Sonochemistry advantages

The choice of the solvent also has a profound influence on the observed sonochemistry. The effect of vapor pressure has already been mentioned. Other Hquid properties, such as surface tension and viscosity, wiU alter the threshold of cavitation, but this is generaUy a minor concern. The chemical reactivity of the solvent is often much more important. No solvent is inert under the high temperature conditions of cavitation (50). One may minimize this problem, however, by using robust solvents that have low vapor pressures so as to minimize their concentration in the vapor phase of the cavitation event. Alternatively, one may wish to take advantage of such secondary reactions, for example, by using halocarbons for sonochemical halogenations. With ultrasonic irradiations in water, the observed aqueous sonochemistry is dominated by secondary reactions of OH- and H- formed from the sonolysis of water vapor in the cavitation zone (51—53). 

By the proper choice of solvent and experimental conditions (i.e., low volatility, highly stable liquids at low temperature e.g., decane, -10° C), the rates of degradation of nonaqueous liquids can be made quite slow, well below those of water. This is of considerable advantage, since one may then observe the primary sonochemistry of dissolved substrates rather than secondary reactions with solvent fragments. In general, the examination of sonochemical reactions in aqueous solutions has produced results difficult to interpret due to the complexity of the secondary reactions which so readily occur. One may hope to see the increased use of low-volatility organic liquids in future sonochemical studies. 

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 ... 

The chemical applications of ultrasound (Sonochemistry) have become an exciting new field of research during the past decade. Recently, Li and coworkers have found an efficient and convenient procedure for the preparation of oximes via the condensation of aldehydes and ketones in ethanol with hydroxylamine hydrochloride under ultrasound irradiation (Scheme 8). Compared with conventional methods, the main advantages of the sonochemical procedure are milder conditions, higher yields and shorter reaction periods. The reason may be the phenomenon of cavitations produced by ultrasound. 

Emerging Greener Technologies and Alternative Energy Sources What are the advantages of microwave-assisted synthesis (57) How can electrochemical methods be applied to synthesis (52) How can sonochemistry be applied to synthesis How can reactions incorporate photochemical methods as an alternative energy source (55) What is process intensification ... 

The various advantages of using ultrasound (as can be inferred from Table 22.1) notwithstanding, sonochemistry continues to be a laboratory curiosity with few industrial applications. The chief reasons are the lack of a scale-up rationale and economics. 

Table 10.2 Possible advantages of using sonochemistry in synthesis...

Several examples of Type la sonochemical activation are found in the literature. It should be clear that the main advantage of the present classification is to open the route to a multitude of experiments within the application of the "approximative correspondence principles". The heuristic richness of these principles precisely originates in their looseness. This looseness has several origins, but the practical application is that a reaction recognized as a photochemically or electrochemically induced chain reaction may lead to far better yields of products under sonication. This bonus may be again amplified by the fact that industrial scaling-up of reactions seems better mastered in sonochemistry than in photochemistry or electrochemistry. To find a reservoir of reactions where sonochemical activation could possibly lead to ameliorations, one may consult a number of reviews. ... 

Sonochemistry has often been allied to electro chemistry (sonoelectrochemistry), as many of sonochemistry s benefits are particularly suitable to electrochemical processes, e.g. degassing electrode surfaces, disrupting diffusion layer, improving transport of ions through the double layer and electrode surface cleaning (Mason and Cordemans, 2005), all of which combine to increase efficiency. These advantages again arise due to micro-jet formation near surfaces. 

The explanation for these phenomena was similar to that of Xu et al. [44]. According to sonochemistry, ultrasound can cause high-energy chemical reactions and increase the reactivity of particles. Therefore, lead zirconate tita-nate (PZT) phase can be formed at lower calcination temperature (400 °C) in the created gels. This advantage, together with low-cost starting materials used, will make the hybrid method an attractive approach for industrial febrication of PZT ceramics. It is also believed to be applicable to other materials similar to PZT. 

The advantage of the sonochemistry-based methods is that they produce nanoparticles with a relatively narrow size distribution. One of the limitations of these methods is that the nanoscale metals produced are generally amorphous... 

Sonochemistry offers some unique advantages to chemists an average, operating temperature close to ambient, a high reaction temperature up to 10" K, precise control over the location of the reaction (the ultrasonic field), and a large number of disbursed, reaction sites (the cavitating bubbles), which should help to achieve high reaction yields. 

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