Structural, magnetic and size transformations induced by isothermal treatment of ferrous oxalate dihydrate in static air conditions
作者： R. Zboril , L. Machala , M. Mashlan , M. Hermanek , M. Miglierini
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摘要: Thermal decomposition of the FeC2O4.2H2O powder has been studied isothermally in static air conditions at minimum temperature 180 °C using 57Fe Mossbauer spectroscopy, XRD, HRTEM, AFM and BET surface area measurements. Dehydration liberation carbon oxides from powdered sample is accompanied by direct oxidation Fe(II) to nanocrystalline Fe2O3 without any indications stabilization magnetite (Fe3O4) phase. Decomposition process completed after two hours as-prepared nanopowder (3–5 nm), with a large about 250 m2/g, comprised ultrafine superparamagnetic particles γ-Fe2O3 (maghemite) α-Fe2O3 (hematite) as proved low XRD HRTEM analysis. The simultaneous formation both polymorphs probably related non-equivalent diffusion on bulk oxalate particles. With increasing time, particle size induced phase transformation maghemite hematite observed XRD. spectra demonstrate that are formed only state (doublet), while magnetic components (sextet) room can be assigned exclusively distribution produced gradual crystallization primary nanoparticles same structure well transition (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
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