Ultrasonic wave interaction

Colloidal potassium has recently been proved as a more active reducer than the metal that has been conventionally powdered by shaking it in hot octane (Luche et al. 1984, Chou and You 1987, Wang et al. 1994). To prepare colloidal potassium, a piece of this metal in dry toluene or xylene under an argon atmosphere is submitted to ultrasonic irradiation at ca. 10°C. A silvery blue color rapidly develops, and in a few minutes the metal disappears. A common cleaning bath (e.g., Sono-clean, 35 kHz) filled with water and crushed ice can be used. A very fine suspension of potassium is thus obtained, which settles very slowly on standing. The same method did not work in THF (Luche et al. 1984). Ultrasonic waves interact with the metal by their cavitational effects. These effects are closely related to the physical constants of the medium, such as vapor pressure, viscosity, and surface tension (Sehgal et al. 1982). All of these factors have to be taken into account when one chooses a metal to be ultrasonically dispersed in a given solvent. 

However, this commonly accepted theory is incomplete and applies with much difficulty to systems involving nonvolatile substances. The most relevant example is metals. For a heterogeneous system, only the mechanical effects of sonic waves govern the sonochemical processes. Such an effect as agitation, or cleaning of a solid surface, has a mechanical nature. Thus, ultrasound transforms potassium into its dispersed form. This transformation accelerates electron transfer from the metal to the organic acceptor see Chapter 2. Of course, ultrasonic waves interact with the metal by their cavitational effects. 

PA Meyer, JL Rose. Modeling concepts for studying ultrasonic wave interaction with adhesive bonds. J Adhes 8 107-120, 1976. 

In order to proceed with this goal, an understanding of the ultrasonic wave interaction mechanisms with an adhesive bond or a layered composite structure must be thoroughly understood. Physical models of a bondline or a composite material structure must be formulated. 

Jones, S., A. Amblard, and C. Favreau, 1986, Interaction of an Ultrasonic Wave with a Bubbly Mixture, Exp. Fluids 4 341 349. (3)... 

Ultrasound is used to obtain information about the properties of a material by measuring the interaction between a high frequency sound wave and the material through which it propagates. This interaction depends on the frequency and nature of the ultrasonic wave, as well as the composition and microstructure of the material. The parameters most commonly measured in an ultrasonic experiment are the velocity at which the wave travels and the extent by which it is attenuated. To understand how these parameters are related to the properties of foods it is useful to consider the propagation of ultrasonic waves in materials in general. 

Side wall reflections. If the angle of diffraction of an ultrasonic wave leaving a transducer is large enough, reflections may occur from the side walls of the cell. This reflected ultrasound will interact with the ultrasound which has traveled directly through the sample and affects both velocity and attenuation measurements. It is therefore important to calculate the diffraction angle of the transducer and ensure that the side walls are far enough apart so that side-wall reflections do not interfere with the measurements [1]. 

Ultrasonics can be used to determine the size of particles in microheterogeneous materials in a manner analogous to light scattering. An ultrasonic wave incident upon an ensemble of particles is scattered by an amount which depends on the size of the particles and the ultrasonic wavelength. The scattered waves, interact with the incident wave, which modifies its phase and amplitude. Thus velocity and attenuation measurements can be used to determine particle size. 

A combination of different techniques can frequently improve yields of final compounds or synthetic conditions, for example a reunion of direct electrochemical synthesis and simultaneous ultrasonic treatment of the reaction system [715]. Reunion of microwave and ultrasonic treatment was an aim to construct an original microwave-ultrasound reactor suitable for organic synthesis (pyrolysis and esterification) (Fig. 3.7) [716], The US system is a cup horn type the emission of ultrasound waves occurs at the bottom of the reactor. The US probe is not in direct contact with the reactive mixture. It is placed a distance from the electromagnetic field in order to avoid interactions and short circuits. The propagation of the US waves into the reactor occurs by means of decalin introduced into the double jacket. This liquid was chosen by the authors of Ref. 716 because of its low viscosity that induces good propagation of ultrasonic waves and inertia towards microwaves. 

Most ultrasonic material analyses rely on measurements of some characteristic of ultrasonic waves propagating through the sample that provides information on the interaction of ultrasonic waves with the inside of the sample, thus enabling analysis of its physical and chemical properties. 

Intermediate wavelength regime. Emulsions which contain fairly large emulsion droplets (typically >10 pm) tend to fall in IWR, especially when relatively high ultrasonic frequencies (>10 MHz) are used. Interactions between ultrasonic waves and emulsion droplets are most complicated in this regime, and a wide variety of scattered waves are generated. 

The study of molecular interactions in liquid mixtures is of considerable importance in the elucidation of the structural properties of molecules. Interactions between molecules influence the structural arrangement and shape of molecules. Dielectric relaxation of polar molecules in non-polar solvents using microwave absorption has been widely employed to study molecular structures and molecular interactions in liquid mixtures [81]. Ever since Lagemann and Dunbar developed a US velocity approach for the qualitative determination of the degree of association in liquids [82], a number of scientists have used ultrasonic waves of low amplitude to investigate the nature of molecular interactions and the physico-chemical behaviour of pure liquids and binary, ternary and quaternary liquid mixtures, and found complex formation to occur if the observed values of excess parameters (e.g. excess adiabatic compressibility, intermolecular free length or volume) are negative. These parameters can be calculated from those for ultrasonic velocity (c) and density (p). Thus,... 

