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

The structural stability of SCS-6 filament was investigated in the tem perature interval 1000-1600-degrees-C by differential scanning calorim etry (DSC) and in situ X-ray diffraction techniques. It was found that this filament is composed mostly of the cubic beta polytype of SiC an d of graphite, and that these phases are stable in the temperature int erval studied. The lattice parameter for beta-SiC was determined betwe en room temperature and 1600-degrees-C, and the calculated average lin ear thermal expansion of the lattice in this temperature interval (5.2 4 x 10(-6)-degrees-C-1) is in agreement with macroscopic thermal expan sion measurements on single filaments. Thermal events observed by DSC occur at 1380-degrees-C on heating and at 1300-degrees-C on cooling, a nd are suggested as being related to the melting and solidification, r espectively, of excess silicon. These results are analysed in relation to the anomalous thermal expansion behavior exhibited by this filamen t.