Laserspektroskopische Charakterisierung von Reaktionsprozessen zur Gasphasensynthese von Nanopartikeln (English shop)

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Nanomaterials are described as one of the key technologies of the 21st century. They make it possible to modify the physical and chemical properties of substances via the size and shape of the particles. One obstacle to the industrial use of these materials is the lack of any means of producing particles with highly defined properties in large quantities in a targeted manner.

The production of nanoparticles from the gas phase is a cost-effective process that can be scaled up to an industrial scale. However, in order to guarantee the generation of specific materials even at high production volumes, the processes inside the reactor must be understood. This requires non-invasive measurements of critical quantities such as temperature and the distribution of individual species within the reactor.

In the context of this work, laser-induced fluorescence spectroscopy, which has been an established method for non-invasive characterisation in combustion diagnostics for decades, was adapted to the synthesis of nanoparticles. The multi-line NO-LIF thermometry method was used for temperature determination. Here, a laser with a tunable wavelength is used to excite different fluorescence transitions of the NO molecule with different ground-state energies. From the fluorescence detected by means of a camera, the temperature can be measured two-dimensionally and spatially resolved.

In order to also be able to measure the concentration of intermediates during nanoparticle synthesis in a spatially resolved manner, a method was developed that quantitatively determines the concentration from a combination of fluorescence and absorption measurements. This method was demonstrated on atomic iron, an important intermediate in Fe2O3 synthesis, but it can also be transferred to other systems.

The techniques developed here were applied during particle synthesis in a low-pressure flame reactor and a microwave plasma reactor. A main focus was on the change in the temperature field when varying different parameters, as they are also varied for different synthesis routes. The influence of precursors on the temperature field inside the reactors was also examined.