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

摘要

Thermodynamic conditions at the SiC surface under oxygen pressure are analyzed from two points of view: (i) the conditions for creation of a first layer of silica and (ii) the conditions for carbon precipitation. The active to passive oxidation transition steady-state is studied using a thermodynamic analysis focused on the chemical potential of silicon and oxygen at the surface of the compound in order to ensure the existence of a clean SiC surface, i.e. a flow balance imposed simultaneously for the Si and C vaporization flows Si/C= 1/1 at the surface. Thermodynamic calculations show that there exists a window in the couple as a function of temperature that corresponds to a bare SiC surface. For such prevailing conditions the SiC erosion flows are calculated as well as the related SiC condensation phenomenon that might explain the SiC transport and vapor phase deposition at high temperature.