This study focuses on the passivation and semiconducting behavior of alloy C in HNO3 solutions. The report includes potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) studies along with Mott-Schottky analysis in order to determine the passive behavior of the alloy and the semiconducting properties of the passive film formed during exposure to acidic solutions. Mott–Schottky plots indicated that the donor densities increase with decreasing HNO3 concentration. Moreover, more positive values of the flat band potential indicate better stability of the passive film with decreasing HNO3 concentration. EIS measurements showed that the reciprocal capacitance (1/C) of the passive film is directly proportional to its thickness which increases with decreasing HNO3 concentration. Therefore, it is clear that dilute HNO3 solutions offer better conditions for forming the passive films with higher protection behavior, due to the growth of a much thicker and more defective passive films.
