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 (gamma-Al2O3 to alpha-Al2O3) and nitridation reaction took place above 1,100 A degrees C for pure alumina fiber. The addition of a small amount of silica (3 wt%) suppressed the formation of alpha-Al2O3 and preserved the highly reactive metastable alumina, and nitridation rate was enhanced. Fine grain (similar to 20 nm) AlN fibers were obtained for pyrolysis at 1,150-1,250 A degrees C for 3 h in ammonia, and AlN was identified as the sole crystalline phase.