Electrodeposition of zinc plus iron alloys -: I.: Analysis of the initial stages of the anomalous codeposition

The electrodeposition of Zn + Fe alloy in a chloride acid bath has been studied on vitreous carbon electrodes. Different Zn(II)/Fe(II) ratios in the solution were used with a total concentration of metallic ion of 0.1 mol dm(-3) and chloride ion of 1 mol dm(-3). Potentiodynamic, potentiostatic and galvanostatic techniques were used to analyze the electrodeposition process. The potentiodynamic stripping of deposits, together with the analysis ex-situ of the deposits using X-ray or microprobe analysis, were used to detect the alloy phases present in the deposits. The presence of zinc(II) inhibits iron electrodeposition, leading to anomalous co-deposition. When significant depletion of zinc(II) takes place in the environment of the electrode, inhibition disappears and normal co-deposition begins. The stirring of the solution maintains the anomalous co-deposition, and a solid solution eta-phase, with hexagonal plate-like morphology, is mainly obtained. Under conditions of normal co-deposition, the alpha-phase, an iron-rich solid solution with cubic morphology, is obtained. Under galvanostatic conditions, the alpha-phase is detected in the first stages of electrodeposition but it does not progress to later deposits. These results suggest that zinc(II) can adsorb on this initial deposit, favouring subsequent zinc electrodeposition at the expense of iron. (C) 1999 Elsevier Science S.A. All rights reserved.