Production and in situ transformation of hematite into magnetite from the thermal decomposition of iron nitrate or goethite mixed with biomass

Among the methods of obtaining hematite ( α -Fe 2 O 3 ), the thermal decomposition of goethite ( α -FeOOH) or iron (III) nitrate (Fe(NO 3 ) 3 ·9H 2 O) is of special importance. These solids can be combined with other materials, thus altering the properties of the oxide obtained. The decomposition of goethite or nitrate mixture with biomass in an inert atmosphere yields hematite/carbonaceous material or magnetite/carbonaceous composites with different morphologies and crystallinities, as observed by scanning electron microscopy and X-ray diffraction, respectively. The transformation of hematite to magnetite occurs at 623 K (for biomass/nitrate mixture) and 723 K (for biomass/goethite mixture). The formation of magnetite is a consequence of the pyrolysis of biomass, which produces a reducing mixture, and the difference in the temperature for obtaining Fe 3 O 4 for the two precursors was investigated by thermal analysis by observing the mass and energy variations at each stage.