New and modified anodic alumina membranes: Part III. Preparation and characterisation by gas diffusion of 5 nm pore size anodic alumina membranes

This paper describes methods for preparation of anodic alumina membranes with pore diameters 65, 50, 40, 11, and 5 nm, Membranes were separated from the aluminium anode by applied electrical pulses rather than by chemical treatments normally used. In this way pore enlargement caused by etching was effectively avoided; particularly important for the smallest pore sizes. For the two smallest pore sizes direct observation by SEM was inconclusive and a gas diffusion technique was used. For a range of eight low molecular weight gases the permeation mechanism of these anodic alumina membranes was Knudsen diffusion and this was used to estimate pore diameters. For the larger pore sizes, good agreements were obtained for estimates from, SEM and Knudsen methods. For the smallest pores Knudsen estimates alone were used.