Ultrasound effects

Gasgnier M (2000) Ultrasound effects on metallic (Fe and Cr) iron sesquioxide (a-, y-Fe203) calcite copper, lead and manganese oxides as powders. Ultrason Sonochem 7 25-39... 

Ultrasound can be used to supplement or replace the microwave radiation. Ultrasound effects a high frequency mechanical vibration that warms the interior of the exposed object. In this case, the sample can exposed, and heated, as a whole. However, because ultrasonic waves can be so readily focused, it is also possible to apply them in bundled form so that they act on certain selected regions of the blank, for instance by sweeping along a raster. 

Sonophotocatalysis is photocatalysis with ultrasonic irradiation or the simultaneous irradiation of ultrasound and light with photocatalyst. Tnis method includes irradiation with alternating ultrasound and light. Ultrasound effects on heterogeneous photocatalytic reaction systems have been demonstrated by Mason,1 Sawada et al.,2) Kado et al.,3) and Suzuki et al.4) In these papers, not only acceleration of photocatalytic reactions but increase in product selectivity by ultrasonic irradiation has also been reported. It was postulated that ultrasound effects, such as surface cleaning, particle size reduction and increased mass transfer, were the result of the mechanical effects of ultrasound.1,5) Lindley reviewed these and other effects.5)... 

If the yield of a silent reaction is n% after a specific period of time while the yield of the corresponding sonochemical reaction is m%, the ratio min higher than 1 is described as the effect of ultrasound. Since its beginning, ultrasound effects have been considered to originate in the general phenomenon of cavitation, which generates high temperatures, pressures, and shock waves. 

When PCP solution (Id4 M) under continuous air bubbling is subjected to ultrasound effects, the characteristic absorption bands decrease and the treatment leads to a complex mixture of products. Carbon-chlorine bonds are rapidly cleaved, and after a 150-min sonication time, 90% of the chlorine is recovered in the solution as chloride ions. PCP transformation in aerated solution occurs together with nitrite and nitrate formation. Carbon dioxide is a product of PCP degradation, and it has long been recognized as an inhibitor for sonochemical reactions. 

Several others parameters can be used [1—3,16,17] which are related to the main field characteristics and a knowledge of these is of crucial importance to understand and monitor ultrasound effects. The methods used for power measurements and testing of transducers will rely on the measurement of one of these characteristics by direct or indirect methods. 

A number of investigations on ultrasound effects have been carried out in the U.S. these include studies on vacuum-arc melting of nickel-containing alloys and steels under an ultrasonic field [19], on a mechanism of grain refinement in as-cast alloys [20,23], on amorphization of metals (Suslick [21]), on ultrasonic atomization (Grant [22]), and on production of composite materials [23]. 

In Great Britain, Crowford [2], Notlingk and Neppiras [24], Chalmers [25], and a number of other scientists have devoted their work to the ultrasound effect on metallurgical processes. Recently the investigations on intensification of various chemical and metallurgical processes under acoustic cavitation field are centered at Coventry University (Mason [26]). 

Similarly to microwaves, the use ofultrasound can dramatically speed-up chemical reactions and increase the product yield. Table 3.7 shows some examples of such ultrasound effects, both in homogeneous and in heterogeneous reaction systems. More data can be found in the review by Thompson and Doraiswamy [149]. 

Gul, R. J., Wan, P. S., Hyimgsu, K., and Wook, L. 2004. Power ultrasound effects for in situ compat-ibilization of polymer-day nanocomp)osites. Journal of Materials Science and Engineering C 24 285. 

An optimized procedure for the preparation of pyrimidine-2-thione derivatives (110) under mild and clean conditions was achieved by Safaei-Ghomi and Ghasemzadeh (2011). Chalcone derivatives (109) were prepared by the condensation of various substituted aryl aldehydes and acetophenone in alkaline ethanol, while pyrimidine-2-thione derivatives (110) were prepared by the combination of chalcones (109) and thiourea (99) under conventional and ultrasonic conditions. Advantages of the ultrasound effect were observed and high yields (73%-82%) of the products were obtained after 20-30 min sonication (Scheme 8.36). 

In order to increase the ultrasound effects, the reduction of all the samples was performed with hydrazine at 80°C for 20 min undertaking the solid-liquid suspension at a sonication of frequency 21 kHz and power 30 W, calculated with the calorimetric method [7]. This particular power was chosen in order to minimize the possible effects of destruction of the support in fact the transformation of the alumina in fine powder, loosing the morphological structure was observed increasing the power just at 45 W. A change in the alumina phase (usually from n to a phase) was also detected in similar condition at room temprature [8],... 

Fig. 7.6 Contact ultrasound effects on mass transfer at cellular and tissue levels. Effects are shown in relation to the distance from the sonicated surface. Temperature effects and sound pressure amplitude are damped in deeper tissue layers, as depicted in the graph on the left. M, cell membrane W, cell wall L, middle lamella I, intercellular spaces P, pore network. Dotted lines represent membrane damage due to dehydration. 1, Loosening of cell-to-cell...

Carcel, J.A., Benedito, J., Bon, J., Mulet, A., 2007. High intensity ultrasound effects on meat brining. Meat Sci. 76 611-619. 

Power is the total energy irradiated by an ultrasonic system per unit of time (J s or W). Power is very important in ultrasound applications, due to the fact that the greater the power applied in a medium, the higher are the observed ultrasound effects. In general, it is convenient to relate the level of applied energy with the size of the considered system, thereby reporting the ultrasonic energy in a relative form. Thus, the ultrasonic intensity is defined by the power applied per unit of treated area (W m ). The ultrasonic intensity, I, is related to the acoustic pressure. Pa, by... 

The specific acoustic impedance, Z, is the resistance of a medium to the propagation of a sound wave. It can be defined as the ratio of acoustic pressure to the so-called particle velocity at a single frequency (McClements, 1997). At an interface, the proportion of wave energy transmitted or reflected depends on the difference in impedance between the two media. Consequently, this difference determines the coupling between emitting surface and the treated medium. If the impedance difference is large, the proportion of energy reflected will be important and the ultrasound effects will be mainly localized at the interface. However, if the... 

Usually, the transducers are attached to a vibrating system, the function of which is to transmit the vibration from the transducer to the medium. The design of this part of the ultrasonic system is fundamental for optimal transmission of the ultrasonic energy to the medium. From the strict point of view of design, the transducer and the vibrating system must be jointly considered, due to their close interaction. Nevertheless, in this chapter, they are considered separately so as to better illustrate the operation of these ultrasonic devices. It is important to address this point because, on many occasions, the use of an ultrasound effect is discarded because of energy transmission problems. 

Therefore, the main factor responsible for ultrasound effects is the actual ultrasonic energy received by the sample. As a consequence, it is interesting to establish the relationship between the actual ultrasonic power applied and the intensification effects induced by ultrasound. 

It is known that the applied ultrasonic energy determines the extent of ultrasound effects. As stated before, a widely accepted classification of the industrial ultrasound applications divides these into two groups, low-intensity and high-intensity applications. While in the former case the ultrasonic intensity used is... 

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