3:45 PM - 4:00 PM
[SIT14-18] Density decrease by hydrogenation of Si-bearing Fe with hcp structure and its implication for the hydrogen content to the Earth's core
Keywords:High-pressure experiments, Light element in the core, Hydrogen, Silicon
Hydrogen is one of the plausible candidates of light elements in the Earth's core because of its strong siderophile behavior under high pressures and temperatures. Also, the incorporation of hydrogen into pure iron induces volume expansion of iron (Figure. 1) and contributes to the density deficit of the Earth's core. At present, the measurements of this volume expansion induced by hydrogen incorporation have been conducted in the Fe-H binary systems. However, it is worth noting that the effect of light elements on this volume expansion has not been extensively examined.
Among the light element candidates, silicon is considered a strong candidate, particularly in the inner core. This is due to its ability to partition relatively well into solid iron (inner core), with a distribution coefficient of approximately DH(solid/liquid) = 1. In this study, we focused on silicon and investigate the effect of silicon coexistence on the hydrogen-induced volume expansion of iron with hcp structure. X-ray and neutron diffraction experiments were conducted on hcp-Fe0.95Si0.05 (at 10–20 GPa and 300–900 K) and its deuterides (13.5 GPa and 900 K and at 12.1 GPa and 300 K), respectively. By combining those results, the determined hydrogen-induced volume expansion of hcp-Fe0.95Si0.05 is 10% greater than that of pure iron with an hcp structure. Furthermore, we discussed and recalculate the hydrogen content in the Earth by using the obtained data. It is worth noting that if silicon does not promote hydrogen-induced volume expansion, the necessary hydrogen content would be 50% higher (Figure. 2). In conclusion, we derived the result that the estimated amount of hydrogen in the Earth's core has to be revised downwards due to Si dissolution based on the experimental results of this study.
Among the light element candidates, silicon is considered a strong candidate, particularly in the inner core. This is due to its ability to partition relatively well into solid iron (inner core), with a distribution coefficient of approximately DH(solid/liquid) = 1. In this study, we focused on silicon and investigate the effect of silicon coexistence on the hydrogen-induced volume expansion of iron with hcp structure. X-ray and neutron diffraction experiments were conducted on hcp-Fe0.95Si0.05 (at 10–20 GPa and 300–900 K) and its deuterides (13.5 GPa and 900 K and at 12.1 GPa and 300 K), respectively. By combining those results, the determined hydrogen-induced volume expansion of hcp-Fe0.95Si0.05 is 10% greater than that of pure iron with an hcp structure. Furthermore, we discussed and recalculate the hydrogen content in the Earth by using the obtained data. It is worth noting that if silicon does not promote hydrogen-induced volume expansion, the necessary hydrogen content would be 50% higher (Figure. 2). In conclusion, we derived the result that the estimated amount of hydrogen in the Earth's core has to be revised downwards due to Si dissolution based on the experimental results of this study.