Electrochemical behaviors and properties of Zn-Ni alloys obtained from alkaline non-cyanide bath using 5,5′-Dimethylhydantoin as complexing agent

Zn-Ni alloys were prepared in an alkaline bath with 5,5′-dimethylhydantoin (DMH) and Na₄P₂O₇ ·10H₂O as the complexing agents. The electrochemical behaviors of Zn-Ni alloy and Zn only on Pt and glassy carbon (GC) electrodes were investigated by cyclic voltammetry (CV), chromoamperometry (CA) and cathode polarization. Results show that DMH is the main complexing agent in the bath. Different behaviors of CV curves on Pt and GC electrodes were observed. The effects of Ni²⁺/Zn²⁺ ratio and bath temperature on CV curves were investigated. The transfer coefficient (α) and diffusion coefficient (D) were also calculated. The nucleation growth processes of Zn-Ni alloy and Zn only show an agreement with three-dimensional progressive growth. Zn-Ni alloy coatings were also characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS). The morphology of deposits is rectangular pyramid. The grain size decreases with the extension of the electrodepositing time and the decrease in the deposition potential can also lead to the decrease of grain size in deposits. The phase structure changes from the mixture of η and γ phases to single γ phase with (411) orientation and the corrosion resistance of deposits increases by decreasing the deposition potential.