Depolarization at the Electrodeposition of the Negative Component of Eutectic Alloys

Abstract

At the electrochemical deposition of alloys various phenomena are observed that lead to changes in the kinetics and thermodynamics of the processes. In particular, as a result of changing in the nature of the electrode surface, both the exchange current densities and the transfer coefficients of each of the components changed. Further, during the formation of solid solutions, the equilibrium potentials of the components change due to the non-zero enthalpy and entropy of mixing. At the deposition of eutectic-type alloys (that is, a mixture of grains of individual components), each of the metals does not deposit on the entire electrode surface but only on its own surface. In the latter case, there is a change in the diffusion pattern of the components as compared to the deposition of individual metals: it remains unchanged in the outer part of the diffusion layer but there is a condensation of the diffusion fields of the components near the surface, similar to the case of diffusion to the matrix of microelectrodes or to individual nuclei of a new phase. This also leads to a change in the diffusion part of the overpotential of the components’ deposition. The diffusion of ions of the discharging negative component of an alloy representing a mechanical mixture of the metals’ A and B grains to the grain surface of this component in the model of a partially blocked electrode is considered. At a constant potential, the local current density of the component is shown to increase as a result of the diffusion acceleration. The magnitude of the relative increase in the current and the corresponding magnitude of apparent depolarization are found, as compared between the deposition of an individual metal and the codeposition of the same component into an alloy.