DECOMPOSITION OF IRON SPINEL UNDER LOW OXYGEN PARTIAL-PRESSURE

Iron spinal (FeAl2O4) was heated at 1200-degrees-C under various low Po2 and decomposed into spinel phase, metallic iron and alpha-alumina. For the spinel phase, the lattice constant was measured by powder X-ray diffraction and the distribution of the iron ions was measured by Mossbauer spectroscopy. The lattice constant decreased with increasing heating time and the decrease was more pronounced at lower Po2. Some iron ions in the spinel phase were reduced to metallic iron, which formed a separate phase, resulting a spinel phase containing vacancies. The ratio of the iron ions in the tetrahedral site to the total number of the iron ions in the spinel phase decreased in the process of the decomposition. It was considered that the iron ions in the tetrahedral site became less stable and easier to be reduced with the contraction of the crystal lattice.