Zn-Mn alloy coatings electrodeposited from acidic sulfate-citrate bath

Abstract

The Zn-Mn alloy electrodeposition on steel substrate from sulfate-citrate bath was investigated using cyclic voltammetry. In a metal ion-free solution, an electrochemical analysis showed that increasing the citrate concentration induces the increase in the overpotential for hydrogen evolution reaction, with an optimum citrate concentration of 0.6 mol dm-3. Cyclic voltammograms recorded in the electrolyte with Zn2+ and Mn2+ ions, reveal that the potential of Zn-Mn alloy electrodeposition (-1670 mVSSE) stands between those of pure Zn (-1500 mVSSE) and pure Mn (-1850 mVSSE) electroreduction. The effect of [Mn2+]/[Zn2+] ratio in the electrolyte on the Mn content in the obtained Zn-Mn coatings was studied. It was found that the Mn content increases with increasing the [Mn2+]/[Zn2+] ratio in the electrolytic bath. The surface morphology and crystalline phase structure of Zn-Mn deposits were characterized by means of scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD), respectively.