INVESTIGATION OF MGO - FE SYSTEM USING MOSSBAUER EFFECT

The MgO:Fe system as subjected to a variety of heat-treatments has been studied using the Mössbauer effect for Fe57. On firing the MgO:Fe samples in air, iron initially dissolves in the lattice in its ferric state and is associated with a charge-compensating vacancy. However, on exceeding a certain concentration, magnesioferrite precipitates out. Hydrogen firing of these samples tends to create clusters of metallic iron and Fe2+ at Mg2+ sites. On refiring the samples in air, metallic iron is converted to Fe2O3 and Fe2+ to Fe3+ which subsequently reacts with the lattice to give magnesioferrite and a small fraction of Fe3+ dissolved in the lattice. These changes are found to be completely reversible. In some cases the magnesioferrite particle size is so small that it exhibits superparamagnetism. Although there is a limit to the solubility of Fe3+ in MgO, Fe2+ can be dissolved to any extent. © 1969 Chapman and Hall Ltd.