Project Details
Projekt
Micro-exploding metal particles and formation of oxide nanoparticles: Development of in situ imaging techniques and advanced morphological image analysis
Applicant
Dr. Niklas Jüngst
Subject Area
Energy Process Engineering
Term
since 2022
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 517038121
Combustion of metal powders and subsequent reduction will contribute to a zero-carbon generation and storage of heat and electricity. Metal powders have a high volumetric energy density, making them more economical to transport than batteries or hydrogen. However, laboratory-scale experiments show fragmentation (also known as micro-explosion) of metal particles during combustion. This can produce metal- and metal-oxide vapor as well as metal-oxide nanoparticles. The latter are easily lost to the environment, posing health risks and impeding recycling. To better understand and control metal-particle micro-explosion and the associated phenomena, in situ diagnostics with very high spatio-temporal resolution are needed. In this project, optical imaging and image-analysis techniques will be developed and used towards two goals, (1) a detailed analysis of the micro-explosion itself, and (2) visualizing the potential metal-oxide nanoparticles produced by those. In the first step it is determined, under what conditions (e.g., ambient oxygen concentration, particle size, and gas temperature) micro-explosions occur, and if they do occur, how often, where, and when in the flame they occur. The second step is to develop an imaging measurement technique to visualize oxide nanoparticles near the fragmenting metal particles. Candidate techniques include elastic light scattering (ELS), laser-induced incandescence (LII), and phase-selective laser-induced breakdown spectroscopy (ps-LIBS). An important figure of merit in the development is how well signal contributions by the large metal particle and its fragments can be rejected. The studies are performed in a modified flat flame burner. A dispersion of metal powder and hydrogen flows through a central opening of the sintered matrix and ignites in a non-premixed flame. A microscope images the shadowgraphs of the fragmenting particles on a high-speed camera. Explicitly programmed and neural-network-based image analysis is used to process the images, to distinguish fragmenting and non-fragmenting particles, and extract their size, shape, and velocity. For ELS, selected geometric illumination-detection arrangement are tested to best suppress the scattered light from the large metal particle. For LII, the spectral excitation-detection-scheme and the choice of laser fluence are critical. Ps-LIBS needs to be optimized such that the laser excitation does not lead to significant ablation of the metal particle or breakthrough of the gas phase while detecting oxide nanoparticles with sufficient signal-to-noise ratio.
DFG Programme
WBP Fellowship
International Connection
Sweden
