SYNTHESIS OF C-SIC COMPOSITE FIBER BY PRECURSOR METHOD

C-SiC composite fiber was obtained by heating a C-SiO2 precursor, prepared from carbon fiber (Kynol) impregnated with ethylsilicate. The mechanism of SiC formation from the precursor has been investigated. The reaction rate was determined by means of a thermobalance in an atmosphere of Ar at temperatures from 1673 to 1973 K. The reaction products were examined by X-ray diffraction and chemical analyses. The reaction products were SiC and SiO. The yield of SiC increased with increasing SiO2 content in the precursor and heat treatment temperature. The particles of SiC coarsened at high temperatures. The SiC layer grew from the surface to the fiber core. The continuous concentration gradient of Si was observed in the reaction layer. The reaction rate was described by the two dimensional contracting-disc formula for diffusion control. The activation energy was 304 kJ/mol. The rate-determining step is probably the diffusion through the SiC layer.