Triboelectric charging

Stricter control of particle size distribution improves powder handling (qv) and transport through the system, and appHcation efficiency. It also reduces blinding of the final filter (69). Additives have been developed which improve the triboelectric charging characteristics (70). 

The double layer can be formed by contact (triboelectric) charging of one surface of the nonconductor, while the opposite surface is in contact with a conductor, e.g., a nonconductive coating on a metal chute or a plastic-lined, metalpipe for powders. A less frequent cause is contact-charging of one surface, while air ions are supplied to the opposite surface. 

There are two types of colored molecule that are used in the toner, namely the colorant and the charge control agent (CCA). The colorant is used to impart color to the toner whereas the CCA is used to help impart and especially control the triboelectric charge on the toner particles. 

Figure 1. Approach, contact, and separation of two dissimilar solid materials leads to triboelectric charge separation. Here, the particle of material A is assumed to have lower work function and much higher electrical resistivity than the material B.

Because of the unavoidable tendency of granular solids to become triboelectrically charged when handled, it is no surprise that electrostatic phenomena are often quite pronounced in fluidized and spouted beds. The vigorous motion of fluidized particles—with constant particle-particle and particle-wall contacts—guarantees that electrical charging will take place. Electrostatic adhesion and cohesion, observed and recorded in the very earliest experimental investigations of fluidization, were immediately identified as experimental nuisances to be overcome. Somewhat later, the hazardous nature of electrostatics came to be appreciated. 

For powders and granular solids, there are two types of antistatic agents surface- and volume-active additives. Surface-active agents, which increase the surface conductivity of individual particles, are effective because triboelectric charge is always situated on the surfaces of individual particles. Most if not all surface-active agents are hygroscopic and thus attract a thin film of water to the surface it is this moisture that is responsible forthe increased surface conduction (van Drumpt, 1991). The effective bulk resistivity of the particles % -may be estimated by assuming that the particles are spherical and of radius R (Jones, 1995). 

Tucholski, D. and Colver, G. M., Triboelectric charging in a circulating fluidized bed, presented at 2nd Int l. Conf. on Applied Electrostatics, Beijing, China (November, 1993)... 

R. Kohnlechner, Triboelectric charging and electrostatic separation of diverse, non-conductive mixed waste, especially plastic, employs enclosed vibro-conveyor followed by in-flight separation influenced by non-linear electrostatic field, DE Patent 19 901 743, assigned to Hamos GmbH Recycling und Separ, July 20, 2000. 

The different parts of a flame detector must be rigid. If bumping the gas chromatograph moves the collector momentarily by 0.1 mm, the capacitance between the collector and the rest of the detector may decrease (or increase) by perhaps 0.1 pF. If the collector is polarized at 300 V, this change in capacitance injects a spike of 30 pC into the electrometer. At the typical flame sensitivity, this spike is equivalent to a very narrow peak of half a pg, a readily detectable amount. The coaxial cable from the detector to the electrometer is also a capacitor sensitive to vibration. It also suffers from triboelectricity (charge... 

Frictional Forces. Dyes have been designed to produce an electrostatic charge when frictional forces are applied. Such dyes, known as charge-control agents, are used in the toners for photocopiers and laser printers to both produce and regulate the triboelectric charge on the toner particles. 

Williams, M. W. (1976). The Dependence of Triboelectric Charging of Polymers on Their Chemical Composition. J. Macromolecular Sci. Rev. Macromol. Chem., C14, 251. 

AhfatNM, et al. 2000. An exploration of inter-relationships between contact angle, inverse phase gas chromatography and triboelectric charging data. Eur. J. Pharm. Sci. 9 271-276. 

In addition to abrasion, triboelectric charging is a serious problem in the production and processing of synthetic fibers. Charged fibers, because of interfiber repulsion, do not form a coherent yam, and it is difficult to wind such yams on bobbins to be transferred to other locations for further processing. To overcome these problems, combinations of oils, fats, and their derivatives are used extensively as... 

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