Transition of gamma-Al2O3 into alpha-Al2O3 during vibro milling
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The results obtained in studying the phase transition of gamma- into alpha-Al2O3 during intense mechanical activation by vibro milling are presented in this paper. It was found that depending on experimental conditions, the gamma -- GT alpha-Al2O3 transition through delta- and theta-phases, can be initiated. X-ray and SEM analyses of activation products show that the phase transition is preceded by intense reduction of gamma-phase particles. The produced alpha-Al2O3 crystallites have a distorted lattice and are larger than the initial crystallites in the starting powder. The change of specific surface area (S-p) with activation time shows the presence of high internal porosity of gamma-Al2O3 which disappears during the complex process of the phase transition. An attempt was made to present the specific surface area change via its gamma- and alpha-phase contributions. In this respect, detailed analyses of gamma-Al2O3 particle size reduction along with reduction of their internal porosit...y and agglomeration of ground powder were performed, which explain the change of the specific surface area with activation time. (C) 2000 Elsevier Science S.A. All rights reserved.