Composition, structure and reduction reactivity of composite materials of the α-Fe2O3–СaFe2O4 system by hydrogen
Vladimir V. Yumashev, Nadezhda P. Kirik, Nina N. Shishkina, Yuriy V. Knyazev, Anatoly M. Zhizhaev, Leonid A. Solovyov
Abstract
In this paper, α-Fe2O3-CaFe2O4 composite materials obtained by solid-phase synthesis from CaO and Fe2O3 oxides with varying Fe2O3 content in the burden from 74 to 95 wt.% were investigated. The synthesized composites are characterized by x-ray diffraction (XRD), scanning electron microscopy with energy-dispersive X-ray microanalysis (SEM-EDS) and simultaneous thermal analysis (STA) in the hydrogen temperature-programmed reduction mode (H2-TPR). Studying of microstructure peculiarities and distribution pattern of Fe and Ca in polished sections revealed formation of the "core-shell" type complex structure of material with the hematite phase as the "core". An investigation of the reduction reactivity by hydrogen of ferrite-containing materials via the STA method in the H2-TPR mode has been allowed to establish, that with an increase in the content of CaFe2O4 from 33.4 to 97.5 wt.% the contribution of low-temperature forms of lattice oxygen in the ranges of 350-510 °C and 510-650 °C from 3.77 to 1.46 wt. % and from 17.75 to 10.56 wt. %, decrease respectively, and the contribution of oxygen form from 5.80 to 10.77 wt.% at the high-temperature range of 650-900 °C increase. Relying on the assessment of lattice oxygen mobility, it is suggested, that the samples with CaFe2O4 content in range 72.9-97.5 wt.% are promising for use as oxygen carriers in chemical looping processes of syngas production.