Deposition of cobalt rich Zn–Co alloy coatings of high corrosion resistance

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

“…Deposits with % m/m Co above 3 % m/m show a diffraction peak that is associated with the formation of the γ-phases 45 . In addition, these phases have been earlier observed in Co-rich coatings containing from 10 % m/m to 15 %m/m 10,43,46 . In the present work, the γ 2 -Zn 13 Co phase was not verified.…”

“…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 . However, it is always considered that certain experimental conditions, such as high values of current density (I), for example, can change the process from anomalous to normal and under these conditions the ZnCo alloy coatings presented a cobalt content higher than that of zinc 11,12 .…”

“…Table 4 presents the experimental values obtained for 2θ and d of the main lines observed for both experiments. Since some phases observed in the electrodeposited Zn-Co alloys were not identified by the available XRD pattern databases 42 , it was also used the literature references 10,43,44 to identify the experimental lines obtained from both experiments.…”

“…Kirilova et al 12 have observed that coatings containing small cobalt content could still be considered as sacrifice coatings, while those with high amount of this metal were nobler than steel, acting as anticorrosive barrier. In addition, Lichušina et al 10 have showed that Co-rich ZnCo coatings (15-18 % m/m Co) presented good appearance and high corrosion resistance in NaCl solution. LimaNeto et al 13 have shown similar results for a Zn-Co alloy coating with 18 % m/m Co.…”

“…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.…”