VARIOUS WAVE PHENOMENA DURING THE OSCILLATORY ELECTRODISSOLUTION OF COBALT

Experimental studies have been carried out with disk-like cobalt sheets in unstirred diluted phosphoric acid under potentiostatic control. Voltages were chosen such that oscillations of the integral current indicating transitions between the active and the passive state of the metal occurred. Spatiotemporal patterns during these transitions, visible due to changes of the reflectivity of the surface, were recorded with a video camera. High-amplitude periodic relaxation oscillations of the integral current are linked to the accelerated propagation of activation waves covering the whole electrode surface. Low-amplitude aperiodic oscillations of the integral current are associated with propagation in a series of pulses, i.e., accelerating and decelerating waves. Often, the stepwise propagating waves emit during acceleration another wave backwards. Annihilation of waves was also observed.