Nanocrystalline growth activation energy of alumina polymorphs synthesised by mechanochemical technique

Abstract

Al₂O₃ nanopowders were synthesised via mechanochemical method using AlCl₃ and CaO as raw materials. The effect of thermal treatment on the structural evolutions and morphological characteristics of the nanopowders was investigated using X-ray diffractometry, transmission electron microscopy, scanning electron microscopy, differential thermal analysis and Rietveld refinement. The results showed that the average crystallite size of Al₂O₃ was <100 nm up to ～1200°C. The activation energy for Al₂O₃ nanocrystallite growth during calcinations was calculated to be ～22?598 and 30?195 J mol^?1 for η- and κ-alumina respectively, while for α-Al₂O₃, it was 8373 and 34?131 J mol^?1 at temperatures up to 1200°C and >1200°C respectively. The mechanism of nanocrystalline growth of Al₂O₃ polymorphs during annealing is also discussed.