Ultrasonic field

The problem of material type determination was decided on the base of data obtained, that is the value of deviation dispersion characteristics from analogous ultrasonic field characteristics in the model heterogeneous flawless medium with given type of structure. 

The scheme of dispersion effects displayed in engineering materials of different structures was considered and an analysis of the causes of their occurrence was performed in our work. The spectrum of structural noise is considered as an element of unified spectral characteristics, reflected interaction of the ultrasonic field with given parameters and heterogeneous medium... 

We used the concept of sound velocity dispersion for explanation of the shift of pulse energy spectrum maximum, transmitted through the medium, and correlation of the shift value with function of medium heterogeneity. This approach gives the possibility of mathematical simulation of the influence of both medium parameters and ultrasonic field parameters on the nature of acoustic waves propagation in a given medium. 

Gengembre N. and Lhemery A., Transient ultrasonic fields radiated by water-coupled transducers into anisotropic solids. Review of Progress in Quantitative Non Destructive Evaluation (Plenum, New-York, 1998), to appear. 

Many inspection problems cannot simply be solved by means of standard NDT equipment Also in the ultrasonic field many applications require a special adaptation of instruments and especially the probes to the requirements of the inspection problem. 

In chemical micro process technology there is a clear dominance of pressure-driven flows over alternative mechanisms for fluid transport However, any kind of supplementary mechanism allowing promotion of mixing is a useful addition to the toolbox of chemical engineering. Also in conventional process technology, actuation of the fluids by external sources has proven successful for process intensification. An example is mass transfer enhancement by ultrasonic fields which is utilized in sonochemical reactors [143], There exist a number of microfluidic principles to promote mixing which rely on input of various forms of energy into the fluid. 

On a laboratory scale, generally an ultrasonic probe (horn) and an ultrasonic cleaner are used. The ultrasonic field in an ultrasonic cleaner is not homogeneous. Sonication extraction uses ultrasonic frequencies to disrupt or detach the target analyte from the matrix. Horn type sonic probes operate at pulsed powers of 400-600 W in the sample solvent container. Ultrasonic extraction works by agitating the solution and producing cavitation in the... 

More recently, Saez et al. [27] have carried out numerical simulations to characterize the ultrasonic field propagation and to obtain the spatial distribution of the mechanical effects. The model is based on the assumption of linear wave propagation in a homogeneous media and the results are based on the solution of the... 

Finally, the intrinsic features of the ultrasonic field, frequency and power, should also be taken into account in the design of the experimental arrangement. It is obvious that the mechanical and chemical effects derived from a low frequency field are quite different than those provided by high frequency fields, and these features should match with features of the electrode materials such dimension, structure and physical and chemical properties [30]. 

Agullo E, Gonzalez-Garcia J, Exposito E et al (1999) Influence of an ultrasonic field on lead electrodeposition on copper using a fluoroboric bath. New J Chem 23 95-101... 

Dalas E (2001) The effect of ultrasonic field on calcium carbonate scale formation. J Cryst Growth 222(l) 287-292... 

Bradley M, Grieser F (2002) Emulsion polymerization synthesis of cationic polymer latex in an ultrasonic field. J Colloids Interface Sci 251 (1) 78—84... 

For the sonochemical studies of divalent ions especially in the aqueous solution, not many references are available in the literature. Nevertheless, in an attempt to discuss the nature of the metal and their metal ions in aqueous chemical reactions, under ultrasonic field, the available references have been reported to confirm the understanding about the behavior of such cations. 

The behavior of Cu(II)(aq) is relatively more understood than other metal ions. Haas and Gedanken [74] found only a partial reduction of Cu2+ ions to Cu+ (95%) instead of metallic copper (5.1%) in the presence of cetyltrimethylammonium bromide in an ultrasonic field and thus obtained CuBr particles instead of Cu. Nevertheless, when polymers such as poly(N-vinyl 2-pyrrolidone) or poly(vinyl alcohol) were used, the end product was metallic copper particles, as expected. They have proposed the reduction of Cu2+ ions to copper as the first stage, however, in the second stage Cu reacted with OH radicals or H2O2, formed by sonolysis of water to produce Cu+ and OH- ions as under ... 

Keeping in mind the above work, experiments were carried out to examine the effects of ultrasound, on the dissolution of zinc metal in an alkaline medium and the decomposition of zinc-dithizone complex in the presence of an ultrasonic field. To examine the effect of power ultrasound on the dissolution of zinc metal in alkaline media, 0.0480 g zinc metal was treated with 10 ml of 5 M NaOH solution. Two samples of this solution were exposed to ultrasound for 15 and 30 min, while, control samples were also kept in the similar condition and for the same duration. To compare their spectra and concentration of dissolved zinc in sonicated and control conditions, zinc-dithizone complex was formed by adding 0.5 ml of 0.005% dithizone solution. The red coloured complex, thus obtained, was extracted in chloroform and made upto to the mark in 25 ml volumetric flask with chloroform. 

