The Aggregation of Thermally Stable Particles in a Premixed Flat Flame Aerosol Reactor

Using a premixed flat flame, the aggregation process of thermally stable particles was studied. Based on the theoretical descriptions of the reaction limited aggregation process (RLAP) and the diffusion limited aggregation process (DLAP), the entire aggregation process was explained by a combination of the RLAP and the DLAP. Experiments were done to test the possibility of this explanation for the dynamic aggregation processes in terms of the parameters that are used in a normal chemical conversion process. By defining the primary particle as the basic unit of the aggregates, the aggregation process was divided into the early stage--when the primary particles are formed--and the stage of aggregation thereafter. Changing the combustion equivalence ratio of the premixed flat flame from 0.7 to 0.98 controlled the sizes of the primary particles. The deficiency of the oxygen in the combustion process controlled the final size of the primary particles in the aggregate. The morphological evolution of particles was well defined due to the stable condition in the flow. Titania and silica that were formed in the flame by the oxidation of TiCl 4 and SiCl 4 were used as the simulation materials of the aggregation process. Depending on the residence time and temperature history in the oxidation process, the aggregates were formed in various fractal dimensions. The thermophoretic sampling and image analysis techniques were used to evaluate the aggregation in the flame region. The coalescence effect on the particle morphology was estimated by using the tubular aerosol reactor.