Ultrasonic vibration, potential differences

The colloid vibration potential (difference) E or CVP is the a.c. potential difference measured between two Identical relaxed electrodes, placed in the dispersion if the latter Is subjected to an (ultra)sonlc field. CVP Is a particular case of the more general phenomenon, ultrasonic vibration potential (UVP), applying to any system, whether or not colloids are present. This field sets the particles into a vibrating motion, as a result of which the centres of particle charge and countercharge are periodically displaced with respect to each other. This phenomenon is the a.c. equivalent of that observed in the Dorn effect. Counterpart to this is the electrokinetic sonic amplitude, ESA, the amplitude of the (ultra)sonlc field created by an a.c, electric field in a dispersion. 

Figure 5.17 Principle of acoustophorcsis. Concerning the UVP (Ultrasonic Vibration Potential - top), an ultrasonic wave applied on a liquid (transducer) induces solvent motion. As the two charged species have a different masses and frictional coefficients, its move differently. The charge heterogeneonsness which appeared in this way generate a macrr opic and thus measurable electric field (electrodes). Concerning the ESA (Electro Sonic Amplitude - bottom), an alternative electric field is applied (electrodes). Eachs ion species moves in opposite direction. This motion induces a detectable ultrasonic wave (transducer).

Figure 4. Inhomogeneity of silica-aluminas prepared by various methods. A series of 17 commercial samples of silica-aluminas from seven different producers was submitted to microanalysis. All of them showed considerable fluctuations of composition at the scale of several tens of nanometers to several micrometers. These samples were prepared by coprecipitation or by the sol-gel method. It is not known whether some of these samples were prepared from alkoxides. Smaller but significant fluctuations at the micrometer scale were also observed for two laboratory samples prepared from alkoxides. The samples were dispersed in water with an ultrasonic vibrator. A drop of the resulting suspension was deposited on a thin carbon film supported on a standard copper grid. After drying, the samples were observed and analyzed by transmission electron microscopy (TEM) on a JEOL-JEM 100C TEMSCAN equiped with a KEVEX energy dispersive spectrometer for electron probe microanalysis (EPM A). The accelerating potential used was 100 kV.

In 1933 Peter Debye formulated a sophisticated theory about all this. He assumed, as is also intuitively obvious, that the supersonic emf, that is, the ionic vibration potential produced by the ultrasonic beam, would be proportional to the difference of the masses of the moving ions. Debye s expression can be reduced to... 

The colloid vibration current (CVI) is the amplitude of the alternating current induced by an ultrasonic held. The potential difference is sensed by two identical electrodes. The theory of instruments based on CVI is discussed in detail in [303]. Recommendations and limitations are similar for CVI and ESA. Both techniques require calibration against standard dispersions or solutions, and then the quality of the results depends on the quality of the standard. 

In 1933 Debye published a theoretical study in which he predicted the origination of an electric field, the so-called ionic vibration potential (IVP), upon the passage of ultrasonic waves through electrolyte solutions [34]. Debye outlined that ultrasonic waves should cause the separation of charges due to the differences in the effective masses and friction coefficients of the solvated anions and cations, and suggested that such an effect might serve as a means... 

Electroacoustic phenomena. They are electrokinetic phenomena that have recently gained interest, both experimentally and theoretically. In the ESA (electrokinetic sonic amplitude) technique, an alternating electric field is applied to the suspension and the sound wave produced in the system is detected and analyzed. The colloid vibration potential (CVP) or colloid vibration current (CVI) is the reciprocal of the former a mechanical (ultrasonic) wave is forced to propagate through the system, and the resulting alternating potential difference (or current) is measured. 

An analogous effect can be measured if a suspension or sol is subjected to ultrasonic vibrations As a consequence of the difference in motion between the particles and the dispersion medium potential differences are generated between the nodes and the antinodes of the ultrasonic wave... 

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