The Join FeNi–FeNiP at 6 GPa

The present work is devoted to the study of phase relationships in the pseudobinary section of the Fe–Ni–P ternary, namely, the join Fe0.5Ni0.5–(Fe0.5Ni0.5)2P, at 6 GPa in the range of 900–1600°C. Experiments were run in ceramic capsules using a multianvil press. The system has two intermediate compounds, (Fe, Ni)3P schreibersite and (Fe, Ni)2P barringerite. The metal-(Fe, Ni)3P eutectic is established at 18 mol % P and 1000°C. (Fe, Ni)3P melts incongruently at 1075°C to form (Fe, Ni)2P and a liquid with 23 mol % P. (Fe, Ni)2P melts congruently at 1400°C. The partition coefficient of phosphorus in the Fe–Ni metal phase and coexisting liquid ( $$D_{{\text{P}}}^{{{\text{SM/LM}}}}$$ , weight ratio) was found to be 0.14 ± 0.01 at 6 GPa and 1050–1450°C. The melt quench products are represented by dendrites of either metal phase at <18 mol % P or phosphides at >18 mol % P: (Fe, Ni)3P at <1100°C or (Fe, Ni)2P at ≥1100°C, embedded in a groundmass containing 20 mol % P in bulk, like (Fe, Ni)4P. However, upon closer examination, the groundmass is represented by a dendritic polyphase aggregate, not melliniite.