Ultrasonics is in many ways the ideal measurement method for fat crystallization studies. The ultrasonic properties of a fat are strongly sensitive to solids content and can be measured in opaque fats and through container walls. In the present work I will describe the basic physics of ultrasonic waves, their interactions with matter (particularly with semi-solid fats), and their measurement. I will then describe ultrasonic studies of fat crystallization in bulk and emulsified fats. Finally I will use some measurements of the effect of applied shear on fat crystallization as an illustration of a study that could not be easily undertaken by other methods. 

Because the energy state of a Jahn-Teller complex depends on the local lattice distortions, the macroscopic long-distant strain that produces an ultrasonic wave should influence it as well. The cross effect is initiated by the Jahn-Teller complexes (1) the dispersion (i.e., frequency-dependent variation of phase velocity) and (2) attenuation of the wave. In terms of the elastic moduli it sounds as appearance (or account) of the Jahn-Teller contribution to the real and imaginary parts of the elastic moduli. For a small-amplitude wave it is a summand Ac. Obviously, interaction between the Jahn-Teller system and the ultrasonic wave takes place only if the wave, while its propagation in a crystal, produces the lattice distortions corresponding to one of the vibronic modes. 

There are two ways in which interaction of the ultrasonic wave and the Jahn-Teller complex can occur by resonant transition between two electron energy levels, or by relaxation between the different possible directions of the Jahn-Teller distortions. 

Scattering of ultrasonic waves dominates over other types of losses in the intermediate wavelength regime (X rp), which represents the case of a system with rather coarse particles (>10 pm) subjected to rather high frequencies (>10 MHz). In the IWR the interaction of ultrasound with the disperse system results in the generation of many types of different waves, and thus many more scattering coefficients are required for the evaluation of the attenuation due to scattering. 

Intrinsic losses are related to the molecular-level interaction of ultrasound with the material of the homogeneous phases making up the disperse system. Ultrasonic waves undergo partial attenuation when they propagate through any homogeneous system. For example, in water this attenuation is very low, 20 dB/cm at 100 MHz [33], In disperse... 

In principle, the ultrasonic techniques described for solid-liquid flow measurement can be applied to measure air flow rate and particle velocity. Direct measurement of air flow rate by measuring upstream and downstream transit times has been demonstrated. But, the Doppler and cross-correlation techniques have never been applied to solid/gas flow because the attenuation of ultrasound in the air is high. Recent developments have shown that high-frequency (0.5-MHz) air-coupled transducers can be built and 0.5-MI Iz ultrasound can be transmitted through air for a distance of at least 1 in. Thus, the cross-correlation technique should be applicable to monitoring of solid/gas flow. Here, we present a new cross-correlation technique that does not require transmission of ultrasonic waves through the solid/gas flow. The new technique detects chiefly the noise that interacts with the acoustic field established within the pipe wall. Because noise may be related to particle concentration, as we discussed earlier, the noise-modulated sound field in the pipe wall may contain flow information that is related to the variation in particle concentration. Therefore, crosscorrelation of the noise modulation may yield a velocity-dependent correlation function. 

The dimensions associated with ultrasound are not on the molecular scale. Thus the chemical effects of ultrasound cannot be attributed to any direct interaction of the acoustic wave with chemical species on a molecular level. Indeed, it is well known now that these effects are the result of the physical processes associated with ultrasonic waves. The most important of these is cavitation. 

The velocity of elastic ultrasonic waves in solution is strongly influenced by solute-solvent and solute-solute interactions which are determined by the chemical structure of the solute and solvent molecules. Still, acoustical methods have made only minor contributions to the detailed description of solute-solvent interactions. Ultrasonic velocity measurements are mostly limited to obtaining hydration numbers of molecules in aqueous solution [Br 75]. The successful application of acoustical methods to physico-chemical investigation of solutions became possible after development of adequate theoretical approaches and methods for precise ultrasonic velocity measurements in small volumes of liquids [Sa 77, Bu 79]. 

The possibility of generating a cloud of droplets by means of ultrasonic waves was first reported by Wood and Lomis [29]. Two different mechanisms have been reported to explain the ultrasonic atomization capillary waves and cavitations. However, the interaction between these two approaches and hmits in which one could predominate over the other depending on the different atomizing situation are challenging for immediate understanding. 

A remarkable effect of strain modulation of the exchange interactions on the elastic properties of the LiTbF4 ferromagnet (see eq. 105) was observed by Aukhadeev et al. (1983). For example, below Tq the velocity v of purely transverse ultrasonic waves of frequency 13 MHz with the wave vector along the [001] direction of the crystal increases sharply, as is evident in fig. 29a which shows the relative variations... 

Fig. 2.18 Principle of ultrasonic attenuation spectroscopy (left) and kinds of particle-wave interaction in sound fields (right)...

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