Decomposition of mullite by volatilization of SiO occurs during elevated temperature exposure to reducing gases. RF induction coupled argon plasma power sources have been used for rapid sintering of a number of ceramics and ceramic matrix composites. During plasma sintering of SIC whisker reinforced mullite matrix composites, whiskers were destroyed and the matrix converted to alumina by accelerated volatilization of silicon containing species. The results of these experiments are interpreted through the use of thermodynamic calculations of SiO pressures in the plasma environment.