Crystallization and phase transformation behaviors of chi-alumina prepared by the thermal decomposition of aluminum isopropoxide in two inert organic solvents

Abstract

Thermal decomposition of aluminum isopropoxide (AIP) in toluene at 315 ํC for 2 h gave chi-alumina product having the high thermal stability and while the reaction at lower temperature resulted in formation of an amorphous product. The thus-obtained chi-alumina transformed directly to alpha-alumina at approximately 1150 ํC, bypassing other transition alumina phases. The amorphous product transformed to gamma-alumina then to theta-alumina, after calcination at high temperature. It was found that when chi-alumina synthesized at 315 degree celicus was recovered by the removal of the solvent at the reaction temperature, the product showed the highest thermal stability. This procedure is convenient avoiding bothersome work-up process yielding large surface area and large pore volume alumina. Thermal decomposition of AIP in mineral oil at 250-300 degree celcius over a 2 h duration results in chi-alumina powders having high thermal stability. The mechanism of the process involves the formation of amorphous complex before further decomposition takes place. Phase transformation of the obtained products was also investigated. It was found that chi-alumina synthesized by this method transformed directly to alpha-alumina at temperature higher than 1000 degree celcius. chi-alumina prepared in both organic solvents attains a critical crystallite size around 15 nm through accretion on calcination and then transforms directly to alpha-alumina through nucleation and growth process