Structural evolution and characteristics of the phase transformations between alpha-Fe2O3, Fe3O4 and gamma-Fe2O3 nanoparticles under reducing and oxidizing atmospheres

The mechanism and conditions for the phase transformations from alpha-Fe2O3 to Fe3O4 and Fe3O4 to gamma-Fe2O3 nanoparticles have been investigated by the thermal analysis method. The morphologies and structures of various nanoparticles after annealing in H-2 : Ar at 294 degrees C and in an O-2 atmosphere at 302 degrees C have been examined and characterized. Finally, we confirmed that the monodisperse, porous and magnetic gamma-Fe2O3 nanoparticles could be obtained by annealing the alpha-Fe2O3 nanoparticles synthesized by the hydrothermal route.