Preparation of aluminum nitride fibers from alumina gel fibers by nitridation in ammonia

Aluminum nitride (AlN) fibers were prepared from alumina gel fibers and by heat-treatment in ammonia. The influence of silica on the formation of AlN was investigated. It was shown that phase transformation of alumina (γ-Al ₂O₃ to α-Al₂O₃) and nitridation reaction took place above 1,100°C for pure alumina fiber. The addition of a small amount of silica (3 wt%) suppressed the formation of α-Al₂O₃ and preserved the highly reactive metastable alumina, and nitridation rate was enhanced. Fine grain (∼20 nm) AlN fibers were obtained for pyrolysis at 1,150-1,250°C for 3 h in ammonia, and AlN was identified as the sole crystalline phase.