Regulating the Corrosion Resistance of AISI 304 Stainless Steel by Electro-Assisted Deposition of Cerium Oxide Films

The beneficial effect of cerium-based films on the enhancement of the passive film stability of the AISI 304 stainless steel was explored in the present work. The protective films were obtained by electro-assisted deposition in cerium nitrate solutions with different cerium ions concentrations. The corrosion resistance was regulated by changing the deposition parameters, namely, the deposition time and current density. The composition of the oxide film was analysed by x-ray photoelectron spectroscopy (XPS). The surface morphology was examined by scanning electron microscopy (SEM), and the distribution of cerium over the surface was evaluated by EDS analysis. The corrosion behavior was assessed in 0.1 M NaCl solution, using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests. The films consisted of a mixture of Ce 3+ (Ce 2 O 3 ) and Ce 4+ (CeO 2 ) species. The Ce 3+ /Ce 4+ ratio was affected by the deposition parameters, being minimized at lower current densities and longer immersion times. The coating morphology changed from an island-type cerium distribution to a homogeneous layer when the cerium concentration in the deposition bath increased from 0.1 M to 0.25 M. The corrosion resistance was related to the Ce 3+ /Ce 4+ ratio. The anodic currents were reduced by the presence of the cerium-based films.