Influence of Manganese Oxide and Silica on the Morphological Structure of Hematite Compacts

• Published in: Steel research international 2010-03, Vol.81 (3), p.178-185
• Main Authors: El-Geassy, A.A., Nasr, M.I., Mousa, E.A.
• Format: Article
• Language: English
• Subjects: Catastrophic failure analysis; Compacts; fayalite; fayalite-manganoan; Ferrite; Firing; gaseous reduction; Iron oxides; manganese oxides; manganese-ferrite; morphological changes; Phases; Reduction; silica; Silicon dioxide; Swelling
• ISSN: 1611-3683; 1869-344X; 1869-344X
• DOI: 10.1002/srin.200900121

Dry compacts of pure Fe2O3 and Fe2O3 doped with either (2–6 mass%) MnO2, (2.5–7.5 mass%) SiO2 or with both (2–6% MnO2 + 7.5% SiO2) were indurated at 1373 K for 6 hours and physically and chemically characterized. The fired compacts were isothermally reduced with pure CO gas at 1073–1373 K. The O2‐weight loss was continuously recorded as a function of time using TGA technique. The external volume of pure and doped compacts was measured at different reduction conditions and the volume change was calculated. The structural changes accompanying the reduction process were visually and microscopically examined and the different phases were identified by X‐ray diffraction analysis. After firing, manganese ferrite (MnFe2O4) phase was identified in MnO2‐doped compacts. In pure Fe2O3 compacts, the external volume of compacts was increased with reduction temperature, showing a maximum swelling value at 1198 K. Catastrophic swelling was observed in MnO2‐doped Fe2O3 compacts, the volume change increased with MnO2 content showing catastrophic swelling in compacts containing 6%MnO2 at 1248 K. The catastrophic swelling was attributed to the formation of dense metallic iron whiskers and plates in a highly porous structure. Unlike in MnO2‐doped samples, no considerable volume changes were detected in SiO2‐doped Fe2O3 and (MnO2 + SiO2)‐doped Fe2O3 compacts where the presence of silica greatly hindered the swelling phenomenon at all reduction temperatures.