Evolution of calcareous deposits and passive film on 304 stainless steel with cathodic polarization in sea water

Abstract

The change of protective current density, the formation and growth of calcareous deposits, and the evolution of passive film on 304 stainless steel (SS) were investigated at different potentials of cathodic polarization in sea water. Potentiostatic polarization, electrochemical impedance spectroscopy (EIS), and surface analysis techniques of scanning electron microscopy (SEM), energy dispersive X-ray (EDX) microanalysis and X-ray diffraction (XRD) were used to characterize the surface conditions. It was found that the protective current density was smaller for keeping polarization at -0.80 V (vs. saturated calomel electrode (SCE), same as below) than that at -0.65 V. The calcareous deposits could not be formed on 304 SS with polarization at -0.50 V while it was well protected. The formation rate, the morphology, and the constituent of the calcareous deposits depended on the applied potential. The resistance of passive film on 304 SS decreased at the first stage and then increased when polarized at -0.80 V and -0.65 V, which was related to the reduction and the repair of passive film. For the stainless steel polarized at -0.50 V, the film resistance increased with polarization time, indicating that the growth of oxide film was promoted.