Influence of water-soluble monomers on the corrosion protection ability of chromium coatings obtained from Cr(III)-based solutions

The effect of water-soluble electropolymerizable monomer additives in Cr(III) sulfate-oxalate electrolytes on the corrosion-electrochemical behavior of chromium coatings and their ability to protect the steel support is studied. The additives into the Cr(III) sulfate-oxalate electrolytes were caprolactam, aniline, and acrylamide. The XPS technique showed that both the surface and bulk layers of chromium coatings obtained from electrolytes with additives contain products of chemical or electrochemical conversions of caprolactam, aniline, and acrylamide, including their polystructures. It is found that caprolactam and aniline produce a positive effect on the protective ability of chromium coatings, while the protective ability of chromium coatings in the presence of acrylamide decreases. These properties are determined primarily by a decrease in the number of defects in chromium coatings in case of caprolactam and aniline and an increase in the number of cracks in the deposits in case of acrylamide. According to the earlier studies, the corrosion-electrochemical behavior of chromium coatings from Cr(III) sulfate-oxalate electrolytes in 0.5 M H2SO4 is determined primarily by the presence of the chromium carbide phase acting as a cathodic agent. The effect of additives on the anodic polarization curve in 0.5 M H2SO4 is most probably determined not only by an increase or decrease in the porosity of chromium deposits, but also by incorporation of the additives and products of their electrochemical conversion that, according to the literature, can act as corrosion inhibitors.