Synthesis of Alumina- and Alumina/Silica-Coated Titania Particles in an Aerosol Flow Reactor

Abstract

In situ coating of titania aerosol particles with alumina and alumina−silica mixtures by chemical vapor deposition, cluster deposition, and sintering was demonstrated in a hot-wall, continuous flow tubular reactor. Titania particles with diameters in the range 0.2−0.8 μm were produced by the reaction of TiCl4 with O2 at 1300 and 1500 °C and were passed through a coating region where they were mixed with AlCl3 or mixtures of AlCl3 and SiCl4. Uniform and dense coatings of Al2O3 were obtained at both 1300 and 1500 °C using AlCl3 inlet concentrations that corresponded to Al2O3 mass loading of less than 1 wt %. The coating thickness could be controlled from 5 to 20 nm which corresponded to deposition rates up to 50 nm/s. Uniform and dense coatings of Al2O3/SiO2 were obtained at 1300 °C when the SiO2/Al2O3 weight ratio was less than 2:1. It is proposed that coating takes place in two modes: (a) chemical vapor deposition of AlCl3 and SiCl4 on the particle surface and (b) gas-phase reactions of the metal chlorides to form Al2O3, SiO2, or Al2O3/SiO2 particles that subsequently collide with the titania particles and sinter into the coating.

Synthesis of TiO2 nanoparticles containing Fe, Si, and V using multiple diffusion flames and catalytic oxidation capability of carbon-coated nanoparticles

“…Such coating could occur due to differences in chemical reaction rates of the precursors (Hung and Katz 1992). At small HMDSO concentrations, few and small SiO2 particles or aggregates can also deposit on the surface of titania particles (Powell et al 1997). Also, the oxidation of TTIP along with the formation of TiO2 is faster as compared with the oxidation of HMDSO for the formation of SiO2 (Hung and Katz 1992;Xiong and Pratsinis 1993).…”

Flame-coating of titania particles with silica

“…Alternatively, HMDSO could react directly on the titania surface. 40 Particles grow further by coagulation and coalescence through the high temperature region (up to HAB ‫ס‬ 6 cm) of the flame (Fig. 2).…”

Gas-Phase Synthesis of Nanostructured Particulate Films

“…Most research in the field has focused on obtaining a powder rather than a film, though. The studies of Kodas and co-workers give examples showing how the particle composition and morphology can be changed by in-situ gas-phase coating processes in hot-wall reactors [45][46][47] . The formation of functional coatings on oxide nanoparticles can also be achieved by introduction of multiple precursors into spray flames 48) .…”