Development of Charging Device for Superfine Particles Using UV/Photoelectron Method

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UV/photoelectron method developed by us is a unique charging technique using the photoelectrons/negative ions emitted from a photoelectron emitter by UV irradiation under an application of weak electric field. In this work, the new type charger of cylindrical photoelectron emitter coated on 254nm of UV-lamp was developed ; cylindrical germicidal lamp with photoelectron emitter composed of Au (10nm) and tin-doped In_2O_3 (ITO) (5nm) was used as UV-light source to generate the photoelectrons/negative ions. Mono-dispersed NaCl particles (particle diameter : 24 and 56nm) were used as sample aerosols in our charging experiments. Superfine NaCl particles were charged with a box type charger developed previously and the above new type charger applying this charging technique and, the validity was examined based on the number concentration measured by a condensation nuclei counter. The considerable predominance of the new type charger over the box type charger was found in comparison of charging ratio and penetration ratio of uncharged superfine particles and, penetration ratio of charged particles (charging-penetration ratio) under the application of direct electric field. Although charging ratio was decreased by the application of alternating electric field in the charging region, charging-penetration ratio, the most important thing in counting the number of charged particles, was increased.