CARBOTHERMAL SYNTHESIS OF ALUMINUM OXYNITRIDE (ALON) POWDER - INFLUENCE OF STARTING MATERIALS AND SYNTHESIS PARAMETERS

Carbothermal synthesis of cubic aluminium oxynitride (ALON) have been performed in a graphite furnace at different temperatures (1700-1860 degrees C) and pressures (0.1-10 MPa). The products were characterized by XRD, SEM and elemental analyses, and the overall compositions were determined by reoxidation in air. The control of excess nitridation was a crucial task in the preparation of ALON. A two-step procedure, first annealing at about 1550 degrees C then at about 1800 degrees C, tvas found to be effective to this end. CO additions to the N-2 gas stimulated ALON formation, but a pressure increase resulted in a lower nitridation rate. The particle size and morphology of ALON depended on mw material type and synthesis parameters such as temperature program, pressure, CO content in the N-2 gas, and sample compartment type. Thermodynamic calculations in the Al-O-C-N system have been performed in order to explain the experimental results.