Characterization of nanocrystalline gamma-Fe2O3 prepared by wet chemical method

Homogeneous maghemite (gamma-Fe2O3) nanoparticles with an average crystal s ize around 5 nm were synthesized by successive hydrolysis, oxidation, and d ehydration of tetrapyridino-ferrous chloride. Morphological, thermal, and s tructural properties were investigated by transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and x-ray diffraction (XRD) techniques. Rietveld refinement indicated a cubic cell. The superstructure reflections, related to the ordering of cation lattice vacancies, were not detected in the diffraction pattern. Kinetics of the solid-state phase tra nsition of nanocrystalline maghemite to hematite (alpha-Fe2O3), investigate d by energy dispersive x-ray diffraction (EDXRD), indicates that direct tra nsformation from nanocrystalline maghemite to microcrystalline hematite tak es place during isothermal treatment at 385 degrees C, This temperature is lower than that observed both for microcrystalline maghemite and for nanocr ystalline maghemite supported on silica.