N_2ガス流通下でのSiO_2-Al_2O_3粉末混合物の熱炭素還元

概要

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SiC-AlN powder mixture was prepared by heating a silica-alumina-graphite powder mixture in flowing nitrogen at temperatures between 1773 and 1973K. The reaction mechanism of the carbothermic reduction and nitridation has been both thermodynamically and kinetically investigated. The reaction rates were determined according to thermol balance and the reaction products were examined by X-ray diffraction. SiO_2 was initially reduced into SiC and subsequently Al_2O_3 was reduced and nitrided into AlN. During reduction of Al_2O_3, AlON, Si_2N_2O, Si_3N_4 and SiAlON were produced as transitional phases. Once graphite is coated by a SiC layer, Al_2O_3 may also be reduced by SiC, with the consequent formation of the above transitional phases. The reaction rates of SiC and AlN formation were described by a three dimensional contracting-sphere formula for diffusion-control. The activation energies were 429kJ/mol for SiC formation and 611kJ/mol for AlN formation. The rate-determining steps of SiC and AlN formation are probably the diffusion through SiC layer formed around graphite particles and AlN layer formed around Al_2O_3 particles, respectively.
社団法人日本セラミックス協会の論文
1999-02-01