The effect of particle shape on unipolar diffusion charging of non-spherical particles with the same mobility was investigated. Diffusion charging characteristics of non-spherical particles found previously to depend on their surface area and capacitance related to the particle shape. In this study, the morphological shape of aggregates was described in terms of mass fractal dimension. Experiments were conducted here with $TiO_2$ agglomerates produced by the thermal decomposition of titanium tetraisopropoxide vapor in the furnace reactor and sintered under gas temperatures from 1000K to 1500K. Due to the instability of the agglomeration structure against heat, the agglomerates would collapse somewhat to result in the change of the corresponding fractal dimension. By varying the temperatures in the sintering furnace, agglomerates with different degrees of compactness and fractal dimension can be produced. The agglomerates were classified according to their electrical mobility using a DMA, and then collected on TEM grid for image processing. The selected agglomerates were then introduced into the photoelectric-charger and charged. The average number of charges per particle was measured by aerosol electrometer and CPC and charge distribution was determined by TDMA (Tandem Differential Mobility Analyzer) system. The experimental results showed that the particles sintered under higher temperature have more charges per particle than particles sintered under lower temperature. TEM image processing showed that particles have more compact structure and fractal dimension increases with increasing the sintering temperature, in contrast the particles with the same mobility but different sintering temperatures have nearly equal projected surface area. This implies that evolution of charge distribution of particles with same mobility is independent of surface area and dependent on capacitance.
