Effect of reaction product of epichlorohydrin and imidazole on the electrodeposition behavior of zn⇓ni alloy from alkaline zincate solution

A Zn–Ni alloy was electrodeposited on a Cu electrode at a current density of 10–5 000 A·m⁻², a charge of 5 × 10⁴ C·m⁻², and temperature of 293 K in an unagitated zincate solution containing the reaction product of epichlorohydrin and imidazole (EI polymer) as a brightener. The effect of the EI polymer on the deposition behavior of the Zn–Ni alloy was investigated. The transition current densities at which the deposition behavior shifted from the normal type to anomalous were 50–100 A·m⁻² and 10–20 A·m⁻² in the EI polymer-free solution and polymer containing solutions, respectively, indicating that the EI polymer decreased the transition current density. The transition current density corresponded to the current density at which the potential of the total polarization curve significantly shifted from the more noble region than the equilibrium potential of Zn to the less noble region. The decrease in transition current density with EI polymer was attributed to the suppression of hydrogen evolution. In addition, the current efficiency for alloy deposition in the high-current-density region decreased due to the suppression of both Zn and Ni depositions. The Ni content of deposited films decreased with EI polymer, indicating that Ni deposition was more suppressed with the EI polymer addition than Zn deposition. With increasing current density, the crystals of the films deposited from the EI polymer-containing solution smoothened and showed significant brightness. The oxidation reaction of the films deposited from the EI polymer-containing solution was suppressed, thus causing the corrosion potential to shift to a noble direction.