JPS60221310A - Production of silicon nitride powder - Google Patents

Abstract

PURPOSE:To produce silicon nitride powder suitable to members for high temp. and high stress with high purity and fine and uniform particle size distribution by heating a compsn. contg. a specified silicon oxide and single substance carbon in an atmosphere of a gaseous N-contg. compd. CONSTITUTION:Air from a duct 2 of a furnace 1 and fuel for the hot air (e.g. propane) from a burner 3, are fed and burnt to generate hot gas contg. steam. On one hand, a decomposable Si compd. expressed by the formula: SinX2n+2 (where X is H or halogen; n is 1-4) is mixed with a decomposable C compd. (e.g. heavy oil A) with a proportion <2.5 of C/Si. The mixture is charged into said hot gas in the furnace 1 from a nozzle 4 to generate a highly uniform and fine aerosol mixture contg. Si oxide and single substance carbon. The dispersed material is discharged from a duct 5 and a carbonaceous compsn. is collected. The collected compsn. is then compressed to >=0.2g/cc bulk density, which is heated at 1,300-1,500 deg.C in an atmosphere of N-compd. contg. gas (e.g. N2) in a W high frequency heating furnace to obtain the titled powder.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing silicon nitride powder, and more particularly, to a method for producing silicon nitride powder that is highly pure, fine, and has a uniform particle size distribution.

Since silicon nitride sintered bodies have excellent heat resistance and high mechanical strength, attempts have been made in recent years to apply them to high-temperature, high-stress members. In order to apply silicon nitride sintered bodies to these parts, chemical stability and physical stability at high temperatures are important.

In particular, physical stability such as heat resistance and mechanical strength are
Since silicon nitride powder, which is the raw material, is highly pure, it is desired to have high purity, fine particles, and uniform particle size.

Conventionally, the following method is generally used to produce silicon nitride powder.

(1) Method of nitriding metal silicon powder 3S+ + 2N2. □5i3Nlf (2) Method 3 of reacting silicon tetrachloride or silane with ammonia in the gas phase 3 S iCl++ 4NH3-→S +BN or +12
HCI (3) Method 3 of nitriding silica in the coexistence of carbon S i OL+6 C+21%-→5IBNIt-
However, since the silicon nitride obtained in method (1) is coarse particles, a pulverization step is required, and there is a drawback that impurities are inevitably mixed in due to wear of the pulverizer itself during pulverization. Method (2) has a low yield and is not suitable for industrial production. Method (3) is a method in which silica and carbon are mechanically mixed using a ball mill, etc., and then nitrided. Therefore, it is important to avoid contamination with impurities during the mixing process, and the work environment is affected by the generation of dust. The problem is serious, and furthermore, the generation of coarse particles, which is presumed to be caused by non-uniform mixing, is unavoidable.

The inventors of the present invention conducted various studies to solve these problems, and as a result, we first produced a composition containing silicon oxide and elemental carbon with a sufficiently high uniformity and fine particle size. By heating in a nitrogen-containing compound gas atmosphere,
We have developed a technology to produce the desired high-purity and fine silicon nitride.

That is, in the present invention, a decomposable silicon compound and a decomposable carbon compound are charged into hot gas containing water vapor to generate a mixed aerosol containing silicon oxide and elemental carbon, and this dispersoid is collected. This invention is a method for producing silicon nitride, characterized in that a carbon-containing composition is compressed to a bulk density of 0.2 sh/cc or more and heated in a nitrogen-containing compound gas atmosphere.

The present invention will be explained in detail below.

The mixed aerosol used in the present invention refers to a mixture of silicon oxide and elemental carbon as a solid substance in a gas. The silicon oxide and elemental carbon in the present invention can be obtained by thermally decomposing, oxidizing, hydrolyzing, etc. a decomposable silicon compound and a decomposable carbon compound in a hot gas containing water vapor.

The resulting mixture of silicon oxide and elemental carbon is much more uniform and fine than conventional mechanical mixing, and can be obtained continuously, reducing the generation of dust and the contamination of impurities. There are no such problems.

To explain the present invention in more detail, first, an aerosol of elemental carbon can be easily obtained by charging a decomposable carbon compound into hot gas. On the other hand, aerosols of silicon oxide can be obtained by pyrolysis, oxidation or hydrolysis when a decomposable silicon compound such as silicon tetrachloride is introduced into a hot gas containing water vapor. By simultaneously charging a carbon compound and a silicon compound into hot gas containing water vapor in this manner, a mixed aerosol containing silicon oxide and elemental carbon can be easily obtained.

