Transition of gamma-Al2O3 into alpha-Al2O3 during vibro milling

The results obtained in studying the phase transition of gamma- into alpha- Al2O3 during intense mechanical activation by vibro milling are presented i n this paper. It was found that depending on experimental conditions, the g amma --> alpha-Al2O3 transition through delta- and theta-phases, can be ini tiated. X-ray and SEM analyses of activation products show that the phase t ransition is preceded by intense reduction of gamma-phase particles. The pr oduced alpha-Al2O3 crystallites have a distorted lattice and are larger tha n the initial crystallites in the starting powder. The change of specific s urface 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, detai led analyses of gamma-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 . (C) 2000 Elsevier Science S.A. All rights reserved.