Phase transformation and gas–solid reaction of Al2O3 during high-energy ball milling in N2 atmosphere

Al2O3 powders were milled in N2 atmosphere using an attritor ball mill. The phase transformation and gas–solid reaction of Al2O3 during high-energy ball milling in N2 atmosphere were investigated. It is found that the γ-Al2O3 transform to α-Al2O3 as milling time increases. Milled for 20 h in N2 atmosphere, Al2O3 becomes partially amorphous and the gas–solid reaction between Al2O3 and N2 takes place. A new phase with cubic aluminum nitride (AlN) structure forms during milling which is different from normal hexagonal AlN produced by carbon thermal reduction processing. As milling energy increases, the amount of this new phase with cubic AlN structure increases. The amount of this new phase is as high as 72% when Al2O3 is milled in N2 atmosphere at 650 rpm for 40 h.