CURRENT OSCILLATIONS WITH SMALL AMPLITUDES DURING ELECTROCRYSTALLIZATION OF CADMIUM IN THE PRESENCE OF N,N-BIS(DECAOXYETHYLENE) OCTADECYLAMINE

Current oscillations with small amplitudes during the electrocrystallization of cadmium from acidic cadmium sulfate solutions in the presence of N,N-bis(decaoxyethylene) octadecylamine (DOOA) were studied by electrochemical methods, electron microscopy and X-ray diffraction. DOOA adsorbed on the surface of a polycrystalline cadmium cathode inhibited the reduction current of cadmium ion (Cd2+) at the potentials more negative than -0.62V. The current oscillations with small amplitudes were observed, which depend on experimental conditions (electrolysis potential, concentrations of Cd2+ and DOOA). The upper current density of the oscillations showed the values which were limited by diffusion of Cd2+ with natural convection, and the lower values showed the ones which were inhibited by adsorption of DOOA. Under the conditions that the current oscillations were observed, the aggregates of cadmium crystals grew toward the direction parallel to (00.1) plane of cadmium crystal. The current oscillations with small amplitudes may result from the periodic appearance of new and fresh surfaces of cadmium which is competitive with the coverage of them by DOOA.