THE CONSTITUTION OF THE SILICON-CARBON SYSTEM

The constitution of the Si-C system was re-investigated between 1400 a nd 3000-degrees-C using an arc-melting furnace and a 350 kHz induction furnace with two pyrometric temperature measurement devices. The expe riments were performed in specially designed graphite crucibles in ord er to avoid the falsification of temperature measurements by the arisi ng vapour species. The samples were further characterized by high temp erature DTA and by X-ray diffraction and X-ray microanalysis. One inte rmediate compound, SiC, occurs in the system. Si and SiC form a degene rate eutectic system; the eutectic temperature and composition are 141 3-degrees-C and 0.02 at.% C, resp. Peritectic formation of SiC was obs erved at 2830-degrees-C according to the reaction {Si0.87C0.13} + [C] = [SiC]. The melt boils incongruently under 1 bar pressure at about 30 00-degrees-C. The condensed vapour consists of Si and SiC containing a ltogether 40 at.% C. SiC is monotropic. Metastable, cubic beta-SiC is formed from the gas phase and from the melt according to Ostwald's rul e. Hexagonal a-SiC seems to be the stable modification in the overall temperature range.