Generation of silica nanoparticles from tetraethylorthosilicate (TEOS) vapor in a diffusion flame

Silica (SiO2) nanoparticles were synthesized by the gas phase thermal oxidation of tetraethylorthosilicate (TEOS) in a laminar diffusion flame reactor. Characteristics of the formation of silica nanoparticles along the axial distance above the burner outlet were investigated. Effects of maximum flame temperature, TEOS concentration, residence time, and water vapor on the particle size were also investigated. Silica nanoparticles less than 20 nm in average particle diameter were synthesized in all of the experiments. Morphological changes of particles were found along axial distance above the burner outlet; many small aggregates of particles (d(p) congruent to 7 nm) were found up to 2 cm, isolated smaller particles (d(p) congruent to 5 nm) at 4 cm, and aggregates of bigger particles (d(p) congruent to 10 nm) at 10 cm, Larger particles at higher TEOS concentrations are generated in the flame synthesis, As the maximum flame temperature increased, the average particle size of silica also increased. Smaller particles were produced with decrease of the residence time of TEOS vapor in the flame, The average particle size decreased with the injection of water vapor to the flame.