HIGH-TEMPERATURE STRUCTURAL STABILITY OF CHEMICALLY VAPOR-DEPOSITED SILICON-CARBIDE FILAMENTS

The structural stability of SCS-6 filament was investigated in the temperature interval 1000-1600-degrees-C by differential scanning calorimetry (DSC) and in situ X-ray diffraction techniques. It was found that this filament is composed mostly of the cubic beta polytype of SiC and of graphite, and that these phases are stable in the temperature interval studied. The lattice parameter for beta-SiC was determined between room temperature and 1600-degrees-C, and the calculated average linear thermal expansion of the lattice in this temperature interval (5.24 x 10(-6)-degrees-C-1) is in agreement with macroscopic thermal expansion measurements on single filaments. Thermal events observed by DSC occur at 1380-degrees-C on heating and at 1300-degrees-C on cooling, and are suggested as being related to the melting and solidification, respectively, of excess silicon. These results are analysed in relation to the anomalous thermal expansion behavior exhibited by this filament.