Synthesis of AlN Nanopowder from γ‐Al 2 O 3 by Reduction–Nitridation in a Mixture of NH 3 –C 3 H 8

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Aluminum nitride (AlN) powders were synthesized by gas reduction–nitridation of γ‐Al 2 O 3 using NH 3 and C 3 H 8 as the reactant gases. AlN was identified in the products synthesized at 1100°–1400°C for 120 min in the NH 3 –C 3 H 8 gas flow confirming that AlN can be formed by the gas reduction–nitridation of γ‐Al 2 O 3 . The products synthesized at 1100°C for 120 min contained unreacted γ‐Al 2 O 3 . The 27 A1 MAS NMR spectra show that Al–N bonding in the product increases with increasing reaction temperature, the tetrahedral AlO 4 resonance decreasing prior to the disappearance of the octahedral AlO 6 resonance. This suggests that the tetrahedral AlO 4 sites of the γ‐Al 2 O 3 are preferentially nitrided than the AlO 6 sites. AlN nanoparticles were directly formed from γ‐Al 2 O 3 at low temperature because of this preferred nitridation of AlO 4 sites in the reactant. AlN nanoparticles are formed by gas reduction–nitridation of γ‐Al 2 O 3 not only because the reaction temperature is sufficiently low to restrict grain growth, but also because γ‐Al 2 O 3 contains both AlO 4 and AlO 6 sites, by contrast with α‐Al 2 O 3 which contains only AlO 6 .