Endothermic Reactions between Mullite and Silicon Carbide in an Argon Plasma Environment

Abstract

Reactions between SiC and mullite in an Ar plasma were investigated using a model composite in which a free‐standing CVD SiC coupon was imbedded in mullite cement. After treatment in a radio frequency (RF) plasma, the Si content of the mullite in contact with SiC was found to be less than that in the starting material, and deposits were found on the walls of the plasma chamber due to the reaction of mullite with SiC as follows: Al6Si2O13(s)+ SiC(s)= 3Al2O3(s)+ 3SiO(g)+ CO(g). This reaction, which is endothermic (1405 kJ/mol at 1500 K), absorbs thermal energy and consequently prevents the rapid sintering which is observed for single‐phase mullite in similar environments. As a consequence, it is suggested that RF plasma sintering probably cannot be used to densify SiC‐reinforced mullite‐matrix composites because of the resulting energy consumption and damage to the SiC phase.