Characterisation of zinc plus cobalt alloy phases obtained by electrodeposition

The anomalous codeposition of Zn + Co alloys on vitreous carbon, copper and nickel substrates in a chloride bath was studied. The results indicate tha t the substrate influences both the initial electrodeposition stages and th e alloy formation. For the same electrodeposition conditions, vitreous carb on and copper substrates favour the formation of deposits richer in zinc th an those obtained over a nickel substrate. In the stripping analysis of dep osits obtained during anomalous codeposition, up to three major oxidation p eaks were observed, the two corresponding to the more negative potentials a re attributable to the zinc oxidation in the alloy and the more positive on e to the oxidation of the remaining porous cobalt matrix of the alloy. Unde r our experimental conditions, two kinds of deposits have been analysed usi ng X-ray diffraction (XRD). XRD analysis showed that deposits with very low cobalt percentage (less than 3%) and a hexagonal platelet structure had a distorted hcp zinc eta -phase. Polyhedral-grained deposits with between 4 a nd 10% cobalt were made up of quasi-pure zinc and a Zn + Co gamma -phase of bcc structure. A correlation between the stripping curve and the type of d eposit has been found. (C) 2001 Elsevier Science B.V. All rights reserved.