Subsolidus Phase Equilibria of the Fe-Ni-O System

The phase equilibria of the Fe-Ni-O system in the temperature range between 800 °C and 1600 °C, at various oxygen partial pressures, in the subsolidus region, have been experimentally studied using equilibration and quenching techniques followed by electron-probe X-ray microanalysis (EPMA). The pseudo-binary ‘Fe₂O₃’-NiO phase diagram in air and isothermal Fe-Ni-O phase diagrams at low oxygen partial pressures, at temperatures between 1000 °C and 1200 °C, have been constructed. In the conditions studied, it was found that the solubilities of iron in bunsenite-(Ni, Fe)O and solubilities of nickel in wustite-(Fe, Ni)O phases are higher than reported in the previous studies. It is suggested that the improved experimental techniques used in the present study ensure the achievement of the true equilibrium state in the system. The isothermal ternary phase diagrams of FeO-NiO-Fe₂O₃ at 1000 °C, 1100 °C, and 1200 °C, modeled using FactSage, have also been presented. The present work has provided new phase equilibria data in the Fe-Ni-O system, as well as provided the basis for further experimental studies and for development of thermodynamic models of higher order complex such as Fe-Ni-X-O (X = Mg, Al, Cr), important to improve extraction of Ni from nickel laterite ores.