Codeposition of zinc with nickel from gluconate solutions

The codeposition of zinc and nickel from slightly acidic chloride, sulfate, and chloride-sulfate solutions containing a gluconate complexing agent was investigated. In all baths, zinc electrodeposition was found to be favorable due to the high nickel deposition overpotential. This behavior was independent of bath speciation and thermodynamic predictions. Two ranges of alloy codeposition potential were observed, i.e., below and above - 1.4 V (Ag/AgCl). The morphology and composition of the alloys were not affected by the type of anions in the electrolyte, but both were seriously affected by the deposition potential. Anomalous codeposition of Zn-Ni alloys occurred according to the instantaneous nucleation model. The surface wettability of the deposits and their corrosion properties in neutral and acidic environments were discussed. Similar studies were carried out for deposits modified with higher carboxylic acids: lauric, myristic, palmitic, and stearic.