High-temperature XRD study of thermally induced structural and chemical changes in iron oxide nanoparticles embedded in porous carbons
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Magnetic carbon-based nanomaterials have promising applications in many fields owing to their biocompatibility and thermal/mechanical stability. This study describes a high-temperature X-ray diffraction (XRD) study of the chemical and structural transformations suffered by superparamagnetic iron oxide nanoparticles embedded in porous carbons. The nanoparticles were prepared from the decomposition of iron pentacarbonyl over porous carbons, resulting in nanometer-sized iron oxides homogeneously dispersed into the carbon matrix. The thermally induced changes in these materials were followed by in situ high-temperature XRD, using synchrotron radiation. The growing of the nanoparticles and of the carbon crystallites were first observed, followed by the reduction of the iron oxides to form α-Fe (at temperatures as low as 400 °C in some cases) and γ-Fe(C). The temperatures at which these chemical reactions occurred were dependent on the total time spent on heating and on the nature of the iron oxides formed in the as prepared materials. A noticeably large thermal expansion coefficient was also observed for the iron oxide nanocrystals. The formation of austenitic iron, stabilized by the presence of carbon, was found to be only partially reversible upon cooling.
KeywordsNanoparticles Iron oxide Porous carbons X-ray diffraction In situ analysis Nanocomposites Magnetism
This study has been supported by the Brazilian Synchrotron Light Laboratory (LNLS) under proposal D10B - XPD 7639. The support of CAPES, CNPq, FAPES, and FINEP is also gratefully acknowledged.
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