JPH03360B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing silicon carbide whiskers, and particularly to a method for producing whiskers useful as reinforcing materials for various composite materials.

BACKGROUND ART Silicon carbide whiskers have excellent heat resistance, oxidation resistance, and high strength, so they are combined with metals, ceramics, resin materials, etc. to produce various composite materials.

As a method for producing such silicon carbide whiskers, there is a method of mixing the ash residue of grasses with carbon black and treating the mixture at high temperature in a non-oxidizing atmosphere (Japanese Patent Application Laid-open No. 57-209813). There are problems in that heat treatment is required and purity is low.

In addition, a method for vapor-phase thermal decomposition of organosilicon compounds having no silicon-halogen bonds using metal or metal compound fine particles as a seed catalyst (Japanese Unexamined Patent Application Publication No. 1989-1999-
9220), but it has the disadvantage that the seed catalyst is not easy to prepare and its purity is also low.

PROBLEM TO BE SOLVED The present invention provides an economical method for producing high purity silicon carbide whiskers having a shape suitable as reinforcement for composite materials, which could not be obtained using prior art techniques. This is what we are trying to provide.

Means for Solving the Problems The method for producing silicon carbide whiskers of the present invention, which can achieve the above object, uses an organosilicon compound or a mixture of an organosilicon compound and a hydrocarbon compound as a reducing compound containing a sulfur compound. Or, in gas phase pyrolysis at high temperature in the presence of an inert carrier gas, the molar ratio of silicon to carbon in the system is
It is characterized by being 0.1 to 2.

As the organosilicon compound used as a raw material in the present invention, silanes or siloxanes having a silicon-carbon bond are used. Among these, examples of silanes include alkyl-substituted silanes such as triethylsilane, tetraethylsilane, and hexamethyldisilane, alkoxy-substituted silanes such as tetramethoxysilane and tetraethoxysilane, and aromatic substituted silanes. Examples include hexamethyldisiloxane, dimethylpolysiloxane, and methylphenylpolysiloxane. In addition, silanols such as trimethylsilanol, alkoxy-substituted siloxanes, etc. can also be used, and mixtures or derivatives of these can also be used as long as they can be gasified.

In the present invention, the hydrocarbon compound used as a raw material by mixing with an organosilicon compound is methane,
Aliphatic hydrocarbons such as ethane and propane, and aromatic hydrocarbons such as benzene and toluene are used, but other elements such as oxygen may be included in small amounts.

The sulfur compounds used in the present invention behave as catalysts, such as hydrogen sulfide, methyl mercaptan, ethyl mercaptan,
Mercaptans such as toluenethiol, or thioethers such as diethyl sulfide and thiophene can be used. When the sulfur compound is an organic sulfur compound, it can be used in place of part or all of the aforementioned hydrocarbon compound as a raw material. Further, when the sulfur compound is an organic compound containing silicon, it can be used in place of at least a part of the above-mentioned organosilicon compound as a raw material. Examples of such catalysts include γ-
Examples include mercapto-modified silanes such as mercaptopropyl-trimethoxysilane and mercapto-modified polysiloxanes.

The carrier gas used in the present invention is a reducing or inert gas, and examples thereof include hydrogen, nitrogen, and argon, among which hydrogen is preferably used.

In the present invention, an organosilicon compound or a mixture of this and a hydrocarbon compound as a raw material is sent to a high-temperature reaction zone together with a catalyst by a carrier gas, and at this time, the silicon and carbon contained in the reaction gas are It is necessary that the molar ratio is 0.1-2. That is, when the molar ratio is lower than 0.1, black carbonaceous whiskers are produced, and silicon carbide whiskers with good purity cannot be obtained. Furthermore, if the molar ratio exceeds 2, a large amount of powdered silicon carbide or silica is produced, and silicon carbide whiskers with good purity cannot be obtained.

There is no particular limit to the amount of sulfur compound used as a catalyst, but if it is too small, the yield of whiskers will decrease, and if it is too large, it will limit the concentration of the raw material. It is preferable to use an effective amount of 1 or less in molar ratio.

The thermal decomposition reaction in the present invention is carried out at 1100-1500°C, preferably 1200-1400°C. As an apparatus for this purpose, for example, a horizontal electric furnace equipped with a heat-resistant reaction tube made of alumina or the like can be used, but the apparatus is not necessarily limited to such an apparatus.

Example 1 Hydrogen containing 3% by volume hydrogen sulfide was supplied as a catalyst at a rate of 200 c.c./min to an electric furnace equipped with a reaction tube with an inner diameter of 70 mm and a length of 1000 mm, and tetramethyl was supplied as a raw material. Disiloxane and benzene were mixed so that the Si/C molar ratio was 0.3, and this was added to the evaporation section of the reaction tube (temperature 150
°C). The vaporized raw material mixed with the carrier gas in this way is thermally decomposed at a temperature of 1300℃ in the reaction tube, and after 2 hours of reaction, the material has a length of 3cm and an average diameter of 0.5μ.
0.2 g of white silicon carbide whiskers were obtained.

Example 2 The same equipment as in Example 1 was used, and the same procedure as in Example 1 was carried out for 2 hours, except that a mixture of hexamethyldisilazane and benzene with a Si/C molar ratio of 0.3 was used as the raw material. The reaction resulted in white silicon carbide whiskers with a length of 3 cm and an average diameter of 0.5 μm.
0.1 g was obtained.

Effects of the Invention According to the method for producing silicon carbide whiskers of the present invention, silicon carbide whiskers that are white, that is, of high purity and have a length suitable for use as a reinforcing material for composite materials can be efficiently obtained, and the growth of the whiskers at that time is achieved. The speed is extremely fast, reaching 0.8 mm per minute, and has the advantage that sufficiently grown whiskers can be produced even if the residence time of the whiskers in the reaction zone is short.

Claims (1)

[Claims] 1. In gas-phase pyrolysis of an organosilicon compound or a mixture of an organosilicon compound and a hydrocarbon compound at high temperature in the presence of a reducing or inert carrier gas containing a sulfur compound, A method for producing silicon carbide whiskers, characterized in that the molar ratio of silicon to carbon therein is 0.1 to 2. 2. The method for producing silicon carbide whiskers according to claim 1, wherein the thermal decomposition temperature is 1100 to 1500°C.