Flame Spray Pyrolysis: Advanced Characterisation via In-Situ Diagnostics

Abstract

Flame spray pyrolysis (FSP) is a nanoparticle synthesis method for the production of an array of nanomaterials and novel functional devices. This thesis provides a detailed experimental analysis of FSP with an emphasis on non-intrusive, in-situ diagnostics. In order to harness the potential of FSP in designing precise material compositions and morphologies, advanced experimental methods are required to understand fundamental processes and to provide a database for modelling efforts. To advance this project, this thesis has two overarching goals. First, to improve the current understanding of stable synthesis conditions. Second, to improve the diagnostic capabilities available to characterise FSP via novel laser-based diagnostics.

To address the impact of flame stability on synthesis quality, in-situ diagnostics, such as high-speed flame luminescence imaging (1-120 kHz) determine combustion stability, and ex-situ particle characterisation techniques, such as thermophoretic sampling, probe in-flame particle growth. It is found that increased flame instabilities promote poor spray break-up and evaporation, which can lead to variations in iron oxide particle morphology and increased concentrations of particle impurities.

To achieve the second goal of improved diagnostic capabilities, CH planar laser-induced fluorescence (PLIF) and picosecond phase-selective laser-induced breakdown spectroscopy (PS-LIBS) are applied for the first time in FSP. The applicability of CH PLIF is demonstrated for FSP, which can provide significant insight into the reaction layer of FSP flames.

Moreover, this thesis demonstrates that picosecond PS-LIBS can provide greater than an order of magnitude plasma emission intensity increase over broad spectral regions (372 - 389.5 nm) to enable single-shot imaging of iron oxide nanoparticles in FSP flames. This is because a strong irradiance dependence on the PS-LIBS emission intensity is found by comparing nano and picosecond excitation sources.