The decomposable silicon compound used in the present invention has the general formula S
It is expressed as in
13, S iH Yu, S i, He, (CH U) 4 S
r, (Q(3%SiC11, Cl13S i C1
3, S i F4, etc. The decomposable carbon compound is preferably a hydrocarbon that is in a gaseous or liquid phase at room temperature, or a hydrocarbon that can easily become a liquid phase by increasing the temperature, or a logenated hydrocarbon. Examples of hydrocarbons include petrochemical products such as methanol, ethanol, acetone, n-hexane, benzene, xylene, naphtha, propane, light oil, kerosene,
Petroleum oils such as heavy oil can be used, as well as refinery residues such as petroleum pitch, methyl oil, anthracene oil, and creosote, and petrochemical residues such as 9-distillate mixtures and ethylene bottoms.

Examples of halogenated carbons include chloroform, vinyl chloride, and chlorobenzene.

It is preferable to use a furnace to obtain the carbon-containing composition of the present invention. The heating device for the furnace is preferably a combustion burner, an energized heating element, etc., but is not particularly limited. The furnace is equipped with a charging nozzle for silicon compounds and carbon compounds, a hot air charging duct, and a mixed aerosol discharge duct, and preferably has a structure surrounded by refractories. FIG. 1 shows one example. Note that there must be a space area in the furnace that is at least 600°C or higher. At temperatures above this temperature, elemental carbon is obtained from the carbon compound, and silicon oxide is obtained from the silicon compound in an atmosphere containing water vapor, and a mixed aerosol, which is a mixture of gas and these solid substances, is generated. The proportions of silicon and carbon in the resulting carbon-containing composition can be adjusted simply by adjusting the amounts of the silicon compound and carbon compound charged into the hot gas from the nozzle.

As a method of obtaining hot gas containing water vapor, water vapor may be injected into hot gas obtained by an electric heating method, a high frequency heating method, or a discharge method, but water vapor can be produced by burning hydrogen, methane, propane, or butane. The method of burning the generated combustibles with air is simple and economical in terms of thermal efficiency. After the obtained mixed aerosol is guided out of the furnace, the solids contained therein are collected using a collection device such as a bag filter or Zyclone, but in order to reduce the heat load on the collection device, it must be cooled beforehand. This is desirable.

Cooling may be achieved by cooling the zone after the reaction or by injecting water into the aerosol.

The carbon-containing composition obtained as described above is heated at 1,300°C to 1,000°C in an atmosphere of a nitrogen-containing compound gas such as nitrogen gas or ammonia using a high-frequency heating furnace, an electric resistance furnace, or the like.
By heating at 500''C; the silicon nitride powder targeted by the present invention can be obtained.

In addition, in the present invention, in the step of heating in the nitrogen-containing compound atmosphere, the carbon-containing composition has a bulk density of 0.2
! It is necessary to heat after tightening to 7/cc or more. When the bulk density of the carbon-containing composition is less than this, silicon nitride that is produced tends to contain whisker-like substances. On the other hand, the bulk density is set to 0.2 Lj/cc in advance.
When tightened to the above level, silicon nitride that is fine and has a uniform particle size can be obtained. This is based on the experimental findings of the present inventors. In addition, tightening as used in the present invention means an operation to increase the bulk density, and can be easily carried out by compression, stirring granulation, etc.

The ratio of silicon and carbon in the carbon-containing composition is determined by the weight ratio (C/S
i) is preferably 2.5 or more.

This is because when C/Si is less than 2.5, the ratio of conversion to silicon-based silicon nitride in the carbon-containing composition is sharply reduced. However, if this ratio is made too large beyond this value, there is nothing to be gained and the result is only a mere loss of the carbon compound. If elemental carbon remains in the silicon nitride obtained as a result of carrying out the present invention, this carbon has an
It can be easily burned and removed by heating it to 800° C., and it can be easily carried out by heating it in air or by burning the fuel with excess air and placing it in a hot gas atmosphere containing oxygen.

The silicon nitride obtained as a result of implementing the present invention does not contain coarse particles and is already a fine powder with a uniform particle size, so there is no possibility of contamination with impurities, which has been a problem with conventional methods of pulverizing powder containing coarse particles. No problems at all. Although the details of why fine silicon nitride powder is easily obtained in the present invention cannot be clarified, it is likely that the mixed form of silicon oxide and carbon in the obtained carbon-containing composition itself is different from the conventional one. This is presumed to be because it is extremely uniform and fine.

