Ultrasound sonoluminescence

Objective To produce, visualise and quantify different forms of luminescence produced by ultrasound sonoluminescence and luminol sonochemical... 

Ultrasound Sonoluminescence Acts as a catalyst in many situations... 

The chemical effects of ultrasound do not arise from a direct interaction with molecular species. Ultrasound spans the frequencies of roughly 15 kH2 to 1 GH2. With sound velocities in Hquids typically about 1500 m/s, acoustic wavelengths range from roughly 10 to lO " cm. These are not molecular dimensions. Consequently, no direct coupling of the acoustic field with chemical species on a molecular level can account for sonochemistry or sonoluminescence. 

The phenomenon of acoustic cavitation results in an enormous concentration of energy. If one considers the energy density in an acoustic field that produces cavitation and that in the coUapsed cavitation bubble, there is an amplification factor of over eleven orders of magnitude. The enormous local temperatures and pressures so created result in phenomena such as sonochemistry and sonoluminescence and provide a unique means for fundamental studies of chemistry and physics under extreme conditions. A diverse set of apphcations of ultrasound to enhancing chemical reactivity has been explored, with important apphcations in mixed-phase synthesis, materials chemistry, and biomedical uses. 

In some literature, there is a description that a bubble with linear resonance radius is active in sonoluminescence and sonochemical reactions. However, as already noted, bubble pulsation is intrinsically nonlinear for active bubbles. Thus, the concept of the linear resonance is not applicable to active bubbles (That is only applicable to a linearly pulsating bubble under very weak ultrasound such as 0.1 bar in pressure amplitude). Furthermore, a bubble with the linear resonance radius can be inactive in sonoluminescence and sonochemical reactions [39]. In Fig. 1.8, the calculated expansion ratio (/ max / Rq, where f max is the maximum radius and R0 is the ambient radius of a bubble) is shown as a function of the ambient radius (Ro) for various acoustic amplitudes at 300 kHz [39]. It is seen that the ambient radius for the peak in the expansion ratio decreases as the acoustic pressure amplitude increases. While the linear resonance radius is 11 pm at 300 kHz, the ambient radius for the peak at 3 bar in pressure amplitude is about 0.4 pm. Even at the pressure amplitude of 0.5 bar, it is about 5 pm, which is much smaller than the linear resonance radius. 

Tronson R, Ashokkumar M, Grieser L (2002) Comparison of the effects of water-soluble solutes on multibubble sonoluminescence generated in aqueous solutions by 20- and 515-kHz pulsed ultrasound. J Phys Chem B 106 11064-11068... 

Didenko YT, Gorrdeychuk TV, Koretz VL (1991) The effect of ultrasound power on water sonoluminescence. J Sound Vib 147 409 -16... 

Abstract Having discussed many aspects of sonochemistry and its application in the previous chapters, a few introductory experiments in sonochemistry and sonoluminescence are presented in this chapter. These physical demonstrations are especially aimed at beginners in the field of sonochemistry making them e.g. aware of the power of ultrasound. 

Procedure Set up an acoustic reactor in a light-proof cabinet with a photomultiplier (PM) tube positioned facing the cell as shown in Fig. 15.3a and b. Fill the cell with distilled water and close the cabinet. A potential should now be applied to the PM tube, the output (spectrally integrated) of which is produced on an oscilloscope (note that the ultrasound cell can easily be placed inside a commercial spectrometer in order to record the emission spectrum). Switch on the ultrasound and you should observe on the oscilloscope a change in voltage, directly proportional to the intensity of sonoluminescence emission. The following experiments can be performed to explore the different types of light emission and some of the factors that influence these emission processes. 

Fig. 15.3 Typical experimental arrangement for the study of multi-bubble sonoluminescence. The ultrasound transducer used here is 515 kHz and produces a standing wave pattern in the reaction cell. A horn-type sonifier (usually 20 kHz) can also be used in such an arrangement...

The book offers a theoretical introduction in the first three chapters, provides recent applications in material science in the next four chapters, describes the effects of ultrasound in aqueous solutions in the following five chapters and finally discusses the most exciting phenomenon of sonoluminescence in aqueous solutions containing inorganic materials in subsequent two chapters, before ending with a few basic introductory experiments of sonochemistry and sonoluminescence in the concluding chapter. 

From the above one might be tempted to attribute ultrasonically enhanced chemical reactivity mainly to the mechanical effects of sonication. However this cannot be the whole reason for the effect of ultrasound on reactivity because there are a variety of homogeneous reactions which are also affected by ultrasonic irradiation. How, for example, can we explain the way in which power ultrasound can cause the emission of light from sonicated water (sonoluminescence), the fragmentation of liquid alkanes, the liberation of iodine from aqueous potassium iodide or the acceleration of homogeneous solvolysis reactions ... 

CONTENTS Introduction to Series An Editor s Foreword, Albert Padwa. Introduction, Timothy J. Mason. Historical Introduction to Sonochemistry, D. Bremner. The Nature of Sonochemical Reactions and Sonoluminescence, M.A. Mar-guli. Influence of Ultrasound on Reactions with Metals, 6. Pugin and A.T. Turner. Ultrasonically Promoted Carbonyl Addition Reactions, J.L. Luche. Effect of Ultrasonically Induced Cavitation on Corrosion, W.J. Tomlinson. The Effects ... 

Sonoluminescence arises from the impact of high energy sound e.g. ultrasound. 

There is a correlation between sonochemical and sonoluminescence measurements, which is usually not observed. Sonoluminescence is the consequence that both the sonochemical production (under air) of oxidizing species and the emission of light reflect the variations of the primary sonochemical acts, which are themselves due to variations of the number of active bubbles. Pulsed ultrasound in the high-frequency range (> 1 MHz) is extensively used in medical diagnosis, and the effects of pulsed ultrasound in the 20-kHz range using an immersed titanium horn has been reported. ... 

Instead, sonochemistry and sonoluminescence derive principally from acoustic cavitation, which serves as an effective means of concentrating the diffuse energy of sound. Compression of a gas generates heat. When the compression of bubbles occurs during cavitation, it is more rapid than thermal transport, which generates a short-lived, localized hot-spot. Rayleigh s early descriptions of a mathematical model for the collapse of cavities in incompressible liquids predicted enormous local temperatures and pressures.13 Ten years later, Richards and Loomis reported the first chemical and biological effects of ultrasound.14... 

Sonoluminescence mainly occurs inside the bubbles (or in their immediate surroundings) and thus cannot be representative of what happens in the liquid phase where most of the events used in ultrasound application occur. In particular the temperature and frequency dependence of sonoluminescence is quite different from that of other effects, thus luminescence decreases with temperature, while liquid-phase effects usually increase to a maximum, and then decrease [19]. 

Sonoluminescence and the Chemical Effects of Ultrasound. Milliard Research Laboratories England MRL Rep., 1951, p. 136. 

Figure 5. A scheme of an experimental setup for investigations on sonoluminescence and cavitation noise in metal melts (a) and dependence of light impulses count rate, N, on time and ultrasound intensity, / (/was increased by 10 mW cm 2-steps at 3-min intervals) (b).

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