Effects of particle shape on the unipolar diffusion charging of nonspherical particles

Abstract

Unipolar diffusion charging of nonspherical particles was investigated for various particle shapes. We researched with TiO2 agglomerates produced by the thermal decomposition of titanium tetraisopropoxide ( TTIP) vapor. TTIP was converted into TiO2 in the furnace reactor and was subsequently introduced into the sintering furnace. Increasing the temperature in the sintering furnace, aggregates were restructured into higher fractal dimensions. The aggregates were classified according to their mobility using a differential mobility analyzer. The projection area and the mass fractal dimension of particles were measured with an image-processing technique performed by using transmission electron microscope ( TEM) photographs. The selected aggregates were charged by the indirect photoelectric charger, and the average number of charges per particle was measured by an aerosol electrometer and a condensation particle counter. For particles of the same mobility diameter, our results showed that the particle charge quantity decreases as the sintering temperature increases. This result is understandable because particles with lower fractal dimension have larger capacitance and geometric surface area.