JPS6144708A - Production of fine silicon carbide powder - Google Patents

Abstract

PURPOSE:To obtain efficiently fine silicon carbide powder of high purity in a short time, by heat-treating fine powder prepared by reacting an alkoxysilane compound in the vapor phase in a nonoxidizing atmosphere. CONSTITUTION:An alkoxysilane compound expressed by the formula (R is chlorine, bromine, iodine, hydrogen, alkyl, allyl or phenyl; R' is alkyl, allyl or phenyl; n is 0, 1, 2 or 3), e.g. tetramethoxysilane or dimethyldimethoxysilane, is prepared. The resultant alkoxysilane compound is then preheated in a preheater and gasified, and the formed gas is mixed with a nonoxidizing gas, e.g. Ar or N2, introduced into a reaction tube and reacted in the vapor phase at about 800-1,500 deg.C. The formed fine powder is then cooled and collected. The resultant fine powder is heat-treated at about 1,350-1,850 deg.C in a nonoxidizing atmosphere, e.g. hydrogen or argon, and crystallized to afford the aimed fine silicon carbide powder.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for producing fine silicon carbide powder. More specifically, the general formula is RnSi(OR')*-r+
(In the formula, R is chlorine, bromine, iodine, hydrogen, an alkyl group,
represents an allyl group or a phenyl group, R' is an alkyl group,
The method is characterized by heat-treating fine powder obtained by gas-phase reaction of an alkoxysilane compound represented by an allyl group or a phenyl group (n is 0, 1.2 or 3) in a non-oxidizing atmosphere. This invention relates to a method for producing fine silicon carbide powder.

[Industrial application field]

Silicon carbide is a material with properties such as high temperature stability, high strength, and high thermal conductivity, and is widely used in nuclear energy materials, chemical equipment, high temperature gas processing, electric heating elements, electronic resistors, etc. Among these materials, they are particularly useful as high-temperature structural materials, and are being developed as materials that play an important role in saving energy and resources.

When used in these applications, the strength of the material is determined by the density of the material itself, and the size of the defective pores present within the material influences the strength of the material.

Therefore, there is a strong demand for such materials that do not have large defective pores and form a dense and homogeneous structure, and in particular, there is a demand for higher quality raw material powders. .

[Conventional technology]

Traditionally, silicon carbide powder has been produced by carbon reduction of silica or other methods, but both methods reduce the particle size.
However, it was difficult to obtain excellent properties due to the variation in particle size and shape.

In order to improve this point, it has been proposed to add silicon nitride, silicon carbide, etc. as a third component in addition to silica and carbon.

However, this method is not economically preferable because the third component used is more expensive than the main raw materials, silica and carbon.

[Means for solving problems]

The present inventors conducted intensive research on obtaining β-type silicon carbide by heat-treating fine powder obtained by gas-phase reaction of an alkoxysilane compound in a non-oxidizing atmosphere in the process of manufacturing silicon carbide powder.

As a result, an amorphous fine powder was obtained by performing a gas phase reaction of the alkoxysilane compound in a non-oxidizing atmosphere such as argon, helium, hydrogen, nitrogen, ammonia, etc., and the fine powder obtained by the above method was further non-oxidized. The present invention was completed based on the discovery that β-type silicon carbide crystalline powder can be obtained by crystallization in a hostile gas atmosphere.

That is, according to the present invention, the fine powder obtained by the gas phase reaction is considered to be a mixture of amorphous silicon dioxide and amorphous carbon, as seen in the reaction formula of formula 1, but the powder is less than 0.5 μm. It is considered to be a spherical substance containing an extremely uniform mixture of carbon and silicon dioxide.

RnSi(OR')4-n-→SiO2+ C Formula 1 Therefore, in the case of the method of the present invention, the step of making silicon dioxide powder and carbon powder into fine powder and the step of uniformly mixing them as in the conventional method is not necessary. In addition, since the fine particles are uniformly mixed, fine silicon carbide powder can be obtained without mixing a third component and with a shorter crystallization time than in the conventional method.

Moreover, since the raw materials can be easily produced by operations such as distillation, the products obtained by the method of the present invention are of extremely high purity.

(Summary of the Invention) In the method of the present invention, the following organic silicon compounds are used as raw materials.

The general formula is RnSi(OR')4-J, where R represents chlorine, bromine, iodine, hydrogen, an alkyl group, an allyl group, or a phenyl group, and Ro represents an alkyl group, an allyl group, or a phenyl group, n is 0.1.2 or 3), examples thereof include tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, trimethylmethoxysilane, dichlorodimethoxysilane, etc. .

These raw materials are purified to extremely high purity by conventional distillation or the like. Furthermore, when supplying to a gas phase reaction, two or more of these raw materials may be mixed. In addition, these raw materials are gasified in advance and introduced into the reaction tube, and at the same time ^rS
It is supplied mixed with a non-oxidizing gas such as HeSNz, H2 and ammonia.

Non-oxidizing gases are important for changing the partial pressure of raw materials in the reaction and controlling the reaction time.

