Kinetic analysis and characterization of the simultaneous reduction–sintering of NiO–Fe2O3 nanoprecursors for ferronickel alloy production

Ni-Fe alloys with varying nickel contents (5%, 10%, 20%, and 30%) were successfully synthesized through a novel simultaneous reduction-sintering of nano-sized NiO-Fe₂O₃ precursors. Non-isothermal reduction was performed in hydrogen gas up to 1000 °C at varying heating rates (10-25 °C/min), followed by sintering in pure argon atmosphere at temperatures between 1000 °C and 1300 °C. Thermal analyses (TG-DTA), X-ray diffraction, and scanning electron microscopy with energy dispersive X-ray analysis identified complex, multi-step reduction reactions and phase transformations influenced by reduction temperature, heating rate and precursor composition. Kinetic analyses indicated a dual control mechanism dominated initially by combined gaseous diffusion and interfacial reactions, transitioning to interfacial chemical reactions at higher temperatures. Sintering characteristics of compacts derived from precursors containing 5-30% NiO-Fe₂O₃ were examined at temperatures from 1000 to 1300°C for 60 min in pure argon. Increased Ni content promoted the formation of intermetallic phases (Fe₇Ni₃ and Fe₃Ni), enhancing compositional homogeneity and reducing grain boundary visibility. Higher sintering temperatures notably improved grain growth, densification, intermetallic formation, reduced porosity, and increased micro-hardness. It was found that the combination of 20-30 wt% NiO with reduction at 900 °C followed by sintering at 1300 °C for 60 min yielded the best overall performance of synthesis Ni-Fe alloys. This optimization is making these materials more suitable for structural and functional applications where high strength and density are required.