Thermally Induced Magnetite-Haematite Transformation

The products of thermal treatments of pure and copper doped magnetites have been investigated using Moessbauer spectrometry, XRD and thermal analysis techniques. The samples were heated in air between RT and 800oC at several heating rates. Samples treated at 520oC during 12 and 24 hours consist only of well-crystallized haematite. On the other hand, magnetites treated at 350oC consisted of mixtures of haematite, maghemite and magnetite, with relative amount of each phase depending on the presence of copper as well as on the heating time. Results show that the transformation of magnetite to haematite goes through the formation of maghemite, and that the presence of copper delays this transformation.