STRENGTH MEASUREMENTS OF MONOLITHIC SIC AND AL2O3/SIC COMPOSITES AFTER EXPOSURE TO COAL SLAG

Four Si-based ceramics-siliconized SIC (SiSiC), sintered alpha-SiC, and two grades of SiC-particulate-reinforced Al2O3-were exposed to a typical western coal ash with high calcium content (Wyodak) and a typical eastern coal ash rich in iron (Illinois #6) at two temperatures for 300 h in a muffle furnace, After exposure, the coupons mere cut into flexure bars and remaining strength was measured in four-point flexure at room temperature, The residual strength mas compared to the as-received strength, and the fracture originating flaws mere identified. The standard grade of the particulate-reinforced Al2O3 showed no corrosive attack under any of the exposure conditions, and a slight strength reduction mas attributed to aging effects, The three other materials showed varying degrees of strength reduction, with corresponding fracture-initiating hams being pits produced during the exposure, A general trend mas that the eastern coal seemed to cause more corrosion than the western, and that 1260 degrees C was a harsher exposure condition than 1093 degrees C.