Polythermal description of the oxygen pressures in the melts of the Subsystems Fe‐FeO n and FeO‐Fe 2 O 3

The phase equilibria in the Subsystem Fe‐FeO of the Compound System FeO ranging from mole fractions of x o = 0 to x o = 52% are characterised by a wide miscibility gap. Using the van Laar formulation, it is possible, up to mole fractions of x o = 51%, to describe the liquidus line of the iron, the phase boundaries of the miscibility gap and, with the resultant activities a Fe and a FeO n , 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‐Fe 2 O 3 (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·Fe 2 O 3 and FeO·Fe 2 O 3 , and also of the dissociation reaction 3(FeO) = (Fe 2 O 3 ) + [Fe] and (Fe 2 O 3 ) = 2(FeO) + [O].