Reaction mechanism in carbon-liquid silicon systems at elevated temperatures

Abstract

The mechanism of reactions which occur in the carbon-liquid silicon system at elevated temperatures is far from being understood although the reactions are utilised for producing manu interesting SiC materials. In the present paper the formation of fibrous β-SiC in this system, which occurs with the SILCOMP SiC/Si material, has been investigated by observing the evolution of the microstructure at successive stages of the reaction and by measuring the thermal effects accompanying the reaction. A model has been developed which permits a rational explanation of the main features of the reaction rate and of the microstructure of the products formed at the first and intermediate stages of the reaction; the microstructure is of a decisive importance for the formation of fibrous β-SiC in the final product. An explanation is given for: (1) the preferential formation of small β-SiC crystals disseminated at random in the Si matrix in localised zones which were previously occupied by the carbon fibres; (2) the high rate of reaction in spite of the low solubility of carbon in silicon at the temperatures, attained by external heating, which are usually used to produce SILCOMP (1680–1880 K). Because analogous reactions occur in the production of SILCOMP, REFEL SiC and other similar materials, the model developed may have a wider range of applications.