Mechanochemical transformation of α-Fe2O3 to Fe3-xO4-microstructural investigation

The effects of wet-milling alpha-Fe2O3 in vacuum for up to 144 h have been investigated by neutron diffraction measurements at room temperature and in situ at similar to950 K. Rietveld refinements show that the main product is iron-deficient magnetite of approximate stoichiometry similar toFe(2.8)O(4). Comparison of the phases derived from the neutron data with results of the Fe2+/Fe3+ oxidation states as determined by chemical analysis reveals that a significant fraction of the unreacted alpha-Fe2O3 occurs in an amorphous-like or disordered state. The wet-milled products are also found to contain similar to8% gamma-Fe2O3. The transformation from the alpha-phase to the gamma-phase occurs as a result of the shearing during the low-energy milling, with the further collisions and impacts leading to defect magnetite on extended milling. While other contributing effects take place, the transformation process from alpha-Fe2O3 to Fe3-xO4 occurs mainly as a result of rupturing the oxide surface layers of alpha-Fe2O3 and releasing oxygen with consequent reduction to Fe3-xO4. (C) 2002 Elsevier Science B.V. All rights reserved.