Silicon carbide (SiC) is strong at a high temperature and excellent in creep resistance and resistance to abrasiveness, oxidation, and corrosion, etc. Silicon carbide is present in a β phase having a cubic crystal structure and in an α phase having a hexagonal crystal structure. The β phase is stable in a temperature range of 1400-1800° C., and the α phase is stable above 2000° C.
Silicon carbide is widely used as an industrial structural material and has been applied in the semiconductor industry recently. For this reason, a high-purity silicon carbide powder which is stable at a high temperature is desired.
A silicon carbide powder may be prepared by, for example, an Acheson method, a carbothermal reduction method, a chemical vapor deposition (CVD) method, etc. According to the Acheson method, an α-phase silicon carbide powder may be obtained by carbothermal reduction of a silicon source and a carbon source at a high temperature (e.g., 2200° C. to 2400° C.). However, since the silicon carbide powder prepared according to the above method is low in purity, an additional purification process is required.
In contrast, a high-purity silicon carbide powder may be obtained by synthesizing a purified material at a relatively low temperature. However, the β-phase silicon carbide fine powder is easily obtained at a low temperature, which causes instability at high temperatures.
On the other hand, β-phase silicon carbide has a lower vapor pressure than α-phase silicon carbide. Thus, β-phase silicon carbide evaporates and agglomerates into α-phase silicon carbide powder when the β-phase silicon carbide powder is heat treated at a high temperature. In this case, there are problems in that the β phase and the α phase coexist when the heat treatment time is short, and although the high-purity α-phase silicon carbide powder may be obtained when the heat treatment time is long, granules grow to a size greater than hundreds of micrometers.
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