R&D: Magnetic Supraparticles Capable of Recording High-Temperature Events

Advanced Functional Materials has published an article written by Andreas Wolf, Department of Chemistry and Pharmacy, Professorship for Inorganic Chemistry, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Egerlandstraße 1, 91058 Erlangen, Germany, and Fraunhofer Institute for Silicate Research ISC, Neunerplatz 2, 97082 Wuerzburg, Germany, Julian Sauer, Department of Chemistry and Pharmacy, Professorship for Inorganic Chemistry, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Egerlandstraße 1, 91058 Erlangen, Germany, Katrin Hurle, GeoZentrum Nordbayern, Mineralogy, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Schlossgarten 5A, 91054 Erlangen, Germany, Stephan Müssig, Department of Chemistry and Pharmacy, Professorship for Inorganic Chemistry, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Egerlandstraße 1, 91058 Erlangen, Germany, Karl Mandel, Department of Chemistry and Pharmacy, Professorship for Inorganic Chemistry, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Egerlandstraße 1, 91058 Erlangen, Germany and Fraunhofer Institute for Silicate Research ISC, Neunerplatz 2, 97082 Wuerzburg, Germany.

Abstract: “Superparamagnetic iron oxide nanoparticles (SPIONs) are prone to oxidation at elevated temperatures (>300 °C) and lose their magnetizability upon transition from magnetite/maghemite (γ-Fe₂O₃ / Fe₃O₄) to hematite (α-Fe₂O₃). Silica (SiO₂) shells can effectively prevent this undesired effect up to ≈1000 °C. Herein, the study shows how to utilize SPIONs with varying SiO₂ shell thickness and thus, different oxidation susceptibility, and how to combine them in micrometers sized assemblies – so-called supraparticles (SPs), to create a structurally emerging magnetic temperature recording functionality. The desired oxidation of non or weakly-protected SPIONs within SPs upon temperature events reduces dipole–dipole interactions of well-protected SPIONs in the confined SP entity. The resulting change of magnetic interactions therefore contains information on the thermal history of the SP, which can be spectrally read out via magnetic particle spectroscopy within seconds. Their working range can be tuned from 400 to 1000°C on two independent structural hierarchy levels, namely the SiO₂ shell thickness and the freely selectable ratios of different building blocks in the SP. The application of such SPs as particulate additives for magnetic recording of high-temperature events, especially relevant in metal, alloy, and ceramic processing, representing a yet unexplored and optically-independent option for bulk temperature recording is proposed.“