EXPERIMENTAL INVESTIGATIONS INTO THE OXID ATION BEHAVIOR OF MONOLITHIC SIC-CERAMIC AND SI3N4-CERAMIC DURING SIMULTANEOUS AERODYNAMIC AND CHEMICAL LOADING

Experimental researches were enforced concerning the oxidation behavio r of monolithic SiC and Si3N4 ceramics in a high-enthalpy gas stream a nd surface temperatures above 1600-degrees-C. The hot gas stream was c reated in a system consisting of a plasma-burner and a post connected mixing chamber. The oxidation behavior was observed in the passive reg ion with formation of an liquid oxid layer as well as in the active re gion. It was turned out that in the passive region bubbles were formed in the oxide layer which in part blow up to a size of 1-2 mm. After b lowing up they burst as a result of an inner overpressure. The ascerta ined erosion rates proved directly proportional to the oxygen partial pressure. It could be pointed out that the transition from passive to active oxidation depends on the streaming velocity of the gas.