THE FORMATION OF NICKEL FERRITE FROM HEMATITE, MAGNETITE AND SPINEL IRONSAND

The reaction of titanium-containing magnetite ironsand with NiO in both air and inert atmospheres up to 1200 °C was compared with the analogous reactions of hematite (Fe2O3) and pure synthetic magnetite (Fe3O4). All three starting materials form NiFe2O4 in air, the reaction in magnetite proceeding via an oxidation step at 220° C. Under inert conditions, the products have larger lattice parameters, indicating the presence of Fe2+; in hematite this is formed at about 1000° C with evolution of oxygen. Mössbauer spectroscopy suggests that the Fe2+in the ferrite spinels is located preferentially in the octahedral sites. Lattice parameter calculations suggest that the present NiFe2O4 formed in air is not fully inverse, as is usually assumed, but contains varying amounts of tetrahedral Ni2+. The calculations confirm the location of Fe2+ in predominantly octahedral sites which, in the case of ironsand-derived spinels, also contain Ti4+. The magnetic saturation moment of the ironsand-derived ferrites formed both in air and nitrogen is smaller than that of products derived from the pure iron oxides. © 1990.