Physicochemical changes during mechanical activation of boehmite

This study deals with the mechanically induced physicochemical changes in boehmite (γ-AlOOH), synthesized by thermal decomposition of gibbsite. The synthesized boehmite which retained the agglomerate structure and unimodal particle size distribution of the precursor gibbsite and was characterized by high surface area (264 m2/g). Mechanical activation was carried out in a planetary mill. After an initial decrease in particle size up to 15 min, the particle size showed an increase with further milling. BET specific surface area of the sample decreased drastically with milling time to 67 m2/g after 240 min. Though XRD pattern did not indicate any new phase formation during mechanical activation, significant changes were observed in the XRD peaks indicating crystallite size reduction, microstrain etc. The reactivity of samples, in terms of decrease in enthalpy of boehmite to γ-Al2O3 transformation, increased with milling time. Detailed analysis of the physicochemical changes carried out to correlate the increase in reactivity with milling is discussed.