The synthesis of functional titanium oxide (TiO2) (size < 100 nm) opens the door to the development of new nanomaterials with applications in ceramics, catalysis, sensors, fuel cells, dental and bone replacement composites, optical fibres and telecommunications, polishing, data storage, coating, and biomedical aids. However, nanoparticle synthesis is a new and emerging area with a number of challenges to overcome. The work reported upon in this thesis develops a new experimental understanding of the flame synthesis of titanium oxide (TiO2) nanoparticles of less than 50 nm in sizes, known as ‘functional particles’. Firstly, a detailed literature review on the combustion synthesis of nanoparticles and on flame synthesis of TiO2 nanoparticles was conducted. Secondly, a novel dual flame burner based nanoparticle synthesis and collection experimental facility was successfully developed. The new facility was based on the design, building and integration of a number of delicate subsystems, namely: (i) a new precursor loading system for injecting particle precursor inside the flame-spaces; (ii) a novel burner configuration with the flexibility to generate different flame-spaces for nanoparticle synthesis using both premixed and diffusion flames; and (iii) two unique particle collection systems to collect nanoparticles from their inception, formation and growth flame-spaces. All of these systems were subsequently integrated and commissioned for the synthesis of particles from the premixed flames. Next a comprehensive experimental methodology was developed to analyse the TiO2 particles, using scanning transmission electron microscopy (STEM) and X-ray diffraction (XRD) spectroscopy, in terms of their size, morphology and phase. Thirdly, studies on establishing the underlying science of the premixed flame synthesis of nanoparticles, and the effect of different chemical and physical factors of premixed flames on the end morphology of nanoparticles, was investigated. In establishing the science of TiO2 synthesis in a premixed flame-space, the effects of flame temperature conditions in the post flame-space regions were studied. Experimental studies were undertaken by isolating the effects of premixed fuel-air stoichiometric conditions to establish the mechanism of functional TiO2 formation in the outer premixed flame-space. Results from the experimental studies demonstrated the generation of predominantly spherical primary nanoparticles in the size range 5-20 nm. The equivalence ratio (the ratio of the actual fuel-air ratio to the stoichiometric fuel-air ratio) ∅ = 1.1 had the highest flame temperature and produced the smallest nanoparticles (5-15 nm) with the highest phase purity (61% anatase). A new scheme for the mechanism of TiO2 particle formation and growth in the outer flame-space of a premixed flame was observed and presented, in which increased residence time led to increasing numbers of agglomerates and aggregates. An experimental study that isolated the effects of precursor loading on the characteristics of functional TiO2 particle size and morphology was presented. The results indicated that the lowest precursor feeding rate (carrier gas 0.8 l/m) generated the smallest spherical primary nanoparticles (5-12 nm) consisting of 83% anatase. The mechanism of particle inception, formation and growth due to the increased loading of the precursor was experimentally observed and presented. Finally, to fully understand the particle formation in the complex inner flame zone of the premixed flame, a novel thermophoretic particle sampling technique was developed. This new technique was implemented in the inner flame-space of the premixed flame-space. Results obtained demonstrated key fundamental information about precursor disappearance and particle inception and formation inside the premixed flame-space.
Premixed Flame Based Synthesis of Titanium Oxide (TiO2) Nanoparticles
Lu, X. (Author). Jun 2019
Student thesis: Doctoral Thesis