Narrowing the size distribution of aerosol-made titania by surface growth and coagulation

The attainment of narrower size distributions than those predicted by the self-preserving theory of coagulation for aerosol-made materials is explored theoretically. Titania formation by titanium-tetra-isopropoxide (TTIP) or titanium-tetra-chloride (TiCl4) oxidation is simulated accounting for gas/surface reactions and coagulation using a moving sectional model for aerosol dynamics. First, model performance is validated by comparing its predictions with data on synthesis of non-agglomerated titania nanoparticles by TTIP oxidation in a premixed flame reactor. Then, the effects of various process parameters such as pressure, temperature and initial precursor molar fraction, on titania particle size and volume-based geometric standard deviation, are illustrated. Ranges of surface reaction rates (of TTIP and TiCl4) and process residence times that lead to particle size distributions narrower than the corresponding self-preserving limit for particle coagulation alone are identified.