MODEL FOR NICKEL-IRON ALLOY ELECTRODEPOSITION ON A ROTATING-DISK ELECTRODE

A model for nickel-iron electrodeposition from a sulfate bath onto a r elating disk electrode based on an alternate description of electrode kinetics from that most commonly used has been presented and analyzed. The reaction mechanism in this model differs in that Ni2+ and Fe2+ ar e the electroactive species and NiOH+ and FeOH+ are not involved whats oever. Transport of each dissolved species is considered to occur via diffusion, convection, and migration. Comparison of simulations with e xperimental data shows that our model can predict characteristic featu res of the nickel-iron system, such as anomalous codeposition and the occurrence of a maximum in iron content in the deposit at intermediate currents, at least as well as the earlier models. Furthermore, the co mputed changes in surface pH are in good agreement with experimental n ear-surface pH measurements reported in the literature and much too lo w for NiOH+ and FeOH+ to be present in significant amounts. Some appro aches for future work for elucidating the reaction mechanism and disti nguish between the various alternatives are discussed.