ELECTROCHEMICAL POLARIZATION AND PASSIVATION OF IRON IN ACID-SOLUTIONS

The potentiodynamic polarization of the iron electrode in sulphuric acid solutions was studied. The formation of a passivating film on the electrode upon anodic oxidation in sulphuric acid solution depends on the concentration of the acid. Addition of Cl- ions to sulphuric acid solutions raises the current densities along both the active and passive regions. The difference between the dissolution current in halogen-containing media and solutions devoid of these ions, i.e., the enhancing effect of Cl- ions, DELTAi, varies with the aggressive ions concentration according to log DELTAi = a5 + b5 log C(agg). Organic carboxylates enhance the active dissolution of iron through their participation in the dissolution mechanism, while they inhibit pitting corrosion through competitive adsorption with Cl- ions for adsorption sites on the metal surface.