CARBON INTERFACIAL LAYERS FORMED BY OXIDATION OF SIC IN SIC/BA-STUFFED CORDIERITE GLASS-CERAMIC REACTION COUPLES

Reaction couples between alpha-SiC and cordierite (2MgO.2Al2O3.5SiO2 = Mg2Al4Si5O18) were prepared by sandwiching (and enclosing) SiC single crystals between plates of Ba-stuffed magnesium aluminosilicate (Ba-MAS) glass and hot-pressing; the Ba-MAS was subsequently crystallized at 1000-degrees to 1200-degrees-C in argon or air. No reaction occurred at the SiC/Ba-MAS interfaces during hot-pressing, by crystallization heat treatments caused formation of amorphous carbon reaction layers at the SiC/cordierite interfaces, due to concurrent oxidation via the reaction SiC + O2 --> SiO2 + C. The thickness of the carbon layer was variable. These results suggest that formation of C layers at SiC/silicate interfaces in other composites (containing Nicalon fibers, for example) depends more on thermochemistry and less on the details of SiC nonstoichiometry than has heretofore been supposed.