JPH0331679B2 - - Google Patents

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to the production of silicon carbide whiskers.

(Prior art and its problems) Silicon carbide whiskers are defect-free single crystals grown in the form of fibers and have very high tensile strength and elastic modulus, and are used in composite materials, especially at high temperatures. It is expected to be used as a material for metal or ceramic composite materials.

Methods for producing silicon carbide whiskers include: (1) using silicon dioxide as a silicon source and reacting it with carbon material by heating in an inert gas stream; (2) using a silicon compound such as tetrachlorosilane or tetramethylsilane; , vapors of carbon compounds such as methane, propane, and carbon tetrachloride are transported by a hydrogen stream to a reactor in a high-temperature atmosphere, reacted in the gas phase, and then precipitated in a low-temperature section downstream of the reactor. (3) A method of reacting metallic silicon with a carbon source is known.

These methods have drawbacks such as the production of many granular crystals as a by-product and the fact that the yield of whiskers is low considering the reaction time because the reaction is a gas phase reaction.

(Means for Solving the Problems) The present invention provides a method for producing silicon carbide whiskers that does not have the above drawbacks.

According to the present invention, a mixture in which amorphous silicon nitride powder is blended with a specific amount of an additive selected from iron, nickel, cobalt, and their compounds, or a mixture in which carbon is further blended with monoxide. A method for producing silicon carbide whiskers is provided, which is characterized by firing in a non-oxidizing gas atmosphere containing carbon and/or carbon dioxide.

The amorphous silicon nitride powder used in the present invention can be obtained by a method known per se, for example, by heating a reaction product obtained by reacting silicon tetrahalide and ammonia in a liquid phase or a gas phase. It is a so-called amorphous powder that does not show any clear diffraction phenomenon in ordinary X-ray diffraction.

As the iron compound, nickel compound, and cobalt compound, those that at least partially decompose during firing to produce iron, nickel, and cobalt, respectively, can be used.
Those that decompose into nickel or cobalt are preferred. Specific examples thereof include oxides, halides, sulfides, and oxyhalides of iron, nickel, and cobalt, and alloys containing iron, nickel, or cobalt as one component. The amount of additives is
0.05 metal equivalent per 100 parts by weight of silicon nitride powder
~10 parts by weight, preferably 0.1 to 2 parts by weight.
If the blending amount of the additive is out of the above range, the yield of whiskers will decrease.

There are no particular restrictions on the form of carbon that may be used in the present invention, and it may be in the form of powder or lumps, but fine powder carbon is preferred. When carbon is used, carbonization of amorphous silicon nitride is promoted, allowing firing at a lower temperature. The amount of carbon used is 3 times or less by mole based on the raw material silicon nitride powder. If the amount of carbon used is outside the above range, a decarburization step after firing will be required.

There are no particular restrictions on the method for preparing the mixture of amorphous silicon nitride powder, additives, and optionally carbon, and methods known per se may be used, such as dry mixing of each raw material, or mixing of each raw material in an inert liquid. A method of removing an inert liquid after wet mixing may be adopted as appropriate. As the mixing device, a V-type mixer, a ball mill or a vibrating ball mill is preferably used. Another method for preparing the above mixture is to mix and disperse additives and optionally carbon into a precursor of amorphous silicon nitride powder, such as silicon diimide or silicon tetraamide, and then heat-treat the dispersion. You can also do that. Each of these preparation methods requires handling under a controlled inert atmosphere since amorphous silicon nitride and its precursors are extremely sensitive to oxygen and water.

Specific examples of the non-oxidizing gas constituting the non-oxidizing gas atmosphere during firing include nitrogen, argon, ammonia, or a mixed gas thereof. The ratio of carbon monoxide and/or carbon dioxide to non-oxidizing gas is preferably 1:0.5 to 2 by volume.

The firing conditions are such that the mixed powder is heated from 1000℃ to the maximum temperature for several seconds to several tens of hours, preferably for 1 to 10 hours.
It is desirable to select conditions that allow the temperature to rise in 20 hours. The maximum temperature is usually below 1900°C, preferably below 1650°C.

There are no particular restrictions on the furnace used for firing the mixed powder, and for example, batch type furnaces, rotary furnaces, fluidization furnaces, pusher furnaces, etc. using a high frequency induction heating method or resistance heating method can be used. .

(Example) Examples are shown below.

Example 1 5 g of amorphous silicon nitride powder obtained by thermally decomposing silicon diimide at 1200° C. and 0.02 g of iron sulfide were placed in a vibrating ball mill under a nitrogen atmosphere and mixed for 1 hour. The mixture was placed in a graphite crucible with an inner diameter of 40 mm and an inner volume of 50 c.c., and the crucible was set in a resistance heating furnace. The above crucible was heated from room temperature to 1650℃ for 250℃ in a mixed gas atmosphere with a ratio of nitrogen and carbon monoxide of 1:1.
The temperature was raised at a rate of 1650° C./min and further maintained at 1650° C. for 5 hours.

When the obtained silicon carbide powder was examined by X-ray diffraction, the crystal form was mainly β type, with a slight α type observed. When observed using a scanning electron microscope, it was in the shape of a whisker with a length of 10-20μ and a diameter of 0.1-2μ.

Example 2 The same method as in Example was repeated except that 0.02 g of iron powder was used instead of iron sulfide.

A whisker-like silicon carbide powder having a length of 10 to 20 μm and a diameter of 0.1 to 5 μm was obtained.

Example 3 The same method as in Example was repeated except that 0.02 g of nickel chloride was used instead of iron sulfide.

A whisker-like silicon carbide powder having a length of 10 to 40 μm and a diameter of 0.1 to 2 μm was obtained.

Example 4 The same method as in Example was repeated except that 0.02 g of cobalt sulfide was used instead of iron sulfide.

A whisker-like silicon carbide powder with a length of 10 to 20 μm and a diameter of 0.1 to 2 μm was obtained.

Example 5 The same method as Example 1 was repeated except that carbon dioxide was used instead of carbon monoxide.

The obtained crystals are β-type and a small amount of α-type silicon carbide whiskers, with a length of 5 to 10μ and a diameter of 0.1
It was ~1μ.

Example 6 0.96 g of activated carbon was added to the mixture in Example 1.
The mixture containing the following was treated in the same manner as in Example 1 except that the firing temperature was changed to 1600°C.

The obtained crystals are β-type and a small amount of α-type silicon carbide whiskers, with a length of 5 to 10μ and a diameter of 0.1
It was ~1μ.

Comparative Example 1 The same method as in Example 1 was repeated except that 1 g of powdered carbon was used instead of iron sulfide.

When the obtained silicon carbide powder was observed with a scanning electron microscope, it was found to be granular silicon carbide.

Claims (1)

[Scope of Claims] 1 A mixture of 100 parts by weight of amorphous silicon nitride powder and 0.05 to 10 parts by weight of an additive selected from iron, nickel, cobalt, and their compounds in terms of metal is mixed with carbon monoxide. and/or a method for producing silicon carbide whiskers, characterized by firing in a non-oxidizing gas atmosphere containing carbon dioxide. 2 Additives selected from iron, nickel, cobalt, and their compounds are added to 100 parts by weight of amorphous silicon nitride powder in an amount of 0.05 to 10 parts by weight in terms of metal, and the amount is three times that of the amorphous silicon nitride. A method for producing silicon carbide whiskers, which comprises firing a mixture containing less than a molar amount of carbon in a non-oxidizing gas atmosphere containing carbon monoxide and/or carbon dioxide.