The Mechanism of Induced Codeposition of Ni-W Alloys

The term induced codeposition was coined by Brenner in 1963, to describe a situation where “a metal, which cannot be deposited alone from its aqueous solution, is codeposited in the presence of another metal, forming an alloy”. An overview of the mechanism suggested in our earlier papers for electrodeposition of Ni-W alloys from solutions containing citrate as the complexing agent, and the experimental observations that support it, are presented in this paper. It is postulated that induced codeposition results from the formation of a mixed-metal complex, such as () () () () [ ] −24 CitHWONi, which is the precursor for deposition of the alloy. Tungsten can only be deposited from this complex, while there are parallel paths for deposition of Ni. The concentration of this complex was calculated on the basis of an observed mass-transport limitation on the partial current for deposition of W