Oscillations and spatio-temporal structures during electrodeposition of AgCd alloys

Abstract

During electrodeposition of cadmium both potentiostatic and galvanostatic oscillations are registered. Experiments under different hydrodynamic conditions show the possibility of formation/destruction of passive layers on the electrode surface, which besides the hydrogen evolution under limiting current density conditions could be an additional promoter of the oscillation behavior of the system. The duration of the observed galvanostatic potential oscillations decreases with increased current density, due to massive hydrogen evolution. XPS investigations confirm the existence of passive films at potentials corresponding to the onset of oscillations. Potential oscillations are observed again during electrodeposition Ag–Cd alloys at high current densities. They appear when the cadmium content in the deposits is more than 45wt.% and they have possibly the same origin as the oscillations during cadmium electrodeposition. The period and regularity of the oscillations depend on the current density, respectively on the cadmium content.At high cadmium content during alloy deposition, the formation of periodical structures consisting of different phases of the alloy is registered. The cadmium content of the different morphological areas of the patterns is almost identical. The XRD spectra of the obtained structured coatings suggest the existence of two textured phases, with a very strong preferred orientations of the crystallites in the direction 〈101〉 for the pure cadmium phase.