impossible to obtain highly pure α-type silicon nitride.

Therefore, if vanadium and vanadium compounds are added to a metal silicon powder bundle, VOCQ3. When 0.01 to 10 parts by weight of at least one of V2O5, VCQ, etc. is added, the transition from α-type silicon nitride to β-type silicon nitride can be suppressed.

If the amount of vanadium or at least one vanadium compound added is less than 0.01 part by weight, the nitriding reaction will be slow, and if it exceeds 10 parts by weight, the purity of the product will deteriorate, which is not preferable. FIG. 1 shows the relationship between the amount of vanadium and at least one vanadium compound added and the reaction rate. The heating conditions were 1350°C and 5 hours. This shows that the nitriding reaction occurs rapidly when the amount added is 0.01 part by weight or less.

The mixed powder consisting of metal silicon and a nitriding reaction catalyst may be used as it is, or after adding an organic binder such as polyvinyl butyral, it may be molded into an appropriate shape and used.

The temperature inside the nitriding furnace is below the melting point of metal silicon (1410°C).
Keep the temperature above 100℃.

Inside the nitriding furnace, there is an atmosphere of nitriding gases such as nitrogen and ammonia.
Alternatively, the atmosphere is a mixture of nitriding gas and non-oxidizing gas such as argon or hydrogen.

Fe, Mn, and Co in addition to at least one of vanadium and vanadium compounds in metal silicon.

N iy A Q t Cr g M o e M g
g T iy Z r pTa, Nb, Ca, Cu,
Zn, Wt Snt Si.

Y, Ba, Cs, La, B, Pb# P, Na, 9S
α Even if it contains one or more elements selected from b, Ho, Ln, In, Bi, Gd, etc. or a compound thereof.
Type silicon nitride products can be manufactured efficiently.

It can also be used as a nitriding reaction catalyst for silicon nitride sintered bodies and silicon nitride-bonded silicon carbide sintered bodies made from metal silicon powder bundles.

[Embodiments of the invention]

A metal silicon powder bundle with a purity of 99.9% and an average particle size of 1 μm,
Additives shown in Table 1 were added in respective proportions (1), mixed in a methanol solution, and then dried.

This mixed powder was placed on a graphite plate and subjected to a nitriding reaction (1
350°C for 5 hours). The product was identified using the obtained silicon nitride powder X-ray diffraction method (40 KV, 100 mA), and the content of q-crystals and the amount of residual metal silicon were determined. Similar results were also obtained with a metal silicon powder bundle having a purity of 99.5%. In the case of the present invention, the production rate of β-type silicon nitride is 3 wt% or less, and if the production method of type silicon nitride is used, α-type silicon nitride with a content of 90 parts by weight or more is produced at a temperature below the melting point of metallic silicon. It is thermoeconomically advantageous, inexpensive, and improves industrial productivity.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between the amount of additives added and the reaction rate of the present invention, and Figure 2 is a powder X-ray diffraction diagram of α-type silicon nitride obtained with Nol in Table 1. , the horizontal axis is the diffraction angle (2θ)
, the vertical axis indicates the X-ray diffraction intensity.

Claims (1)

[Claims] 1. A method for producing α-type silicon nitride, which comprises nitriding a mixture of metallic silicon powder to which 0.01 to 10 parts by weight of at least one of vanadium and vanadium compounds is added at a temperature below the melting point of metallic silicon. .