Effect of Solution Temperature on Electrodeposition Behavior of Zn-Ni Alloy from Alkaline Zincate Solution

Abstract

Zn–Ni alloys were electrodeposited on a Cu electrode at 10–5000 A·m⁻² and 5 × 10⁴ C·m⁻² in an unagitated zincate solution at 293, 313, and 333 K. The effect of solution temperature on the electrodeposition behavior of Zn–Ni alloys from alkaline zincate solutions was investigated. The transition current density at which the deposition behavior shifted from a normal to anomalous codeposition was almost similar at 293 and 313 K but increased at 333 K. The transition current density increased at 333 K due to the enhanced hydrogen evolution and Ni deposition. The current efficiency for alloy deposition increased with solution temperature in both normal (10–50 A·m⁻²) and anomalous (500 A·m⁻²) codepositions region. In a normal codeposition region, Ni deposition and hydrogen evolution mainly occurred, and the current efficiency increased with solution temperature due to a larger promotion effect of increase in solution temperature on the Ni deposition. In an anomalous codeposition region at 500 A·m⁻², Zn deposition and hydrogen evolution mainly occurred, and Zn seems to proceed under a mixed rate-determining process of the charge transfer and diffusion of Zn ions. The current efficiency increased with solution temperature since the diffusion of Zn ions was accelerated. The Ni content in the deposited films increased with solution temperature at all the current densities, since Ni deposition was more accelerated than Zn deposition with increasing solution temperature in the region where the charge transfer process was rate-limiting. The γ phase of the deposited films increased with increasing solution temperature.