KINETIC-STUDIES ON BETA-SIC FORMATION FROM HOMOGENEOUS PRECURSORS

The kinetics of the carbothermic reduction of SiO2 by carbon to produce beta-SiC from a homogeneous organic precursor has been investigated over the temperature range 1500 to 1800-degrees-C in nitrogen by the use of a high-temperature thermobalance. The kinetic behaviour differed significantly from that of the heterogeneous reaction of SiO2 and carbon particles. The weight-loss curves could be fitted well by the Avrami-Erofe'ev equation with an exponent of 1.5. The result was interpreted as showing instantaneous nucleation in a homogeneous matrix followed by the diffusion-controlled growth of beta-SiC. The obtained activation energy of 391 kJmol-1 was consistent with the assumption that the reaction is controlled by the diffusion of carbon through the amorphous matrix to the growing surface of beta-SiC.