Electrochemical Reduction of the Precipitated Hydroxide Obtained from the Zn-Ni Alloy Plating Bath.

With electrodeposition of Zn-Ni alloy from a sulfate bath, less noble Zn preferentially deposits compared to noble Ni. This behavior is classified as “anomalous codeposition.” The anomalous codeposition of Zn-Ni may be due to the preferential precipitation of zinc hydroxide on the cathode and the inhibition of nickel deposition according to the hydrogen production at the cathode and the pH increase. However, when both Zn2+ and Ni2+ coexist in the solution, the zinc hydroxide does not precipitate while the double hydroxide of both metals does. In this paper, the role of the double hydroxide obtained from a plating bath containing Zn2+ and Ni2+ has been clarified. The double hydroxide production process and the electroreduction of the hydroxide have been investigated.