Analysis of the electrodeposition process of Fe–Mn films from sulfate electrolytes

Fe–Mn alloys with different composition and structure have great importance in a wide range of applications, which requires a detailed knowledge of a variety of production methods. In the present work, Fe–Mn thin films were electrochemically deposited from sulfate aqueous solutions under different conditions on Cu substrates. The effects of several applied potentials for deposition, concentrations of reagents and speed of rotation of the electrode were investigated. Chronoamperometry tests were performed and the curves obtained were analyzed through the models for nucleation and growth from Scharifker et al and from Isaev et al considering apparent diffusion coefficient for the deposition of the alloy. The approach with both these models point to a process close to the instantaneous nucleation limit. Globally, the results indicate a mixed transport-kinetic control for most of the conditions, but a behavior with characteristics of diffusion controlled growth can be established for specific conditions of speed of rotation and concentrations. Koutechký-Levich analysis has been applied to current-potential curves at the rotating-disk electrode providing the determination of the apparent diffusion coefficients and heterogeneous rate constants for electron transfer. Fe is preferentially deposited with a much higher rate of reduction than Mn in the employed solutions. The whole deposition process is very sensitive to the presence of (NH₄)₂SO₄, which affects also the quality of the deposits. The samples were further characterized by scanning electron microscopy and x-ray dispersive energy spectroscopy. (paper)