Electrodeposition of Nickel‐Iron Alloys: I . Effect of Agitation

Agitation effects on electrodeposition have been systematically investigated using a rotating ring‐disk electrode. Alloy compositions and bath current efficiencies have been shown to vary widely over the range of plating current densities and rotation speeds used. An analysis of partial currents as a function of electrode potential has shown that the Fe deposition reaction is mass‐transport controlled at sufficient cathodic potentials, and that the diffusivity of the Fe²⁺ ion is the same for both the reduction to Fe⁰ and the oxidation to Fe³⁺. In agreement with the observations of Dahms and Croll, the Ni deposition reaction is inhibited when Fe is codeposited. This inhibition effect, manifest as a cathodic shift in the Ni polarization curve, increases in magnitude with increased agitation. The dependence of Ni inhibition on agitation is seen only under conditions at which Fe deposition is mass‐transfer influenced, which suggests that Ni inhibition is primarily dependent on the flux of Fe²⁺ to the electrode surface. The rate of hydrogen evolution during deposition shows the same dependence on potential and agitation as it does in a Ni²⁺‐ and Fe²⁺‐free bath on a substrate.