Electrodeposition Behavior of Zn-Ni Alloy from Alkaline Zincate Solution

Electrodeposition behavior of Zn-Ni alloys was investigated at current densities of 10 to 500 A.m(-2) and at amount of charge of 5 x 10(4) C m(-2) in unagitated zincate solution containing triethanolamine to form a stable complex with Ni2+ ions at 308K. At low current densities, the deposition of Zn-Ni alloy showed a normal type codeposition, in which electrochemically more noble Ni deposited preferentially, while at high current densities, it showed an anomalous codeposition, in which less noble Zn deposited preferentially. The Ni deposition and H-2 evolution were significantly suppressed in the region of anomalous codeposition at high current densities, showing the formation of inhibitor of deposition resulting from Zn ions in the cathode layer. In the region of normal codeposition at low current densities, the underpotential deposition of Zn apparently occurred with Ni. Because the Zn-Ni alloys are composed of stable intermetallic compound of Ni5Zn21, the activity coefficient of Zn in deposit seems to decrease remarkably.