Solid state transformations of iron-bearing hydrated sulfate to a-Fe2O3

Iron oxides are transition metal oxides of paramount importance for their technological applications. Their synthesis can be performed by a variety of methods, most of which are chemical methods. Hematite, α-Fe2O3, can also be produced from iron sulfates by heating them sufficiently in air. In this work we have employed the thermal decomposition method to obtain hematite from the dehydration of fibroferrite, FeOH(SO4)·5H2O, a secondary iron-bearing hydrous sulfate. The study was performed via Rietveld refinement based on in-situ synchrotron X-ray powder diffraction combined with thermogravimetric analysis and mass spectrometry. The integration of the data from these techniques allowed to study the structural changes of the initial compound, determining the stability fields and reaction paths and its high temperature products. Six main dehydration/transformation steps from fibroferrite have been identified in the heating temperature range 30-798 °C. In the last step of the heating process, above 760 °C, hematite is the final phase. The temperature behavior of the different phases was analyzed and the heating-induced structural changes are discussed.