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 10–500 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 an anomalous co-deposition was almost identical at 293 and 313 K but increased at 333 K, due to enhanced H₂ evolution and Ni deposition at 333 K. The current efficiency for alloy deposition increased with solution temperature in both the normal (10–50 A·m⁻²) and anomalous (500 A·m⁻²) co-deposition regions. In the normal co-deposition region, Ni deposition and H₂ evolution mainly occurred, and the current efficiency increased with solution temperature due to the stronger promotional effect of increase in solution temperature on Ni deposition. In the anomalous co-deposition region at 500 A·m⁻², Zn deposition and H₂ evolution mainly occurred, and Zn deposition appeared to proceed based on a mixed rate-determining process comprising the charge transfer and diffusion of Zn ions. The current efficiency increased with solution temperature due to the acceleration of the Zn ions diffusion. The Ni content in the deposited films increased with the solution temperature at all the current densities, since Ni deposition was accelerated to a greater degree than Zn deposition by increasing the solution temperature in the region where the charge transfer process was rate-limiting. The γ-phase of the deposited films also increased with increasing solution temperature.