THE APPLICATION OF INFRARED-SPECTROSCOPY TO THE STUDY OF RUST SYSTEMS .2. STUDY OF CATION DEFICIENCY IN MAGNETITE (FE3O4) PRODUCED DURING ITS TRANSFORMATION TO MAGHEMITE (GAMMA-FE2O3) AND HEMATITE (ALPHA-FE2O3)

Infrared spectroscopy, magnetic testing and X-ray diffraction were used to study the low temperature oxidation of magnetite. Results indicate that the transformation of magnetite to hematite goes through the formation of gamma-Fe2O3, maghemite. Infrared spectroscopy is applied to study the phase transformation and the assessment of the relative amounts of cation vacancies generated in the transformation process of magnetite to alpha-Fe2O3. The activation energy for the transformation of magnetite to an intermediate defective spinel form with a cation vacancy content of about 1.82 vacancy per unit cell was calculated to be 8.5 kcal mol-1. Defect contents in the various samples were determined from the variations in the lattice parameter of the spinel phase and correlated to saturation magnetization of the oxidized samples and variations in the absorption bands in the IR spectra. The spectra given can be used as guides to estimate the cation vacancy content in any magnetite sample obtained from the field.