THE APPLICATION OF ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY AND IDENTIFICATION PROCEDURES TO THE INVESTIGATION OF THE DISSOLUTION AND PASSIVATION OF IRON IN CARBONATE-BICARBONATE BUFFERS AT 25-DEGREES-C

An electrochemical impedance spectroscopy study of the dissolution and passivation of polycrystalline iron in carbonate-bicarbonate buffers at 25-degrees-C is reported. The impedance spectra analysis was performed by using an identification procedure to estimate initially the dynamic parameters from the measured impedance obtained by employing both sinusoidal and pseudo-random binary sequence perturbations, followed by a quantitative fitting on the basis of reaction schemes in terms of formal rate constants. Impedance spectra and steady-state polarization characteristics are accounted for by a reaction model involving the parallel formation of Fe(OH)2 and soluble Fe (II) species. The concentration of bicarbonate ions determines the overall current in the prepassive potential range.