CHARACTERISTICS OF SIO2 TIO2 NANOCOMPOSITE PARTICLES FORMED IN A PREMIXED FLAT FLAME/

Nanometer sized (d(p) = 15 nm) SiO2/TiO2 particles were generated in a premixed flat flame aerosol reactor from three sets of precursors: Si Br4/TiCl4, SiCl4/TiCl4, and hexamethyl disiloxane (HMDS)/TiCl4. Single component silica and titania aerosols were also generated from SiBr4, SiCl4, HMDS and TiCl4. The choice of silica precursor had no observab le effect on the particle size of the single component aerosols, or oi l the distribution of species in the mixed aerosol, as determined by t ransmission electron microscopy (TEM) and by interparticle chemical an alysis of the mixed aerosol using energy dispersive X-ray spectrometry (EDS). These results suggest that for this flame configuration, chemi cal processes are not rate determining for particle size and do not af fect the arrangement of species for mixed systems. Within the particle s, small (3-12 nm in diameter) crystalline regions enriched in titaniu m were observed using electron energy loss spectrometry (EELS) coupled with scanning transmission electron microscopy (STEM). A mechanism in which segregation occurs during particle growth by diffusion within t he particles is proposed. (C) 1998 Elsevier Science Ltd. All rights re served.