The preparation and characterization of alumina membranes with ultra-fine pores: Part 1. Microstructural investigations on non-supported membranes

Alumina films less than 20 μm thick are prepared by a process in which a boehmite sol is successively gelled, dried and calcined. The resulting structure has the unique property that only ultra-fine pores with a narrow pore size distribution are present within large crack-free layers. The microstructure can be influenced by the sintering temperature and the acid concentration of the precursor sol. The minimum modal pore size which has been obtained is 2.5 nm. A consistent model of the microstructure of the membranes and an explanation of its uniformity are presented.