Preparation of alumina membranes for micro- and ultrafiltration applications

A very thin disc type ceramic membrane (0·3-0·8 mm thickness, 25-30 mm diameter) made of pure alumina and suitable for microfiltration applications has been prepared by a tape casting process. A sol coating was applied to the disc to form an ultrafiltration membrane. T he pore size of the membrane could be varied in the range 0·1-0·7 μ m and porosity in the range 25-55% by optimising the ex perimental parameters. The most important factor for determining the pore size of the membrane was found to be the initial particle size distribution of the ceramic powder. Firing temperature and soaking time are other crucial parameters affecting volumetric porosity. Water permeability through the membrane under suction and under positive pressure is comparable with that of ceramic membranes prepared by conventional methods. In addition, a typical membrane shows a very narrow pore size distribution in the range 0·1-0·4 μm, with a median pore size of 0·28 μm. A very sharp drop in the pore size distribution pattern around 0·4 μm indicates that no pores larger than this exist. This implies that all particles with radius > 0·4 μm are trapped in the membrane, providing excellent separation efficiency. Results of microbial separation tests confirmed the possibility of micro-organism separation through these membranes.