| Aerosol charging by ions or electrons is a charge transfer process that has applications in the fields of aerosol measurement, cloud physics, air pollution, industrial contamination control, material synthesis and processing using powders, and other electrostatic applications. In this thesis, a fundamental study of diffusion charging of fine aerosol particles was performed to improve the understanding of the transition and free-molecule charging regimes.; An unipolar aerosol charger was developed for use as a practical device for charging fine aerosol particles in several gases, and at different conditions of pressure and flow rate. The performance of the charger was predicted by a simplified charging model that included equations for the ions and particles of charge p. The charger was evaluated in air at atmospheric and subambient pressures, showing high charging efficiency and low particle losses when used at optimum operating conditions.; A modified version of the unipolar charger was used for a fundamental study of ionic charging in high-purity helium. Experimental data of the combination coefficient of positive helium ions with neutral particles were obtained and compared with several available charging theories in the transition and free-molecule regimes. It was found that Fuchs (1963) limiting-sphere charging theory provided the best agreement with the experimental results.; Free electron charging experiments of fine aerosol particles in high-purity helium and nitrogen were performed to measure the electron-neutral particle combination coefficient as a function of particle diameter. The data were compared with predictions of electron charging models and of modified ionic charging theories. The results suggested a free-molecule diffusion charging mechanism. Fuchs (1963) charging theory with the proper electron properties and the assumption of an accommodation coefficient at the surface of the particles provided good agreement with the experimental data.; A sonic jet bipolar corona ionizer was designed, built, and evaluated experimentally in terms of ion output and particle generation. The ionizer was optimized for minimum particle generation and high ion output required for fast charge neutralization of surfaces. An aerosol neutralizer using the corona ionizer was designed and tested with monodisperse aerosol particles. |
