Sonochemistry probe systems

Most chemists working on sonochemistry in the laboratory will either use some form of ultrasonic bath or a commercial probe system. The latter instruments are often equipped with a pulse facility which was originally designed for biological cell disruption where temperature control is important. This pulse facility enables the power ultrasound to be delivered intermittently and thereby allow periods of cool-... 

For the probe system, whatever design of horn is used, a large maximum power density can be achieved at the radiating tip. This can be of the order several hundred W cm . The working frequencies are normally of the order 20 - 40 kHz. A number of probe devices are commercially available and, up to a few years ago (before the advent of sonochemistry) were referred to as cell disrupters. The majority operate at 20 kHz and utilise a wide range of different metal probes. The advantages of the probe method of energy input are threefold ... 

Thermal probe systems are inexpensive, easy to handle in almost all ultrasonic devices and particularly those used in sonochemistry. Field distributions and optimization of the geometry of the system can be rapidly obtained and the accuracy of the method is high enough to ensure reproducibility. Chemists who make use of ultrasonic equipment should, as a very minimum, consider this method to calibrate and optimize sonication conditions prior to carrying out sonochemical reactions. 

The stimulation of chemical reactions has been known for a many years [1-15] and it has been suggested that some of them might be used as standards for the measurement of the efficiency of ultrasonic systems. Unfortunately, as is the case in the use of sonoluminescence as a probe, there seems to be no theoretical correlation between chemical effects and ultrasonic power. Nevertheless it is an undeniable fact that when sonochemistry is reported in the literature it would be extremely useful if the response of the system used to a standard sonochemical reaction could be included. 

Commercially available high-intensity ultrasonic probes (10 to 500Wcm ) are the most effective sources for laboratory scale sonochemistry. A typical system operates at 24 kHz with an adjustable total power output of up to 200W and also adjustable irradiation times per pulse of a few tenths of a second. Lower intensities can often be used in liquid-solid heterogeneous systems of interest here because of the reduced liquid tensile strength at the liquid-solid interface, and a common ultrasonic cleaning bath (about lWcm ) can often be adequate for SAE. 

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