Effect of Ultrasonic Waves on Concentration Gradients

Schlieren techniques have been used to study the effects of ultrasonic waves on concentration gradients produced by electrochemical methods. With standing waves at intensities below cavitation levels, the zones of depleted electrolyte at the cathode stratify at the displacement nodes of the standing waves while the zones of excess electrolyte at the anode stratify at the displacement loops. These stratification effects provide an explanation for the ripples produced on the surfaces of metals electrodeposited in standing waves. Microschlieren techniques indicate that ultrasonic waves at cavitation levels reduce the effective thickness of the diffusion layer at an electrode to a value of 10−3 cm or less. The mechanism for the disruption of the gradients is believed to involve the microdisturbances associated with cavitation bubbles at or near the electrode surface.