Laser Diagnostics in Spray Flame Mixing Processes during the Synthesis of Metal Oxide Nanoparticles

The increasing demand for functional nanoparticles requires reliable and controllable production routes for the synthesis of nanoparticles with tailored mechanical, electrical, thermal and optical material properties that are of high interest for a wide variety of applications. Flame spray pyrolysis (FSP) is an established technology for the synthesis of tailored nanoparticles that is capable of producing many metal oxide nanomaterials with high purity and narrow particle size distributions. Though FSP has already been applied to design specific single- and multicomponent nanoparticles, the high process complexity impede the industrial scale-up. In this thesis, "Laser Diagnostics in Spray Flame Mixing Processes during the Synthesis of Metal Oxide Nanoparticles", the atomisation and mixing process in spray flames are investigated in detail in order to spatially and temporarily resolve the reaction conditions and spray flow field to open windows for development potential in FSP.

Using phase Doppler anemometry (PDA), the droplet sizes and velocities of precursor-free and precursor-laden solutions in the spray are locally resolved and correlated by droplet size and velocity.
The temporal evolution of nanoparticle-producing spray flames is analysed by the concept of mean flight times from droplet and gas and reveals the formation of a temporal self-similarity. A key finding of this thesis is the revealment of the occurrence of droplet μ-explosions during FSP that has already proved in single droplet experiments to play a key role in the release of precursor material.