Mass ultrasound effects

Compton R G, Ekiund J C, Page S D, Mason T J and Walton D J 1996 Voltammetry in the presence of ultrasound mass transport effects J. Appl. Electrochem. 26 775... 

Sonophotocatalysis is photocatalysis with ultrasonic irradiation or the simultaneous irradiation of ultrasound and light with photocatalyst. Tnis method includes irradiation with alternating ultrasound and light. Ultrasound effects on heterogeneous photocatalytic reaction systems have been demonstrated by Mason,1 Sawada et al.,2) Kado et al.,3) and Suzuki et al.4) In these papers, not only acceleration of photocatalytic reactions but increase in product selectivity by ultrasonic irradiation has also been reported. It was postulated that ultrasound effects, such as surface cleaning, particle size reduction and increased mass transfer, were the result of the mechanical effects of ultrasound.1,5) Lindley reviewed these and other effects.5)... 

The effect of ultrasound on electrochemical processes 69 Sonovoltammetric experiments practical considerations 70 Mass transport effects a simple description 71 Sonotrodes 77... 

The mass transport effects under ultrasound have been modeled. They offer a number of benefits per se, for microscale analytical studies and macroscale syntheses, including lessened power requirements to run at constant current, the need for lower concentrations of electrolyte salts and scope for different solvent systems, with altered product distributions if reaction pathways involve different kinetic regimes. 

Fig. 7.6 Contact ultrasound effects on mass transfer at cellular and tissue levels. Effects are shown in relation to the distance from the sonicated surface. Temperature effects and sound pressure amplitude are damped in deeper tissue layers, as depicted in the graph on the left. M, cell membrane W, cell wall L, middle lamella I, intercellular spaces P, pore network. Dotted lines represent membrane damage due to dehydration. 1, Loosening of cell-to-cell...

Carcel, f. A., Nogueira, R. 1., Garda-Perez, J. V., Sanjuan, N., Riera, E., 2010. Ultrasound effects on the mass transfer processes during drying kinetic of olive leaves (Olea europea, var. Serrana). Defect Diffus. Forum 297-301 1083-1090. 

The effects of ultrasound-enlianced mass transport have been investigated by several authors [73, 74, 75 and 76]. Empirically, it was found that, in the presence of ultrasound, the limiting current for a simple reversible electrode reaction exhibits quasi-steady-state characteristics with intensities considerably higher in magnitude compared to the peak current of the response obtained under silent conditions. The current density can be... 

Birkin P R and SilvaMartinez S 1995 The effect of ultrasound on mass-transport to a microelectrode J. Chem. See., Chem. Commun. 17 1807... 

Apphcations of ultrasound to electrochemistry have also seen substantial recent progress. Beneficial effects of ultrasound on electroplating and on organic synthetic apphcations of organic electrochemistry (71) have been known for quite some time. More recent studies have focused on the underlying physical theory of enhanced mass transport near electrode surfaces (72,73). Another important appHcation for sonoelectrochemistry has been developed by J. Reisse and co-workers for the electroreductive synthesis of submicrometer powders of transition metals (74). 

In a biphasic solid-liquid medium irradiated by power ultrasound, major mechanical effects are the reduction of particles size leading to an increased surface area and the formation of liquid jets at solid surfaces by the asymmetrical inrush of the fluid into the collapsing voids. These liquid jets not only provide surface cleaning but also induce pitting and surface activation effects and increase the rate of phase mixing, mass transfer and catalyst activation. 

In the literature we can now find several papers which establish a widely accepted scenario of the benefits and effects of an ultrasound field in an electrochemical process [13-15]. Most of this work has been focused on low frequency and high power ultrasound fields. Its propagation in a fluid such as water is quite complex, where the acoustic streaming and especially the cavitation are the two most important phenomena. In addition, other effects derived from the cavitation such as microjetting and shock waves have been related with other benefits reported for this coupling. For example, shock waves induced in the liquid cause not only an enhanced convective movement of material but also a possible surface damage. Micro jets of liquid, with speeds of up to 100 ms-1, result from the asymmetric collapse of cavitation bubbles at the solid surface [16] and contribute to the enhancement of the mass transport of material to the solid surface of the electrode. Therefore, depassivation [17], reaction mechanism modification [18], surface activation [19], adsorption phenomena decrease [20] and the mass transport enhancement [21] are effects derived from the presence of an ultrasound field on electrode processes. We have only listed the main phenomena referring to the reader to the specific reviews [22, 23] and reference therein. 

Ultrasound frequency has revealed as the most important operational variable. Low frequency (20-60 kHz) has been most used to obtain mechanical effects such mass transport enhancement, shock waves, microjetting and surface vibration, especially used in the nanostructure preparation. It has been reported [118] that... 

The proposed mechanism of effect of surfactant and ultrasound is reported in Fig. 7.5. The long chain surfactant molecules attach to surface of nanoparticles due to physical adsorption. Only thin layer is adsorbed onto the CaC03 nanoparticles. Due to presence of ultrasound and use of surfactant will control the nucleation. Surfactant keeps the particles away from each other by preventing flocculation due to change in surface tension of reaction mass. The concentration of additives was changed from 0.2 to 1.0 g/L. Addition of 0.2 g/L tripolyphosphate shows the increase in the rate of precipitation which is determined from the Ca(OH)2 consumption. Polyacrylic acid shows the least rate of precipitation (0.115 mol/1), which... 

Procedure Effects of ultrasound on the following reaction can be seen clearly, when the reactions are carried out both in the ultrasonic field as well as under normal conditions. The yield in most of the reactions increased due to cavitation and mass flow but a decrease could also be sometimes expected due to volatility of one of the reagents. The average increase/decrease in the yield of product, reported here, is an average of two sets of reactions carried out separately under sonicated and mechanical stirring conditions. 

---