Isothermal transformation kinetics was studied in mechanically treated and untreated gibbsite powders heated in air. The mechanical treatment enhanced the nucleation of α-Al2O3, but did not affect the growth rate as evidenced by this similar values in the activation energy for transformation to α-Al2O3 of untreated and milled gibbsite. The accelerated transformation kinetics are believed to be due to the change in phase evolution during heating, as induced by the mechanical treatment. During heating the untreated powders, the δ and θ phases as a transition phase were observed but in the mechanically treated sample, the α and χ phases appeared. It has been found that a higher energy is needed for the Θ→α-Al2O3 transformation than for κ, χ→α-Al2O3.

Keywords: Mechanical activation, phase transformation kinetics, gibbsite, aluminum oxide phase transformation, ball-milling