10th International Aerosol Conference
September 2 - September 7, 2018
America's Center Convention Complex
St. Louis, Missouri, USA

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Measurements and Simulations of Nanomaterial Formation and Gas Phase Intermediates' Behavior in Buoyancy Opposed Flame Synthesis Reactor

IGOR RAHINOV, Johannes Sellmann, Sebastian Kluge, Hans Juenger, Alexey Fomin, Matthieu Raphael Lalanne, Sergey Cheskis, Christof Schulz, Hartmut Wiggers, Andreas Kempf, Irenaeus Wlokas, The Open University of Israel

     Abstract Number: 1195
     Working Group: Materials Synthesis

Abstract
Production of the iron oxide nanoparticles with tailored properties by flame-assisted synthesis should rely on detailed understanding of the mechanisms governing their formation and nucleation from the gas phase. Specifically, nanoparticle formation in flames is strongly influenced by the residence-time–temperature history inside the flame [1,2]. We study how the temperature history can be intentionally modified by orienting flames either in an upward-firing or downward-firing configuration. We also investigate the influence of unintended residence-time modifications caused by sampling nozzles. These phenomena are investigated by experiments and simulations for the synthesis of iron oxide nanoparticles from premixed iron-pentacarbonyl-doped hydrogen/oxygen flat flames[3,4]. The experiments apply molecular-beam sampling with a particle mass spectrometer to measure particle sizes and a quartz microbalance to detect the presence of condensed matter [5]. Laser-Induced Fluorescence (LIF) and Intracavity Laser Absorption Spectroscopy (ICLAS) were applied to monitor gas-phase Fe and FeO, respectively[4,6,7]. The simulations rely on a finite-rate chemistry approach with detailed diffusion, particle dynamics are described by a bi-modal population balance model. The results revealed a strong impact of the reactor orientation on the velocity field. It is demonstrated that the downward-burning flame forms a detached stagnation point, causing longer residence times at elevated temperature than an upward- or horizontally firing flame, permitting the growth of larger particles. These iron oxide particles are eventually formed in the recombination zone of the flame, but no condensed matter was found in the reaction zone. In presence of a probing nozzle, the overall shape of the flame changes, depending on the distance of the probe from the burner dramatically. The corresponding residence times are also strongly affected by the probe. Due to strong stagnation effects the 1-D model cannot be applied directly to this "nominally flat" flame configuration. Rather, the experimentally determined Fe and FeO concentrations were compared to outputs of detailed reaction mechanisms in one-dimensional models using the previously determined flow field. This allowed to draw suggestions for further optimization of iron-chemistry mechanism.

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[7] I. Rahinov, A. Fomin, M. Poliak, S. Cheskis, Absorption electronic spectrum of gaseous FeO: in situ detection with intracavity laser absorption spectroscopy in a nanoparticle-generating flame reactor, Appl. Phys. B 117, 317-323 (2014).