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Electrostatic forces can be used to control the motion of charged particles. In this article, particle charging and motion in an electric field under ultraviolet (UV) irradiation were investigated. When the particle layers deposited on an insulating substrate were irradiated with UV light in a downward electric field, photoelectrons were emitted, and positive charges moved to the bottom of the particle layers. Subsequently, by reversing the direction of the electric field, the positive charges in the bottom moved upward; thus, the particles in the top layer were positively charged and levitated by Coulomb forces. The flux of the levitated particles increased with an increase in the strength of the electric field (downward and upward). As the upward electric field strength increased, the number of agglomerated particles in the levitation increased; however, the particle charge decreased. As the thickness of the particle layers increased, the time delay for particle levitation increased; however, the flux of the levitated particles decreased. The ratio of agglomerated particles to the total levitated particles increased. These results can be explained by the mechanisms of charge transfer and particle levitation. [ABSTRACT FROM AUTHOR]

The charging and levitation of particles using UV irradiation in an upward electric field were investigated. Glass beads with a mass median diameter of 61 μm were used for the experiments. The particle layers formed on a glass plate were irradiated by UV light with wavelengths ranging from 240 to 400 nm. The particles in the top layer were positively charged by photoemission and levitated by the electrostatic forces. The fluxes and motions of the levitated particles were analyzed by digital processing of the images obtained with a high-speed camera. The charge of each levitated particle was determined by fitting the results calculated using the equation of motion to the experimentally obtained particle motion. The charge of the particles beginning to be levitated was determined by the force balance and thus was not affected by the UV irradiance. The positive charge of the levitated particles could be increased by continuous photoemission from the particles and decreased by the capture of photoelectrons emitted by other particles. Approximately 40% of the levitated particles descended because of the negative charge clouds formed by the photoemission from the particle layers and the levitated particles. Furthermore, in a second set of experiments, an upward electric field was applied after UV irradiation. In these experiments, the particles in the top layer were levitated after applying the electric field. These particles could be gain more excess charges than the particles for which the levitation was governed by the force balance. [ABSTRACT FROM AUTHOR]

It is well known that particles can be freely levitated in an electric field due to the charge induced on the particles by the external field. The charge depends upon the electric field strength and particle properties. This paper studies some of these factors to investigate the fundamentals of induction charging for granular materials. An experimental apparatus was set up to collect the levitated particles in a filter contained in a Faraday pail and the charge-to-mass (Q/M) ratio was obtained based on the charge and mass measurements for the samples in the filter. Furthermore, the particle size distribution was measured and analyzed by laser diffraction and microscopy and the surface mean diameter (Ds) and volume mean diameter (Dv) were obtained. In these experiments irregular shaped Al2 O3 particles and spherical glass beads with a size range of 42-390 μm were used and tested at different electric field strengths. By combining the results of Q/M, Ds and Dv, the charge per particle was calculated and the results compared with theoretical values. It was confirmed that the particle charge is dependent upon the electric field strength and the particle properties of size, shape, density, resistivity, and adhesive force. [ABSTRACT FROM AUTHOR]