Carbothermic reduction of Fe ₂ O ₃ /C compacts: comparative approach to kinetics and mechanism

Abstract

Fe 2 O 3 /C compacts prepared by mixing of nanosized Fe 2 O 3 (40–150 nm) with charcoal in a molar ratio of 1∶4 were isothermally reduced at 950–1100°C in argon gas flow. The rate of reduction was calculated from the direct measurements of the mass–loss using TG technique. In addition, the QMS gas analyser was used to monitor CO and CO 2 concentrations in the off gases. The different phases developed in the composites were identified by X-ray diffraction and their structures were microscopically examined. The effect of temperature and particle size of Fe 2 O 3 on the reduction rates was studied. The reduction of Fe 2 O 3 was found to proceed in a stepwise manner up to metallic iron. Alternatively, the carbon solution loss reaction resulted from the gasification of charcoal plays a significant role in the carbothermic reduction process. Incubation periods were detected in QMS analysis at the beginning of reduction process. The charcoal volatiles interfered with the O 2 weight loss measurements, upon applying TG technique, resulting higher values of total weight loss than that measured by QMS. Comparison of the reduction testing techniques shows the differences in the actual reduction extents. The reduction kinetics were correlated with the microstructure of the reduced products and directed to the elucidation of the reduction mechanism.