Optical in situ diagnostics of droplets, nanoparticles and aggregates in spray-flame synthesis

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The product properties of nanoparticles from spray flame synthesis (SFS) do not only depend on their chemical composition but also to a large extent on their particle morphology. Within the project advanced laser optical methods are employed to investigate particle growth and aggregation and correlates particle properties with the boundary conditions of the synthesis (precursor type, concentration, solvent, volume flow). It can thus make a significant contribution to process understanding. In the first phase of the project, the method of Wide-Angle Light Scattering (WALS) approach was enhanced to measure droplet sizes in the spray flame. In this project phase, evaluation routines will be further improved allowing for a more accurate and faster determination. The WALS method is also used for in situ measurement of the characteristics of nanoparticles and aggregates (radius of gyration, fractal dimension) in an extended range of the flame. For selected material systems (especially iron oxide) these investigations are complemented by the use of time-resolved Laser-Induced Incandescence (TiRe-LII) for the measurement of primary particle size, allowing for the determination of key properties essential for the process chain. The combined measurement techniques are also used to investigate various questions which have come into the focus of interest especially due to the work of the groups in the SPP. On the one hand, these concern the formation of a preferred route of particle formation (directly from droplets or from the gas phase) depending on the composition of the solvent. On the other hand, the effect of pulsations observed in the process on the particle properties is investigated. For this purpose, time-resolved flame luminescence is combined and correlated with WALS measurements, which are performed in single shot mode.In addition to the exchange with the central project regarding material systems, process conditions and data, a cooperation with several experimentally working groups of the SPP is carried out to directly provide mutually complementary data. Furthermore, collaboration with groups working in the field of numerical simulation have been agreed upon and first mutually interesting and accessible material systems have been defined. On the one hand, the data of this project serve for the direct validation of the simulation, on the other hand the numerical projects provide further information, e.g. on the form of a particle size distribution, to enable a model-based and thus improved evaluation of the WALS data.