Process ultrasound

High quality one-dimensional copper sulfide (CuS) nanorods (50-200 nm) have been demonstrated using template assisted electrochemical deposition, a sonoelec-trochemical method. Thus generated nanorods were also electrically characterized as p-type semiconductors [64]. In this process, ultrasound assists the electrochemical deposition by the combination of any of the following three processes ... 

E.S. Tarleton and R.J. Wakeman, Ultra-sonically assisted separation processes. Ultrasound in Food Processing, M.J.W. Povey... 

J.A. Gallego-Juarez, Some applications of air-bome power ultrasound to food processing. Ultrasound in Food Processing, M. Povey and T.J. Mason (eds.), Blackie Academic and Professional, 1998,... 

There are at present only a few commercial applications of ultrasound in the plastics industry. The best knovm is probably the welding of thermoplastics, a process which now lends itself readily to automation. In common with the welding of metals, the ultrasonic welding of plastics is primarily a hot stage. In the process ultrasound is applied to two layers of plastic, heat is generated at the interface causing the material... 

The electrodeposition process is complicated, but can be simply thought of as the transfer of ions to and/or from the metal surface [58], It is well known that when a metal is immersed in an aqueous solution a diffusion layer (Nemst diffusion layer) forms at the metal/solution interface. If an electrochemical reaction is to occur at the metal surface it is therefore necessary for ions to be transported across this diffusion layer. Any process which can affect this layer will therefore influence the electrochemical process. Ultrasound is known to reduce the thickness of this diffusion layer [26] but is unlikely to completely remove it as was suggested by early Russian workers. Ultrasound can also effect electrochemical reactions since it produces surface cavitation and acoustic streaming both of which assist diffusion to and from the metal surface, this movement often being the rate-controlling step in electrochemical processes such as deposition. 

The power requirements are not large (400 W for 400 kg of final product in a 4-m batch) and therefore are rather interesting. Moreover, in the process, ultrasound... 

With respect to pol5unerization processes, ultrasound has significant potential as a clean and safe technology. After the production of most types of polymers, catalyst and initiator residues contaminate the product. Since ultrasound generates the radicals in situ (4,5), no initiator or catalyst is required to start a polymerization reaction. An additional advantage of ultrasound is the intrinsic safe... 

For the development of sustainable polymer processes, ultrasound is an interesting technology, as it allows for polymerizations without the use of initiator. The radicals are generated in situ by cavitation events [116, 117], which make possible a dean and intrinsically safe polymerization reaction. As a result of the high strain rates outside the bubble, cavitation can also induce chain scission [118,119], which provides an additional means to control the molecular weight of the polymer produced. In Sections 21.3.1 and 21.3.2 the physical background of ultrasound-induced cavitation and radical formation will be described. Subsequently (see Section 21.3.3), an overview of the several types of ultrasound-induced polymerizations will be given, namely bulk, predpitation, and emulsion polymerization. 

Speckle shearing interferometry, or shearography, is a full field optical inspection teclmique that may be used for the nondestructive detection of surface and, sometimes, subsurface defects. Whilst being more sensitive in the detection of surface defects, it may also be considered for pipe inspection and the monitoring of internal conoslon. In contrast, laser ultrasound and other forms of ultrasound, are point by point measurement techniques, so that scanning facilities and significant data processing is required before information on local defects is extracted from any examination of extensive areas [1 - 3]. 

The weld depths penetration for gold-nickel alloy and tantalum cylinders have been well controlled by an entirely contactless ultrasound method. Nevertheless, the development of signal and image processing will allow to increase the resolution of the ultrasonic images. Moreover, in order to be able to size quite well the lacks of weld penetration, the simulation of the interaction beam-defect is presently developed in our laboratory. 

Homogeneous sonochemistry typically is not a very energy efficient process (although it can be mote efficient than photochemistry), whereas heterogeneous sonochemistry is several orders of magnitude better. Unlike photochemistry, whose energy inefficiency is inherent in the production of photons, ultrasound can be produced with neatly perfect efficiency from electric power. A primary limitation of sonochemistry remains the small fraction... 

