Thermodynamic approach to the vaporization and growth phenomena of SiC ceramics. II. The SiC surface under oxidative conditions

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

“…Indeed, Ta has a well-known large solubility for oxygen that could have been stored during the first step i.e., vaporization of silica. Then, after silica departure, the sopurified SiC grains vaporized under active oxidation conditions -attested by the residual SiO(g) partial pressure -as already explained in a preceding paper by Honstein et al 9 from a theoretical point of view. In this vaporization regime, the pressures of the different SiC vaporizing species were determined and are shown in Fig.…”

“…2 shows that such a kinetic barrier does not occur for pure SiC vaporization under active oxidation since the various powder size samples gave the same partial pressures and these pressures were within the non-stoichiometric domain of SiC. Calculations of pure SiC vaporization flows by thermodynamics therefore remain applicable, as performed for instance by Honstein et al 9 for the active oxidation regime of SiC.…”

“…This result can be related to the earlier release of silica by vaporization (initial CO(g) pressures more important) and consequently the longer duration in the SiC active oxidation state. Honstein et al 9 in fact predicted higher Table 4 Particle size distributions using the CILAS laser analyzer for the (0.5 + 5 m) and (0.5 + 10 m) SiC sieved powder mixtures before and after heat treatment. growth rates in the active oxidation state at the SiC-C phase limit combined with lower erosion rates.…”

“…The present experimental work is a follow-up to the two theoretical thermodynamic analyses performed to identify vaporization and condensation flows of silica and silicon carbide and their mixtures by Honstein et al 6,9 Preceding investigations dealing with active or passive oxidation domains as summarized by Vaughn and Mass 10 and recently by Honstein et al 9 let suppose that one of these two domains may be the only convenient conditions for growth and the only way to check for these conditions is to measure vapor pressures during the SiC powders consolidation heat treatments associated with post experimental micro-structural characterizations.…”

Characterization and functionalization by sol–gel route of SiC foams

“…SiC is known to possess a thin protective layer of an amorphous SiO x C y oxide on its surface 17 ; this layer grows and evolves into SiO 2 during the passive oxidation of SiC. 18 XRD analysis of ground SiC foam after different heat treatments enables to identify the different steps of oxidation (Fig. 9).…”