The silicon nitride powder obtained in the present invention is a powder with high purity, fineness, and uniform particle size, and is suitable for use as a high-temperature, high-stress member, for example.

The present invention will be specifically explained below using Examples.

Note that all the numbers shown in Examples and Comparative Examples represent weight ranges.

Example 1 Using the furnace shown in FIG. 1, air was supplied from the duct 2 and propane was used as a hot air fuel from the combustion burner 3.]
The mixture was charged at a flow rate of 00 Nm/i (r, 3 N m'/I-1r), and heavy oil as a carbon compound and 8iCl+ as a silicon compound were mixed in advance at a weight ratio of 1.5:1.0. Nozzle 4 with a flow rate of 25k17/■4
It was then charged into the furnace. The combustion zone was maintained at a temperature of approximately 1200°C.

The aerosol produced in the furnace was cooled and collected with a bag filter to obtain a carbon-containing composition of 8.9 kg/h. The carbon-containing composition contained 39.4% silicon dioxide and 60.9% carbon.

The bulk density of the carbon-containing composition of the present invention taken out from the bag filter was 0.09 g/cc.

To tighten the material, put this 30 liters in a cylindrical container and compress it uniaxially.
．． After achieving a bulk density of 38 g/Cc, N was heated using a high frequency furnace.
Heated at 1400°C for 8 hours in 2 atmospheres, then heated in air for 7 hours.
9. Heat to 00°C and burn off remaining elemental carbon.
A powder of Oq was obtained. As a result of X-ray diffraction, the obtained powder was α-
It was confirmed that it was 8i3N4t. As a result of electron microscopic image analysis, the average particle size was 0.15 μI11, and the particle shape was spherical with a uniform particle size distribution.

Examples 2 to 4 Using methane and hydrogen in addition to propane as hot air fuel,
Carbon-containing compositions having the compositions shown in Table 2 were obtained in the same manner as in Example 1 using the silicon compounds and carbon compounds shown in Table 1, respectively. The obtained carbon-containing composition was prepared in Example 1.
After compressing and tightening in exactly the same manner as above, heating was performed using NH3 gas in addition to N as the nitrogen-containing compound at the temperatures and times shown in Table 1 to obtain powder. As a result of X-ray diffraction, it was confirmed that all of the obtained powders contained 3% α-8i. As a result of electron microscope image analysis, the average particle size was
The particle shapes were all spherical with uniform particle size distribution according to the values shown in the table.

Comparative Example 1 The carbon-containing composition 6 obtained in Example 1 had a bulk density of 0.0.
Except for heating with 977cc as it is, the same procedure as in Example 1 was carried out with N2. The mixture was heated in an atmosphere at 1400°C for 8 hours, and further heated in air at 700°C to burn off the remaining elemental carbon to obtain a powder of 1.7!7. The obtained powder was confirmed to be α-8i3N9 as a result of X-ray diffraction.

As a result of electron microscopic observation, the particle shape was whisker-like and thick.

Comparative Example 2 Ecosil 39.19 with a specific surface area of 2 oom/9 and carbon black 60.99 with a specific surface area of 120 m/g were mixed using a ball mill to have the same composition as the carbon-containing composition obtained in Example 1. Mixed for an hour. This 30 pieces were placed in a cylindrical container and uniaxially compressed to give a bulk density of 0.38 VCc, and then heated and elemental carbon was removed under exactly the same conditions as in Example 1 to obtain 8.8 g of powder. As a result of X-ray diffraction, the obtained powder was confirmed to be α-8i, 3N. However, as a result of electron microscopic image analysis, the average particle diameter was 0.77 μm, and many coarse particles of 1 μm or more were observed, and the particle size had a wide distribution.

Table 1 Published 1

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing one example of a furnace used in carrying out the present invention. In the drawing, 1...furnace material 2...duct 3...combustion bar 4...nozzle 5...duct is shown. Patent applicant Mitsui Toatsu Chemical Co., Ltd.

Claims (1)

[Claims] (1) A carbon-containing mixture obtained by charging a decomposable silicon compound and a decomposable carbon compound into hot gas containing water vapor to generate a mixed aerosol containing silicon oxide and elemental carbon, and collecting this dispersoid. A method for producing silicon nitride powder, which comprises heating the composition in a nitrogen-containing compound gas atmosphere while compressing the composition to a bulk density of 0,2q,/Cc or higher.