The effects of NH4Cl addition and particle size of Al powder in AlN whiskers synthesis by direct nitridation

•The diameters of AlN whiskers were from 140 nm to 340 nm by using different amounts of NH4Cl and 3 μm Al powder.•In the case of using NH4Cl more than 40wt%, pure AlN without any unreacted Al was formed as final products.•Using of NH4Cl and Al powder with particle size of 45 μm, leads to obtain AlN whiskers with 630 nm to 870 nm in diameter.•By adding 50wt% NH4Cl, pure AlN was formed. The diameter of the whiskers was increased by increasing in NH4Cl content in starting materials.•Increase in diameter of AlN whisker was resulted by using coarse Al powder. By adding NH4Cl to Al, thermodynamically spontaneous cholororination-nitridation reactions in vapor phase were increased and whiskers and pure AlN powder were produced.

In this study, AlN whiskers were prepared in a tube furnace at 1000 °C for 1 h under 500 cc/min nitrogen gas flow. Al powders with particle sizes of 3 μm and 45 μm and NH4Cl were used as raw materials. SEM, TEM and XRD analyses were applied to characterize AlN whiskers. The diameters of AlN whiskers were from 140 nm to 340 nm by using different amounts of NH4Cl and 3 μm Al powder. In the case of using NH4Cl more than 40 wt.%, pure AlN without any unreacted Al was formed as final product. Using NH4Cl and Al powder with a particle size of 45 μm leads to obtain AlN whiskers with 630 nm to 870 nm in diameter. By adding 50 wt.% NH4Cl, pure AlN was formed. The diameter of the whiskers was increased by increasing the NH4Cl content in starting materials (about 200 nm). Also increase in diameter of AlN whisker was resulted by using coarse Al powder. By adding NH4Cl to Al, thermodynamically spontaneous chlorination–nitridation reactions in vapor phase were increased and whiskers and pure AlN powder were produced. It seems that the formation of whiskers in this work was related to solid–gas (VS) mechanisms.