The first improvement of the Bucherer-Bergs reaction was the Bucherer-Lieb variation using the diluted alcoholic solution as described at the end of section 7.2.2. The Bucherer-Lieb variation is possibly the most popular process for synthesizing hydantoins. Another notable variation is the Henze modification using fusing acetamide as the solvent in place of water, benzene or 50% alcohol. Recently, ultrasound-promoted hydantoin synthesis has been reported to accelerate the reaction. 

Unlike vibration monitoring, ultrasonics monitors the higher frequencies, i.e. ultrasound, produced by unique dynamics in process systems or machines. The normal monitoring range for vibration analysis is from less than 1 Hertz to 20,000 Hertz. Ultrasonics techniques monitor the frequency range between 20,000 and 100 kHz. 

In the contact mode, a metal rod acts as a waveguide. When it touches a surface, it is stimulated by the high frequencies, ultrasound, on the opposite side of the surface. This technique is used to locate turbulent flow and or flow restriction in process piping. 

Most disease-specific molecular and cellular processes involve low concentrations and have low capacities. Therefore, molecular imaging requires highly sensitive imaging modalities to detect and quantify the imaging probes as it is done with short-lived radioisotopes. Optical imaging and ultrasound are next in sensitivity. MRI would require too high contrast agent concentrations... 

Thus the product in such cases can exist as two pairs of enantiomers. In a di-astereoselective process, one of the two pairs is formed exclusively or predominantly as a racemic mixture. Many such examples have been reported. In many of these cases, both the enolate and substrate can exist as (Z) or (E) isomers. With enolates derived from ketones or carboxylic esters, (E) enolates gave the syn pair of enantiomers (p. 146), while (Z) enolates gave the anti pair. Addition of chiral additives to the reaction, such as proline derivatives, or (—)-sparteine lead to product formation with good-to-excellent asynunetric induction. Ultrasound has also been used to promote asymmetric Michael reactions. Intramolecular versions of Michael addition are well known. ... 

An interesting way to retard catalyst deactivation is to expose the reaction mixture to ultrasound. Ultrasound treatment of the mixture creates local hot spots, which lead to the formation of cavitation bubbles. These cavitation bubbles bombard the solid, dirty surface leading to the removal of carbonaceous deposits [38]. The ultrasound source can be inside the reactor vessel (ultrasound stick) or ultrasound generators can be placed in contact with the wall of the reactor. Both designs work in practice, and the catalyst lifetime can be essentially prolonged, leading to process intensification. The effects of ultrasound are discussed in detail in a review article [39]. 

Ultrasound can thus be used to enhance kinetics, flow, and mass and heat transfer. The overall results are that organic synthetic reactions show increased rate (sometimes even from hours to minutes, up to 25 times faster), and/or increased yield (tens of percentages, sometimes even starting from 0% yield in nonsonicated conditions). In multiphase systems, gas-liquid and solid-liquid mass transfer has been observed to increase by 5- and 20-fold, respectively [35]. Membrane fluxes have been enhanced by up to a factor of 8 [56]. Despite these results, use of acoustics, and ultrasound in particular, in chemical industry is mainly limited to the fields of cleaning and decontamination [55]. One of the main barriers to industrial application of sonochemical processes is control and scale-up of ultrasound concepts into operable processes. Therefore, a better understanding is required of the relation between a cavitation coUapse and chemical reactivity, as weU as a better understanding and reproducibility of the influence of various design and operational parameters on the cavitation process. Also, rehable mathematical models and scale-up procedures need to be developed [35, 54, 55]. 

Schlaberg, H.I., Yang, M., and Hoyle, B.S. (1997) Ultrasound reflection tomography for industrial processes. 17th Ultrasonics International Conference (U1 97), 1997, Delft. 

Yang, M. et al. (1999) Real-time ultrasound process tomography for two-phase flow imaging using a reduced number of transducers. IEEE Trans. Ultrason. Ferroelectr. Freq. 

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