Anomalous Electrodeposition of Alloys

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Anomalous deposition of alloys is defined by the less noble metal depositing preferentially to the more noble metal under certain conditions. This project aims to understand the mechanism of anomalous codeposition in plating processes using experiments and mathematical modelling. Previous work on the codeposition of nickel-iron suggests that change transfer in the monohydroxide species causes the anomaly; this work ascertains whether or not this mechanism can be extended to explain anomalous codeposition of the mutual alloys of nickel iron, cobalt, and zinc. The effect of buffering the pH of the plating bath is also investigated. Mathematical modelling consists of two parts: equilibrium calculations and one- dimensional diffusion modelling which includes the effects of buffering and of hydrolysis reactions. This phenomenon is most commonly encountered with the mutual alloys of iron, cobalt, nickel, and zinc. These alloys are widely used in electroplated films because of their high strength, hardness, and magnetic properties. Electrodeposited zinc-nickel provides corrosion protection for steel; high-iron nickel-iron (such as Invar) is used where low thermal expansion is required including microwave guides. optics. laser housings, and printed circuit boards; ferromagnetic alloys such as cobalt-nickel, iron-cobalt, and nickel-iron are widely used in electronic and magnetic devices including computer memory, magnetic shielding, and magnetic recording heads.