Cavitation, ultrasonic

For general aspects on sonochemistry the reader is referred to references [174,180], and for cavitation to references [175,186]. Cordemans [187] has briefly reviewed the use of (ultra)sound in the chemical industry. Typical applications include thermally induced polymer cross-linking, dispersion of Ti02 pigments in paints, and stabilisation of emulsions. High power ultrasonic waves allow rapid in situ copolymerisation and compatibilisation of immiscible polymer melt blends. Roberts [170] has reviewed high-intensity ultrasonics, cavitation and relevant parameters (frequency, intensity,... 

Ultrasonic cavitation (using high-energy ultrasonic vibrations to generate high temperatures and pressures). 

Feng R, Zhao Y, Zhu C, Mason TJ (2002) Enhancement of ultrasonic cavitation yield by multi-frequency sonication. Ultrason Sonochem 9 231-236... 

Doulah MS (1977) Mechanism of disintegration of biological cells in ultrasonic cavitation. Biotech Bioeng 19 649-660... 

Virone C, Kramer H, Rosmalen G, Stoop A, Bakker T (2006) Primary nucleation induced by ultrasonic cavitation. J Cryst Growth 294( 1) 9—15... 

Sivakumar M, Towata A, Yasui K, Tuziuti T, Iida Y (2005) Ultrasonic cavitational activation a simple and feasible route for the direct conversion of zinc acetate to highly monodispersed ZnO. Chem Lett 35(1) 60—61... 

The amount of precipitated bismuth decreased as the concentration of bismuth salt increased (Table 9.16) and the duration of sonication required to bring about hydrolysis also increased. The initial reaction was spontaneous as per Eq. (9.111), which, however, seemed to be facilitated by ultrasonic cavitation at high concentration of bismuth. Since the H+ ions were also produced during the formation of bismuthyl ion, at the point where the sum of concentration of H+ ions present initially and formed by Eq. (9.110) was equal to the concentration required to shift the equilibrium of Eq. (9.111) towards left side, the hydrolysis did not occur even after sonication. 

Lindstrom O (1955) Physico-chemical aspects of chemically active ultrasonic cavitation in aqueous solutions. J Acoust Soc Am 27(4) 654-671... 

It seems reasonable to note that the micro-jet stream generated by the ultrasonic cavitation promotes mass transport. Such an effect was discussed for proton transport in aqueous solutions (Atobe et al. 1999). Understandably, a proton moves in the solution as a hydrated particle. Nevertheless, we should pay attention on the similarity between proton and electron, in the sense that both are essentially quantum particles. A solvated electron, therefore, can be considered as a species that is similar to a hydrated proton. Hence, the micro-jet stream can promote electron transfer. 

Fuciarelli AF, Sisk EC, Thomas RM, Miller DL (1995) Induction of base damage in DNA solutions by ultrasonic cavitation. Free Radical Biol Med 18 231-238 Fulford J, Bonner P, Goodhead DT, Flill MA, O Neill P (1999) Experimental determination of the dependence of OH radical yield on photon energy a comparison with theoretical simulations. J Phys Chem A 103 11345-11349... 

Sirotyuk (ref. 25) found that the complete removal of solid particles from a sample of water increased the tensile strength by at most 30 percent, indicating that most of the gas nuclei present in high purity water are not associated with solid particles. Bernd (ref. 15,16) observed that gas phases stabilized in crevices are not usually truly stable, but instead tend to dissolve slowly. This instability is due to imperfections in the geometry of the liquid/gas interface, which is almost never exactly flat (ref. 114). Medwin (ref. 31,32) attributed the excess ultrasonic attenuation and backscatter measured in his ocean experiments to free microbubbles rather than to particulate bodies this distinction was based on the fact that marine microbubbles in resonance, but prior to ultrasonic cavitation (ref. 4), have acoustical scattering and absorption cross sections that are several orders of magnitude greater than those of particulate bodies (see Section 1.1.2). 

In line with discussions included in previous sections, ultrasonic experiments carried out on fresh water by different investigators indicate that the stabilization of gas microbubbles, acting as gas nuclei for ultrasonic cavitation, is always attributable to the presence of surface-active substances in the water (ref. 15-17,25). As a starting point, one should consider that laboratory tests with various tap waters, distilled waters, and salt solutions have shown that no water sample was ever encountered that did not contain at least traces of surface-active material (ref. 46). Sirotyuk (ref. 25) estimates that the content of surface-active substances in ordinary distilled water amounts to 10 7 mole/liter, and in tap water it is 10"6 mole/liter or higher. These values indicate the appreciable content of such substances in both cases (ref. 122), although they differ by roughly an order of magnitude in absolute value. It is essentially impossible to completely remove... 

