Electrochemical applications of acoustic streaming generated by a focused ultrasonic source

Various aspects of mass transport toward a static disk electrode embedded in a planar surface in the presence of convective flow induced by a focused ultrasonic source have been examined by electrochemical means using the reduction of solution phase [Fe(CN)₆]^3- in an aqueous electrolyte as a probe redox reaction. Experiments were performed by placing the main axis of the acoustic transducer normal to the plane of disk electrodes of various radii. The results obtained revealed that the limiting current for the reduction of [Fe(CN)₆]^3- is proportional to the acoustic power, P_ac to the 3/8 power, and also to the concentration of the redox active species in the electrolyte. Numerical calculations based on Kamakura's formalism (Kamakura, T. et al. J. Acoust. Soc. Am., 1995, 97, 2740-2746) have shown that the axial velocity induced at the focal point of the source is proportional to the square root of the acoustical pressure. On this basis, the behavior of the system under the conditions employed is analogous to that of the jet impinging electrode geometry in the wall jet regime.