SIMULATION OF AGGREGATE PACKING AND ANALYSIS OF AGGREGATING PROCESS OF ULTRA-FINE POWDER BY BROWNIAN DYNAMIC METHOD

Dense and uniform packing of ultra-fine powders, the primary particle size of which ranges from 1 nm to 0.1-mu-m, is very difficult because of strong and sparse aggregation. In this paper, the aggregating process of ultra-fine powder is examined by Brownian dynamic methods, and the effects of interaction between the primary particles and the initial concentration on aggregate shape and size is analyzed quantitatively by Fractal dimension and Weibull's distribution function. Furthermore, the packing of aggregates, which are of various shapes and are composed of different numbers of particles, is investigated by computer simulation. The effect of the geometrical characteristics and size distribution of aggregate on the porosity and distribution of micropore diameter in a packed bed is analyzed. If many aggregates consist of hundreds of particles, the porosity is more than 94%. The porous structure is composed by bridging among several aggregates. The large spaces in ultra-fine powder composed by bridging are confirmed experimentally by mercury porosimetry. The effect of shape and size distribution of aggregates on packed bed structure is remarkable in the case of weak aggregated powder, which means that the number of constituent particles is below 10.