Influence of mechanical activation time, annealing, and Fe/O ratio on Fe3O4/Fe composites formation from Fe2O3 and Fe powders mixture

Commercially, iron (alpha-Fe) and hematite (alpha-Fe2O3) powders were used for the synthesis of composite powders of Fe2O3/Fe type by mechanical milling. Several ratios of Fe2O3/Fe were chosen for the composite synthesis; the atomic percent of oxygen in the starting mixtures ranged from 21 to 46 %. The Fe2O3/Fe composite samples with various Fe/O ratios were milled for different milling times. The milled composite samples were subjected to the heat treatments in argon up to 900 A degrees C. During the heat treatment at temperatures that do not exceed 550 A degrees C, Fe3O4/Fe composite particles are formed by the reaction between the Fe2O3 and Fe. Further increase of the heat treatment up to 700 A degrees C leads to the reaction of the Fe3O4/Fe composite component phases, resulting thus in the formation of FeO/Fe composite. The heat treatment up to 900 A degrees C of the Fe2O3/Fe leads to the formation of a composite of FeO/Fe3O4/Fe independent of the milling time and Fe2O3/Fe ratios. The onset temperatures of the Fe3O4 and FeO formations decrease upon increasing the milling time. Another important aspect is that, in the case of the same milling time but with a large amount of iron into the composite powder the formations temperatures of Fe3O4 and FeO are also decreasing. The influence of the mechanical activation time, heat treatment temperature, and Fe/O ratio on the formation of the (Fe3O4, FeO)/Fe composite from Fe2O3+Fe precursor mixtures was studied by differential scanning calorimetry and X-ray diffraction techniques.