Ultrasound dispersion

Liang F, Fan J, Guo Y, Fan M, Wang J, Yang H (2008) Reduction of nitrite by ultrasound-dispersed nanoscale zero-valent iron particles. Ind Eng Chem Res 47(22) 8550-8554... 

Average particle size (mean diameter) = APS from Malvern light scattering method after 30 seconds ultrasound dispersion... 

Formation of liposomes was carried out by an ultrasound dispersant UZDN-2T in 0.1 M C2H2OH aqueous solution of lipids from the liver and brain of mature outbreed mice (female, 12-13 wk aged) and soy bean lecithin (native - experiments No. 1 and No. 3 - and oxidized -experiment No. 2). That procedure was in detail presented in [6, 9]. The total number of animals in experiments with liposomes was 60. Experiments were repeated two tines in September (experiment No. 1) and May (experiment No. 2). Besides, the 80 white outbreed miee (females) were choice as the experimental animals to investigate interrelations between the different parameters of the LPO regulatory system in the murine organs with the different antioxidant status. These experiments were repeated three times (in November-December, May-June and... 

Reproduced from Characterization of CMP Slurries A New Composite Method Comprised of Acoustic and Electroacoustic Spectroscopy and Sedimentation Monitored with Ultrasound, Dispersion Technology Inc., http //www.dispersion.com/characterization-of-cmp-slurries-part2... 

When comparing the figures we can see that ultrasound dispersion of one and the same nanocomposite in media different by polarity results in the changes of distribution of its particles. In water solution the average size of Cu/C nanocomposite equals 20 run, and in alcohol medium - greater by 5 nm. 

The attenuation of ultrasound (acoustic spectroscopy) or high frequency electrical current (dielectric spectroscopy) as it passes through a suspension is different for weU-dispersed individual particles than for floes of those particles because the floes adsorb energy by breakup and reformation as pressure or electrical waves josde them. The degree of attenuation varies with frequency in a manner related to floe breakup and reformation rate constants, which depend on the strength of the interparticle attraction, size, and density (inertia) of the particles, and viscosity of the Hquid. 

The samples were examined before and after catalysis by SEM (Phihps XL 20) and HREM by both a JEOL 200 CX operating at 200 kV and a JEOL 4000 EX operating at 400 kV. The specimens for TEM were either directly glued on copper grids or dispersed in acetone by ultrasound, then dropped on the holey carbon grids. 

With special techniques for the activation of the metal—e.g. for removal of the oxide layer, and the preparation of finely dispersed metal—the scope of the Refor-matsky reaction has been broadened, and yields have been markedly improved." The attempted activation of zinc by treatment with iodine or dibromomethane, or washing with dilute hydrochloric acid prior to use, often is only moderately successful. Much more effective is the use of special alloys—e.g. zinc-copper couple, or the reduction of zinc halides using potassium (the so-called Rieke procedure ) or potassium graphite. The application of ultrasound has also been reported. ... 

P. V. Nelson, M. J. W. Povey, Y. Wang 2001, (An ultrasound velocity and attenuation scanner for viewing the temporal evolution of a dispersed phase in fluids), Rev. Sci. Instrum. 72, 4234. 

Use of ultrasounds in catalyst preparation leads to higher penetration of the active metal inside the pores of the support and greatly increases the metal dispersion on the support [185]. Major advances in ultrasonic technology have increased the acoustic power and sensitivity of transducers. 

Figure 12.23 Rate of reduction of indigo with and without ultrasound [237], 0.1 g/l Indigo, 40 °C 2.5 ml/l hydroxyacetone 5.0 g/l sodium hydroxide, pH 12.7 0.03 g/l anionic dispersing agent...

The sonochemistry of the other alkali metals is less explored. The use of ultrasound to produce colloidal Na has early origins and was found to greatly facilitate the production of the radical anion salt of 5,6-benzo-quinoline (225) and to give higher yields with greater control in the synthesis of phenylsodium (226). In addition, the use of an ultrasonic cleaning bath to promote the formation of other aromatic radical anions from chunk Na in undried solvents has been reported (227). Luche has recently studied the ultrasonic dispersion of potassium in toluene or xylene and its use for the cyclization of a, o-difunctionalized alkanes and for other reactions (228). 

The chemical and biological effects of ultrasound were first reported by Loomis more than 50 years ago (4). Within fifteen years of the Loomis papers, widespread industrial applications of ultrasound included welding, soldering, dispersion, emulsification, disinfection, refining, cleaning, extraction, flotation of minerals and the degassing of liquids (5),(6). The use of ultrasound within the chemical community, however, was sporadic. With the recent advent of inexpensive and reliable sources of ultrasound, there has been a resurgence of interest in the chemical applications of ultrasound. 

The possible mechanisms which one might invoke for the activation of these transition metal slurries include (1) creation of extremely reactive dispersions, (2) improved mass transport between solution and surface, (3) generation of surface hot-spots due to cavitational micro-jets, and (4) direct trapping with CO of reactive metallic species formed during the reduction of the metal halide. The first three mechanisms can be eliminated, since complete reduction of transition metal halides by Na with ultrasonic irradiation under Ar, followed by exposure to CO in the absence or presence of ultrasound, yielded no metal carbonyl. In the case of the reduction of WClfc, sonication under CO showed the initial formation of tungsten carbonyl halides, followed by conversion of W(C0) , and finally its further reduction to W2(CO)io Thus, the reduction process appears to be sequential reactive species formed upon partial reduction are trapped by CO. 

However, ultrasonic rate enhancements of heterogeneous catalysis have usually been relatively modest (less than tenfold). The effect of irradiating operating catalysts is often simply due to improved mass transport (58). In addition, increased dispersion during the formation of catalysts under ultrasound (59) will enhance reactivity, as will the fracture of friable solids (e.g., noble metals on C or silica (60),(62),(62) or malleable metals (63)). 

Halides of the less electropositive metals are quickly reduced to highly dispersed and very active metal powders if they are exposed to ultrasonic waves in the presence of lithium and other group I metals(20). Ultrasound not only accelerates the reduction of the halides but also increases the rate of subsequent reactions of these less active metals. These reactions are covered in the chapter by K. Suslick. 

Liposphere formulations are prepared by solvent or melt processes. In the melt method, the active agent is dissolved or dispersed in the melted solid carrier (i.e., tristearin or polycaprolactone) and a hot buffer solution is added at once, along with the phospholipid powder. The hot mixture is homogenized for about 2 to 5 min, using a homogenizer or ultrasound probe, after which a uniform emulsion is obtained. The milky formulation is then rapidly cooled down to about 20°C by immersing the formulation flask in a dry ice-acetone bath, while homogenization is continued to yield a uniform dispersion of lipospheres. 

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