Die Messung der Ultraschall‐Diffusion an einer Elektrode und ihre praktische Anwendung

Under the action of ultrasound (Iup to 2 W/cm2) quasi‐stationary current voltage curves were obtained, from which the densities of the exchange, the diffusion‐limited currents and the transfer coefficient were calculated. The acceleration of diffusion with ultrasound was attributed to surface cavitation involving pulsating bubbles surrounded by microstreaming. At higher sound intensities a limiting current due to cavitation saturation was observed. In order to explain this saturation effect a Langmuir kinetic for the enrichment and the depletion of cavitation bubbles beyond the threshold intensity was proposed. In the case of acoustic resonance (h=nλ/2) standing waves are generated in the solution. At the pressure loops the sound action has then a maximum. — Reproducible results were only obtained in the presence of cavitation nuclei, how they are given at rough surfaces or at smooth surfaces after adsorption of colloidal particles. The measurements were performed with Pt, glassy carbon and graphite electrodes in solutions of Fe3+/Fe2+and [Fe(CN)6]3‐/[Fe(CN)6]4‐. According to the obtainedi0values it is suspected that the complex bounded cyanid ions are favoring the exchange of electrons between the central atom and the electrode surface by an inner‐sphere mechanism.