SiO_2とCから合成されるSiCウィスカーの成長機構

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Synthesis reactions of SiC whiskers from silica and carbon were studied. Blended raw materials containing silica, carbon, and catalysis were heated to a temperature from 1300°to 1500℃ in a stream of hydrogen. The obtained SiC whiskers had diameters from 0.3 to 0.5 micron and lengths from 10 to 100 micron. The SiC whiskers were beta-type silicon carbide. Total yield of the whiskers based on quantities of Si in the raw materials ranged from 92 to 95%. Scanning electron microscopic analysis revealed that SiC whiskers grew by the VLS process in which materials were transported through the vapor phase. It is considered that Si atoms transferred as SiO (g) and C atoms as hydrocarbon such as CH_4 and C_2H_2. Rate-determining steps of the whisker synthesis reaction were analyzed by measuring the volume of CO(g) generated as a function of reaction time. Depending on the reaction time, the rate-determining step varied from one to the other. The first step is the removal of CO (g) from the reaction system, because the reaction rate under a given experimental condition remained constant during the first stage and the reaction rate in this stage increased with an increase in hydrogen flow rate. The reaction rate in the second stage decreased with time and gave good agreement with Mampel's reaction rate equation (phase boundary controlled reaction) . The activation energy derived from the rate constant of the Mampel's equation was approximately 20 kcal/mol. Therefore, the second rate-determining step was considered to be the formation of hydrocarbons on surface of car bon raw materials.
社団法人日本セラミックス協会の論文
1989-12-01

SiO_2とCから合成されるSiCウィスカーの成長機構

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