Zn-Ni-Cd alloy was electrodeposited from an alkaline electrolytic bath under potentiostatic conditions. Bath analyses using a pH concentration diagram reveal that addition of a complexing agent is essential to maintain the bath stability. Introduction of a low concentration of CdSO4 reduces the anomalous nature of the Zn-Ni deposit. Deposits obtained from the electrolytic bath which contains 60 g/L of ZnSO4·7H2O, 40 g/L of NiSO4·6H2O, 1 g/L of CdSO4, and 80 g/L of (NH4)2SO4 in the presence of additives and ammonium hydroxide at pH 9.3 has a composition of 50 wt % of Zn, 28 wt % of Ni, and 22 wt % of Cd. By optimizing the Cd concentration in the bath, it is possible to control the amount of Ni in the deposit. At large overpotentials, the surface of the electrode is covered with hydrogen which lowers the deposition current density. Rotating disk electrode studies indicated that the deposition of Cd is under mass control, while Ni deposition is under kinetic control.
Journal of the Electrochemical Society, 2003, pages C81-C88.
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Publisher's link: http://dx.doi.org/10.1149/1.1534599