Growth kinetics of passive films

A new model of growth of passive films is presented which includes both the transport through the film in the presence of a strong and varying electric field and the transport through the film—electrolyte interface by a reaction with a varying potential drop at the interface. By neglecting the second mechanism the Cabrera-Mott and Vetter model is obtained as a special case of the general model. Galvanostatic and potentiostatic results for passive iron in acid and neutral solutions are explained qualitatively and quantitatively. Only this new model is in overall agreement with experimental findings for different pH values. The thickness of the passive layer is calculated to be 2.7 ± 0.5 nm in 1 N H2SO4 at 1.08 VH which is in excellent agreement with experimental values.