Application method ultrasonic activation

The application of arylpyruvic acids 256 in place of pyruvic acid in three-component reactions leads to dramatic changes in the direction of the process. Refluxing of starting compounds for 3 hours of irradiating with microwave at 170°C for 20 minutes in acetic acid yielded 3-hydroxy-4,5-diaryl-l-azolyl-2,5-dihydro-li/-2-pyrrolones 258 [203] (Scheme 3.73). Under ultrasonic irradiation in ethanol with the addition of catalytic amounts of hydrochloric acid or in acetic acid, the reaction proceeds in a different direction with the formation of pyrimidinecarboxylic acids 259. In the case of pyruvic acid the course of the three-component reaction does not so drastically depend on the activation method or solvent type as well as from temperature mode [202]. 

Another example of ultrasound use is leaching of organic impurities from different kinds of samples. The main analytes of interest are PAHs, which are widespread in soil, sediment, dust, and particulate samples [55]. USE is recommended as a fast, efficient, and direct environmental sample preparation method for determination of PCBs, nitrophenols, pesticides, or polymer additives. Organometallic and biologically active compounds (such as vitamins A, D, and E) present in samples in trace quantities, can be extracted from animal and plant tissues with the aid of ultrasonic wave energy [59]. Table 6.6 presents some typical applications of USE in trace analysis of biological and environmental samples [60]. 

Because of its many applications, a few attempts are known in which ultrasonic waves have been applied for the synthesis of nanosized titania. Yu and coworkers [126] discovered a novel method for preparing highly photoactive nano-sized Ti02 photocatalysts with anatase and brookite phases. The method has been developed by hydrolysis of titanium tetraisopropoxide in pure water or a 1 1 Et0H H20 solution under ultrasonic irradiation the photocatalytic activity of Ti02 particles prepared by this method exceeded that of Degussa P25. 

Due to their high costs, weight and size conventional NDE ultrasonic transducers are not suited for active SHM applications. However, novel 1-3 composite transducers such as piezo fiber composites (PFC) are adapted quite well to SHM applications. They can be used for passive as well as for active methods i.e. as transmitters and receivers for ultrasonic waves. PECs are small, lightweight and extremely robust and thus can be structurally embedded for e-NDE purposes in a large number. 

As can be observed in Fig. 8.10, in the case of conventional drying, the dependence of effective diffusivity fitted an Arrhenius-type equation adequately, the activation energy being a characteristic of the product. For ultrasonically assisted dried samples an Arrhenius behavior was observed at low temperatures however, when the temperature reached 70 °C the identified diffusivity was quite similar for both methods of drying, with and without ultrasound application. 

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