ELECTRODEPOSITION OF ZN-NI ALLOYS IN SULFATE ELECTROLYTES

The electrodeposition of Zn-Ni in sulfate solutions has been investiga ted by means of polarization curves, morphological analysis and electr ochemical impedance using a rotating disc electrode. The polarization curves showed two parts, the first one related to the Zn-Ni normal cod eposition 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 g reat influence on the Zn-Ni alloy deposition and affected both parts o f polarization curves. The electrolyte composition had no influence on the Zn-Ni anomalous codeposition, but it affected the transition curr ent density between normal codeposition and anomalous codeposition. Th e impedance diagrams were obtained in sulfate electrolytes and showed four loops at low frequency domain at the beginning of anomalous codep osition: three capacitive loops and one inductive. For the high polari zations, one of the capacitive loops disappears. These results were di scussed comparatively to those previously obtained for chloride electr olyte, in view of establishing a kinetic model for the sulfate electro lyte.