Morphologically selective synthesis of nanocrystalline aluminum nitride

Aluminum and N-2 (1 atm) react at 900-1100 degrees C to give AIN. The nitridation reactions of four types of starting Al powder-nanocrystalline Al of two different origins, and 2-mu m and 20-mu m Al powders from commercial sources-are described. All four Al powders undergo nitridation to give nanocrystalline AlN; however, only the nanocrystalline Al powders undergo nitridation completely at the low temperatures employed. The nanocrystalline AW is formed in two principal particle morphologies, equiaxed nanoparticles and nanowhiskers, in relative amounts that depend on reaction conditions and the starting Al powders. Added AlCl3 is an effective promoter of nanowhisker growth. Either AIN morphology may be produced with a high selectivity; samples containing predominately equiaxed nanoparticles or predominately nanowhiskers are readily obtained. The results are consistent with a growth model in which the equiaxed AW nanoparticles precipitate at or near the surface of coalesced liquid Al droplets, whereas the AlN nanowhiskers grow apart from the Al droplets in a vapor-transport process mediated by AlCl3 and Al subchloride intermediates.