Mechanism of anodic dissolution of iron-chromium alloys investigated by electrode impedances—I. Experimental results and reaction model

Stainless steels are characterized by their ability to passivate spontaneously in a corrosive medium. This ability is dependent on many factors, among them the kinetics of the anodic process has a particular importance. In fact, the addition of chromium to iron decreases drastically the critical current density, that is the current maximum during the alloy dissolution, making the passivation process easier to set up. Steady-state polarization curves and electrode impedances measured on FeCr alloys of various chromium contents show how the chromium addition modifies the kinetics of iron dissolution. On the basis of experimental results a reaction model for the dissolution-passivation process of iron—chromium alloy in acidified sulfate media is proposed. The reaction mechanism of alloy is depicted as that of iron perturbed by the chromium addition.