The electrodeposition of Zn-Ni in sulfate solutions has been investigated by means of polarization curves, morphological analysis and electrochemical impedance using a rotating disc electrode.
The polarization curves showed two parts, the first one related to the Zn-Ni normal codeposition and the second one to the Zn-Ni anomalous codeposition. The mass transport influenced only the Zn-Ni normal codeposition and had no influence on the anomalous codeposition. The temperature showed a great influence on the Zn-Ni alloy deposition and affected both parts of polarization curves. The electrolyte composition had no influence on the Zn-Ni anomalous codeposition, but it affected the transition current density between normal codeposition and anomalous codeposition.
The impedance diagrams were obtained in sulfate electrolytes and showed four loops at low frequency domain at the beginning of anomalous codeposition: three capacitive loops and one inductive. For the high polarizations, one of the capacitive loops disappears. These results were discussed comparatively to those previously obtained for chloride electrolyte, in view of establishing a kinetic model for the sulfate electrolyte.