Passivation Model of AISI 316L Stainless Steel in a Simulated Concrete Solution by Electrochemical Impedance Spectroscopy

In this study, the corrosion resistance of AISI 316L stainless steel in a simulated concrete solution (0.1 M NaOH + 0.1 M KOH) has been examined using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). For this purpose, passive films were formed at open circuit potential for 1 until 12 hours and then potentiodynamic polarization and EIS measurements were done. For EIS measurements, an excitation voltage of 10 mV and an applied frequency ranging from 100 kHz to 10 mHz have been used. The polarization curves suggested that AISI 316L stainless steel showed comparable passive behaviour in a simulated concrete solution. EIS results showed that the best electrical equivalent circuit presents two time constants: The high medium-frequencies time constant can be correlated with the charge transfer process and the low frequencies time constant has been associated with the redox processes taking place in the surface film. Also, EIS results showed that passive film and charge transfer resistance and therefore polarization resistance increase with formation time from 1 until 12 hours, due to the thickening of passive film.