AC Impedance Study of Anodically Formed Salt Films on Iron in Chloride Solution

AC impedance measurements of mass‐transfer‐limited dissolution of iron into a 4.0 M electrolyte are presented. The influence of disk rotation speed and applied potential on the ac impedance is investigated. The results are interpreted with a model that assumes the presence of a salt film. This film has a duplex structure composed of an inner layer through which ferrous ions migrate by high‐field conduction and an outer, porous layer where ionic, low‐field conduction occurs in the electrolyte filling the pores. The thickness of the inner layer increases with applied potential and that of the porous layer decreases with increasing disk rotation speed.