Carbothermal synthesis of aluminium nitride at elevated nitrogen pressures
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The particle size and morphology of AlN product powders from carbothermal synthesis have been studied by scanning electron microscopy, surface-area measurement and microarea elemental analysis. AlN powders with widely variable grain size and morphology could be produced by varying the pressure, gas-flow rate and alumina type. Discrete AlN particles (∼ 0.5-3 μm) were obtained by using fine γ-Al2O3 as starting material at 1600 °C over the pressure and gas-flow rate ranges 0.1–5 MPa and 1–10 l min−1. When coarse α-Al2O3 was used as raw material, large aggregates of AIN particles normally formed, unless the reaction was run at high nitrogen pressure (5 MPa) and low gas-flow rate (1 l min−1). Occasionally, whiskers formed at relatively low temperatures and pressures, e. g. 1500 °C and <0.5 MPa. It was possible to obtain a discrete and fine AlN powder (∼ 0.5 μm) without seeding. The results suggest that reactions including aluminium-containing gas species play an important role in the control of morphology in carbothermal synthesis of AlN.
KeywordsNitrogen Pressure Product Powder Aluminium Nitride High Nitrogen Pressure Alumina Type
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