FORMATION OF AGGLOMERATE PARTICLES BY COAGULATION AND SINTERING .2. THE EVOLUTION OF THE MORPHOLOGY OF AEROSOL-MADE TITANIA, SILICA AND SILICA-DOPED TITANIA POWDERS

A two-dimensional particle size distribution model is used to describe gas phase synthesis of titania and silica powders. By incorporating a coalescence term along with a particle sintering rate in the governin g population balance equation, the model traces the evolution of both the volume and surface area of aerosol particles. The simultaneous cal culation of particle volume and surface area distribution leads to a d irect characterization of the primary particles (grains) as well as pa rticle aggregates. The effects of residence time, temperature and part icle material properties on powder morphology are investigated. Effect ive sintering rates for pure titania, silica and silica-doped titania are deduced by comparing grain sizes obtained by model simulations and those measured experimentally from specific surface area and microsco pic analyses.