High Pressure and High Temperature Equation-of-state of Gamma and Liquid Iron

Shock-wave experiments on pure iron preheated to 1573 K were conducted in the 17-73 GPa range. The shock-wave equation of state ofy-iron at an initial temperature of 1573 K can be fit with u, = 4.102 (0.015) km/s + 1.610(0.014) up with p 0 = 7.413±0.012 Mg/m• We obtain for y-iron's bulk modulus and pressure derivative the values: 124.7±1.1 GPa and 5.44±0.06, respectively. We present new data for sound velocities in theyand liquid-phases. In they-phase, to a first approximation, the longitudinal sound velocity is linear with respect to density: VP= -3.13 (0.72) + 1.119(0.084) p(units for VP and pare km/sand Mg/m3, respectively). Melting was observed in the highest pressure (about 70-73 GPa) experiments at a calculated shock temperature of 2775±160 K. This result is consistent with a previously calculated melting curve (fore-iron) which is close to those measured by Boehler [l) and Saxena et al. [2]. The liquid iron sound velocity data yields a Grilneisen parameter value of 1.63±0.28 at 9.37±0.02 Mg/m at 71.6 GPa. The quantity yp is 15.2±2.6 M~m , which agrees with the uncertainty bounds of Brown and McQueen [3] (13.3-19.6 Mg/m ). Based on upward pressure and temperature extrapolation of the melting curve of y-iron, the estimated inner core-outer core boundary temperature is 5500±400 K, the temperature at the core-mantle boundary on the outer core side is 3930±630 K.