Sonochemistry ultrasonic frequency

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...

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... 

Beckett M, Hua I (2001) Impact of Ultrasonic Frequency on Aqueous Sonoluminescence and Sonochemistry. J Phys Chem A 105 3796-3802... 

The formation of cavitation bubbles decreases with increasing ultrasonic frequency. A simple qualitative explanation of this effect could be that, at very high frequency the rarefaction (and compression) cycle is extremely short and the formation of a cavity in the liquid requires a hnite time to permit the molecules to puU apart. Hence, when the wavelength approaches or becomes shorter than this time, cavitation becomes more difficult to achieve. For this reason, and due to mechanical problems with transducers at high frequencies, the frequencies generally used for sonochemistry are between 20 KHz and 40 KHz. 

In contrast to other oxidative processes run under silent conditions, no PTC is necessary. In a two-phase system consisting of aqueous KMn04 and indane in benzene, an 80% yield can be obtained, provided the pressure in the reaction vessel is reduced to ca. 450 torr. This effect is interpreted by a resonance between the ultrasonic frequency and the vibration frequency of the bubbles, the radii of which is a function of the pressure (Ch. 2, p. 54). Optimal energy transfer is ensured under these conditions, and the importance of the pressure parameter, not frequently evidenced in sonochemistry, is illustrated. 

M. Capocelli, E. Joyce, A. Lancia, T.J. Mason, D. Musmarra, M. Prisciandaro, Sonochemical degradation of estradiols Incidence of ultrasonic frequency. Chem. Engn. J. 210,9-17 (2012) M.A. Beckett, I. Hua, Impact of ultrasonic frequency on aqueous sonoluminescence and sonochemistry. J. Phys. Chem. A 105, 3796-3802 (2001)... 

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. 

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,... 

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...

Homogeneous non-aqueous sonochemistry is typified by the sonolysis of chloroform which has been studied using ultrasonic irradiation of frequency 300 kHz (I = 3.5 W cm ) to yield a large number of products amongst which are HCl, CCI4 and C2CI2 [42]. Decomposition was found to only occur in the presence of... 

Sonochemistry is defined as the chemical effects produced by ultrasonic waves. Ultrasound, with frequencies roughly between 15 kHz and 10 MHz, has a drastic effect on chemical reactions. It is the most important... 

Sonochemistry is concerned with the effect of ultrasonic waves on chemical reactivity (Mason, 1991) and is an area of rapidly growing importance in a diversity of applications. Ultrasound has a frequency above that which is audible... 

A series of fundamental studies on sonochemistry by Feng Ruo and his collaborators has been undertaken over a number of years. Their studies have focused on how the parameters of an ultrasonic field, such as sound intensity, frequency, shape of wave, etc., affect the cavitation yield which was detected by different methods. 

The term sonochemistry indicates the use of sound waves to generate chemical and physical effects which can be harnessed in multiple applications (Fig. 1). Although such effects can be obtained at a wide range of frequencies, the word sonochemical is invariably linked to ultrasound, i.e. sound we cannot hear (typically above 20 kHz). Natural phenomena are good sources of both ultrasonic (e.g. animal communication or navigation) and infrasonic waves (such as earthquakes and tidal motion). Ultrasonics is currently of interest to lay people because of medical imaging, metal cleaning, industrial and dental drills and non-destructive material characterisation. 

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. 

The role of frequency is discussed with respect to its physical implications in Ch. 1 (p. 3) and topological consequences for the ultrasonic field in Ch. 8. (pp. 302, 316, 323). In contrast to many applications of diagnostic ultrasounds, which make use of frequencies above 3-5 MHz, sonochemistry employs the lower range of the spectrum. Frequencies below 50 kHz are preferred for heterogeneous systems due to the more intense mechanical effects. The problem is less clear for solutions. The frequency is chosen, more or less arbitrarily, among a few values considered as important, 20, 30, or 50 kHz for the lower, 500 or 800 kHz in the medium range (recently 200 and 300 kHz), 7,8 and 1,1.5, or 2 MHz for the highest values. 

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. 

P. Kanthale, M. Ashokkumar, F. Grieser, Sonoluminescence, sonochemistry (H2O2yield) and bubble dynamics Frequency and power effects. Ultrason. Sonochem. 15, 143-150 (2008)... 

---