Other Ultrasound-Assisted Methods

The hydrothermal method to synthesize perovskites thin films and powders has a number of advantages, such as high purity and high quality of the product. In order to promote hydrothermal reactions, Ohta et al. [57] developed an ultra-sonic-assisted hydrothermal method and confirmed that it produces dense and thick lead zirconate titanate (PZT) films. For this film, ultrasonic irradiation was used from the beginning of the reaction for 18h, followed by a 6h deposition without ultrasonic irradiation. These results indicate that the ultrasonic irradiation mainly promotes the nucleation process and during the ultrasonic irradiation, the number of grains increases. 

Gedanken and coworkers [64] sonochemically synthesized LaFeOs nanocrys-talline material with high purity and good homogeneity. It was obtained with lower processing temperatures and shorter annealing times. The obtained nanoferrite powder is expected to be used in applications for functional ceramics (sensors, solid oxide fuel cells (SOFCs), electrodes, or even magnetic and ferroelectric applications). 

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Application of Microwave and Ultrasound Irradiation in the Synthesis of Perovskite-Type Oxides ABO 5.22.2 Other Microwave-Assisted Methods... 

In liquid-solid extraction (LSE) the analyte is extracted from the solid by a liquid, which is separated by filtration. Numerous extraction processes, representing various types and levels of energy, have been described steam distillation, simultaneous steam distillation-solvent extraction (SDE), passive hot solvent extraction, forced-flow leaching, (automated) Soxh-let extraction, shake-flask method, mechanically agitated reflux extraction, ultrasound-assisted extraction, y -ray-assisted extraction, microwave-assisted extraction (MAE), microwave-enhanced extraction (Soxwave ), microwave-assisted process (MAP ), gas-phase MAE, enhanced fluidity extraction, hot (subcritical) water extraction, supercritical fluid extraction (SFE), supercritical assisted liquid extraction, pressurised hot water extraction, enhanced solvent extraction (ESE ), solu-tion/precipitation, etc. The most successful systems are described in Sections 3.3.3-3.4.6. Other, less frequently... 

Ultrasound-assisted extraction (USE) is an effective method for leaching many analytes from different kinds of samples [52-55]. It is simple, fast, efficient, and inexpensive in comparison with conventional extraction techniques such as solvent extraction in the Soxhlet apparatus. Ultrasound-assisted solid-liquid extraction is an effective and time-saving extraction method. Sonication accelerates the mass-transfer process between two phases. Use of ultrasound results in a reduction in operating temperature, allowing the extraction of temperature-sensitive components. The ultrasound apparatus is cheaper and its operation is easier in comparison with other novel extraction techniques such as MAE. 

An important problem in this type of analysis is the presence of a matrix, the components of which hamper analysis by falsifying the results or generally making determination impossible. Therefore, in addition to developing appropriate methods of analysis, it is necessary to remove interferents and also to isolate and enrich analytes. For this purpose, various types of extractions are applied, usually LLE and SPE, but also others such as microextraction by packed sorbant (MEPS) and ultrasound-assisted emulsification microextraction (USAEME). 

Ultrasound-assisted slurry formation versus other sample preparation methods... 

Ultrasound-assisted emulsification in aqueous samples is the basis for the so-called liquid membrane process (LMP). This has been used mostly for the concentration and separation of metallic elements or other species such as weak acids and bases, hydrocarbons, gas mixtures and biologically important compounds such as amino acids [61-64]. LMP has aroused much interest as an alternative to conventional LLE. An LMP involves the previous preparation of the emulsion and its addition to the aqueous liquid sample. In this way, the continuous phase acts as a membrane between both the aqueous phases viz. those constituting the droplets and the sample). The separation principle is the diffusion of the target analytes from the sample to the droplets of the dispersed phase through the continuous phase. In comparison to conventional LLE, the emulsion-based method always affords easier, faster extraction and separation of the extract — which is sometimes mandatory in order to remove interferences from the organic solvents prior to detection. The formation and destruction of o/w or w/o emulsions by sonication have proved an effective method for extracting target species. 

