Sonication

Ultrasonication was reported for the extraction of triazines from soil, previously sieved to 2 mm and stored at -18 °C, prior to analysis using CC/NPD and CC/lTD. A 5-g soil sample was placed in a polypropylene column and extracted for 15 min with 4 mL of ethyl acetate in an ultrasonic bath at room temperature. Subsequently, the solvent was filtered and collected in a graduated tube, and the extraction was repeated for another 15-min period using a second 4-mL portion of ethyl acetate. The two extracts 

With the advent of recent technological advancement the ultrasonic waves may be exploited as a means of agitation, otherwise known as sonication. The most commonly used assembly makes application of a simple ultrasonic bath, in which the reaction vessel is positioned as illustrated in Fig. 3.12. 

Alternatively, ultrasonic probes may also be employed and are invariably arranged well inside the reaction vessel itself, as depicted in Fig. 3.13. This specific reaction assembly is particularly suitable as well as desirable under two arising situations, namely  

however, pertinent to mention here that in either of the two situations (a) and (b) above, the ultrasonic waves are normally produced inside the reaction vessel whereby agitation of its contents can be caused effectively and progressively. 

Nevertheless, the sonication is specifically beneficial for such reactions that essentially involve insoluble solids. In such a situation the ultrasonic waves help to break up the solid lumps/pieces into corresponding very small particles that ultimately facilitate tremendously the solvolysis phenomenon and hence the reaction process. 

Sonochemistry started in 1927 when Richards and Loomis [173] first described chemical reactions brought about by ultrasonic waves, but rapid development of ultrasound in chemistry really only began in the 1980s. Over the past decades there has been a remarkable expansion in the use of ultrasound as an energy source to produce bond scission and to promote or modify chemical reactivity. Although acoustic cavitation plays 

Use of ultrasounds in catalyst preparation leads to higher penetration of the active metal inside the pores of the support and greatly increases the metal dispersion on the support [185]. Major advances in ultrasonic technology have increased the acoustic power and sensitivity of transducers. 

For general aspects on sonochemistry the reader is referred to references [174,180], and for cavitation to references [175,186]. Cordemans [187] has briefly reviewed the use of (ultra)sound in the chemical industry. Typical applications include thermally induced polymer cross-linking, dispersion of Ti02 pigments in paints, and stabilisation of emulsions. High power ultrasonic waves allow rapid in situ copolymerisation and compatibilisation of immiscible polymer melt blends. Roberts [170] has reviewed high-intensity ultrasonics, cavitation and relevant parameters (frequency, intensity, 

Low-intensity ultrasound uses power levels (typically 1 W cm 2) that are considered to be so small that the ultrasonic wave causes no physical or chemical alterations in the properties of the material through which the wave passes, i.e. it is nondestructive. However, 

The main advantages of US are that it is relatively inexpensive, rapid, precise, nondestructive and noninva-sive and can be applied off-line or on-line to systems that are concentrated and optically opaque. One of the major disadvantages of US techniques is the attenuation of US by small gas bubbles. 

Ultrasonic waves can also be employed as a means of agitation. The most common arrangement is to use a simple ultrasonic bath, in which the 

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The basics of the method are simple. Reflections occur at all layers in the subsurface where an appreciable change in acoustic impedance is seen by the propagating wave. This acoustic impedance is the product of the sonic velocity and density of the formation. There are actually different wave types that propagate in solid rock, but the first arrival (i.e. fastest ray path) is normally the compressional or P wave. The two attributes that are measured are... 

The sonic tool measures the time taken for a sound wave to pass through the formation. Sound waves travel in high density (i.e. low porosity) formation faster than in low density (high porosity) formation. The porosity can be determined by measuring the transit time for the sound wave to travel between a transmitter and receiver, provided the rock matrix and fluid are known. 

Hiller, D., and Ermert, H., System Analysis of Ultrasound Reflection Mode Computerized Tomography, IEEE Trans. Sonic Ultrasonic SU-31, pp 240-250, (1984). 

Rowell and co-workers [62-64] have developed an electrophoretic fingerprint to uniquely characterize the properties of charged colloidal particles. They present contour diagrams of the electrophoretic mobility as a function of the suspension pH and specific conductance, pX. These fingerprints illustrate anomalies and specific characteristics of the charged colloidal surface. A more sophisticated electroacoustic measurement provides the particle size distribution and potential in a polydisperse suspension. Not limited to dilute suspensions, in this experiment, one characterizes the sonic waves generated by the motion of particles in an alternating electric field. O Brien and co-workers have an excellent review of this technique [65]. 

Phospholipid molecules form bilayer films or membranes about 5 nm in thickness as illustrated in Fig. XV-10. Vesicles or liposomes are closed bilayer shells in the 100-1000-nm size range formed on sonication of bilayer forming amphiphiles. Vesicles find use as controlled release and delivery vehicles in cosmetic lotions, agrochemicals, and, potentially, drugs. The advances in cryoelec-tron microscopy (see Section VIII-2A) in recent years have aided their characterization [70-72]. Additional light and x-ray scattering measurements reveal bilayer thickness and phase transitions [70, 71]. Differential thermal analysis... 

This somewhat lengthy experiment provides a thorough introduction to the use of GG for the analysis of trace-level environmental pollutants. Sediment samples are extracted by sonicating with 3 X 100-mL portions of 1 1 acetone hexane. The extracts are then filtered and concentrated before bringing to a final volume of 10 mL. Samples are analyzed with a capillary column using a stationary phase of 5% phenylmethyl silicone, a splitless injection, and an EGD detector. 

Solutions of solids may need to be converted into aerosols by pneumatic or sonic-spraying techniques. After solvent has evaporated from the aerosol droplets, the residual particulate solid matter can be ionized by a plasma torch. 

The flow velocity is thus proportional to the difference in transit time between the upstream and downstream directions and to the square of the speed of sound in the fluid. Because sonic velocity varies with fluid properties, some designs derive compensation signals from the sum of the transit times which can also be shown to be proportional to C. 

The flow velocity in this design is therefore proportional to the difference between the frequencies but independent of sonic speed within the fluid. 

Vibration-dampening properties at sonic and ultrasonic frequencies are excellent. However, the thickness of the resin must be sufficient to absorb... 

In water, a particle of lecithin exhibits myelin growth, ie, cylindrical sheets that are formed by bdayers and are separated by water which may break up into liposomes (vesicles with a single bilayer of Hpid enclosing an aqueous space). PhosphoHpids more generally form multilamellar vesicles (MLV) (5). These usually are converted to unilamellar vesicles (ULV) upon treatment, eg, sonication. Like other antipolar, surface-active agents, the phosphoHpids are... 

In the manufacture of meltblown fabrics, a special die is used in which heated, pressurized air attenuates the molten polymer filament as it exits the orifice of the dye or nozzle (Fig. 9). Air temperatures range from 260—480°C with sonic velocity flow rates (43). 

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