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Dynamic and stationary charging of heavy metallic and dielectric particles against a conducting wall in the presence of a dc applied electric field

J. Appl. Phys. 47, 4839 (1976); doi:10.1063/1.322526

Issue Date: November 1976

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G. M. Colver
Department of Mechanical Engineering, Aeronautical Engineering and Mechanics, Rensselaer Polytechnic Institute, Troy, New York 12181
Dielectric and metallic paricles (both spherical and irregular in shape) in the range 29−4760 µm in diameter are electrically charged while in dynamic or stationary contact with either wall of a charged parallel-plate capacitor. The charge distribution received tends to remove any particle from the wall. Particles larger than 127 µm are studied individually with dc electric field strengths of 2−15 kV/cm. Smaller particles are studied mainly in the form of clouds. In the presence of gravity and standard atmosphereic air, the particle motion, once initiated, is continuous between the parallel plates both dynamic and stationary charging and the resulting particle motion are experimentally and theoretically studied considering the particles as capacitors in themselves. For copper particles a single formula of the form Q= (piepsilon) a2EK applies 2EK applies with K=1.64 whether or not charging is dynamically or statically acquired. The presence of an oxide film does not alter K. Dielectric particles followed a similar equation (K<1.64) when contact (triboelectric) charging was assumed small and surface electrical conductivity was sufficiently large. K for dielectrics is dependent on surface conductivity, permittivity, diameter, and contact time. Induced average particle velocities in atmospheric air were tested from 40 to 105 cm/s. Inelastic particle-wall collisions and a conservative body force such as gravity resulted in a critical lower limit electric field strength for sustained particle motion. Gaseous discharge from a particle to a wall of opposite sign can occur with sufficient particle size and electric field strength. Journal of Applied Physics is copyrighted by The American Institute of Physics.
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PACS

  • 77.90.+k
    Dielectric properties and materials Other topics in dielectric properties and materials
  • 03.50.Fg
    Classical and quantum physics; mechanics and fields Classical electrodynamics and classical field theory Electrostatics and magnetostatics
  • 72.90.+y
    Electronic transport in condensed matter Other topics in electronic transport in condensed matter
  • 73.90.+f
    Electronic structure and electrical properties of surfaces, interfaces, and thin films Other topics in electrical properties of surfaces, interfaces, and thin films
  • YEAR: 1976

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PUBLICATION DATA

ISSN:
0021-8979 (print)   1089-7550 (online)
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REFERENCES (23)
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  1. E. W. B. Gill and G. F. Alfrey, Nature 163, 172 (1949).
  2. J. W. Peterson, J. Appl. Phys. 25, 501 (1954).
  3. R. F. Wuerker, H. Shelton, and R. V. Langmuir, J. Appl. Phys. 30, 342 (1959).
  4. K. C. Thong and F. J. Weinberg, Proo. R. Soc. London A 324, 201 (1971).
  5. J. D. Cobine, Gaseous Conductors (Dover, New York, 1958), Chaps. 2, 7, and 8.
  6. S. L. Soo, Fluid Dynamics of Multiphase Systems (Blaisdell, Waltham, Mass., 1967), Chap. 10, p. 208.
  7. The disks were cut from printed circuit board; copper layers separated by phenolic.
  8. An alternative experimental method will be discussed which accurately accounts for the modulation.
  9. An improved value QDIM = 1.64 for copper particles will be discussed.
  10. Neglecting charge distribution and image force attraction, both of which are small force effects except for regions near a wall.
  11. The low projected value of coefficient of restitution e = 0.62 for the 388 µm copper particle is attributed to the experimental uncertainty in measuring a small mass.
  12. W. R. Harper, Philos. Mag. 24, 202 (1957).
  13. Assuming both sufficiently large particle and electric field strength.
  14. Peterson (Ref. 2) showed reduced contact charging from back leakage at relative humidities greater than 40% due to increased surface conductivity for 2-mm borosilicate glass spheres rolled on nickel; Wagner (Ref. 15) reported reduced saturation contact charging by 27% for quartz spheres on copper with the lowered work function of copper oxide present, as most certainly is present here.
  15. P. E. Wagner, J. Appl. Phys. 27, 1300 (1956).
  16. H. J. White, Industrial Electrostatic Precipitation (Addison-Wesley, Reading, Mass., 1963), p. 135.
  17. To be discussed.
  18. This result is interesting since it is opposite in trend to Eq. (21) for the saturation charge on an isolated dielectric sphere.
  19. The 3M Superbrite glass bead data calculated excess charge by Eq. (22) compared to Eq. (20) (see Fig. 13). This is probably due to uncertainty in the calculated mass of the glass particles [Eq. (22)].
  20. An AES test revealed the elements copper, zinc, oxygen, carbon, sulfur, and traces of nitrogen at the surface of the aged copper spheres. Chlorine appeared only on particles after cleaning in hydrochloric acid. The relative proportions of copper and oxygen in the film could be estimated as satisfying either of the structures Cu2O or CuO (average formulas Cu1.5O have been formed in low temperature films of copper, Ref. 22).
  21. Significant oxide film resistances between the particle and the wall were measured using the constant current characteristic of the electrometer (the details are being omitted). Average resistance over the particle surface gave a straight line (log-log scales) from 5×104 Omega at 10−4 A to 10×1010 Omega at 10−11 A for the larger particles, thought to be aged over one year. These particles appeared black-brown in color. The same particles, cleaned in hydrochloric acid, measured film reistance an order of magnitude or so less even after short runs (< 3 min). Particles cleaned but not run measured negligible contact resistance.
  22. P. Kofstad, Nonstoichiometry, Diffusion and Electrical Conductivity in Binary Metal Oxides (Interscience, New York, 1972), p. 328.
  23. In application of these results to actual run cases it is assumed that electrical breakdown depends only on the potential difference between the sphere and the wall and further that static and surge breakdown voltages are the same (acceptable for x/2a<1, Ref. 5).

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