Technical Report 213, c4e-Preprint Series, Cambridge

Authors: Manoel Y. Manuputty, Casper Lindberg, Maria Botero, Jethro Akroyd, and Markus Kraft

Reference: Technical Report 213, c4e-Preprint Series, Cambridge, 2018

Associated Themes:
 

• A TEM sampling method is presented which relies on impaction and diffusion mechanisms for particle deposition.
• A semi-automated image analysis algorithm is employed for aggregate morphological characterisation.
• The ratio of gyration to spherical equivalent sizes from projected area analysis is proposed as a measure of particle sphericity/degree of aggregation.
• Detailed morphological information generated includes primary particle size, aggregate size, and degree of aggregation distributions.

A detailed morphological characterisation is performed on TiO₂ nano-aggregates synthesised in a premixed stagnation flame using transmission electron microscopy (TEM) image analysis. The size-dependent collection efficiency of the TEM sampling method is accounted for with a simple correction for particle deposition through impaction and diffusion. The TEM-derived sizes show excellent agreement with electrical mobility measurements. Primary particle size, aggregate size, and degree of aggregation distributions were obtained for two different flames and varying precursor loading. The degree of aggregation is defined as the ratio of gyration to spherical equivalent sizes from the projected area analysis, allowing identification of particles with spherical and non-spherical morphologies. The size distributions are found to be strongly affected by precursor loading but not by flame mixture or maximum temperature. In all cases, approximately 60-70% particles have spherical morphology while the rest form small aggregates. Aggregation is likely to occur only very late in the growth stage, leading to the similarity between the primary particle and spherical particle size distributions. The detailed morphological information reported provides the much-needed experimental data for studying the early stage particle formation of TiO₂ from titanium tetraisopropoxide (TTIP) in a well-defined burner configuration.

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