Abstract
Hematite particles of four morphologies (polyhedral, platelike, needlelike, and disk shape) were synthesized by the hydrothermal method. The morphology and average particle diameter (1.4, 7.4, 0.2, and 0.12 μm, respectively) were determined by transmission electron microscopy (TEM) combined with electron diffraction. The hematite samples were subjected to mechanochemical activation, in order to investigate the effect of different particle morphologies on the sequence of phase transformations induced in hematite by high-energy ball milling. The hematite sample of polyhedral morphology underwent a reversible phase transformation to magnetite, followed by the transformation of magnetite to hematite for milling times up to 58 h. The platelike hematite suffered a phase transformation to wustite, with the occurrence of magnetite as an intermediate product. The hematite samples with needlelike and disk-shape morphologies were found to undergo a complete phase transformation to wustite, during the milling time periods investigated. The sequence of phases during the mechanochemical activation of haematite was followed by transmission Mossbauer spectroscopy. The results clearly show that the particle morphology plays a crucial role in determining the phase transformations induced in hematite by high-energy ball milling.
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