Mechanochemical transformations in α-Fe₂O₃ - ICEMS study

Integral conversion electron Mössbauer spectroscopy has been used to investigate the phases and transformations which occur when α-Fe₂O₃ is wet-milled in vacuum for up to 144 h. In addition to the transformation to off-stoichiometric Fe_3-xO₄ observed previously by transmission Mössbauer spectroscopy, the room temperature ICEMS spectra reveal the presence of ∼10-15% γ-Fe₂O₃ on the surfaces of particles milled for more than 24 h. Time-of-flight neutron diffraction of an α-Fe₂O₃ sample wet-milled for 200 h also provides evidence of the occurrence of a small fraction (∼4%) of γ-Fe₂O₃ in the milled product. The γ-Fe₂O₃ is likely to occur as a surface oxide layer and does not appear to play a significant role in the mechanochemical transformation of α-Fe₂O₃ to Fe_3-xO₄.