Vaporization of mixed SiC powders. Partial pressures and grain morphology changes under vacuum conditions

Vaporization study of SiC and SiC–2 mol% SiO2 powder mixtures. Grain morphology changes at high vapor pressures under pumping

“…Consequently, the Knudsen cell method as used previously by Honstein et al,5 is no longer available to determine the vapor pressures in the reactor. For the experiments described here, with SiC containing SiO 2 , and when condensation of SiO(g) vapor occurs at the reactor outlet, it is still possible to observe the remaining permanent CO(g) gas flow by introducing this flow into a spectrometer through a capillary tube.…”

“…The purity of the SiC powders was analyzed and published in a previous paper by Honstein et al 5 The oxidized bimodal SiC mixture was made from ≈33 mol% 0.5 m diameter and ≈67 mol% 10 m diameter sieved grain size powders and heat treated in air at 500 • C for about 30 h. The characteristics of the SiO 2 powders are presented in Table 1.…”

“…Other vapors as predicted by thermodynamics (see Table 2 Quadrupole mass spectrometric measurements performed with capillary sampling. 5 ) condensed as black glasses in the top of the cover before being able to enter (and clog) the capillary tube.…”

“…This thermodynamic study was followed by a Knudsen Cell Mass Spectrometric study in which Honstein et al, 5 observed the conditions of vaporization of either "pure" SiC powders and also pre-oxidized SiC powders in the low vapor pressure domain (<10 Pa). These experiments were performed as steady-state vaporizations under a very small controlled and known matter loss (the effusion process) and without any temperature gradients that could favor any growth processes by matter transport.…”

“…As in the previous Knudsen Cell Mass Spectrometric study, the heat-treated powder samples were characterized before and after treatment by grain size analysis, X-ray diffraction, Raman spectroscopy and Scanning Electron Microscopy with Field Emission Gun (SEM-FEG) as already described by Honstein et al 5 …”