IMPROVEMENT OF THERMAL-STABILITY OF POROUS NANOSTRUCTURED CERAMIC MEMBRANES

Unsupported crack-free lanthana-doped alumina and titania membranes and yttria-doped zirconia membrane were prepared by the sol-gel method. A novel solution-sol doping method was employed to coat the dopant oxide on the grain surface of these nanostructured ceramic membranes. The pore and phase structure data of these membranes after heat treatment from 450 to 1100-degrees-C under an atmosphere of air and a steam/air mixture show a substantially improved thermal and hydrothermal stability of these doped ceramic membranes. Doping lanthana (in gamma-alumina and titania membranes) and yttria (in zirconia membrane) raises the gamma-alumina to alpha-alumina, anatase to rutile, and tetragonal zirconia to monoclinic zirconia phase transformation temperature by about 200-degrees-C (for alumina), 150-degrees-C (for titania) and 300-degrees-C (for zirconia), respectively. At temperatures lower than the phase transformation temperatures, doping retards the surface area loss and pore growth of the three membranes. For the three ceramic membranes investigated, the effects of stabilizing the pore structure decrease in the following order: zirconia > titania > gamma-alumina.