AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Mass-Mobility Characterization of Flame-made ZrO2 Aerosols: the Primary Particle Diameter and Extent of Aggregation
MAX L. EGGERSDORFER, Arto Groehn, Chris Sorensen, Peter McMurry, Sotiris E. Pratsinis, ETH Zurich
Abstract Number: 125 Working Group: Instrumentation and Methods
Abstract Gas-borne nanoparticles undergoing coagulation and sintering form irregular or fractal-like structures affecting their transport, light scattering, effective surface area and density. Significant advances have been made in characterization of agglomerates (physically – bonded particles) of monodisperse particles in point contact. However, once coalescence or sintering starts between these primary particles, sinter necks are formed between them converting the agglomerates to aggregates (chemically- or sinter-bonded particles) [1].
Here, zirconia (ZrO$_2) nanoparticles are generated by scalable spray combustion and their mobility diameter and mass are obtained by differential mobility analyzer (DMA) and aerosol particle mass (APM) analyzer measurements. Using these data, the density of zirconia and a power law between mobility diameter and primary particle diameter [2], the structure of fractal-like particles is determined (mass-mobility exponent, prefactor and average number and surface area mean diameter of primary particles). The primary particle diameter determined by DMA-APM measurements and this power law is in good agreement with those obtained by nitrogen adsorption and microscopic analysis. That way the effect of flame spray process parameters (e.g. precursor solution and oxygen flow rate as well as zirconium concentration) on fractal-like particle structure characteristics is investigated in detail during particle synthesis. The primary particle diameter varied between 5 and 25 nm and the mobility diameter from 30 – 400 nm depending on process conditions. Longer particle residence times at high temperatures and high precursor concentrations resulted in larger primary particles with increased degree of aggregation.
[1] Eggersdorfer, M.L., Kadau, D., Herrmann, H.J. and Pratsinis, S.E., Multiparticle sintering dynamics: from fractal-like aggregates to compact structures, Langmuir 27 (2011) 6358-6367.
[2] Eggersdorfer, M.L., Kadau, D., Herrmann, H.J. and Pratsinis, S.E., Aggregate morphology evolution by sintering: Number and diameter of primary particles, J. Aerosol Sci. 46 (2012) 7-19.