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 use d to study the low temperature oxidation of magnetite. Results indicat e that the transformation of magnetite to hematite goes through the fo rmation of gamma-Fe2O3, maghemite. Infrared spectroscopy is applied to study the phase transformation and the assessment of the relative amo unts of cation vacancies generated in the transformation process of ma gnetite to alpha-Fe2O3. The activation energy for the transformation o f magnetite to an intermediate defective spinel form with a cation vac ancy 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 var iations in the absorption bands in the IR spectra. The spectra given c an be used as guides to estimate the cation vacancy content in any mag netite sample obtained from the field.