[S-IT19] Deep Earth Sciences

[SIT19-P10] Effect of silicon dissolution on hydrogenation of iron

*Yuichiro Mori¹, Hiroyuki Kagi¹, Katsutoshi Aoki¹, Sho Kakizawa², Yuji Higo², Yoshinori Tange², Asami Sano-Furukawa³, Takanori Hattori³ (1.The University of Tokyo, 2.JASRI, 3.J-PARC Center, JAEA)

Keywords:High-pressure and high-temperature experiments, Multi anvil press, Light element, Hydrogenation

Seismic wave observations have revealed that the density of the Earth's core is several percent less than that of pure iron under corresponding PT condition. Some light elements (i.e., elements lighter than iron) are believed to dissolve into the core and solve this density deficit. Identification of light elements in the core has long been discussed and is still an unsolved question.

Among the candidates for light elements, hydrogen is one of the most promising light elements that has been actively studied. Hydrogen dissolves into iron at high pressures and temperatures, greatly increasing the unit cell volume and decreasing the density. The volume expansion induced by the dissolution of one hydrogen atom is defined as hydrogen-induced volume expansion, Δv_H.

Using neutron diffraction experiment under high pressure and high temperature conditions, the hydrogen-induced volume expansion of iron was directly determined on the hcp and fcc structures. However, almost no experiments have yet been carried out to determine how the hydrogen-induced volume expansion coefficient actually changes in the presence of light elements in addition to hydrogen.

Here, I focused on Si, another light element and determined the hydrogen-induced volume expansion coefficient of Fe_0.95Si_0.05. The obtained hydrogen-induced volume expansion coefficient of hcp-Fe_0.95Si_0.05 was about 1.4 times that of pure iron. Accordingly, the dissolution of silicon may enhance the effect of density reduction caused by hydrogenation. This result suggests that the amount of hydrogen in the core has to be reconsidered if silicon is a major light element.