The mixture of Al2O3 and AlN at a mole ratio of 7 to 3 was heated at various temperatures from 1973 to 2048 K in N2 atmosphere, to investigate the effects of crystal type of Al2O3 and of additives on the formation rate of aluminum oxynitride spinel (ALON). ALON was formed more rapidly for γAl2O3 than for αAl2O3. The addition of CaB4O7 to the mixture accelerated the formation of ALON, whereas the additives such as NaF, CaF2 and CaCl2 retarded its formation. It was found by the analysis of EPMA that the formation of ALON proceeded topochemically from the surface of Al2O3 particles to the inside. On the basis of the XPS analysis of AlN/Al2O3 interface, the diffusion of the O2− and N3− through the ALON layer was presumed to be a rate-determining step of the formation reaction. According to kinetic analysis of a solid-diffusion controlled equation, the apparent activation energy in the formation reaction using αAl2O3 was estimated to be 1143 kJ/mol for no additive and to be 1085 kJ/mol for the addition of 1 mass%CaB4O7. Whereas the apparent activation energy in the formation reaction using γAl2O3 was estimated to be 515 kJ/mol for the addition of 1 mass%CaB4O7.
