The roles of metal (Me) ions (Cu(II) and Cr(III)) in the morphologies and structures of hematite particles, produced from a forced hydrolysis reaction of FeCl 3 −HCl at various concentrations of metal ions ranging from 0 to 0.8 in the Me/(Fe + Me) atomic ratio ( X Me ), were investigated by separation of the reaction into two steps: precipitation of β -FeOOH and phase transformation from β -FeOOH to hematite. The metal ions inhibited the particle growth of β -FeOOH at a lower concentration region, while they promoted the particle growth at a higher concentration region with incorporation of these ions into the crystal lattice. The β -FeOOH particles produced with metal ions exhibited high specific surface areas and microporosities. It was suggested that the phase transformation from β -FeOOH to hematite is strongly affected by the metal ions incorporated into β -FeOOH particles but not by those adsorbed on the particle surface.
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Kandori et al. (2000) studied this question.