Polythermal description of the oxygen pressures in the melts of the Subsystems Fe‐FeOn and FeO‐Fe2O3

Abstract

The phase equilibria in the Subsystem Fe‐FeO of the Compound System FeO ranging from mole fractions of xo = 0 to xo = 52% are characterised by a wide miscibility gap. Using the van Laar formulation, it is possible, up to mole fractions of xo = 51%, to describe the liquidus line of the iron, the phase boundaries of the miscibility gap and, with the resultant activities aFe and aFeOn, the oxygen pressures of the liquid phases either side of the miscibility gap, in a manner consistent with the temperature‐dependent, experimental data of the relevant literature. In the overlap range (oxygen mole fractions of 50 − 52%) to the adjacent Subsystem FeO‐Fe2O3 (oxygen mole fractions of 50 − 60), a continuous transition is achieved to the experimentally ascertained oxygen pressures in the liquid oxide melts, these being characterised by a tendency towards Compound formation. These ‐values are very accurately described polythermally by the modified short‐range‐order model with stipulation of the short ranges 3FeO·Fe2O3 and FeO·Fe2O3, and also of the dissociation reaction 3(FeO) = (Fe2O3) + [Fe] and (Fe2O3) = 2(FeO) + [O].