AlN fibers were synthesized by the gas-reduction-nitridation of Al2O3 fibers with different characteristics. The constituent phase in Al2O3 raw fibers changed from γ-Al2O3 to α-Al2O3, while the surface roughness increased and the specific surface area decreased through the heat treatment. The extent of nitridation of resultant fibers decreased with the decrease in specific surface areas, and with the increase in crystallite size of the raw materials. In particular, the samples transformed to α-Al2O3 were found to have lower reactivity. The enhancement of reduction-nitridation reaction can be attributed to (1) the nitridation progress at a low temperature because of the similarity in crystal structure between AlN and transition aluminas, and (2) the persistence of γ-Al2O3 at a high temperature, due to the suppression of the polymorphic transformation of alumina by the preceding formation of AlN.
