Characterization of monodispersed haematite particles by gas adsorption and Fourier-transform infrared spectroscopy

Monodispersed spherical and cubic haematite particles prepared by forced hydrolysis have been characterized by various techniques. Electron microscopy and X-ray diffraction measurements indicated that these two kinds of particles were formed through the recrystallization of β-FeOOH to haematite accompanying the dissolution of β-FeOOH. The relationship between the absorbance of the IR band due to the inner OH groups and the weight loss by heating in vacuo suggested that the monodispersed cubic haematite particles are polycrystalline and constructed by the aggregation of fine hydrous iron(III) oxide particles during dehydration. This mechanism was supported by the formation of micropores in cubic haematite particles that were outgassed in vacuo at 150 and 200 °C. On outgassing at 300 °C, the particles became non-porous or less porous but the inner OH bands were observed above 400 °C. A similar mechanism of formation was confirmed regarding the formation of spherical haematite particles, although the spherical haematite particles were more crystalline than the cubic particles.