Reduction kinetics of hematite to magnetite under hydrothermal treatments

The phase transformation of alpha-Fe2O3 to Fe3O4 was observed by the hydrothermal treatment of a ferric solution at 160-220 degrees C with the addition of both KOH and EDA into the reaction system. The reactions began with the formation of alpha-Fe2O3 hexagonal plates followed by the phase transformation involving the dissolution of the alpha-Fe2O3 hexagonal platelets, the reduction of Fe3+ to Fe2+, and the nucleation and growth of new Fe3O4 polyhedral particles. The activation energies for the phase transformation of alpha-Fe2O3 to alpha-Fe2O3 under hydrothermal conditions are estimated to be 96.4 +/- 11, 113.1 +/- 5, and 118.3 +/- 11 kJ mol(-1) for the addition of 0.5, 1 and 1.5 ml of EDA, respectively, which are about the same for the typical phase transformation of alpha-Fe2O3 to Fe3O4 in a hydrogen atmosphere.