EMPI - Reactive Fluids

We are pioneering advanced optical diagnostic techniques for in situ measurements in nanoparticle synthesis. We leverage the chemical and physical characterization of the reaction zone and the products to develop a better understanding of nanoparticle formation in flame and microwave plasma reactors. By coupling our measurements with kinetics simulations of particle formation and computational fluid dynamics (CFD) simulations, we aim to achieve a comprehensive understanding of the nanoparticle synthesis process. This integrated approach allows us to optimize synthesis parameters and achieve desired nanoparticle properties with high precision.

Below are the key techniques we utilize:

NO and OH laser-induced fluorescence (LIF) for gas-phase temperature measurement

Laser-induced fluorescence (LIF) is a powerful technique for measuring the temperature in combustion environments. By exciting NO and OH, we can determine the gas-phase temperature based on the fluorescence signals. These measurements are crucial for understanding the thermal conditions during nanoparticle synthesis.

LIF for measurement of intermediates in precursor decomposition

We use LIF to detect and measure intermediates formed during the decomposition of precursors such as atomic (e.g., Fe) or molecular species (e.g., SiO). This technique helps in identifying transient species that play a critical role in the formation and growth of nanoparticles. Understanding these intermediates is key to optimizing synthesis conditions for desired particle properties.

Laser-induced incandescence (LII) for particle size measurement

LII is utilized to measure the size and spatial distribution of nanoparticles. By heating the particles with a laser pulse, we induce incandescence, and the resulting emission intensity is related to the particle size. This technique is especially useful for real-time monitoring of particle growth during synthesis. While mainly used for soot, we systematically expand this method for non-soot (e.g., graphene) and non-carbonaceous (e.g., Si, Fe) nanoparticles.

Laser-induced breakdown spectroscopy (LIBS) and elastic scattering for particle formation measurement

LIBS is a robust method for analyzing the elemental composition of particles formed during synthesis. By focusing a high-energy laser pulse on the particles, we induce a plasma that emits characteristic spectral lines. In an intermediate laser fluence regime, LIBS originates from particles only (ps-LIBS) and therefore provides an alternative method for detecting the occurrence of nanoparticles in reacting flows. Additionally, elastic scattering techniques are used to measure particle sizes and distributions. Together, these methods provide comprehensive information about particle formation dynamics.

Pyrometry for particle temperature measurement

Pyrometry is used to measure the temperature of particles during synthesis. This non-contact method relies on detecting thermal radiation emitted by the particles, allowing us to determine their temperature accurately. Understanding particle temperature is crucial for controlling synthesis processes and achieving desired particle characteristics.

Combined absorption and emission measurements

Optical properties of nanoparticles are phase dependent. Therefore, absorption and emission spectra and cross-sections change when liquid particles solidify and they can be different for different crystal structure and stoichiometry (e.g., the various colors of iron oxides). We investigate these optical properties top derive various optical detection methods for particles. Such data resulting from detailed spectroscopic characterization are crucial for LII and pyrometry measurements. We also demonstrated absorption measurements for the detection of the solidification of silicon nanoparticles formed in plasma flows.

Particle image velocimetry (PIV) for gas-phase velocity measurement

Particle image velocimetry (PIV) is employed to measure the velocity of gas flows. By seeding the flow with tracer particles and illuminating them with a laser sheet, we capture images that allow us to compute the velocity field. This information helps in understanding the dynamics of gas-phase interactions and their influence on nanoparticle formation

Our integrated approach, leveraging these advanced optical diagnostics, enables us to gain deep insights into the complex processes involved in nanoparticle synthesis. These techniques not only enhance our understanding but also help in optimizing synthesis parameters for producing nanoparticles with specific properties.