Synthesis of AlN Powder by Carbothermal Nitridation of Al2O3 at Elevated N2 Pressures
AlN is a potentially important ceramic material for use in heat engines. In this paper we report some results of synthesizing AlN powder by carbothermal reduction of Al2O3 at elevated nitrogen pressures. Small charges of C + Al2O3 powder mixtures were heat-treated (1300 – 1700°C) in a reactor permitting controlled flows of pressurized N2 (0.1 – 5 MPa) through the sample space. The samples were characterized by XRD, SEM and chemical analyses (N,O).
The rate of conversion to AlN was found to be a function of temperature, gas flow rate, C/Al2O3 ratio and also, to some extent, of nitrogen pressure.
The residual oxygen content obtained after a 1-hour run at 1600°C and 1 MPa was considerably lower (0.4 wt-%) than the corresponding value obtained at atmospheric pressure (3%2), using starting mixtures of carbon black (80 m2/g) and α-Al2O3 (0.6 m2/g).
The AlN particle size (in the range 0.5 – 3 µm) and the degree of agglomeration were also found to be dependent on gas flow rate and pressure, as well as on raw-material type.
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