Crystallization process and magnetic properties of amorphous iron oxide nanoparticles

Abstract

This paper studied the crystallization process, phase transition and magnetic properties of amorphous iron oxide nanoparticles prepared by the microwave heating technique. Thermal analysis and magnetodynamics studies revealed many interesting aspects of the amorphous iron oxide nanoparticles. The as-prepared sample was amorphous. Crystallization of the maghemite γ-Fe2O3 (with an activation energy of 0.71 eV) and the hematite α-Fe2O3 (with an activation energy of 0.97 eV) phase occurred at around 300 °C and 350 °C, respectively. A transition from the maghemite to the hematite occurred at 500 °C with an activation energy of 1.32 eV. A study of the temperature dependence of magnetization supported the crystallization and the phase transformation. Raman shift at 660 cm−1 and absorption band in the infrared spectra at 690 cm−1 showed the presence of disorder in the hematite phase on the nanoscale which is supposed to be the origin of the ferromagnetic behaviour of that antiferromagnetic phase.

Synthesis of nanostructured iron oxides dispersed in carbon materials and in situ XRD study of the changes caused by thermal treatment

“…The DSC curve obtained for the support (sample BC) shows only the first endotherm (which is narrower in this case), associated with the release of moisture (as also verified by TG). In the case of sample BC_OxFe, the broader endotherm indicates the release not only of moisture, but also of water molecules more tightly bound to the iron oxides (Phu et al 2011). The exothermic peaks detected in the DSC curve of sample BC_OxFe are due to the crystallization stages involved in the formation of hematite (a-Fe 2 O 3 ) from the amorphous and/or nanostructured iron oxides present in the as-prepared sample (Ayyub et al 1988;Phu et al 2011).…”

Enhanced anion sensing by γ-irradiated polyphenol capped iron oxide nanoparticles

“…As seen in the image, amorphous iron oxide nanoparticles have spherical shape which can be divided into two parts: the surface shell and core. The former has more porous structure compared to that of the latter [23]. The structure of the surface shell is size dependent and it may play an important role in the properties of the nanoparticles.…”

“…3). This is particularly of emphasis as we know the stability of the amorphous nanoparticles against crystallization is of great interest owing to its higher functionality [23]. With this thought we synthesized the nanoparticles in presence of irradiation for two different time intervals and measured the XRD pattern of the non irradiated nanoparticles and compared the result with those of 15 min and 24 h irradiated sample.…”

Features of magnetic properties of ferritic powders obtained by plasma - electrolytic atomization of iron-carbon alloys

“…Существует большое количество методов синтеза ферропорошков, которые можно разделить на физи-ко-химические и химические [3]. Их применение при-водит к получению продукта с различными характери-стиками и показателями устойчивости к структурному старению.…”