Leaching Behavior of H-BN Ceramics under Hydrothermal Conditions

Abstract

The leaching behavior of hot-pressed and pyrolytic boron nitride (BN) was studied under hydrothermal conditions at 150°C and 0.48MPa for 1-10 days. A large degree of weight loss was observed in the hot-pressed BN specimens at the initial stage, due to dissolution of a grain boundary phase. The weight of the pyrolytic BN specimen decreased slowly with increasing time. SEM observation and EPMA of leached specimens and chemical analyses of leached solutions revealed that BN reacted with H₂O to produce H₃BO₃ and NH₃, and the grain boundary phase was rapidly dissolved, and the hydrated layer was not left. These results suggested that the chemical stability of h-BN ceramics under hydrothermal conditions depends on the difference in the grain boundary structure, though BN is fairly stable.