Melting Experiments on Fe‐O‐H and Fe‐H: Evidence for Eutectic Melting in Fe‐FeH and Implications for Hydrogen in the Core

Abstract

Abstract We examined liquidus phase relations in Fe‐O ± H at ∼40 and ∼150 GPa, and in Fe‐H at 45 GPa. While it has been speculated that Fe and FeH form continuous solid solution to core pressures, our experiment on Fe‐H showed that FeH0.20 forms with the hcp structure, different from fcc for stoichiometric FeH, and melts at temperature lower than that for FeH, suggesting eutectic melting between Fe and FeH. It is consistent with the liquidus phase diagram in Fe‐O‐H, which implies the Fe‐FeH binary eutectic liquid composition of FeH0.42 at ∼40 GPa. These experiments also demonstrated the partition coefficient of H between solid Fe and liquid, DH (solid/liquid) = 0.77–0.89. We estimated the outer core liquid composition based on the liquidus phase relations, solid‐liquid partitioning, and outer/inner core densities and velocities, indicating that O and either H or Si are important core light elements.

Keywords

• core
• high pressure
• Fe‐H
• Fe‐O‐H
• hydrogen
• light elements