Low-power ultrasonics

Recently, Somorjai, Yang et al. [143] examined this reaction over lwt.% Pt/SBA-15 utilizing an elaborate preparation protocol. Preformed Pt nanoparticle sols of five different mean sizes, obtained by alcohol reduction in the presence of a protecting polymer (PVP) were combined with SBA-15 silica exhibiting 9nm pores. After 3h low-power ultrasonic treatment, the Pt particles were evenly distributed throughout the pores of the support (Figure 12 (a)-(e)). 

Final sample concentrations ranged from 0.05% to 1.0% (by weight), depending on latex particle size, In order to generate chromatographic signals in the linear range of the detector. Diluted samples were placed in a low power ultrasonic bath (Ultrasonics, Plainview, New York) for 60 seconds just prior to injection. Peak areas were determined for each injection. Each sample was injected until three consecutive areas differed by less than two percent from one value to the next. 

There are a number of examples of the use of ultrasound to increase the productivity of food products through the enhancement of efficiency of whole cells without disrupting the cell walls. A simple example of this is in the use of low-power ultrasonic activation of a liquid nutrient media to enhance the rate of growth of algal cells. Essentially this results in an increase in the production of protein (up to three-fold) and represents a real possibility for the production of food materials from unusual sources for human or animal consumption [18]. 

Concentration using aCi8 SPE Continuous-flow (methanol), high-temperature (65°C), sonicated extraction system to isolate APEO metabolites from sediment samples (low-power ultrasonic energy) sediment extraction was complete after 7 min with a total solvent consumption of 3.5 ml/sample two-step cleanup, normal-phase SPE, reversed-phase... 

These methods are based on the response of the bonded joint to loading by low-power ultrasonic energy. Ultrasonic methods are especially useful in detecting unbonds of the following types ... 

Sonic Inspection. Sonic and ultrasonic methods are, at present, the most popular NDT techniques for use on adhesive joints. Simple tapping of a bonded joint with a coin or light hammer can indicate an unbonded area. Sharp, clear tones indicate that adhesive is present and adhering to the substrate in some degree duU, hollow tones indicate a void or unattached area. Ultrasonic testing basically measures the response of the bonded joint to loading by low-power ultrasonic energy. 

Visual identification prior to failure is difficult due to the typical tightness of stress-corrosion cracks. A low-power hand lens will greatly aid determination. Crack enhancement may be achieved through the use of dye penetrants. Severe cracking may be detectable using ultrasonic, radiographic, or acoustic emission techniques. 

Occasionally, corrosion of this type produces large cavities covered by a thin outer skin of weld metal (Fig. 15.5). Even close examinations of such sites under a low-power microscope may fail to reveal the cavities. Compare Figs. 15.6 and 15.7. Generally, such sites are detected either by fluid leakage or by nondestructive testing techniques such as radiography and ultrasonics. 

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. 

In recent years, the technology of ultrasonic degradation has been studied and extensively used to treat some organic pollutants. The ultrasound with low power was employed as an irradiation source to make heat-treated Ti02 powder. This method was used for decomposition of parathion with the nanometer rutile titanium dioxide Ti02) powder as the sonocatalyst after treatment in high-temperature activation [373]. 

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