Textural stability of titania-alumina composite membranes

Textural evolution (porosity reduction, pore and crystallite growth) in titania-alumina composite membranes was studied using thermal analysis, XRD, field emission SEM and N2 physisorption techniques. The presence of alumina in the membranes improved the thermal stability of the porous texture by retarding the anatase-to-rutile phase transformation and grain growth of the anatase phase. Pure unsupported titania membranes lose their porosity completely after calcination at 600 C for 8 h, whereas the titania-50 wt% alumina composite membranes retained a porosity of about 40% even after calcination for 30 h at 800 C. The anatase-to-rutile phase transformation temperatures for pure unsupported titania and the titania phase of the unsupported titania-alumina composite membranes (50 wt% alumina) were found to be 580 and 960 C, respectively, as observed from the DSC data. From XRD results it was found that pure unsupported titania and the unsupported titania-alumina (50 wt% alumina) composite membranes transformed to more than 95% of rutile after heat treatment for 8 h at 600 and 900 C, respectively. The anatase-to-rutile phase transformation kinetics were studied using DSC data and applying a non-isothermal form of the Avrami equation. 15 refs.