In this study, passive behavior and semiconducting properties of Alloy 22 in hydrochloric acid solutions were evaluated. Corrosion and passive current density was measured from potentiodynamic polarization plots. Also, passive film resistance and passive film capacitance were estimated by electrochemical impedance spectroscopy (EIS), and finally defect (donor and acceptor) density was drawn from Mott–Schottky analysis. Mott–Schottky plots revealed that Alloy 22 in hydrochloric acid solutions behave as n-type and p-type semiconductors. Also, this analysis indicated that both donor and acceptor densities are in the range 1021 cm-3 and increased with solution concentration. In conclusion, EIS and Mott–Schottky analysis revealed that dilute hydrochloric acid solutions offer better conditions of the passive film formation on Alloy 22 with higher protection behavior than concentrated hydrochloric acid solutions, due to the growth of a much thicker and less defective films.
