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Suspended particles, electrostatic

Electrophoresis (qv), ie, the migration of small particles suspended in a polar Hquid in an electric field toward an electrode, is the best known effect. If a sample of the suspension is placed in a suitably designed ceU, with a d-c potential appHed across the ceU, and the particles are observed through a microscope, they can all be seen to move in one direction, toward one of the two electrodes. AH of the particles, regardless of their size, appear to move at the same velocity, as both the electrostatic force and resistance to particle motion depend on particle surface this velocity can be easily measured. [Pg.390]

Electrical Precipitators When particles suspended in a gas are exposed to gas ions in an electrostatic field, they will become charged and migrate under the ac tion of the field. The functional mechanisms of electrical precipitation may be listed as follows ... [Pg.1609]

A review of preparative methods for metal sols (colloidal metal particles) suspended in solution is given. The problems involved with the preparation and stabilization of non-aqueous metal colloidal particles are noted. A new method is described for preparing non-aqueous metal sols based on the clustering of solvated metal atoms (from metal vaporization) in cold organic solvents. Gold-acetone colloidal solutions are discussed in detail, especially their preparation, control of particle size (2-9 nm), electrophoresis measurements, electron microscopy, GC-MS, resistivity, and related studies. Particle stabilization involves both electrostatic and steric mechanisms and these are discussed in comparison with aqueous systems. [Pg.250]

Modem coal combustion employs two principal techniques combustion in a fluidized bed or pulverization, followed by combustion of fine particles suspended in moving air. Figure 1 shows a schematic of pulverized coal combustion, a process much used in steam-raising plants. Each process produces a characteristic residue fluidized bed combustion gives rise mainly to a clinker-like or granular product, whereas pulverization, followed by combustion, produces mainly a much finer, micrometre-sized ash residue. Pulverization also yields a coarser fraction, the so called bottom ash , which is periodically removed without difficulty. However, the finer fly ash has to be recovered by filtration and electrostatic precipitation. Commercially, fly ash has... [Pg.211]

It is important to note that the concept of osmotic pressure is more general than suggested by the above experiment. In particular, one does not have to invoke the presence of a membrane (or even a concentration difference) to define osmotic pressure. The osmotic pressure, being a property of a solution, always exists and serves to counteract the tendency of the chemical potentials to equalize. It is not important how the differences in the chemical potential come about. The differences may arise due to other factors such as an electric field or gravity. For example, we see in Chapter 11 (Section 11.7a) how osmotic pressure plays a major role in giving rise to repulsion between electrical double layers here, the variation of the concentration in the electrical double layers arises from the electrostatic interaction between a charged surface and the ions in the solution. In Chapter 13 (Section 13.6b.3), we provide another example of the role of differences in osmotic pressures of a polymer solution in giving rise to an effective attractive force between colloidal particles suspended in the solution. [Pg.105]

An electrostatic precipitator is a gas-solid separator in which particles suspended in a gas stream are charged and removed by electrostatic force. Since the separation force is directly applied to the particles without the need of accelerating the gas phase, an electrostatic precipitator usually requires much less hydraulic power than other separation systems. Hence, electrostatic precipitation is widely recognized as an important technique of gas-solid separation. This technique is characterized by low pressure drop, relative high... [Pg.309]

The electrostatic stabilization theory was developed for dilute colloidal systems and involves attractive van dcr Waals interactions and repulsive double layer interactions between two particles. They may lead to a potential barrier, an overall repulsion and/or to a minimum similar to that generated by steric stabilization. Johnson and Morrison [1] suggest that the stability in non-aqueous dispersions when the stabilizers are surfactant molecules, which arc relatively small, is due to scmi-stcric stabilization, hence to a smaller ran dcr Waals attraction between two particles caused by the adsorbed shell of surfactant molecules. The fact that such systems are quite stable suggests, however, that some repulsion is also prescni. In fact, it was demonstrated on the basis of electrophoretic measurements that a surface charge originates on solid particles suspended in aprotic liquids even in the absence of traces of... [Pg.199]

Figure 14 Effect of RH on the uptake of water by an ammonium sulfate particle. The measurements were made for a single particle suspended in an electrostatic trap. Arrows denote particle response to change in RH in the indicated direction. Temperature, 25 °C (courtesy of T. Onasch, Brookhaven National Laboratory cf. Tang (1996) and... Figure 14 Effect of RH on the uptake of water by an ammonium sulfate particle. The measurements were made for a single particle suspended in an electrostatic trap. Arrows denote particle response to change in RH in the indicated direction. Temperature, 25 °C (courtesy of T. Onasch, Brookhaven National Laboratory cf. Tang (1996) and...
According to Deijaguin-Landau-Verwey-Overbeek (DLVO) theory, a cornerstone of modem colloid science, two types of forces exist between colloidal particles suspended in a dielectric medium electrostatic forces, which result from an unscreened surface charge on the particle, and London-van der Waals attractive forces, which are universal in nature. The colloidal stability and rheology of oxide suspensions, in the absence of steric additives, can be largely understood by combining these two forces (assumption of additivity). [Pg.179]

Park. U. et al.. The effect of electrostatic repulsive forces on the stability of BaTiO, particles suspended in non-aqueous media. Colloids Surf. A. 135, 77, 1998. [Pg.1027]

A sol-gel process is an important method to synthesize many materials in a variety of shapes and forms such as particles, films, and bulks. This method is especially suited for the synthesis and preparation of ultrafine rare earths oxide particles at relatively low temperatures. A sol is a stable colloidal dispersion of small particles suspended in a liquid. The particles are amorphous or crystalline and particle aggregation is prevented by electrostatic repulsion. The particles in some sols interact to form a continuous network of connected particles called a gel, instead of aggregating to form larger particles (precipitates). [Pg.141]

Heterocoagulation is the mutual adhesion of particles of a dissimilar nature upon collision, as a result of their individual Brownian motion. Brownian motion is a stochastic, or random, movement of colloidal particles suspended in a fluid (or gas) as a result of the internal thermal energy of the system, and thus of collisions with the solvent (or gas) molecules, as pointed out independently by Einstein and Smoluchowski. Derjaguin pointed out that the term heteroadagulation should be used for adhesion of small particles that move through Brownian motion onto much larger objects, whose Brownian motion can be neglected, such as fibers [1]. For example, Jachowicz and Berthiaume [2] reported the deposition of cationic, anionic, and neutral silicon oil droplets in the form of oil-in-water emulsions on native or cationically modified human hair fibers, driven by electrostatic forces. [Pg.20]


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Electrostatic particles

Suspended particles

Suspending

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