The electrochemical behavior of alloy C in NaOH solutions under open circuit potential (OCP) condition was investigated in this research by using potentiodynamic polarization, Mott–Schottky analysis and electrochemical impedance spectroscopy (EIS). Potentiodynamic polarization curves suggested that alloy C showed excellent passive behavior in NaOH solutions. Mott–Schottky analysis revealed that the passive films displayed p-type semiconductive characteristics, where the Ni(II) vacancies (over the oxygen vacancies and interstitials) preponderated. Also, the Mott–Schottky analysis indicated that the acceptor density decreases with decreasing NaOH concentration. EIS measurements showed that dilute NaOH solutions offer better conditions for forming passive films with higher protection behavior, due to the growth of a much thicker and less defective films.
