Abstract:Alumina precursors with different morphologies were synthesized using Al₂(SO₄)₃·18H₂O as reactant, urea as precipitator and mixture solution of ethanol and water (volume ratio of 2:1) as solvent by a hydrothermal treatment method. The microstructures, thermolysis processes of as-synthesized powders were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM), differential scanning calorimeter and thermo gravimetric analysis(TG-DSC). The results show that, under the same conditions, hydrothermal temperature affects the morphology of the alumina precursor and the phase transition temperature of α-Al₂O₃. With increasing the hydrothermal temperature, their phases change from amorphous to boehmite with high crystallinity, at the meantime, the phase transition temperature of α-Al₂O₃ of their calcined products increase gradually. The average apparent activation energies of thermolysis of precursors obtained on three hydrothermal temperature 100, 140 and 160 ℃ are calculated to be 150.68、155.46 and 171.09 kJ/mol, using the Doyle-Ozawa and Kissinger methods, respectively. The reaction order and frequency factor are determined by Kissinger method. The kinetics equations of thermolysis of precursors obtained at different hydrothermal temperatures are deduced.

Key words: alumina precursor; thermolysis; apparent activation energy; Doyle-Ozawa method; Kissinger method