Aerosol Science 35 (2004) 405–420 www.elsevier.com/locate/jaerosci Narrowing the size distribution of aerosol-made titania by surface growth and coagulation Stavros Tsantilis, Sotiris E. Pratsinis * Particle Technology Laboratory, Department of Mechanical and Process Engineering (D-MAVT), Swiss Federal Institute of Technology, Institute of Process Engineering, ETH Z urich, Sonneggstrasse 3, ML F25, CH-8092 Zurich, Switzerland Received 14 April 2003; accepted 29 September 2003 Abstract The attainment of narrower size distributions than those predicted by the self-preserving theory of coag- ulation for aerosol-made materials is explored theoretically. Titania formation by titanium-tetra-isopropoxide (TTIP) or titanium-tetra-chloride (TiCl 4 ) oxidation is simulated accounting for gas/surface reactions and co- agulation 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 ame reactor. Then, the eects 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 TiCl 4 ) and process residence times that lead to particle size distributions narrower than the corresponding self-preserving limit for particle coagulation alone are identied. ? 2003 Elsevier Ltd. All rights reserved. Keywords: Surface reaction; Titania; Coagulation 1. Introduction Aerosol-made commodities such as carbon black, fumed silica (SiO 2 ), pigmentary titania (TiO 2 ), as well as lamentary nickel or iron are produced in ow reactors at high temperatures. Product particles of various sizes are made depending on the end application while their distributions follow that predicted by the self-preserving theory for coagulation as high precursor concentrations are ∗ Corresponding author. Tel.: +41-1-632-3180; fax: +41-1-632-1595. E-mail address: pratsinis@ivuk.mavt.ethz.ch (S.E. Pratsinis). 0021-8502/$ - see front matter ? 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.jaerosci.2003.09.006