M.G. Sirotyuk, Experimental investigation of ultrasonic cavitation, in L.D. Rozenberg (Ed.), Physics and Technology of High-Intensity Ultrasound, Vol. 2, High-Intensity Ultrasonic Fields, Nauka, Moscow, 1968. 

D.R. Gross, D.L. Miller and A.R. Williams, A search for ultrasonic cavitation within the mammalian cardiovascular system, Fed. Proc. 43 (1984) 297. 

Chow et al. (2004) reported dynamic video images of the influence of ultrasonic cavitation on the sonocrystallization of ice at a microscopic level. The ultrasonic device was used in combination both with an optical... 

Methods which would produce a surface morphology dependent on the local hardness might, however, be applicable. One such experimental technique uses ultrasonic cavitation to detect hardness differences (18). The sample and an ultrasonic transducer placed near the surface to be studied are immersed in a liquid. 

Another major chemical phenomenon related to ultrasonic cavitation is sonolumi-nescence, by which a tiny light is formed in a cool liquid. This form of light emission results from the high-temperature formation of reactive chemical species in excited electronic states. Emitted light from such states provides a spectroscopic probe for the cavitation effect. Some electrical and thermal theories on this phenomenon have been reported [25]. 

Miller MW, Miller DL, Brayman AA (1996) A review of in vitro bioeffects of inertial ultrasonic cavitation from a mechanistic perspective. Ultrasound Med Biol 22 1131-1154... 

Miller DL, Pislaru SV, Greenleaf IE (2002) Sonoporation mechanical DNA delivery by ultrasonic cavitation. Somat Cell Mol Genet 27 115-134... 

All the effects reflect the physical phenomenon of acoustic or ultrasonic cavitation. With this, to initiate the cavitation one must apply a certain threshold sound pressure designated as a cavitation threshold and determine the cavitation strength of a liquid. 

One of the most interesting problems of ultrasonic cavitation is the existence of the diffusive growth of bubbles in a sound field. As, without any field, a gas bubble should slowly dissolute due to gas diffusion from the bubble to a liquid, directional gas diffusion from liquid to the bubble arises under conditions of the bubble surface... 

Considering the results of the ultrasonic degassing action on the melt of commercial aluminum in a wide range of ultrasonic intensity, one can note that the dependence given in Figure 11 is characterized by three specific regions. The formation of these regions may be interpreted as the initiation and development of ultrasonic cavitation in a liquid metal [48]. 

Accordingly, the following stages of the process of cleaning and degassing (corresponding to the peculiarities of ultrasonic cavitation of liquid metal) occur simultaneously or sequentially in the melt subjected to the ultrasonic treatment in the mode of developed cavitation ... 

Irrespective of the conditions ensuring the abnormally rapid movement of a liquid in a capillary under acoustic cavitation effect, it is important to note that the sonocapillary effect follows all the major effects of the ultrasonic treatment of melts. Among such phenomena are wetting and activation of solid nonmetallic impurities in a liquid metal as well as fine filtration of a melt through porous filters under action of the ultrasonic cavitation treatment. For both processes, ultrasonic cavitation and sonocapillary effect with formation of cumulative jets provide the accelerated mass transfer of a melt to slots and cracks in the surface of nonwettable solid particles and into capillary channels of fine filters. 

The occurrence of ultrasonic cavitation and corresponding loss of acoustic power result in the appearance of intensive streams which change the direction of liquid metal movement, typical for casting under silent conditions of casting, from the bath surface to the solidification front. With this, the surface of solidification becomes more flat and the volume of the liquid metal in the bath somewhat increases. 

From the theory of irreversible thermodynamic processes, one can conclude that mass transfer in porous capillary walls occurs much more effectively with the pressure difference along the channel length rather than diffusion. In other words, the pressure difference in the capillary channel entrance can ensure abnormally rapid filling of the capillary with a liquid. Seemingly, this mechanism provides the filling of cracks of nonsoluble solid particles of plankton under action of ultrasonic cavitation. There is no necessity for long exposures for the activation of plankton particles because two or three periods of cavity pulsation (about 100-150 ps) are sufficient for the cavity collapse and filling of the capillary with a liquid metal under action of the impulse of 102 MPa. 

Under conventional casting conditions (without ultrasonic cavitation), the supercooling of a melt arising at the solidification front can spread into the liquid metal with a simultaneously decrease of the degree of supercooling. This process is due to convective streams and, particularly, due to forced movement of the melt with electromagnetic or mechanical stirring. 

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