Browsing by Author "Cherkezova-Zheleva Z."

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    Glass–crystalline materials with high iron oxide concentration: Phase composition, redox ratio and magnetic properties Vitrocerámicas con alta concentración de óxido de hierro: Composición de fases, relación redox y propiedades magnéticas
    (2024-01-01) Harizanova R.; Mihailova I.; Cherkezova-Zheleva Z.; Paneva D.; Georgieva M.; Tzankov D.; Avdeev G.; Rüssel C.
    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 (α-Fe2O3) and ɛ-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. Mössbauer 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, ɛ-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.