Mass spectrometric and thermodynamic analyses of (SiC-SiO2) powders vaporization behavior

The high temperature vaporization of (SiC-SiO2) powders mixtures has been studied under vacuum using the Knudsen Cell Mass Spectrometric method in order to determine their vapor pressures as a function of their composition and to check their morphology change with time during the heat treatment. Various characterization methods – grain size distribution analysis, XRD, Raman spectra and Scanning Electron Microscopy – were used before and after heat treatment in the mass spectrometer in order to observe the growth of any possible links between SiC grains. The present study showed that as long as silica was present, links growth could not be observed. Lower SiO(g) and CO(g) partial pressures than equilibrium were observed and the evaporation coefficients have been determined. Then the origin of such low pressures was related to the control of the vaporization by oxygen diffusion in the silica layer existing at the surface of the SiC grains.

► The vaporization behavior of the pseudobinary SiC–SiO2 was kinetically controlled.
► Evaporation coefficients were determined.
► Vaporization mechanisms are elucidated by reference to thermodynamics.
► Oxygen diffusion in silica layers is limiting step.