Abstract
In this paper, the direct nitridation of Al powder was carried out under N2 and NH3 atmosphere in temperature range from 900 to 1400°C, respectively. The structures, morphologies and compositions of the products were measured and analyzed by XRD, SEM and EDX. The SEM results showed core–shell structures of Al/AlN below 900°C under N2 atmosphere, whereas tadpole-like and branches structures of AlN over 1200°C under NH3 atmosphere. EDX results demonstrated that Al-rich AlN with extensive N/Al ratio could form in the direct nitridation process. The XRD results indicated that the pure AlN powders were obtained at 1400°C under N2 atmosphere and at 1100°C under NH3 atmosphere, respectively. The reaction analysis revealed that intensive passivation effect of Al occurred below 900°C under NH3 atmosphere and hindered the nitridation, while the passivation effect was eliminated beyond 1000°C and nitridation was boosted. In contrast, Al crust formed below 1100°C under N2 atmosphere and ceased the nitridation, while the crust became unstable because of convection originated from intensive evaporation beyond 1200°C and the nitridation was accelerated. So the reaction process played essential roles in preparing pure AlN by the direct nitridation of Al powder.
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