09:35 〜 09:50
[SIT18-04] Effects of nickel on hydrogenation of iron: High-PT neutron diffraction measurements on Fe0.9Ni0.1Dx
キーワード：核、鉄水素化物、中性子回折、密度欠損、高圧
Density of the Earth’s inner core is estimated to be about 5% lower than that of Fe0.9Ni0.1 alloy. Hydrogen, the most abundant element in our solar system, is one of the most promising light elements contained in the core. We focused on site occupancy of hydrogen and volume expansion induced by incorporation of hydrogen in Fe–Ni–H systems. In the present study, neutron diffraction measurements on Fe0.9Ni0.1Dx were carried out at high-PT conditions up to 12 GPa and 1000 K to clarify the effects of nickel on hydrogenation of iron. Crystal structure of Fe0.9Ni0.1Dx including site occupancy of hydrogen was refined using the Rietveld method.
Our results indicated that hydrogen-induced volume expansion coefficients vD of fcc and hcp Fe0.9Ni0.1Dx are ~11% and ~33% larger than those of FeDx, respectively. The maximum hydrogen content of the Earth’s inner core was calculated to be about one to two times the ocean mass. Hydrogen atoms in fcc Fe0.9Ni0.1Dx did not occupy tetrahedral sites at all while 10–20% tetrahedral-site occupancy was previously reported in fcc FeDx. Therefore, the effect of 10% nickel on hydrogenation of iron cannot be ignored in the Earth’s core. However, the P-T conditions in this study were much lower than those of the Earth’s core. It is essential to perform neutron diffraction measurements on the iron–nickel–hydrogen systems at higher P-T conditions to directly reveal the site occupancies of hydrogen and the density reduction by hydrogenation in the Earth’s core.
Our results indicated that hydrogen-induced volume expansion coefficients vD of fcc and hcp Fe0.9Ni0.1Dx are ~11% and ~33% larger than those of FeDx, respectively. The maximum hydrogen content of the Earth’s inner core was calculated to be about one to two times the ocean mass. Hydrogen atoms in fcc Fe0.9Ni0.1Dx did not occupy tetrahedral sites at all while 10–20% tetrahedral-site occupancy was previously reported in fcc FeDx. Therefore, the effect of 10% nickel on hydrogenation of iron cannot be ignored in the Earth’s core. However, the P-T conditions in this study were much lower than those of the Earth’s core. It is essential to perform neutron diffraction measurements on the iron–nickel–hydrogen systems at higher P-T conditions to directly reveal the site occupancies of hydrogen and the density reduction by hydrogenation in the Earth’s core.