Electrification of powders

B5. Berg, T. G. O., Femish, G. C., and Flood, W. J., Investigation of the electrification of powders in flow through tubes and nozzles. Aerojet-General Corp. Rept. 0395-04(08)SP, Contr. DA-18-108-405-CML-829 (1963). 

The operational safety of this recovery installation is far from perfect. Explosions in driers caused by the impact of steel or even brass tools against iron, by the friction of powder strips against the iron edge of driers or by the electrification of powder strips, are well known. 

Murtomaa, M. Savolainen, M. Christiansen, L. Rantanen, J. Laine, E. Yliruusi, J. Static electrification of powders during spray drying. J. Electrostat. 2004, 62, 63-72. 

Chao Tse-san [328, 329] studied the electrification of powders on blowing through a copper tube 40 mm in diameter and 0.46 m long. The most widespread minerals were taken for study quartz, microcline, calcite, muscovite, biotite, gypsum, and hornblende. 

Nitrocellulose powders is particularly sensitive to friction when hot. Accidents have been caused by the ignition of hot powder on removal from the drier, in all probability due to friction. Here electrification of the powder on drying also plays an important part (see below, pp. 542, 616) giving rise to the possibility of an electric discharge while it is being taken out. This had led to the regulation that the powder must not be taken out of the drier before it has been cooled. 

Langevin and Biquard [33] showed that the evaportion of a liquid (alcohol, ether, benzene) does not electrify the residual solvent. Hence evaporation of the solvent in driers cannot lead to electrification of the powder. In the opinion of these authors nitrocellulose powder may be ignited by the discharge of the condenser at a voltage of 3000 V, if the condenser charge is greater than 0.3 fiF. 

The research and innovations in the area of electrostatics for pharmaceutical systems were reviewed in this article. The electrification, influence, and applications of charged solid particles and liquid droplets were discussed. Certain areas have been explored more extensively than others by researchers over the years, such as the electrostatics of powder handling and... 

When subjected to attrition, powders can acquire an electrostatic charge, the intensity of which is often proportional to physical force applied, as static electrification of two dissimilar materials occurs by the making and breaking of surface contacts... 

B. D. Pollock, W. B. Ziinny, C. R. Westgate, Electrification of Lead Azide Powders under Ambient Conditions, Tech. Rept. No. 4214, Picatinny Arsenal, Dover, N.J.. 1971. 

Contact electrification of insulative materials, predominantly in film form, has been studied in many laboratories. In this paper, electric field dependent charging of polymeric and polymer-carbon black powders in contact with a metallic electrode has been studied. Results show the charging behavior to be strongly dependent on the composition of the powder surface. Carbon black loading, type of carbon black and degree of dispersion are methods used to alter the powder surface. The field dependent contribution to the charge exchange dominates over the zero field values. 

Triboelectric Series. Prediction of triboelectric behavior in granular solids is hampered by difficult-to-control factors such as particle shape, prior mechanical contacts, material purity, and particle moisture content (which is usually related to airborne humidity). In the absence of any reliable predictive model for powder electrification, the practical requirements of industry necessitate an empirical approach (Taylor and Seeker,... 

It has long been known that smokeless powder is readily electrified and that an electric discharge may cause its ignition. When dried it is particularly readily electrified by the frictions produced by the current of warm, dry air. The powder is also subject to very strong electrification when polished due to friction of the grains against each other and against the wooden balls. 

The dielectric polymer particles can be electrostatically charged in the outer electric field, in the gas discharge, following the contact electrification mechanism, or through triboelectrization. The presence of Cl, whose electric conductivity differs from that of the polymer, in the powder composition considerably affects these mechanisms. 

Supuk, E. Hassanpour, A. Ahmadian, H. Ghadiri, M. Matsuyama, T. (2011) Tribo-electrification and associated segregation of pharmaceutical bulk powders. KONA Powder and Particle Journal 29, 208-223. 

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