Electrochemical and chemical characterization of electrodeposited zinc surface exposed to new surface treatments

A new environmentally friendly passivation treatment for electrogalvanized steel has been investigated in this study. The passivation treatments consisted of immersion in solutions containing hexahydrated cerium nitrate and organic additive. The effect of citric acid as an additive into the treatment solution has also been evaluated. For comparison reasons, the electrogalvanized steel was passivated in a commercial chromating and the corrosion performance of the new treatments compared to this last one. The effect of the proposed treatments on the corrosion resistance of the surface was investigated by electrochemical impedance spectroscopy (EIS) in sodium chloride solution. The morphology of the treated surface was investigated by field emission gun scanning electron microscopy (SEM-FEG). The treated surfaces were chemically characterized by X-ray Photoelectron Spectroscopy (XPS). The electrochemical results showed higher impedances along the time of exposure to the electrolyte for one of the new proposed treatments compared to the surface passivated in the chromating solution. XPS results suggested that the new treatments resulted in the formation of an organic film on the electrogalvanized steel surface. The cerium ions showed a synergistic effect with the organic film formed resulting in long-term protection of the metallic substrate in the corrosive electrolyte. The layer formed apparently acted as anchoring sites for inhibiting corrosion products leading to prolonged protection of the surface film formed.