Oxidation of Aluminum Oxynitride-Boron Nitride (AlON-BN) Composite Prepared by Reaction Sintering

摘要

AlON-BN composite was prepared by heating a mixed powder compact with A1_2O_3-AlN-20 mass percent BN-3 mass percent Y_2O_3 (A1_2O_3/AlN = 2.4 in molar ratio) at 1850 deg C for 2 h in N_2. The relative density of the heated compact was 70 percent. Oxidation characteristics of AlON-BN composite were investigated over the temperature range of 1000-1500 deg C in air. AlON and BN were oxidized to form A1_2O_3 and B_2O_3 at the initial stage, respectively. The reaction between the formed B_2O_3 and A1_2O_3 yielded A1_4B_2O_9 and A1_(18)B_4O_(33). Below 1200 deg C, oxygen penetrated into the composite through the open pores and oxidation occurred since the surface layer was porous owing to an insufficient amount of the formed B_2O_3 liquid. At 1100 and 1200 deg C, volume expansion accompanied by the formation of A1_(18)B_4O_(33) caused the occurrence of cracks in the composite. At 1300 deg C, a relatively dense layer with B_2O_3 liquid surrounded the composite and suppressed the penetration of oxygen into it. At 1500 deg C, oxidation was promoted to cause the deformation of the composite.