Sonochemistry acoustic frequency

Sonochemistry is strongly affected by a variety of external variables, including acoustic frequency, acoustic intensity, bulk temperature, static pressure, ambient gas, and solvent (47). These are the important parameters which need consideration in the effective appHcation of ultrasound to chemical reactions. The origin of these influences is easily understood in terms of the hot-spot mechanism of sonochemistry. 

Sonochemistry is strongly affected by a variety of external parameters, including acoustic frequency, acoustic intensity, bulk temperature, static pressure, choice of ambient gas, and choice of... 

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. 

Fig. 1.1 The regions for transient cavitation bubbles and stable cavitation bubbles when they are defined by the shape stability of bubbles in the parameter space of ambient bubble radius (R0) and the acoustic amplitude (p ). The ultrasonic frequency is 515 kHz. The thickest line is the border between the region for stable cavitation bubbles and that for transient ones. The type of bubble pulsation has been indicated by the frequency spectrum of acoustic cavitation noise such as nf0 (periodic pulsation with the acoustic period), nfo/2 (doubled acoustic period), nf0/4 (quadrupled acoustic period), and chaotic (non-periodic pulsation). Any transient cavitation bubbles result in the broad-band noise due to the temporal fluctuation in the number of bubbles. Reprinted from Ultrasonics Sonochemistry, vol. 17, K.Yasui, T.Tuziuti, J. Lee, T.Kozuka, A.Towata, and Y. Iida, Numerical simulations of acoustic cavitation noise with the temporal fluctuation in the number of bubbles, pp. 460-472, Copyright (2010), with permission from Elsevier...

Fig. 1.4 The calculated results for one acoustic cycle when a bubble in water at 3 °C is irradiated by an ultrasonic wave of 52 kHz and 1.52 bar in frequency and pressure amplitude, respectively. The ambient bubble radius is 3.6 pm. (a) The bubble radius, (b) The dissolution rate of OH radicals into the liquid from the interior of the bubble (solid line) and its time integral (dotted line). Reprinted with permission from Yasui K, Tuziuti T, Sivaknmar M, Iida Y (2005) Theoretical study of single-bubble sonochemistry. J Chem Phys 122 224706. Copyright 2005, American Institute of Physics...

Hatanaka et al. [50], Didenko and Suslick [51], and Koda et al. [52] reported the experiment of chemical reactions in a single-bubble system called single-bubble sonochemistry. Didenko and Suslick [51] reported that the amount of OH radicals produced by a single bubble per acoustic cycle was about 10s 106 molecules at 52 kHz and 1.3 1.55 bar in ultrasonic frequency and pressure amplitude, respectively. The result of a numerical simulation shown in Fig. 1.4 [43] is under the condition of the experiment of Didenko and Suslick [51]. The amount of OH... 

Concerning the laboratory devices used for sonochemistry, common cleaning baths are constructed aroimd one or more ceramics fitted to the external face of a tank (p. 304). Such devices work at a single frequency, generally between 20-50 kHz, fixed by the manufacturer with an acoustic power of ca, 1 W. Immersion horns are used when more acoustic power is required. Emitters are composed of a "pancake" of PZT ceramics compressed between a titanium rod and a steel countermass (p. 305). Usually horn devices work from 20 to 100 kHz, and the acoustic power emitted can reach several tens of W. For higher frequencies, piezoceramics are simply fixed to the reactor. The reader interested in the construction of ultrasonic devices should consult Ref. 21. 

To make sonochemistry work, a number of elementary rules should be observed, related to chemistry, acoustics (the frequency, the necessary ultrasonic power and its proper transmission into the reaction medium), and a few important external parameters (the sonication time, the temperature or pressure conditions, the physical properties of the propagation medium). This chapter will relate mostly to the last two points, purely chemical parameters being discussed in previous chapters. 

Keywords Ultrasound Acoustic cavitation Cavitation bubbles Ultrasound frequency Bubble temperature Sonochemistry... 

Ultrasound is sound pitched above the frequency bond of human hearing. It is a part of sonic spectrum ranging from 20 kHz to 10 MHz (wavelengths from 10 to 10 cm). The application of ultrasound in association with chemical reactions is called sonochemistry. The range from 20 kHz to aroimd 1 MHz is used in sonochemistry, since acoustic cavitation in liquids can be efficiently generated within this frequency range. However, common laboratory and industrial equipment typically utilize a range between 20 and 40 kHz. 

In this section, we shall examine first the relaxation behaviour of a polymer material when irradiated with a sound wave, acoustic relaxation. Then we consider how the interactions may be influenced by increasing the intensity of the sound wave. Since most of the work in this area has been carried out in the ultrasonic frequency region, the phenomena are sometimes designated as ultrasonic relaxation. The irradiation of materials with high intensity ultrasonic waves is usually referred to as sonochemistry. 

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