Transport Limited Currents Close to an Ultrasonic Horn

Abstract

The effect of changing the distance of an ultrasonic horn tip from a stationary platinum disk electrode on limiting current density at various electroanalyte concentrations, ultrasonic frequencies ͑20 and 40 kHz͒, and ultrasonic intensities was studied in an attempt to find the optimum position required for maximum sonoelectrochemical effect in "face-on" mode. Our findings were compared to mathematical models available in the literature, for the mass transport of electroactive species to the electrode under hydrodynamic flow conditions normal to the ultrasonic horn. A good fit with experimental results was found and confirmed the dependence of limiting current to operating parameters such as ultrasonic power, electrode-to-horn distances and electroactive species diffusion coefficient, and also highlighting the importance of ultrasonic frequency. From mass balance equations, it was then possible to develop an approach by analogy to an electrode subjected to pure hydrodynamic flow. A Levich-like equation relating the limiting current density, the square root of ultrasonic intensity, and the inverse square root of the electrode-horn distance was generated for ultrasonic frequencies of 20 and 40 kHz, allowing the generation of an "equivalent" flow velocity under sonication, an important and useful parameter in chemical engineering.

Characterization of transient cavitation in gas sparged solutions exposed to megasonic field using cyclic voltammetry

“…can be calculated to be $5.5 and 4.0 lm in the absence and presence (2 W/cm 2 ) of megasonic field using the equation d = nFADC B / I lim , where I lim is the limiting current, n(=1) is the number of electrons transferred in the reduction of ferricyanide, F is the Faraday constant, D (=0.7 Â 10 À5 cm 2 /s [18,19]) and C B are the diffusion coefficient and bulk concentration of ferricyanide, respectively. It may also be seen from Fig.…”

“…The shape of current transient data may be used to estimate the distance (r) of the (center of) imploding cavity from the electrode surface. Current is proportional to the concentration of the electro- active species at the electrode surface [19,21] and this concentration, which is a function of 'r' and time, may be calculated using appropriate models. Only for certain 'r' values, the shape of the concentration versus time data may be expected to match the shape of the transient peak.…”

Current topics on sonoelectrochemistry

“…The relative position between emitter surfaces and electrodes is also a key point [97], especially because there are several aspects to be considered here. For example, the characterization of the cavitating devices and the influence of the presence of the electrodes is the subject of study by electrochemical [98,99], visual [100] and numerical methods [101]. The ultrasonic intensity distribution and its relation with the geometry and frequency is another important aspect studied not only in sonochemical arrangement by experimental [102] and numerical methods [103,104] but also in sonoelectrochemical devices [105].…”

The influence of ultrasounds on the process of uranium desorption

“…Recently [23] an experimental method has been developed for the efficient removal of methylene blue in the presence of ultrasounds (40 kHz), using the process of adsorption on activated coal impregnated with gold nanoparticles.…”