Vaporization study of SiC and SiC-2mol% SiO_2 powder mixtures. Grain morphology changes at high vapor pressures under pumping

摘要

The heat treatment of SiC powders, SiC-2mol% SiO_2 powder mixtures, and bimodal SiC powder mixtures has been studied with a quadrupole mass spectrometer linked by capillary tube to a special heat treatment reactor. Silica release was monitored on the CO(g) vaporized flow and the samples were analyzed by Raman spectroscopy and Scanning Electron Microscopy after the experiments. The present study showed that silica release by vaporization - first step in heating processes - is needed before any SiC growth process could start. The second step involving active SiC oxidation conditions by the remaining oxygen was conducive to the growth of "neck-like" connections between SiC grains and growth process was observed in the 1273-1600 K range. When the CO(g) release decreased as a result of higher temperatures or longer treatment times, carbon precipitation at the SiC surface was observed as the third step in the mass loss process.