An experimental investigation of gas-phase combustion synthesis of SiO 2 nanoparticles using a multi-element diffusion flame burner

Abstract

The current work presents the results of an experimental investigation of gas-phase combustion synthesis of silica (SiO 2) particles using a multi-element diffusion flame burner (MEDB, a Hencken burner). Silane (SiH 4) was added to hydrogen/oxygen/argon (H 2/O 2/Ar) flames to produce SiO 2 nanoparticles at various burner operating conditions (φ = 0.47–2.16). To characterize the burner performance, temperature measurements were made using water absorption spectroscopy and uncoated, fine-wire thermocouples. The results demonstrated the non-premixed flow arrangement of the fuel tubes and oxidizer channels of the MEDB provided uniform, ∼1D conditions above the surface of the burner, with temperature variations of less than ±3% in the transverse direction (parallel to the surface of the burner) for elevations above the mixing region (z = 0–7 mm), extending to heights ≥ 30 mm. At heights above the mixing region, approximately constant axial temperatures are also observed. Silica particle formation and growth were examined for comparison with current understanding of the physical mechanisms important in combustion synthesis of SiO 2. The particle properties were determined using transmission electron microscope (TEM) imaging. Geometric mean diameters of the primary particles varied from d̄ p = 9 to 18 nm. The current study demonstrates the utility of the MEDB in providing a controlled environment for fundamental studies of gas-phase combustion synthesis phenomena, as well as offering broad flexibility in experimental design with control over process variables such as temperature field, particle residence time, scalable reactant loading, and particle precursor selection.