Papers by Keyword: Silicification

Abstract: A route based on a technique of polymerization - induced phase separation and pyrolysis (PIPSP) has been developed to fabricate complex-shaped SiC parts. The capability of this process to produce complex component shapes has been demonstrated, and corresponding reactive mechanisms have been also discussed. Three types of porous carbon preforms, i.e. mesoporous carbon monoliths (MCMs), hierarchical porous carbon monoliths (HCMs) and porous carbon foam (PCFs) were obtained, which has different pore size distributions. The pore structures of the preforms can be controlled through changing starting mixture composition and polymerizing conditions. The apparent porosity of the preform was changed from 19.9 to 60%, which was a key parameter to obtain dense SiC parts. After reactive infiltration of the preform with Si, the SiC parts were obtained. Geometry of SiC parts were controlled by molds. The dimension shrinkage of SiC parts was less than 3% before/after siliconization and no distortion occurred. Compared with other molds assistance route, the wax mold assistance route was a most potential technique to fabricate SiC parts industrially because of its suitable forming precision, recycled mold materials and low-cost. The mechanism of the reactive infiltration of MCMs was different from that of the reactive infiltration of preforms with bigger pore size, i.e. the pore channels of MCMs were restructured at transitional stage of reaction.

Abstract: A thin film including β-silicon carbide was synthesized by a reaction of silicon monoxide gas and carbon source derived from polyimide film (PIF) at 1400°, 1500°, 1600°, 1700° and 1800°C. Formation mechanism of the SiC film was investigated thermodynamically and kinetically through the relationships among the conversion ratio of SiC, synthesis temperature and time. The formation processes were simulated based on the calculation of differential equations concerning thermodynamic and kinetic constants of 7 chemical equations. The sample obtained had a film shape similar to that of the carbon source film. The results of the time dependence curves of the conversion ratio of SiC calculated from 7 chemical equations, 14 rate constants, 2 diffusion constants, 10 chemical species and 10 differential equations are in good agreement with the experimental results of the SiC conversion ratio as a function of synthesis time. The calculation results of solving each constant suggest that the formation processes of SiC are "rate-controlled reaction at the interface" at the initial stage of the reaction, and then they gradually change to "diffusion-controlling reaction in the reacted region". In the long term synthesis, we recognized that the waste SiO with non-stoichiometric oxygen can also be used as a silicon source.