A comparative study on thermal and hydrothermal stability of alumina, titania and zirconia membranes

Thermal and hydrothermal stabilities of sol-gel derived γ-alumina, titania and zirconia membranes have been investigated using comprehensive experimental data on the pore and phase structure of these three membranes after heat treatment at high temperatures under air and steam/air atmospheres. For all three ceramic membranes heat treatment results in a decrease in the surface area and an increase in the pore size. The effect of sintering on the change of the pore structure of the three membranes decreases in the order: zirconia > titania > alumina. The presence of steam enhances the pore structure change of these three membranes at elevated temperatures, and the extent of the enhancing effects for the three membranes decreases in the same order. At temperatures higher than 900 (alumina), 600 (zirconia) and 450°C (titania), metastable to stable phase transformation occurs, causing a substantial change in the pore structure of all three membranes, for which the extent of the pore structure change decreases in the order: alumina > zirconia > titania. Presence of steam in the phase-transformation region also enhances the pore structure change, especially of zirconia and titania membranes. Doping drying control chemical additive alters the pore structure of these three ceramic membranes. These comprehensive experimental data are explained using the surface diffusion sintering mechanism, surface nucleation mechanism as well as the microstructure of the sol-gel synthesized ceramic materials.