EIS study on passive films of AISI 304 stainless steel in oxygenous sulfuric acid solution

Electrochemical impedance spectroscopy (EIS) and Kramers-Kronig (K-K) transforms were made on American Iron and Steel Institute (AISI) 304 stainless steel (SS) in naturally aerated sulfuric acid solution at room temperature. The K-K relations testify that the systems under investigation comply with the linearity, causality, and stability constraints of linear system theory (LST) and thereby validate the EIS data. The polarization resistance decreased with removing of passive film and pitting formed in the passive layer, due to layer thinning or pitting caused by chloride. The impedance data for 304 SS with passive films can be accurately modeled using individual components of the equivalent circuits. The polarization resistances (Rp) of the 304 SS can be confirmed by Nyquist plots and estimated from the anodic polarization curves. The reaction model of the dissolution-passivation process of 304 SS in acid solution is proposed.