Browsing by Author "Paneva D."

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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.
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    Mössbauer study of iron-based perovskite-type materials as potential catalysts for ethyl acetate oxidation
    (2010-01-01) Paneva D.; Dimitrov M.; Velinov N.; Kolev H.; Kozhukharov V.; Tsoncheva T.; Mitov I.
    La-Sr-Fe perovskite-type oxides were prepared by the nitrate-citrate method. The basic object of this study is layered Ruddlesden-Popper phase LaSr3Fe3O10. The phase composition and structural properties of the obtained materials are investigated by Mössbauer spectroscopy, X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS) and temperature programmed reduction (TPR). The preliminary catalytic tests show a high potential of these materials for volatile organic compounds (VOCs) elimination as they possess high conversion ability and selectivity to total oxidation of ethyl acetate. Catalytic performance of LaSr3Fe3O10 is depended on the stability of structure and Fe4+-oxidation state. © 2010 IOP Publishing Ltd.