Mechanism of anodic oxide growth on bismuth

Abstract

The mechanism of anodic oxide film growth on bismuth has been investigated by the constant current method and by the galvanostatic pulse method in phosphate and borate buffer solutions of pH 8.2. The investigations have been carried out at various temperatures between 0.5 and 60°C in the range of current density from 150 to 500 μA cm−2. Experimental results show that, depending on the thickness of the layer, the mechanism of the charge transfer changes significantly. For very thin layers—formed immediately next to metal—the current-field relation obtained has been satisfactorily described by the model of ionic transport in the low field. For barrier layers—formed in the continuation of the formation of the layer—the basic factor controlling the kinetics of growth is the transport of interstitial cations through non-stoichiometric oxide in the high field. On the basis of such views it was possible, from the experimental results, to determine kinetic parameters of the layer growth, activation energy and half jump distance.