Sonication/cavitation techniques

SnO has received much attention as a potential anode material for the lithium-ion-secondary-battery. The conventional techniques require temperatures above 150°C to form phase pure SnO. Whereas, sonication assisted precipitation technique has been used to prepare phase-pure SnO nanoparticles at room temperature by Majumdar et al. [25]. In this study, ultrasonic power has been found to play a key role in the formation of phase pure SnO as with a reduction in the ultrasonic power authors have observed a mixed phase. For the case of high ultrasonic power, authors have proposed that, intense cavitation and hence intense collapse pressure must have prevented the conversion of SnO to Sn02-... 

A very important point occurs in the transmission of acoustic power into a liquid which is termed the cavitation threshold. When very low power ultrasound is passed through a liquid and the power is gradually increased, a point is reached at which the intensity of sonication is sufficient to cause cavitation in the fluid. It is only at powers above the cavitation threshold that the majority of sonochemical effects occur because only then can the great energies associated with cavitational collapse be released into the fluid. In the medical profession, where the use of ultrasonic scanning techniques is widespread, keeping scanning intensities below the cavitation threshold is of vital importance. As soon as the irradiation power used in the medical scan rises above this critical value, cavitation is induced and, as a consequence, unwanted even possibly hazardous chemical reactions may occur in the body. Thus, for both chemical and medical reasons there is a considerable drive towards the determination of the exact point at which cavitation occurs in liquid media, particularly in aqueous systems. Historically, therefore, the determination of the cavitation threshold was one of the major drives in dosimetry. 

Calorimetric methods are quite general they can be used under cavitating conditions and in either free or restricted ultrasonic fields. Essentially the technique consists of measuring the rate of temperature increase in the sonicated liquid and from this calculating the power input according to Eq. (7),... 

The formation of iodine during sonication can be visualized by adding soluble starch to the medium and observing the blue color which appears. This technique has been used to identify the positions in a reactor where cavitation is most intense [ 19]. In this way standing waves can be detected since the blue color appears in the zones of maximum amplitude (maximum sonochemical activity). 

The formation of free radial OH and H in a naturally air-saturated aqueous solution exposed to traveling ultrasonic wave of 820 kHz was investigated using a spin-trapping agent, 5,5-dimethyl-l-pyrroline-l-oxide (DMPO) and ESR techniques [75]. It was shown that the cavitation threshold occurred at 0.537-0.632 W cm-2, and no further increase was observed above 3 W cm-2. At a fixed sound intensity the yield of OH increased linearly with the sonication time. 

Ultrasound (sonication) This is a chemical-free process to cause cell disruption by inducing cavitation (bubbles) into a solution. The bubbles generate turbulence and pressure differences during both formation and bursting that can lead to rupture of microorganisms. The technique is still under research. 

---