Glass-crystalline materials with high iron oxide concentration: Phase composition, redox ratio and magnetic properties

The synthesis of glass-crystalline materials in the system Na2O/CaO/SiO2/Fe2O3 with high concentrations of Fe2O3 (20, 25 and 30 mol%) by applying the melt-quenching technique is reported. The melts spontaneously crystallize during pouring and the formation of magnetite (Fe3O4), hematite (01-Fe2O3) and e-Fe2O3, as identified by X-ray diffraction (XRD) is observed. The microstructure and the elemental composition of the prepared materials are further investigated by scanning electron microscopy (SEM) and two different morphological types of Fe-containing crystals - needle-like and dendrite-shaped are detected. Mossbauer spectroscopy showed the presence of Fe3+ and Fe2+, as well as the existence of iron ions both in tetrahedral and octahedral coordination and the precipitation of hematite, e-Fe2O3 and magnetite. The magnetic measurements on the prepared samples reveal ferrimagnetic properties with well defined hysteresis curves, although due to relatively small volume fraction of the iron-rich crystalline phases, the net magnetic moment is quite low compared to the bulk values for magnetite. (c) 2023 The Authors. Published by Elsevier Espan similar to a, S.L.U. on behalf of SECV. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/ by-nc-nd/4.0/).