Mass Transfer Measurements The Electrochemical Probe

The preceding methods are all in some way related to the mechanical effects of ultrasound. It is also possible to make direct measurements of mass transfer 

A similar approach was recently initiated for the monitoring of mass transfer through sonication. The basic principle of the method is derived from Nemst equation. Under diffusion controlled conditions, the intensity of the limiting current is related to the mass transfer coefficient of the active species at the electrode by the relation, 

Two further observations from this study are worthy of note. At low power, when the tip of the probe is at a nodal position, the mass transfer coefficient near the tip (x = 2 cm) dramatically increases as the power is increased. It is somewhat inexplicable that the distance between two maximum does not correspond to the half wavelength of sound in this medium as observed by Contamine using a cup-horn configuration. 

The influence of the input power to the hom (measured with an oscilloscope) was then monitored with the probe located at different fixed places in the beaker. 

Quite curiously the peak value of kd at W2 = 8 W is much higher than further values of kd at much higher input power. A possible explanation is that at low power ( 10 W) acoustic streaming is low, and permanent cavitation at the surface of 

---