Comparison of the carbothermal reduction and nitridation reactivity among γ-, δ-, and α-Al₂O₃

Abstract

The carbothermal reduction and nitridation (CRN) reactivity of alumina (Al₂O₃) to aluminum nitride (AlN) under a flow of nitrogen was investigated for transition aluminas (γ- and δ-Al₂O₃) and α-Al₂O₃ with the same particle size and mixing homogeneity with carbon. The aluminas were obtained by calcining a (hydroxo)(succinato)Al(III) complex under a flow of nitrogen, argon, or mixed gas of nitrogen and carbon monoxide. The transition aluminas were converted to AlN without any transformation into α-Al₂O₃. The CRN reactivity of Al₂O₃ decreased in the following order: γ-Al₂O₃ > δ-Al₂O₃ >> α-Al₂O₃. The difference in their CRN reactivities was attributed to the difference in the ratio of AlO₄ sites to AlO₆ sites among the three phases. The CRN reactivity decreased with increasing crystallinity.