Ultrasound-assisted electrolytic reduction of emulsions of activated unsaturated systems provides a method for hydrogenation of water-insoluble materials in an aqueous environment [284]. The effect of ultrasound on electrochemical reactions in emulsions may vary depending on the reaction in some cases solubilization of an insoluble reaction product is furthered, whereas in other cases the heterogeneous rate constant is influenced [284]. 

One other major group of pollutants for which ultrasound-assisted leaching is an effective extraction method is that of polychlorinated biphenyls (PCBs) [43-45]. Their persistence and accumulation in the environment has led to their inclusion in monitoring programme analyses. In most cases, ultrasonic extraction is recommended as a fast, efficient, straightforward choice for these compounds, particularly in routine analyses [44]. 

FIGURE 2.34 Experimental setup used for the two modes of continuous ultrasound-assisted leaching and the possibilities of their coupling to other steps of the anal)dical process. One, two or three steps can he used in a single method. Abbreviations used are LC, leaching carrier PP, peristaltic pump UP, ultrasonic probe EC, extraction chamber WB, water bath W, waste SV, selection valve EX, extract E, eluent IV, injection valve SPC, solid-phase column DR, derivatization reagent RC, reaction coil and D, detector. (Reprinted from Luque-Garcia, J. L. and Luque de Castro, M. D., Trends Anal. Chem., 22, 41-47, 2003. With permission from Elsevier.)... 

A comparison of mechanosynthesis with other synthetic methods showed the superiority of microwave-assisted method and solution conditions over mechanoehemical and ultrasound reactions for the less-reactive carbodiimides. More-reactive carbodi-imides provide full conversion under aU conditions, while best yields were obtained in MW and solution reactions (entries 6 and 7). 

The capsaicinoids are extracted using different solvents and more recently ultrasound-assisted extraction [61], extraction by means of supercritical fluids [65], extraction by pressurized liquids [58] and enzymatic extraction [59], and analyzed by HPLC [64,93-95], GC [72-76], hyphenated systems as HPLC-MS [96-100], and GC-MS [77]. Normally the GC methods require derivatization of the compounds to make them sufficiently volatile for determination. There are many other reported papers have been found in the literature for the analytical separation, quantitation, and identification of naturally occurring capsaicinoids in different matrices. Select matrices are discussed here. 

In this chapter are presented, two different liquid phase chemical synthesis methods for the preparation of M50 steel and iron nano-powders. Also, the compaction of these powders into a consolidated sample and a structural and morphological study of the powders and compacts is described here. One synthetic methodology involves the ultrasound assisted decomposition (26-28) of organometallic precursors and the other involves the use of a reducing agent to produce the fine particles from the elemental halides. In addition, the ultrasound-assisted synthesis of pure iron nanopowders, its compaction and the physical properties are reported. 

Ultrasound has also been used to enhance extraction of oil from oilseed rape (Wei et al., 2008). As with other studies, extraction efficiency was significantly affected by extraction time and extraction power, and then the liquidisolid ratio. A liquidisolid ratio of 1 4 (L g), an ultrasound-assisted extraction time of 60 min, and power of 500 W were found to be optimal for extracting up to 20 mg of ground oilseed rape, when compared to a standard Soxhlet extraction method. 

Ultrasonic-assisted extraction (UAE) is the other common method that accelerates the extraction process [83]. The principle behind the UAE is similar to MAE, where the cell wall is destroyed by ultrasound that leads to active constituents being leached out from ruptured cells without modifying the polysaccharides. In general, UAE is able to extract polysaccharides at lower temperatures, which is about 25-70 °C at 120/300 W of ultrasonic power [89]. The extraction time is between 5 and 40 min. 

Many methods have been reported for production of nanodiamonds (NDs) such as laser ablation, " plasma-assisted chemical vapor deposition," autoclave synthesis from supercritical fluids, ion irradiation of graphite, chlorination of carbides, electron irradiation of carbon onions, and ultrasound cavitation. Smaller NDs can be prepared by detonation processes that yield aggregates of NDs with sizes of 4-5 nm embedded in a detonation soot composed of other carbon allotropes and impurities. An explosive mixture having an overall negative oxygen balance provides a source of both carbon and energy for the conversion. Because of their small size (2-10 nm) detonation NDs have also been referred to as ultradispersed, nanocrystalline... 

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