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Abstract
The processes of oxide film formation on the surfaces of Zn, Zn–Co (0·6 wt-%), Zn–Fe (0·5 wt-%) and Zn–Ni (12%) coatings during anodic polarisation in bicarbonate media have been investigated. The composition, thickness, porosity and protective ability of these films were studied by applying X-ray photoelectron spectroscopy, voltammetric and electrochemical impedance spectroscopy measurements with the aim of establishing the influence of Zn alloying on the properties of the oxide layer and the nature of a higher corrosion resistance of some Zn alloys. The oxide films formed on Zn–Ni surface were found to possess a lower thickness, with respect to that of other investigated samples, but at the same time, they exhibited a higher passivating capacity. No significant difference in the composition of the inner layer of the oxide film between different samples was detected, and only the porosity of the oxide film on Zn–Ni was lower, with respect to that of other investigated coatings. It can be assumed that thinner, and at the same time, more compact (less porous), films on a Zn–Ni surface make these oxide layers more resistant.
The authors wish to acknowledge Dr Aloyzas Sudavičius for the XPS measurements.