Abstract
Passive layers were formed on electrolytic Zn-Co alloy coatings in an ethanolic solution with sodium hydroxide by anodic oxidation. The obtained thin films were characterized by their morphology (OM, SEM), chemical analysis (XPS), thickness and deep-profile chemical analysis (GDOES) and corrosion properties (NSS test, EIS). Because of the appearance of interference colours with all of the samples, they were also characterized by UV-Vis absorption spectroscopy. The colours varied and were related to the thicknesses of the obtained thin films, which ranged from 91 to 220 nm. The passive films grew linearly with the terminal voltage. Based on the XPS results, mixed (oxide-alkoxide) compositions were found to have a beneficial influence towards providing improved corrosion resistance. According to the conducted corrosion studies, the best protection was ensured when the coatings were anodized at terminal voltages between 30 and 50 V.
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