Sound Velocities and Densities of Liquid Fe-8.6wt% Si at High Pressure and Temperature: Implications for a Si-rich Core

Using dynamic compression technique, we measured the longitudinal sound velocity V_P of liquid Fe-8.6Si(weight percent) up to 298 GPa and 5500 K. A discontinuity in V_P along Hugoniot indicates that the melting starts at 216.4 GPa (4200 K) and completes at 260.5 GPa (4530 K). At 330 GPa, the extrapolated melting temperature of Fe-8.6 wt% Si is 5000 K. Combing the measurements of Hugoniot data and V_P, we established a thermodynamic model to calculate the equation of state (EOS) and V_P for Fe and liquid Fe-8.6Si. The calculated EOSs and V_P for liquid Fe and Fe-8.6 Si are consistent with measurements by static and dynamic compression. Under the outer condition, EOS and V_P of liquid Fe-8.6Si simultaneously match the data of the outer core. If Si is only light element, its maximum concentration in the outer core is 7.6~8.6 wt %.