Ultrasonic agglomeration

A second form of desolvation chamber relies on diffusion of small vapor molecules through pores in a Teflon membrane in preference to the much larger droplets (molecular agglomerations), which are held back. These devices have proved popular with thermospray and ultrasonic nebulizers, both of which produce large quantities of solvent and droplets in a short space of time. Bundles of heated hollow polyimide or Naflon fibers have been introduced as short, high-surface-area membranes for efficient desolvation. 

Sedimentation (qv) techniques, whether based on gravitational forces or centrifugation, derive the particle size from the measured travel rates of particles in a Hquid. Before the particle analysis is carried out, the sample is usually dispersed in a medium to break down granules, agglomerates, and aggregates. The dispersion process might involve a simple stirring of the powder into a Hquid, but the use of an ultrasonic dispersion is preferred. 

When ultrasound emitter and electrode are different elements in the system, electrode-apart-transducer configuration, Fig. 4.2a, ultrasound removes the nanoparticles from the cathode to form suspended seeds. The ultrasonic agitation maintains a suspension of these preformed nanoparticles, which move continuously around, hit the electrodes, and these charged particles attach to one another and grow in suspension [90]. In this case, ultrasound keeps the larger structures from agglomeration. 

From the above, it could be observed that ultrasound broke down the agglomerated precipitate of Ni-DMG complex to very fine particles, resulting in the formation of colloidal solution of Ni-DMG complex in the presence of an ultrasonic held. The settlement of particles was slow in the sonicated sample than in control sample. However, in the normal reaction, green precipitate of nickel (II) hydroxide dissolved in the excess NH3 solution and formed deep blue solution of hexammi-nenickel(II) ions, as under ... 

Agglomerated sol particles (10 nm use of ultrasonic waves, laser scattering)... 

Laser diffraction of organic dispersion using weak ultrasonics 20 Detecting agglomerates... 

FIGURE 9.7 Agglomerate mean diameter as a function of ultrasonic irradiation time. The primary particle size of the type L006 SiC powder is 100 mn. The input power is 40 W and the solvent is 2-propyl alcohol. Taken from Aoki et al. [34]. Reprinted by permission of the American Ceramic Society. 

USAL has also been used in the determination of trace impurities in high-purity materials. This type of analysis is mandatory with a view to controlling their quality and studying the synergistic action of, and correlation with, impurities. The accuracy and precision of the analytical results depend strongly on the particular separation procedure used before the determination step, as shown in the multi-element quantitative USAL of impurities such as iron, copper, lead and bismuth in high-purity silver metal. For this purpose, a silver sample was dissolved in nitric acid and treated with chloride, after which the solution was evaporated to dryness and the impurities were redistributed on the surfaces or in the interstitial spaces of agglomerates of matrix crystals. Then, the impurities were leached into 0.1 M nitric acid with the aid of ultrasonic irradiation [91]. 

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