Strength Measurements of Monolithic SiC and A12O3/SiC Composites after Exposure to Coal Slag

Abstract

Four Si‐based ceramics—siliconized SiC (Si‐SiC), sintered α‐SiC, and two grades of SiC‐particulate‐reinforced A12O3—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 were cut into flexure bars and remaining strength was measured in four‐point flexure at room temperature. The residual strength was compared to the as‐received strength, and the fracture originating flaws were identified. The standard grade of the particulate‐reinforced A12O3 showed no corrosive attack under any of the exposure conditions, and a slight strength reduction was attributed to aging effects. The three other materials showed varying degrees of strength reduction, with corresponding fracture‐initiating flaws being pits produced during the exposure. A general trend was that the eastern coal seemed to cause more corrosion than the western, and that 1260°C was a harsher exposure condition than 1093°C.