15:45 〜 16:10
[SIT18-07] Density of liquid FeO and thermodynamic modeling of Fe-FeO melting phase relations at high pressure
★Invited Papers
Phase relations of Fe-light-element alloys at high-pressure and -temperature conditions constrain the compositions of both the outer and inner cores. Previous experiments have shown that the pressure could dramatically change the phase relations in the Fe-FeO system: Fe and FeO liquids are immiscible at pressures less than ~30 GPa (Frost et al., 2010), while they form a eutectic system at higher pressures with an increasing oxygen content in the eutectic liquid with pressure (Oka et al., 2019). Such pressure-induced changes in melting phase relations can be described by thermodynamic modeling using equations of state of solid and liquid (Komabayashi, 2014; Yokoo et al., 2024). However, the equation of state of liquid FeO has not been determined by experiments.
Here, we present the thermal equation of state of liquid FeO based on high-pressure experiments using a diamond-anvil cell (DAC) and first-principles molecular dynamics (FPMD) simulations. The density of liquid FeO was experimentally obtained from diffuse scattering signals in X-ray diffraction patterns at ~20–70 GPa and ~3000 K (Kuwayama et al., 2020). By applying pressure corrections to pressure-volume-temperature relations obtained by FPMD simulations such that they are consistent with the results of DAC experiments at the investigated pressure range, we obtained the thermal equation of state of liquid FeO to the Earth’s core pressures.
The equation of state was then used to construct a thermodynamic modeling of Fe-FeO melting phase relations to the inner core boundary pressure. While we only used eutectic temperatures as constraints from experimental studies, predicted eutectic oxygen contents are also consistent with those in experimental studies (e.g., Oka et al., 2019). Using the modeled melting phase relations, we will discuss the ICB temperature from possible outer core compositions.
Here, we present the thermal equation of state of liquid FeO based on high-pressure experiments using a diamond-anvil cell (DAC) and first-principles molecular dynamics (FPMD) simulations. The density of liquid FeO was experimentally obtained from diffuse scattering signals in X-ray diffraction patterns at ~20–70 GPa and ~3000 K (Kuwayama et al., 2020). By applying pressure corrections to pressure-volume-temperature relations obtained by FPMD simulations such that they are consistent with the results of DAC experiments at the investigated pressure range, we obtained the thermal equation of state of liquid FeO to the Earth’s core pressures.
The equation of state was then used to construct a thermodynamic modeling of Fe-FeO melting phase relations to the inner core boundary pressure. While we only used eutectic temperatures as constraints from experimental studies, predicted eutectic oxygen contents are also consistent with those in experimental studies (e.g., Oka et al., 2019). Using the modeled melting phase relations, we will discuss the ICB temperature from possible outer core compositions.