Equations of state of α, ϵ and liquid iron and Iron's melting curve —thermodynamic calculations

Abstract

The melting curve between ϵ and liquid iron (100GPa< P <300GPa) has been derived by computing Gibbs free energies at high pressures and high temperatures from equations of state of the α, ϵ and liquid phases. The most uncertainty lies in the equation of state (EOS) of the ϵ phase. By comparing the calculations to experimental data, the internal thermodynamic consistency of the three phases are examined. The best fits to the melting curves of Boehler [1993] and Williams et al. [1987] can be obtained with lower bulk moduli than determined by static compression. Using available equations of state of the iron phases, our calculations indicate that if sub-solidus iron is of the ϵ phase, Boehler's melting curve is thermodynamically more consistent than Williams et al.'s. The problem is complicated by the possible existence of a new phase between the ϵ and the liquid fields.