The Sonochemical Cell

A schematic of the sonochemical apparatus is illustrated in Figure 4. The heart of the sonicator is an element called the transducer. This is a ceramic disk whose crystal structure has a specific direction (in this case, in the vertical direction) in response to an applied ac voltage. In most high-intensity experiments, the transducer is being displaced 20,000 times a second (20 kHz). Since the transducer displacement and the (resulting pressure wave) is relatively small, the signal is amplified by physically coupling the transducer to a stiff, durable mass such as a titanium horn which has the effect of increasing the ultrasonic power by several orders of magnitude, so that over 50 W/cm2 is typically produced at the sonicator tip. Because the ultrasonic waves are being produced by the metal shaft being vibrated up and down by a small amount 20,000 times a second, frictional heating occurs when the shaft is surrounded by a liquid. In order to keep the temperature inside the cell arrangement close to room temperature, the cell arrangement is thermostated using a cooling bath, resulting in optimum temperature for carrying out most of the sonochemical experiments. Gas and liquid inlets and outlets allow a variety of experiments to be performed under different atmospheres with or without oxygen being present.

Figure 4. Schematic of the sonochemical apparatus used for carrying out reactions. Ultrasound can easily be introduced into a chemical reaction in which there is good control of temperature and ambient atmosphere. The titanium horn immersed in the reaction liquid is driven by a piezoelectric, which vibrates when subjected to an alternating current electric field. The common piezoelectric ceramic used is PZT, a lead zirconate titanate material. Reprinted with permission from [16], K. S. Suslick, MRS Bull. 20, 29 (1995). © 1995, Materials Research Society.

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