THE CONSTITUTION OF THE SILICON-CARBON SYSTEM

The constitution of the Si-C system was re-investigated between 1400 and 3000-degrees-C using an arc-melting furnace and a 350 kHz induction furnace with two pyrometric temperature measurement devices. The experiments were performed in specially designed graphite crucibles in order to avoid the falsification of temperature measurements by the arising vapour species. The samples were further characterized by high temperature DTA and by X-ray diffraction and X-ray microanalysis. One intermediate compound, SiC, occurs in the system. Si and SiC form a degenerate eutectic system; the eutectic temperature and composition are 1413-degrees-C and 0.02 at.% C, resp. Peritectic formation of SiC was observed at 2830-degrees-C according to the reaction {Si0.87C0.13} + [C] = [SiC]. The melt boils incongruently under 1 bar pressure at about 3000-degrees-C. The condensed vapour consists of Si and SiC containing altogether 40 at.% C. SiC is monotropic. Metastable, cubic beta-SiC is formed from the gas phase and from the melt according to Ostwald's rule. Hexagonal a-SiC seems to be the stable modification in the overall temperature range.