Gas‐Phase and Solid‐State Simultaneous Mechanism for Two‐Step Carbothermal AlON Formation

Abstract

AlON powders were synthesized by two‐step carbothermal reduction nitridation method, which includes thermal treatment of Al2O3/C mixtures at 1200°C–1600°C for 2 h, followed by subsequent heating at 1750°C for 1.5 h in N2 flow. The effects of soaking temperatures of the first step on phase compositions and morphologies of the final products were investigated. It is found that the variation in precalcination does not have impact on phase compositions of the final products, which are all single‐phase AlON. However, it impacts the AlON morphology significantly. Lower precalcining temperature results in severer agglomeration of AlON powder. Obvious terrace surface morphology was also observed on AlON particles with lower precalcination. Both the agglomeration and terrace‐like morphology are attributed to the gas‐phase reaction induced by the residual carbon in the AlON formation process. An AlON formation mechanism including simultaneous solid‐state reaction between Al2O3 and AlN, and gas‐phase reaction among Al (g), O2 (g), and N2 (g) with the presence of residual carbon is proposed based on the experiment, kinetics, and thermodynamics. The mechanism was further examined by carefully designed control experiments, which was confirmed to be both experimentally and theoretically valid.