Electrodeposition of Zn–Mn alloys in the presence of thiocarbamide

The influence of thiocarbamide additions (0.5–2.0 g l−1) on the electrodeposition of Zn–Mn alloys from a sulfate–citrate bath is studied. Investigations of alloy composition were carried out by atomic absorption spectroscopy, EDX and XPS. The morphology of the coatings was studied by SEM. The crystal structure was investigated by powder and thin-film XRD. The corrosion behaviour of Zn–Mn alloys was tested by measurement of free corrosion potentials in aerated NaCl solution. The use of thiocarbamide allows higher Mn contents (70–80%) with respect to similar plating systems. High Mn deposits are composed of a nanocrystalline globular ε phase. Air exposure gives rise to the formation of mixed Zn and Mn oxides. No carbon or sulfur incorporation in the bulk of the deposits was detected by XPS.