Transformation kinetics of theta- to alpha-phase of alumina powders prepared from different alumina salts by chemical processing

Abstract

The aim of this study was to produce nanosized alumina powders from two different aluminum salts (AlCl3 and AlNO3.9H(2)O) by precipitation method and to investigate transformation kinetics of alpha-Al2O3 crystallization obtained from quantitative DTA curves via Kissinger-Akahira-Sunose (KAS) method. Precipitates are dried at 80 A degrees C for 24 h and then calcinated at 1200 and 1300 A degrees C for 1 h. Dried powders have bayerite [Al(OH)(3)] and calcinated powders have theta- (theta) and alpha (alpha)-alumina phases which confirmed by XRD analysis, and the crystallite size of powders determined by Scherrer equation is about 30 nm for dried powders and ranged from approximately 15-35 nm for calcinated powders. Scanning electron microscopy studies revealed that the morphology and size of powders precipitated from two different salts are similar to each other, and powders contain mainly sub-micrometer-sized particles and close to spherical form. Activation energy values determined by KAS equation range from 717 to 411 kJ mol(-1) for powders produced from aluminum nitrate salt and from 844 to 476 kJ mol(-1) for powders produced from aluminum chloride salt depending on the transformation rate.