EMPI - Reactive Fluids

The systematic development of tailored syntheses of functional nanomaterials from the gas phase requires knowledge of the underlying reaction mechanism, precursor decomposition, and particle formation kinetics. For this purpose, uni- and bimolecular elementary reactions, heterogeneous reactions, as well as particle formation and growth mechanisms must be investigated. Shock tubes and flow reactors are ideally suited for this challenging task, as they enable measurements under precisely defined conditions, independent of flow influences. Highly sensitive species detection methods enable us to unravel reaction mechanisms and determine the kinetics of individual elementary reactions.
The first step is always to investigate the decay kinetics of the precursors used for particle synthesis. For this purpose, atomic absorption spectroscopy (ARAS) can be used in cases where the precursors decay to the desired atoms (e.g., SiH₄ to Si and Fe(CO)₅ to Fe atoms), as well as gas chromatography and time-resolved time-of-flight mass spectrometry for more complex decay systems (e.g., tetraethyl orthosilicate as a precursor for silicon dioxide).
To investigate the reaction mechanism of nanoparticle formation in oxidative systems, both the bimolecular reaction rates of semimetal and metal atoms with O₂ (with ARAS) and the bimolecular reactions of precursors with OH (with ring dye laser spectroscopy) and H (with ARAS) can be determined. The determination of ignition delay times provides additional means for validation of the oxidation mechanisms.
Various techniques are used to investigate particle formation mechanisms. Direct homogeneous nucleation of metal atoms can be investigated with ARAS, heterogeneous nucleation can be determined in a flow reactor by measuring particle sizes with differential mobility analysis. Particle growth is measured in shock tubes with time-resolved laser-induced incandescence (TiRe-LII). Particle inception times determined with laser extinction and EDX analyses of the particle composition further contribute to the understanding of particle formation.