The anodic oxidation of zirconium—II. Growth and morphology of anodic ZrO2 films

Measurements of the rate of growth of anodic barrier films, the stresses in these films, and the relative film thicknesses after anodising in electrolytes which may contain fluoride ions have been interpreted as showing that the incorporation of F^? ions into the oxide leads to a greater flux of zirconium ions which in turn may lead to tensile stresses in the oxide. These stresses can cause oxide fracture and the development of corrosion products.The incorporation of F^? ions into the oxide depends upon the F^? ion concentration in the electrolyte and the surface pH of the electrode. This latter is in turn dependent upon the bulk pH of the electrolyte and the applied current density. At high current densities the surface pH shifts to smaller values which leads to enhanced pick-up of F^? ions; at low current densities higher surface pH's can prevent the pick-up of fluoride ions.