Electrolytic aluminium oxide membranes — a new kind of membrane with reverse osmotic characteristics

Abstract

Porous aluminium oxide membranes have been produced by a complete anodic oxidation of thin aluminium folia in acid media. The electronic microscopy investigation had shown that the membranes have an asymmetrical porous structure with a very dense barrier layer and that they are, therefore, potentially applicable, in the reverse osmosis field. Investigation of the membrane pure water permeability under pressure differences from 10 to 30 atm gave high initial permeability values (about 100 times higher than those of thermally untreated cellulose acetate membranes) which decreased rapidly during experiments. By heating the membranes above 600°C, or by their additional hydration in hot water, initial permeability decreases, with further decrease during the experiments. In addition, the hydrated membranes have better mechanical characteristics than untreated ones. The separation characteristics of aluminium oxide membranes were tested with aqueous solutions of sucrose and phenol, under the same conditions as in the permeability tests. The membranes exhibited distinct selectivity in both cases.