Kinetics of the simultaneous ZnCo electrodeposition

C.R. TOMACHUK; A.R. DI SARLI; C. I. ELSNER

San Pablo

Congreso; XIX Simpósio Brasileiro de Eletroquímica e Eletroanalítica (SIBEE 2013); 2013

SIBEE

In order to be adopted by the industrial field, the alloys electrodeposition process must produce electrodeposits with the same composition and properties in as wide as possible electrodeposition parameters region. This implies the need to know not only the metals? electrodeposition kinetics in aqueous electrolytes containing both metals but also how that kinetics is affected by the metals relative concentration. Electrodeposition of zinc + cobalt alloys is classified as anomalous co-deposition due to the preferential deposition of the less noble metal [1], although preferential deposition of zinc occurs under certain experimental conditions [2-4]. Various explanations for anomalous co-deposition are given in the literature. As a result, the existing interpretations of the mechanism are ambiguous and need to be supported by additional arguments. The aim of the present work was to analyse the alloy deposition process by potentiostatic and galvanostatic techniques using solutions with different Zn(II)/Co(II) ratios, maintaining at pH 3 and the total metallic ion and chloride ion concentrations at 0.1 mol.dm-3 and 1 mol.dm-3, respectively, under various experimental conditions (applied potential, deposition time, current density), particularly during the initial stages of deposition. The experiments were carried out in a conventional three-electrode cell. The working and counter electrodes were both vitreous carbon rods. The morphology, composition and phases of the deposits were observed by SEM, AES and XRD, respectively, as a function of the deposition current density. The results showed that the presence of zinc in the bath inhibited the cobalt deposition. This inhibition depends strongly on both the metallic ion ratio in solution and the applied current density. For Zn(II)/Co(II) ratios greater than 1/9, low current densities favoured homogeneous and compact deposits that were rich in Zn and were mainly composed of g-phases of Zn+Co alloy. However, when high current densities were used and/or when the Zn(II)/Co(II) ratio was very low (<1/9), dendritic and non-homogeneous cobalt-rich deposits were obtained