Sonovoltammetric experiments practical considerations

Section 2 described a number of general concepts surrounding the experimental design of a general voltammetric experiment this section focuses upon how 

Ultrasonic baths will be familiar from their everyday use in the laboratory where they are commonly used for cleaning surfaces and to aid dissolution. A bath essentially comprises a number of transducers of fixed frequency, commonly 20-100 kHz, attached beneath the physical exterior of the bath unit. Baths typically deliver ultrasonic intensities between 1 and 10 W cm to the reaction medium. For sonovoltammetry (or sonoelectrosynthesis) the bath may be filled with distilled water and a conventional electrochemical cell is placed inside the bath at a fixed position (Walton et al., 1995) so that the cell is electrically isolated from the sound source. Alternatively, the internal metal casing of the bath can be coated so that the full volume is available to use as an electrochemical cell (Huck, 1987). For both arrangements results can be highly sensitive to positioning and/or cell geometry effects. 

An ultrasonic horn transducer consists of a transducer unit attached to a horn (rod) usually made from titanium alloy and which has a length a multiple of half-wavelengths of the sound wave. For the commonly encountered 20-kHz horn this corresponds to 12.5 cm. The horn is then partially inserted into the fluid medium of interest and intense ultrasound is generated at its tip so that, for adequately large intensities, a cloud of cavitation bubbles is visible. This arrangement permits significantly higher ultrasonic intensities (10-1000 W cm ) to be applied than are achievable with a bath. 

An often-adopted sonovoltammetric design is that shown in Fig. 35 built around a conventional three-electrode cell and which allows the ultrasound intensity and the distance between the horn and electrode to be continuously varied at a fixed ultrasound frequency of typically 20 kHz. This arrangement is much less sensitive to the shape and dimensions of the electrochemical cell than when a sonic bath is utilized. A further and important point of contrast is that the direct contact of the (metallic) horn with the electrochemical system may dictate the use of a bipotentiostat to control its electrical potential relative to that of the reference electrode (Marken and Compton, 1996). Alternatively, the horn may be electrically isolated (Huck, 1987 Klima et al., 1994). A significant merit of the design shown in Fig. 35 is that the mass transport characteristics may be empirically but reliably established. It is to this essential topic we next turn. 

Probably the most important consequence of introducing ultrasound into a voltammetric experiment is the increase, often dramatic, of the rate of mass 

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The effect of ultrasound on electrochemical processes 69 Sonovoltammetric experiments practical considerations 70 Mass transport effects a simple description 71 Sonotrodes 77... 

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