Phase Transition of Electrooxidized Fe3O4 to γ and α-Fe2O3 Nanoparticles Using Sintering Treatment

In this work, electrosynthesis of Fe3O4 nanoparticles was carried out potentiostatically in an aqueous solution of C4H12NCl which acts as supporting electrolyte and electrostatic stabilizer. gamma-Fe3O4 nanoparticles were synthesized by controlling oxidation of the electrooxidized Fe3O4 nanoparticles at different temperature. Finally the phase transition to alpha-Fe2O3 nanoparticles was performed at high temperatures using sintering treatment. The synthesized particles were characterized using X-ray diffraction, Fourier transformation, infrared scanning electron microscopy with energy dispersive X-ray analysis, and vibrating sample magnetometry. Based on the X-ray diffraction results, the transition from Fe3O4 to cubic and tetragonal gamma-Fe2O3 was performed at 200 degrees C and 650 degrees C, respectively. Furthermore, phase transition from metastable gamma-Fe2O3 to stable alpha-Fe2O3 with rhombohech-al crystal structure was approved at 800 degrees C. The existence of the stabilizer molecules at the surface of Fe3O4 nanoparticles was confirmed by Fourier transformation infrared spectroscopy. According to scanning electron microscopy images, the average particles size was observed around 50 nm for electrooxidized Fe3O4 and gamma-Fe2O3 nanoparticles prepared at sintering temperature lower than 900 degrees C, however by raising sintering temperature above 900 degrees C the mean particles size increases. Energy dispersive X-ray point analysis revealed that the nanoparticles are almost pure and composed of Fe and O elements. According to the vibrating sample magnetometry results, saturation magnetization, coercivity field, and remnant magnetization decrease by phase transition from Fe3O4 to Fe2O3.