Investigation of the Electrochemical Behavior of 304 Stainless Steel in Transpassive Region

In this study, the properties of transpassive film formed on 304 stainless steel in 0.5 M sulfuric acid has been examined using electrochemical impedance spectroscopy (EIS). For this purpose, transpassive films were formed potentiostatically at selected potentials for 3 minutes and then EIS measurements were done. For EIS measurement s, an excitation voltage of 10 mV and an applied frequency ranging from 100 kHz to 10 mHz have been used. Results showed that in the potential rang 0.85-0.90 VSCE, a high frequency capacitive and a low frequency inductive observed. The high frequency capacitive loop reflects the high field assisted migration of defects in the transpassive film, and the inductive loop at intermediate frequencies is due to the relaxation of the negative surface charge formed by the accumulation of cation vacancies at the transpassive film/solution interface. In addition, in the potential rang 0.95-1.00 VSCE, the faradic pseudo capacitance is detected. In this region, by increasing the potential, Rt, RSC and LSC are decreased.