EQUATIONS OF STATE OF ALPHA-IRON, EPSILON-IRON AND LIQUID-IRON AND IRONS MELTING CURVE - THERMODYNAMIC CALCULATIONS

The melting curve between epsilon 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 alpha, epsilon and liquid phases. The most uncertainty lies in the equation of state (EOS) of the epsilon 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 at [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 epsilon 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 epsilon and the liquid fields.