High frequency impedance spectroscopy study of passive films formed on AISI 316 stainless steel in alkaline medium

Passive films formed on AISI 316 in deaerated 0.1 M NaOH solution were studied using cyclic voltammetry, impedance spectroscopy and X-ray photoelectron spectroscopy techniques. The impedance spectra were recorded between 10 kHz and 1 mHz as a function of the electrode potential. Impedance spectra for a two-electrode cell were also recorded between 40 MHz and 100 Hz. The high frequency region of the impedance spectra reveals the existence of a time constant in that region that has been interpreted as a topotactic growth of the passive film, which is highly affected by O2 availability at the metal|electrolyte interface. Low O2 concentration favours the development of low conductivity areas that can prevail after potentiodynamic cycling.