Design of high-temperature, gas-phase synthesis of hard or soft TiO2 agglomerates

Conditions for high temperature, aerosol synthesis of titania (TiO2) with controlled degree of agglomeration are identified. Accounting for simultaneous gas phase and surface reactions, coagulation and sintering during formation and growth of titania by oxidation of Ti-tetraisopropoxide (TTIP) and TiCl4 vapors, the evolution of the primary particle and agglomerate collision diameters is presented at nonisothermal conditions neglecting the polydispersity of the particle-size distribution. Hard- or soft-agglomerate formation is identified at the end of full coalescence and sintering, respectively. The role of surface reaction on the evolution of the agglomerate state is examined. Diagrams for the degree of hard-agglomeration as well as the size of the primary TiO2 particles are developed in terms of maximum process temperature, cooling rate and precursor initial molar fraction and compared with experimental data on synthesis of nonagglomerated TiO2. (c) 2005 American Institute of Chemical Engineers