Transition of γ-Al2O3 into α-Al2O3 during vibro milling

The results obtained in studying the phase transition of γ- into α-Al2O3 during intense mechanical activation by vibro milling are presented in this paper. It was found that depending on experimental conditions, the γ→α-Al2O3 transition through δ- and θ-phases, can be initiated. X-ray and SEM analyses of activation products show that the phase transition is preceded by intense reduction of γ-phase particles. The produced α-Al2O3 crystallites have a distorted lattice and are larger than the initial crystallites in the starting powder. The change of specific surface area (Sp) with activation time shows the presence of high internal porosity of γ-Al2O3 which disappears during the complex process of the phase transition. An attempt was made to present the specific surface area change via its γ- and α-phase contributions. In this respect, detailed analyses of γ-Al2O3 particle size reduction along with reduction of their internal porosity and agglomeration of ground powder were performed, which explain the change of the specific surface area with activation time.