As could be seen in the Fig. 9.2, the peak of Zn-dithizone complex gradually decreased as the time of sonication increased (10-30 min). It could be due to the dissociation of Zn-dithizone complex in the presence of an ultrasonic field. 

Ultrasound enhanced the rate of dissolution of zinc metal in alkaline media, 2-3 times in sonicated condition rather than the unsonicated condition, due to the cleaning of metal surface in ultrasonic field. Decomposition of Zn-dithizone complex was also observed in ultrasonic field. In sonicated samples, the peak of... 

Zn-dithizone complex gradually decreased (Fig. 9.2). Mechanism for the decomposition of this complex could thus be explained that the complex was broken into zinc ions and dithizone before dithizone molecules were oxidised to S=C (N=NC6H5)2, which, however, did not react further with metal ions [114] and therefore, the Zn-dithizone complex was decomposed. The decomposition of Zn-dithizone complex could thus be attributed to the oxidation of dithizone molecule in ultrasonic field. 

The precipitation of arsenic with H2S gas in the normal condition could occur only in strongly acidic medium whereas another cation of the second group Cd(II), precipitates only in faintly acidic medium, therefore, the precipitation of both cadmium and arsenic with H2S gas in the same solution was not easily possible. To precipitate both in the same solution, the H2S gas is conventionally first passed into the strongly acidic original solution of basic radicals followed by its bubbling into the diluted solution. To examine the role of ultrasound on the precipitation of arsenic in faintly acidic or neutral medium, few experiments were carried out. The results obtained showed effective precipitation of arsenic even in mild reaction solutions, with their pH ranging from 5.1 to 8.8. under ultrasonic field. Hence Cd2+ and As3+/5+ both could be precipitated in the same solution at low pH under the... 

A scheme could thus be proposed for the precipitation and removal of arsenic in the ultrasonic field in the ppm and ppb range at normal pH as provided in Fig. 9.3. 

Virtanen AJ, Ellfolk NJ (1950) Nitrogen fixation in an ultrasonic field. J Am Chem Soc 72 1046-1047... 

Virtanen AJ, Ellfolk NJ (1952) Inhibition of oxidative nitrogen fixation in ultrasonic field by volatile substances. Acta Chem Scand 6(5) 660-666... 

Baranchikiv AE, Ivanov VK, Muraveva GP, Oleinikov NN, Tretyakov Yu D (2004) Kinetics of the formation of zinc ferrite in an ultrasonic field. Dokl Chem 397(Part I) 146-148... 

Pankaj, Manju C (2006) pH independent precipitation of arsenic as sulphide under ultrasonic field. J Ind Council Chem 23(1) 41 f3... 

Preliminary observations of the reactions of Fe(II) and Fe(III) in an ultrasonic field revealed conversion of Fe(II) to Fe(III) and vice-versa, even without any external oxidant/reductant, which were subsequently confirmed experimentally and sequentially through the following four qualitative conversions. The details are available in the literature [35]. 

General sonochemical studies of both chromium and manganese have been reported separately due to strong oxidising nature of these ions. However, comparative strength of their oxidising powers, in an ultrasonic field, is of some technical... 

How a piece of kitchen aluminium foil in water could be eroded in an ultrasonic field due to acoustic cavitation. The foil, after a few minutes of sonication, had several holes. 

Procedure Effects of ultrasound on the following reaction can be seen clearly, when the reactions are carried out both in the ultrasonic field as well as under normal conditions. The yield in most of the reactions increased due to cavitation and mass flow but a decrease could also be sometimes expected due to volatility of one of the reagents. The average increase/decrease in the yield of product, reported here, is an average of two sets of reactions carried out separately under sonicated and mechanical stirring conditions. 

Fig. 17.5 Ultrasonically levitated microdroplet dye laser. Left. Photograph of a lasing levitated microdroplet. Right. Schematics of ultrasonic field with the microdroplet being trapped at a node in the ultrasonic field. Reprinted from Ref. 11 with permission. 2008 Optical Society of America...

Some design concepts for generating uniform droplets have been proposed by Lee et al.[88] These include (a) centrifugal type chamber, (b) atomization by two opposing air-liquid jets, and (c) spinning disk coupled with an ultrasonic field. Some other conceptions include (d) rocket nozzle chamber, (e) frozen particles, (f) rotating brush, and (g) periodic vibrations using saw-tooth waves, etc. 

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