Thermodynamic aspect in synthesis of AlN powders by carbothermal reductionand nitridation process

A thermodynamical calculation shows that AlN powders were synthesized in th e process by the overall reaction Al2O3(s)S+3C(s)+N-2(g)=2AlN(s)+3CO(g) and its minimum reaction temperature T-0=1852 K, if all reactants and products were in standard states. In the practical experiments, AlN phase appeared obviously at only 1300 degrees C, the major reasons are related to the part ial pressure of its gaseous product p(co) and the mixed free energy. The sy nthesis temperature could be towered by either increasing N-2 flow rate or elevating N-2 pressure. On the other hand, as the temperature decreases, th e equilibrium constant K-m also reduces, and the reducing rate strongly dep ends on the temperature: the lower the temperature, the higher the rate.