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 an d 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 e xamined. The best fits to the melting curves of Boehler [1993] and Wil liams et at [1987] can be obtained with lower bulk moduli than determi ned by static compression. Using available equations of state of the i ron phases, our calculations indicate that if sub-solidus iron is of t he epsilon phase, Boehler's melting curve is thermodynamically more co nsistent than Williams et al.'s. The problem is complicated by the pos sible existence of a new phase between the epsilon and the liquid fiel ds.