Charging mechanisms

Fig. 12. Comparison of actual and predicted charging rates for 0.3-pm particles in a corona field of 2.65 kV/cm (141). The finite approximation theory (173) which gives the closest approach to experimental data takes into account both field charging and diffusion charging mechanisms. The curve labeled White (141) predicts charging rate based only on field charging and that marked Arendt and Kallmann (174) shows charging rate based only on diffusion.

Table 13.1 covers general information for different particulates, liquids in gas, typical particles and gas dispersoids, behavior of particles in the human body, charging mechanisms, principles of particle size analysis, methods for particle size analysis, and an estimation of the general collection efficiency of available commercial particle removal equipment. 

In general, all electrostatic separator systems contain at least four components (i) a chargingdischarging mechanism (ii) an external electric field (iii) a nonelectrical particle trajectory device and (iv) feed and product collection systems. Depending primarily on the charging mechanism involved, the electrostatic separator systems are classified into three categories (i) free fall separators (ii) high tension separators and (iii) conduction separators. 

Charging by contact electrification is an active mechanism whenever dissimilar particles make and break contact with each other, or whenever they slide over a chute or an electrode. This charging mechanism is most frequently used to charge selectively and obtain an electrostatic separation of two species of dielectric materials as realized in a free fall electrostatic separator. 

General process Special case or conditions Possible charging mechanisms... 

Mercury is a special type of liquid and behaves essentially as a metal for which charging mechanisms are discussed in Section V, F, 3. Dodd (D5) determined the charge acquired by mercury drops in contact with glass and various insulators. The mercury was always positively charged with ps values of the order of 0.01 V/micron. 

Figure 15. Schematics showing various discharge and charge mechanisms of battery electrodes, which serve as examples of the battery electrode charge/discharge mechanisms discussed in the text.

One of the common charging mechanisms is the preferential adsorption of an ion from a solution on an initially uncharged surface. An example of this mechanism is the binding of a Ca2+ ion on a zwitterionic (which implies that the surface group consists of surface dipoles but no net charge) head group of a lipid layer. 

TABLE 11.1 Examples of Charging Mechanisms that Lead to Charges at an Interface8... 

P-A. Paramonov et al, Ibid 1967(63/20), 156—65 CA 69, 4085d( 1968) (Since it was found that mixts of coarsely dispersed AN and TNT of high-d were not suitable when, charged mechanically in borehole because they could not ensure complete detonation,... 

Listed below are some of the energy sources which are capable of unintentionally initiating EED s electrically connected circuitry (induction), electromagnetic radiation, electrostatic charges, mechanical, thermal and chemical action... 

Complex Oxides Charging Mechanisms and Zero "Point of Charge... 

In this section we discuss five different materials as examples with different charging mechanisms mercury, silver iodide, oxides, mica, and semiconductors. Mercury is one example of an inert metal. Silver iodide is an example of a weakly soluble salt. Oxides are an important class of minerals. For most biological substances like proteins or lipids a similar charging process dominates. Mica is an example for a clay mineral. In addition, it is widely used as a substrate in surface force measurements and microscopy. We also included a general discussion of semiconductors because the potential in the semiconductor can be described similarly to the diffuse layer in electrolytes and there is an increasing effort to make a direct contact between a liquid or a living cell and a semiconductor. 

One of the important characteristics of gas-solid multiphase flows is concerned with the electrostatic effect. Particles can be charged by surface contact in a collision, by corona charging and scattering in an ionized gas, by thermionic emission in a high-temperature environment, and by other charging mechanisms such as colloidal propulsion... 

In the following discussion on these charging mechanisms, three basic assumptions are imposed i.e., all particles are spherical particles of the same size are charged to the same degree and interacting effects between particles are negligible. 

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