Investigation of the interaction of precursor and flame chemistry

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The detailed numerical and experimental investigation of spray flame synthesis of nanoparticles is entering "uncharted territory" in chemistry. The understanding of the interaction of the species crucial for the flame (especially radicals) with metal atoms and precursor decomposition intermediates is growing slowly and has been studied for only a few materials systems so far. The investigation and mechanistic description of this interaction is the goal of this project and a basic prerequisite for the physically correct simulation of the reactive flow systems of spray flame synthesis.A special challenge is the investigation of the interaction in precursors, which - as in SPP - cannot be pre-evaporated but are present dissolved in droplets. For this purpose, a matrix burner was developed, which allows the chemical processes to be investigated in a laminar flow with the simplest possible geometry, even for solution-based precursors isolated from spray formation, evaporation, and turbulence. Operation at low pressure results in a spatially extended flame, which is investigated by molecular beam techniques (time-of-flight mass spectrometry and particle mass spectrometry) and optical methods. To quantify disturbances caused by sampling and buoyancy effects, the experiments are accompanied by flow simulations.An additional question has arisen from the work in the first project period: Numerous precursors require the use of fuel mixtures as solvents to prevent (or control) precipitation in the droplet on the one hand and to support mass transfer on the other hand. Here, solution components for which no combustion mechanisms have been available so far (e.g. ethylhexanoic acid or diols) have proven to be effective. For these fuels, combustion mechanisms must be developed - initially independently of the precursors - and optimized on the basis of flame velocity measurements.The results of the first period show that the initial decay steps of the precursor and solvents can often be well mapped by optimized global reactions. The high-temperature kinetics, on the other hand, are represented by detailed or skeletal sub-mechanisms, which also describe the interaction with the metal oxide intermediates. Based on the work on iron-doped flames, the interaction mechanisms for alkaline earth metals and for cerium are developed and optimized using literature data and new experiments. The mechanism for the iron-doped flames will be continuously validated and re-optimized depending on the data situation.Reduced (skeletal) reaction mechanisms are developed for the flow simulations of the synthesis process, which depend on a direct solution of the reaction kinetics. The reduction methodology is based on genetic algorithms which are also used for development and optimization, but with a set of optimization targets and tolerances adapted to the problem. It is crucial that the interaction mechanisms between the flame radicals and metal oxide intermediates are preserved.