THE EFFECT OF ULTRASONIC FREQUENCY AND INTENSITY UPON LIMITING CURRENTS AT ROTATING-DISC AND STATIONARY ELECTRODES

The limiting current from Fe(CN)(6)(3-)/Fe(CN)(6)(4-) redox in dilute aqueous KCl at a platinum electrode appears to be little affected by t he frequency of simultaneous ultrasonic irradiation in the range 20-80 0 kHz, and is not influenced by choice of bath or probe as sonic sourc e, provided measurements are made at constant ultrasonic intensity. Th e limiting current is dependent on ultrasonic intensity at constant fr equency. In contrast, the peak potential of the redox couple varies wi th ultrasonic frequency in the same range, but does not vary with ultr asonic intensity at constant frequency. Application of ultrasound to a rotating disc electrode provides an increase in limiting current acro ss the frequency range, the magnitude of which varies with both concen tration and rotation speed. The average maximum increase is some 1.5-f old which corresponds to an effective rotation rate of 100 000 rpm (16 67 Hz) for a silent solution in order to achieve the same transport ra tes. It is shown that changes in macroscopic temperature throughout th e experiment are insufficient to cause the observed enhanced diffusion . Copyright (C) 1996 Elsevier Science Ltd.