Ultrasonic Apparatus

The practising chemist has four types of laboratory ultrasonic apparatus which are commercially available. One of these, the whistle reactor, relies on mechanical generation of ultrasonic power whereas the other three - the bath, probe and cup-horn systems - are driven by electromechanical transducers. The construction of such systems is discussed below and a summary of their relative advantages (and disadvantages) in sonochemical usage are summarised in Tab. 7.1. 

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Titanium IV) oxide, T1O2. See titanium dioxide. Dissolves in concentrated alkali hydroxides to give titanates. Mixed metal oxides, many of commercial importance, are formed by TiOj. CaTiOj is perovskite. BaTiOa, per-ovskite related structure, is piezoelectric and is used in transducers in ultrasonic apparatus and gramophone pickups and also as a polishing compound. Other mixed oxides have the il-menite structure (e.g. FeTiOj) and the spinel structure (e.g. MgjTiO ). 

Ultrasonic cleaning is another major application for power ultrasound. It is now such a well-established technique that laboratories without access to an ultrasonic cleaning bath are in a minority. It is important to recognise the historical significance of the development of ultrasonic cleaning technology on the growth of sonochemistry because, in the early years, the humble laboratory cleaner was almost certainly the first ultrasonic apparatus used by chemists. 

Barium titanate has many important commercial apphcations. It has both ferroelectric and piezoelectric properties. Also, it has a very high dielectric constant (about 1,000 times that of water). The compound has five crystalline modifications, each of which is stable over a particular temperature range. Ceramic bodies of barium titanate find wide applications in dielectric amplifiers, magnetic amplifiers, and capacitors. These storage devices are used in digital calculators, radio and television sets, ultrasonic apparatus, crystal microphone and telephone, sonar equipment, and many other electronic devices. 

Ultrasonication apparatus, with 100 W minimum output. We used a 100-W ultra-some disintegrator with a titanium exponential microprobe with a tip diameter of 3 mm (1/8 m ) The nominal frequency of the system is 20 kc/s, and the amplitude used is 12 p. 

Of the four types of laboratory ultrasonic apparatus commercially available for practising chemists in general (namely, whistle reactors, ultrasonic cleaning baths, probes and cup-horn devices) analytical chemists, except for a few specialists working in (or with) ultrasound detectors, use mainly cleaning baths and probes both of which are usually operated at a fixed frequency dependent on the particular type of transducer, that is usually 20 kHz for common probe systems and 40 kHz for baths. Both types of devices are described below. 

Possibly, the high value added to the processed food will facilitate the implementation of non-invasive ultrasonic apparatus for the removal of fouling in food processing equipments. With this aim, an ultrasonic apparatus operating at a frequency of 40 kHz was developed for dislodging biofilms from food processing equipments in order to assess the effectiveness of cleaning protocols. The optimum sonication conditions for the removal... 

Before proceeding with the operation, the energy provided by the electrostrictive device of the ultrasonic apparatus is calibrated by the temperature increase of a fixed volume (v) of distilled water while applying ultrasound by the relationship... 

Figure 5.11 Schematic diagram showing layout of ultrasonic apparatus used for measurement of elastic constants. (From Dyer et al., J. Phys. D (1992))...

Figure 6.12 Schematic diagram showing layout of ultrasonic apparatus used for measurement of elastic constants.

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