A modified direct nitridation method for formation of nano-AlN whiskers

The direct nitridation of metallic aluminium under isothermal conditions was studied. Aluminium with 99% purity in both compacted and loose powder forms was nitrided in nitrogen gas flow at the temperature range of 600–1000 °C. Compacted Al samples showed very low nitridation tendency till 1000 °C. High nitridation conversions were achieved in the powder Al samples where the nitridation started after the melting point of Al and the conversion was greatly improved with increasing the nitridation temperature. The nitridation time and the nitrogen flow rate were found not to be critical for improving the conversion extent. The addition of pre-synthesized AlN powder to the starting Al powder retarded the nitridation conversion whereas the addition of NH4Cl powder enhanced the AlN yield to near completeness. It is found that the addition of NH4Cl promotes the growth of AlN whiskers.