Magnetite Oxidation: A Proposed Mechanism

All magnetites are oxidized topotactically with formation of solid solution at temperatures below 400°C. The oxidation of hematite-free magnetites proceeds to γFe2O3, whereas in the presence of hematite epitaxial growth of αFe2O3 takes place, with excess iron ions being returned to the solid solution. A method for synthesizing maghemite from natural magnetites is indicated.