Activity of phosphorus in α-Fe and phase diagram of Fe-Fe₂P system above 1273 K

Phosphorus distribution between liquid Fe_tO-P₂O₅ slag and iron crucible has been observed under H₂O-H₂ atmosphere from 1623 K to 1698 K. The phosphorus content in the solid iron phase at the slag-crucible interface was determined by extrapolating the concentration profile of phosphorus in solid iron phase to the interface. The activity of phosphorus in the solid iron phase at the interface was determined by combining activity of P₂O₅ in the slag and a thermodynamic model of the solid Fe-P alloy on the assumption of local equilibrium at the slag-crucible interface. The activity of phosphorus in the α-Fe phase shows positive deviation from Henry's law and the deviation becomes larger with increasing phosphorus content in the alloy. Based on the present experimental results and the thermodynamic data in the literatures, the phase diagram of Fe-Fe₂P system is assessed above 1273 K.