Mechanically induced formation of metastable χ- and κ-Al2O3 from boehmite

Nanocrystalline boehmite (gamma-AlOOH) powder was treated by high-energy planetary ball milling. With an increase in milling time and centrifugal force, boehmite was transformed into chi- and kappa-Al2O3 as a metastable phase of alumina. These metastable alumina phases were confirmed by comparing with X-ray diffraction patterns of the thermally treated gibbsite (gamma-Al(OH)(3)). Eventually, the milling of boehmite resulted in the formation of thermodynamically stable alpha-Al2O3. Although boehmite is normally decomposed into gamma-Al2O3 by heating, the phase transformation route of boehmite induced by mechanical milling differed from that induced by thermal process. We have proposed that the different phase transformation route can be attributed to the crystal deformation of boehmite by milling. (C) 2016 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.