In the method of the present invention, the reaction temperature is 800°C to 1500°C.
It is appropriate to select within the range of 800°C, and when the temperature is lower than 800°C, the reaction progresses insufficiently, resulting in a low production amount.
On the other hand, if the temperature exceeds 1500° C., it is not economical due to equipment restrictions and a large amount of energy required. The partial pressure of the raw material gas and the reaction time are determined by considering the particle size and yield of the product, but the raw material partial pressure is 0.01 to several atm and the reaction time is 120 to 0.01 sec. is preferred. If the raw material partial pressure is lower than these values and the reaction time is long, the reactor will be large-sized, which is industrially disadvantageous.

On the other hand, if the partial pressure is high and the reaction time is short, the reaction may not proceed or the amount of carbon in the product may increase, which is not preferable.

For example, if the raw material is a liquid, a predetermined amount of liquid is introduced into a preheater and gasified, mixed thoroughly and uniformly with a predetermined amount of non-oxidizing gas, and then heated externally. Lead to the reaction tube of the formula. The type of reaction tube used is either an empty column or a packed column type, but it is important to have a structure in which the gas flow is not pulsating or irregular and is heated evenly in order to obtain uniformity of the fine powder produced. It is. After cooling, the generated fine powder is guided to a collector and collected. As the collector in this case, a commonly used filter type dust collector, electric dust collector, cyclone, etc. can be appropriately used.

The resulting fine powder obtained in this way is amorphous with no peak observed in X-ray diffraction, and has a uniform particle size of 0.5 μm.
These are the following spherical particles.

The carbon content of this fine powder is 37.5% to 50% by weight.
is preferred.

If the carbon content is too low, unreacted silicon dioxide bones may remain,
Formation of silicon oxynitride is observed. Although there is no particular disadvantage if the carbon content is large, it is economically unfavorable.

In addition to controlling the reaction temperature and partial pressure, the following methods can be used to adjust the amount of carbon. The first method is when the carbon content of the alkoxysilane compound is small (for example, in the case of tetramethoxysilane or methyltrimethoxysilane), the raw materials are hydrocarbons such as benzene and hexane, and halogens such as chloroform and methylene chloride. Method of adding hydrogenated hydrocarbon compounds. As a second method, when the carbon content of the alkoxysilane compound is large, the carbon content can be adjusted by introducing ammonia or the like together with Ar or the like in a gas phase reaction.

The atmosphere used during crystallization is a non-oxidizing gas such as hydrocarbon, carbon oxide, argon, hydrogen, nitrogen, or ammonia. The temperature during crystallization is 1350 to 1850°C in an atmosphere of carbon monoxide and argon (1550 to 1850°C in the case of nitrogen and ammonia gas), preferably 1400 to 1700°C.

It should be noted that if the firing temperature is less than 1350°C, it will be difficult to generate silicon carbide, and if the firing temperature exceeds 1850°C, grains will grow and it will not be possible to make them fine, which is not preferable.

In addition, if the non-oxidizing atmosphere is nitrogen or ammonia gas, silicon nitride will be generated at temperatures below 1550°C.
It is necessary to bake at a temperature higher than .

The firing time varies depending on the degree of crystallinity, but is usually 0°5-5.
It's time. There are no particular restrictions on the specific method of carrying out the calcination, and a method may be used in which the product is filled in a crucible or a flow reaction tube and an inert gas is passed through it.

Furthermore, if the amount of carbon is excessive, unreacted carbon powder remains, but it can be removed by oxidizing the carbon at 600 to 850° C. in an oxidizing atmosphere after firing.

The crystalline silicon carbide fine powder obtained in this way is
No formation of iO□ or Si is observed, and it has an extremely high β phase.

The method of the present invention will be explained in more detail below with reference to Examples, but the method of the present invention is not limited to these Examples.

〔Example〕

Example 1 Using a device consisting of a high-purity alumina reaction tube with an inner diameter of 25 mm and a length of 7° Qmm installed in an electric furnace and a collector attached to the outlet of the reaction tube, the temperature of the electric furnace was raised to 1200°C. held. 5i (OEt), which has been gasified in advance with a preheater
)4 and Ar (volume ratio 1:20) were thoroughly mixed and then introduced into the reaction tube.

The product powder obtained in the collector was amorphous according to X-ray diffraction, and was spherical particles with a particle size of 0.2 microns or less.

Next, this product was filled into an alumina tube and heat treated at 1600° C. for 2 hours under an argon atmosphere.

Unreacted carbon was removed by heat treatment at 800° C. for 13 hours in air. The obtained fine powder was determined by X-ray diffraction to be β-3iC.
It was a massive crystal particle of 0.3 microns or less.

Example 2゜Example 1. Various organic silicon compounds were reacted using the same experimental method. The experimental conditions and the results obtained are shown in Tables 1 and 2.

Procedural amendment May 8, 1985

Claims (1)

[Claims] The general formula is RnSi(OR')_4_-_n (wherein R represents chlorine, bromine, iodine, hydrogen, alkyl group, allyl group, or phenyl group, and R' represents an alkyl group, allyl group, or phenyl group. , n is 0, 1, 2, or 3) A method for producing fine silicon carbide powder, characterized by heat-treating fine powder obtained by gas-phase reaction in a non-oxidizing atmosphere.