Combustion Synthesis of Nanomaterials Using Various Flame Configurations

  • Mohamed Ismail

Student thesis: Doctoral Thesis

Abstract

Titanium dioxide (TiO2) is an important semiconducting metal oxide and is expected to play an important role in future applications related to photonic crystals, energy storage, and photocatalysis. Two aspects regarding the combustion synthesis have been investigated; scale-up in laboratory synthesis and advanced nanoparticle synthesis. Concerning the scale-up issue, a novel curved wall-jet (CWJ) burner was designed for flame synthesis. This was achieved by injecting precursors of TiO2 through a central port into different flames zones that were stabilized by supplying fuel/air mixtures as an annular-inward jet over the curved wall. This provides a rapid mixing of precursors in the reaction zone with hot products. In order to increase the contact surface between the precursor and reactants as well as its residence time within the hot products, we proposed two different modifications. The CWJ burner was modified by adding a poppet valve on top of the central port to deliver the precursor tangentially into the recirculating flow upstream within the recirculation zone. Another modification was made by adopting double-slit curved wall-jet (DS-CWJ) configuration, one for the reacting mixture and the other for the precursor instead of the central port. Particle growth of titanium dioxide (TiO2) nanoparticles and their phases were investigated. Ethylene (C2H4), propane (C3H8), and methane (CH4) were used with varying equivalence ratio and Reynolds number and titanium tetraisopropoxide (TTIP) was the precursor. Flow field and flame structure were quantified using particle image velocimetry (PIV) and OH planar laser-induced fluorescence (PLIF) techniques, respectively. TiO2 nanoparticles were characterized using high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman Spectroscopy, and BET nitrogen adsorption for surface area analysis. The flow field quantified by PIV consisted of a wall-jet region leading to a recirculation zone, an interaction jet region, followed by a merged-jet region. The modified CWJ burner revealed appreciable mixing characteristics between the precursor and combustion gases within these regions, with a slight increase in the axial velocity due to the precursor injection. This led to more uniformity in particle size distribution of the synthesized nanoparticles with the poppet valve (first modification). The double-slit modification improved the uniformity of generated nanoparticles at a very wide range of stable experimental conditions. Images of OH fluorescence showed that flames are tightly attached to the burner tip and TTIP has no influence on these flames structures. The particle size was slightly affected by the operating conditions. The phase of TiO2 nanoparticles was mainly dependent on the equivalence ratio and fuel type, which impact flame height, heat release rate and high temperature residence time of the precursor vapor. For ethylene and methane flames, the anatase content is proportional to the equivalence ratio, whereas it is inversely proportional in the case of propane flames. The anatase content reduced by 8% as we changed Re between 8,000 and 19,000, implying that the Re has a slight effect on the anatase content. The synthesized TiO2 nanoparticles exhibited high crystallinity and the anatase phase was dominant at high equivalence ratios (φ >1.6) for C2H4, and at low equivalence ratios (φ
Date of AwardFeb 2016
Original languageEnglish (US)
Awarding Institution
  • Physical Science and Engineering
SupervisorSuk Ho Chung (Supervisor)

Keywords

  • Flame synthesis
  • Curved wall-jet burner
  • titanium dioxide
  • Multiple diffusion Flames
  • Nanoscale Coating
  • Fe-doped Titania

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