Synthetic route for high-yield α′′-Fe16N2 submicron-sized powder using CaH2 drying agent

Abstract

The rare-earth-free magnetic material α′′-Fe₁₆N₂ is known to be a high-performance magnetic material. However, a synthetic route for high-yield α′′-Fe₁₆N₂ powder has not yet been established. In this study, a high-yield α′′-Fe₁₆N₂ submicron-sized powder was synthesized from Fe₃O₄via H₂ reduction, and subsequent nitridation using a CaH₂ drying agent. Here, controlling the crystallite diameter of α-Fe is crucial to promoting nitridation. α-Fe powder with a crystallite diameter of approximately 20 nm was produced by lowering the reduction temperature and water vapor partial pressure. Thus, a high-yield α′′-Fe₁₆N₂ phase of 97 wt% could be obtained. Microstructural observations indicated that α′′-Fe₁₆N₂ submicron-sized powder with primary particles of 20–30 nm diameter could be synthesized. The α′′-Fe₁₆N₂ powder had much higher coercivity than that of the α-Fe powder. Thus, the process suggested in this study is expected to contribute to the development of applications of α′′-Fe₁₆N₂ in magnetic materials.