(220b) Design of High Temperature, In-Situ Coating of Aerosols: Efficiency & Texture

Aerosol coating is a promising one-step process to modify nanoparticle surfaces. Here gas-phase coating of TiO₂ particles with SiO₂ films is investigated theoretically, accounting for SiO₂ monomer generation, coagulation, sintering and surface growth by HMDSO (hexamethyldisiloxane) precursor. The evolution of the SiO₂ coating particle population is simulated distinguishing the fine and coarse modes of SiO₂ coating particles. The fine mode deposits fast on TiO₂ particles forming a smooth coating while the coarse deposits further downstream and may contribute to rough coatings depending on SiO₂ sintering kinetics (1).

Coating starts by injecting the HMDSO after the TiO₂ particles have reached their optimal primary particle size that no longer changes by sintering (2). That way TiO₂ primary particles and aggregates have attained a self-preserving distribution that can be represented by a single size facilitating the simulations. Sintering may take place on the surface of the TiO₂ particles and transform rough into smooth coatings depending on process conditions.

The influence of TiO₂ particle size and concentration, process temperature, cooling rate, mixing time and HMDSO precursor concentration on SiO₂ coating thickness and texture are investigated. Especially the evolution of SiO₂ coating thickness and surface area of the rough SiO₂ coating on the TiO₂ core particles surface are discussed.

1. A. Teleki, S.E. Pratsinis, K. Wegner, R. Jossen, F. Krumeich "Flame-coating of titania particles with silica", J. Mater. Res., 20, 1336-47 (2005).

2. A. Teleki, M.C. Heine, F. Krumeich, M.K. Akhtar, S.E. Pratsinis, "The Role of Gas-Aerosol Mixing during In-Situ Coating of Flame-Made Titania Particles?, Ind. Eng. Chem. Res., accepted for publication (2008).