Solid-state reduction mechanism of Fe and Ni in Fe-Ni-O-C systems

Experimental studies on reduction behaviors of Fe and Ni in Fe-Ni-O-C systems (NiO + C,Fe₂O₃ + C,NiFe₂O₄ + C, NiO + Fe₂O₃ + C,and Ni + Fe₂O₃ + C) under different conditions were carried out by differential scanning calorimetry (DSC) analysis and X-ray diffraction (XRD) detection. The results show that due to the formation of NiFe₂O₄ and Fe-Ni alloys,the starting temperature of the NiO + Fe₂O₃ system is higher than that of pure NiO,while both of the temperatures corresponding to the maximum reduction rate and ending point are lower than those of pure Fe₂O₃. Compared with the system of NiO + Fe₂O₃,the reduction of NiFe₂O₄ shows higher starting and ending temperatures and lower reduction rates. The reduction of Fe₂O₃ by C could be divided into three stages,and the presence of Ni can obviously promote the transfer of iron oxides (Fe₂O₃,Fe₃O₄,and FeO) into metallic Fe. The data reveal that the reduction process of NiFe₂O₄ by C can also be divided into three stages,and the products in different stages show great difference.