Effect of raw materials on carbothermal reduction synthesis of γ-aluminum oxynitride spinel powder

Abstract

The effect of starting Al2O3 materials on synthesis of γ-aluminum oxynitride spinel (γ-AlON) powder by carbothermal reduction has been investigated. Whether using Al(OH)3, boehmite, dried gel, or calcined alumina as an alumina source, the reaction rate is faster than that using α-Al2O3. That is because the oxygen distribution in γ-Al2O3 is cubic close packed as the non-metal arrangement in AlON spinel is whereas that in α-Al2O3 is hexagonal close packed. When hydrated aluminas used lose structural water and transform into γ-Al2O3 in heating cycle, γ-Al2O3 is easily reduced and nitrided into AlON spinel after a slight adjustment in the cation positions and proportions is made in the reduction process of alumina. The particle morphology of the product after carbothermal reduction was strongly influenced by the type of alumina source employed, which suggests the mechanism of Al2O3/C powder mixtures in a flowing N2 stream is the absorption of aluminum-containing gas, such as Al(g), Al2O(g), etc., on the surface of aluminum oxide in the initial stages, followed by reaction with N2 gas to form AlON and AlN phases with nucleation, and growth on Al2O3 particle surfaces.