Phase Transition of Electrooxidized Fe₃O₄to γ and α-Fe₂O₃Nanoparticles Using Sintering Treatment

Abstract

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. -Fe2O3 nanoparticles were synthesized by controlling oxidation of the electrooxidized Fe3O4 nanoparticles at dierent temperature. Finally the phase transition to -Fe2O3 nanoparticles was performed at high temperatures using sintering treatment. The synthesized particles were characterized using X-ray diraction, Fourier transformation, infrared scanning electron microscopy with energy dispersive X-ray analysis, and vibrating sample magnetometry. Based on the X-ray diraction results, the transition from Fe3O4 to cubic and tetragonal -Fe2O3 was performed at 200 C and 650 C, respectively. Furthermore, phase transition from metastable -Fe2O3 to stable -Fe2O3 with rhombohedral crystal structure was approved at 800 C. The existence of the stabilizer molecules at the surface of Fe3O4 nanoparticles was conrmed by Fourier transformation infrared spectroscopy. According to scanning electron microscopy images, the average particles size was observed around 50 nm for electrooxidized Fe3O4 and -Fe2O3 nanoparticles prepared at sintering temperature lower than 900 C, however by raising sintering temperature above 900 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 eld, and remnant magnetization decrease by phase transition from Fe3O4 to Fe2O3.