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Electrodeposition of Cobalt Rich Zn-Co alloy Coatings from Citrate Bath

“…The electrodeposition processes of Zn-Ni, Zn-Fe, and Zn-Co alloys are considered anomalous, that is, the deposition of less noble metal ion Zn (II) is favored when compared to the other alloy metal ions 5 . This anomalous process is reported by many works in the literature 4,[6][7][8][9] and various explanations of the anomaly have been suggested, e.g. underpotential codeposition (UPD), kinetic behavior, the hydroxide suppression mechanism, and the influence of Co (III) 10 .…”

“…Rashwan et al 7 showed that, for the steel polarization in a Zn-Co electrolyte containing glycine 1 mol L -1 , the curve of the alloy lied between those of isolated metals, indicating that glycine electrolyte was able to brought the reduction potentials of the metallic ions together and the nobler metal (cobalt) deposited at less negative potentials, while the less noble metal (zinc) co-deposited at more negative potentials 7,31,32 . Therefore, normal co-deposition would take place, independent of the current density or potential applied.…”

“…have reported the dependence of % m/m Co on I, even though none of these authors have obtained normal deposition. In fact, it is usually found in the literature reports concerning the anomalous nature of Zn-Co alloy electrodeposition process, both in the absence and in the presence of complexant agents and/or additives 2,6,7,33,34 . ].…”

“…For this purpose, a complexant agent or a leveling additive can be added to an electrodeposition bath, causing several changes on the reduction mechanism of the ions in the solution and/or in the activation energy of the electrode surface [15][16][17] . For this reason, it is possible to find several works concerning the production of Zn-Co coatings from acidic or alkaline baths, containing additives and/or complexant agents 7,8,10,18 . Despite its well known toxicity and the rigorous maintenance control to avoid environmental problems 19,20 , the traditional cyanide-containing alkaline baths are sometimes used for electroplating of Zn and Zn alloys.…”

“…Despite its well known toxicity and the rigorous maintenance control to avoid environmental problems 19,20 , the traditional cyanide-containing alkaline baths are sometimes used for electroplating of Zn and Zn alloys. Following the general trends for the electrodeposition of alloy coatings, however, most of the current researches found in the literature deals with nontoxic or environmentally friend complexant agents and additives 2,7,8,[21][22][23][24] . Earlier, we have used a nontoxic citrate bath to produce Cu-Zn and Cu-Co alloy coatings on steel substrate 25,26 .…”