The latest advances of flame aerosol technology for inexpensive synthesis of nanoparticles with precisely controlled characteristics are presented. More specifically, it has been shown how to use the mode of reactant gas mixing in diffusion flame reactors to widely control the primary particle size and crystallinity of product powders (1) and even make unagglomerated or non-aggregated particles (2). Furthermore, electric fields can be used to narrowly control the characteristics of product powders by spraying ions or by attracting the flame generated ions for synthesis of TiO2, SiO2, SnO2 (3) and even composite fumed silica-carbon black particles (4).
Here the focus is on scale-up of this process and measurement of particle size and structure using small angle x-ray spectroscopy as well as the competition between gas phase chemistry and surface chemistry of TiCl4 oxidation for synthesis of titania nanoparticles. Synthesis of silica particles from hexamethyldisiloxane is presented assuring chlorine free silica nanoparticles. Diffusion flame aerosol reactors are presented that eliminate nanoparticle deposition and production of undesirable coarse particles. The effect of various process variables on the characteristics of the particles are presented with emphasis on the use of electric fields. For the first time, it is shown that electric fields can be used in large scale production of nanoparticles. Synthesis of composite silica-carbon nanoparticles resulting from the use of electric fields is discussed also.
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S.E. Pratsinis, "Flame Aerosol Synthesis of Ceramic Powders" Prog. Energy Combust. Sci. 24, 197-219 (1998).
S. Vemury, S.E. Pratsinis, "Corona-Assisted Flame Synthesis of Ultrafine Titania Particles", Appl. Phys. Lett. 66, 3275-7 (1995).
P.T. Spicer, C. Artelt, S. Sanders, S.E. Pratsinis "Flame Synthesis of Composite Carbon Black - Fumed Silica Nanostructured Particles", J. Aerosol Sci. 29, 647-59 (1998).
Prof. Sotiris E. Pratsinis
Institute fuer Verfahrenstechnik, ETH Zentrum
Zuerich 8092, Switzerland