Influence of current density on transport numbers in anodic oxide films on an anodized Al–5.7at.%W alloy

Abstract The ionic transport numbers in barrier anodic films, formed on an Al–5.7at.%W alloy in 0.1 M sodium tungstate electrolyte at 293 K, have been measured for current densities from 0.1 to 1000 mA cm−2. For this purpose, a xenon marker was ion implanted with a fluence of 1.5 × 1015 ions cm−2 into a film formed to 10 V on the alloy, which was then further anodized to 150 V. The position of the marker layer in the final film was determined by transmission electron microscopy and Rutherford backscattering spectroscopy. The cation transport number was ∼0.38, with no dependence upon current density to an accuracy of ∼10%.