Mechanistic Study of Particle Formation from Burning Droplets
Final Report Abstract
Functionalized materials in the submicron and nano size range have increasingly become attractive in many applications. Reactive spray synthesis offers the opportunity of scalable production of nanoparticles with high purity in a one-step process. The properties of the nanoparticles are intrinsically related to the formulation of the liquid precursor solution, which influences the transport processes from the liquid into the gas-phase. To obtain detailed information on the fundamental mechanisms, the aim of this project was the development and implementation of an experimental method for investigating the combustion of reactive spray precursor solution droplets in the submicron size range. An experimental system with a high reproducibility and diffusion controlled transport processes was developed and implemented. This allowed to investigate the fundamental transport processes occurring during the combustion of metal-organic precursor solution droplets. The resulting nanoparticles produced with the developed system was measured “ex-situ” and compared to reactive spray nanoparticles. Both being in very good agreement, revealing similar physicochemical mechanisms occurring and enabling the fast probing of different metal-organic precursor solutions with the developed system. Solvents that are miscible with water are subject to flame extinction, while immiscible solvents burn according to the d² law. Selective vaporization for metal-organic precursor solution droplets were not observed. In contrast, the solution droplets exhibit “in-droplet” reactions, triggering micro explosions that enhance the vaporization rate of the droplets and lead to the desired fine agglomerated nanoparticles. This is in contrast to the previous literatures, which suggest that “in-droplet” reactions lead to large partially hollow nanoparticles. However, flame extinction during the droplet combustion and micro explosion lead definitely to undesired nanoparticles as was shown for Nitrate based metal-organic precursor solution droplets. The fast probing ability of the single isolated droplet showed that tailored precursor solutions can be established to utilize unsuitable metal-organic precursor, making them economically valuable. E. S. Reich: Nanoparticle blast caught on film, Nature News 492, 2012 (https://www.nature.com/news/nanoparticle-blast-caught-on-film-1.11933?nc=1371424729216)
Publications
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“Disruptive burning of precursor/solvent droplets in flame-spray synthesis of nanoparticles”, AIChE Journal 59 (12), 2013
C.D. Rosebrock, N. Riefler, T. Wriedt, S.D. Tse and L. Mädler
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“Influence of atomization and spray parameters on the flame spray process for nanoparticle production”, Atomization and Sprays 24 (6), 2014
D. Noriler, C.D. Rosebrock, L. Mädler, H.F. Meier, U. Fritsching
