Spark ablation: a new route towards tunablemagnetic La-Fe-Si alloy nanoparticles

Abstract

The development of humanity has led to an increase in energy demand. To keep up with this need, scientists and engineers are constantly pushing the limits of technology to develop lighter, stronger and more energy efficient devices. Some recent developments in magnetocaloric materials have made it possible to use the magnetocaloric effect for cooling near room-temperature. Compared to vapor-compression refrigeration systems, magnetocaloric cooling systems can save up to 30% of energy. These materials also allow for greener, simpler and more reliable cooling systems. One of the promising materials is the La(Fe,Si)13 alloy. However, research showed that the magnetocaloric efficiency of these materials could be increased by converting it into nanoparticles. In this thesis, we report a novel, elegant and green method for the production of high purity-ternary alloy nanoparticles through high-frequency spark ablation in the gas-phase. Here, the nanoparticles were produced by the ablation of LaFe11.5Si1.5 electrodes. Then the composition, morphology, crystallinity, and magnetism of these particles was characterized. The results indicated that the oxidation of the nanoparticles is a key factor in the magnetic behavior. Based on these findings, some further experiments were performed. The first step was to add hydrogen to the carrier gas. This is known to reduce the oxidation and in this case, forms LaFe11.5Si1.5Hx. From these experiments, it became apparent that the concentration of hydrogen present during the formation of the particles played a significant role in their magnetic behavior. Next, we performed a study on the influence of the post-treatments on the particles magnetic response. Finally, we demonstrated that it is possible to create core-shell particles. Here, the shell can protect the core against oxidation and has the potential to prevent particle-particle interactions which could lead to superparamagnetism. The nanoparticles, as produced during this thesis, are not yet ready for the use in commercial and industrial applications. Nevertheless, this research introduces new insights of use for the further development of ternary alloy nanoparticles, core-shell particles, and La-Fe-Si alloy (magnetic) nanoparticles.Aerospace EngineeringAerospace Structures and Material