MECHANISM OF ALN FORMATION THROUGH THE CARBOTHERMAL REDUCTION OF AL2O3 IN A FLOWING N2 ATMOSPHERE

Mixtures of Al2O3 and C powders in a molar ratio of 1:3 were reduced i n a N2 atmosphere. The effects of time, temperature, particle size of both reactants, and N2 flow rate were investigated. Kinetics show that the rate-limiting process is the combustion of carbon, which leads to the reaction mechanism through the following basic steps: Al2O3 = 2Al + 3/2O2 3C + 3/2O2 --> 3CO (slow, with or without intermediate format ion of CO2) 2Al + N2 = 2AlN (fast) All of the experimental results hav e been discussed on the basis of this model, which allows one to predi ct the best conditions for preparing AlN powders.