A combined composition and morphology study of electrodeposited Zn–Co and Zn–Co–Fe alloy coatings

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

“…At lower I values, heterogeneous surfaces with several clumps and irregular grains were obtained, while fine grains and higher surface homogeneity was observed from the samples produced from experiment 4. Similar results have been found in literature for Zn-Co and Zn-Ni coatings 9,38 . These results show that the variable I actually interfered in both the composition and the morphology of the deposited layers.…”

“…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 .…”

“…However, an amplification of the diffratograms (Figure 8b) show broad and low intensity peaks, which can be explained by the low thickness of the coatings and the small particle diameters (26 nm and 22 nm, for experiments 1 and 4, respectively). In fact, several authors have showed that XRD analysis is not always able to identify the deposited Zn-Co or Zn-Ni alloys phases because of the presence of a large amount of crystallites too small to be resolved by this technique 9,14,[38][39][40] .…”

“…Moreover, all coatings were produced at room temperature and the thermal mismatch could also contribute to macroscopic residual stress as well as to the microhardness values of the electrodeposited layers [39][40][41] . In some cases, non cataloged crystalline phases were obtained 9,14,41 . Table 4 presents the experimental values obtained for 2θ and d of the main lines observed for both experiments.…”

SVET study of the corrosion protection of electrodeposited Zn and Zn‐Co‐Fe alloy coated steels

“…The reduction of oxygen or water that produces hydroxyl ions (as shown by Equation 2) results in an increase in local pH which further leads to the formation and non-uniform precipitation of Zn(OH) 2 . The decrease in the anodic and cathodic current densities and variation of active sites on the Zn surface with the time of exposure can be attributed to the formation of a passive layer of Zn(OH) 2 that blocks the dissolution of zinc, also reported by others [13,[20][21][22].…”