Nanoporous α-alumina membranes with tunable pore diameters prepared by anodizing and heat treatment

Nanoporous and single phase α-alumina membranes with pore diameters tunable over a wide range of approximately 30–350 nm were successfully fabricated by optimizing the conditions for anodizing subsequent detachment by modified anodic polarization and through-hole methods and programmed heat treatment in addition to ceramic plates used as the restriction load. Even with the 23% volume shrinkage resulting from the change in density associated with the transformation from the amorphous state to α-alumina, flat α-alumina membranes, each with a diameter of 25 mm and a thickness of 50 μm, were obtained without thermal deformation. The α-alumina membranes exhibited high chemical resistance in various concentrated acidic and alkaline solutions as well as when exposed to high temperature steam under pressure. Furthermore, when used for filtration, the α-alumina membrane exhibited a level of flux higher than that of commercial ceramic membrane.