Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Non-metallic inclusions in metallic materials are a key challenge in metallurgical processing such as steelmaking. Aiming to control the population of inclusions and to remove them from the metal in its molten state, gas bubbles are commonly used for melt stirring, homogenisation and purification during ladle treatment. However, the effects of bubble–inclusion interactions in molten metals are not yet well researched, as experimental investigations at high processing temperatures are challenging. To circumvent these harsh conditions, model experiments are performed at room temperature, employing low-melting alloys based on gallium. In such laboratory-scale experiments, the interactions between gas and solid phases in the liquid metal are observable by means of transmission imaging with X-rays or neutron radiation.

Starting from the essentials of the measurement principle, this contribution presents two exam-ples of dynamic X-ray and neutron radiography studies in liquid metals, thus showcasing the unique capabilities as well as limitations of imaging measurements at high spatial and temporal resolution. X-ray radiography is able to image both, gas bubbles and solid particles in the liquid metal, at high contrast-to-noise ratio, but only if these particles are rather coarse and heavy [1]. Using neutron radiography, the focus is on a configuration motivated by a single bubble: the particle-laden liquid metal flow around a cylindrical obstacle, measured at 100 Hz imaging frame rate [2]. Combining particle image velocimetry and particle tracking algorithms, we detected particle trajectories in the cylinder wake flow [3], derived particle residence times and velocity statistics [4]. Such radiography studies provide valuable insights into multi-phase liquid metal flows, and the experimental findings may improve the understanding of the inclusion behaviour in bubble-stirred metallurgical reactors.

References
[1] Lappan T., Sarma M., Heitkam S. et al. Materials Processing Fundamentals 2021, 13-29, 2021.
[2] Lappan T., Sarma M., Heitkam S. et al. Magnetohydrodynamics, 56(2-3), 167-176, 2020.
[3] Birjukovs M., Zvejnieks P., Lappan T. et al. Experiments in Fluids, 63, 99, 2022.
[4] Birjukovs M. et al. Experiments in Fluids, 2024, accepted for publication.