Influence of precursor concentration on spray and particle formation in flame spray pyrolysis
Malte Bieber  1, *@  , Ricardo Tischendorf  2@  , Hans-Joachim Schmid  2@  , Manuel A. Reddemann  1@  , Reinhold Kneer  1@  
1 : Institute of Heat and Mass Transfer, RWTH Aachen University
Augustinerbach 6, 52062 Aachen -  Germany
2 : Particle Technology Group, Paderborn University
Warburger Str. 100 33098 Paderborn -  Germany
* : Corresponding author

Liquid atomization is expected to be a key process in Flame Spray Pyrolysis, as it determines the primary droplet
size and velocity distribution, which represent initial conditions for flame shape and temperature field. A well-defined
manipulation of atomization may be achieved by variation of nozzle geometry, injection parameter or fluid properties.
However, change of fluid properties, e.g. varying solvents or increasing the precursor concentration, also influences
the final particle properties.
In this work, the influence of precursor concentration on fluid properties, spray and particle formation in Flame
Spray Pyrolysis is experimentally investigated. High-speed shadowgraphy and Phase-Doppler measurements are
conducted in a semi-closed combustion chamber with a well-defined burner geometry (SpraySyn burner) that is
based on a coaxial atomization principle.
By adding precursor to the flammable solvent, resulting spray characteristics, flame shape and appearance are
changed in color, shape and mean droplet size distribution. Compared to resulting mean droplet sizes of pure
solvent mixtures, mean droplet sizes in the center of the precursor flame at 30mm above the burner
are generally smaller. Persisting high share of small droplets in the droplet size distribution are
presented, that presumably origin from an accumulation of metal organic precursor at the droplet surface during
combustion, that acts as a diffusive barrier for high volatility solvent and thus reduces droplet evaporation.
Sufficiently high above the nozzle exit, increasing the precursor concentration does not affect the radial distribution
of mean droplet sizes but leads to increased mean particle sizes. More precursor presumably leads to higher
concentrations of prime particles in the flame, thus probability of particle collusion and agglomeration.
High-speed imaging at nozzle exit revealed random fluctuations of initial jet diameter, paired with jet axis shifting
around ~1000 Hz. These superposed fluctuations determine the initial conditions for atomization, induce pulsations
in the flame and thus initiate the entire chain of the particle synthesis process.

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