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Journal Articles

Hydrogenation of silicon-bearing hexagonal close-packed iron and its implications for density deficits in the inner core

Mori, Yuichiro*; Kagi, Hiroyuki*; Aoki, Katsutoshi*; Takano, Masahiro*; Kakizawa, Sho*; Sano, Asami; Funakoshi, Kenichi*

Earth and Planetary Science Letters, 634, p.118673_1 - 118673_8, 2024/05

 Times Cited Count:1 Percentile:73.79(Geochemistry & Geophysics)

To investigate silicon effects on the hydrogen-induced volume expansion of iron, neutron diffraction and X-ray diffraction experiments were conducted to examine hcp-Fe$$_{0.95}$$Si$$_{0.05}$$ under high pressures and high temperatures. Neutron diffraction experiments were performed on the deuterated hcp-Fe$$_{0.95}$$Si$$_{0.05}$$ at 13.5 GPa and 900 K, and at 12.1 GPa and 300 K. By combining the P-V-T equation of state of hcp-Fe$$_{0.95}$$Si$$_{0.05}$$, present results indicate that the hydrogen-induced volume expansion of hcp-Fe$$_{0.95}$$Si$$_{0.05}$$ is 10% greater than that of pure hcp iron. Using the obtained values, we estimated the hydrogen content that would reproduce the density deficit in the inner core, which was 50% less than that without the effect of silicon. Possible hydrogen content, $$x$$, in the inner core and the outer core was calculated to be 0.07 and 0.12-0.15, respectively, when reproducing the density deficit of the inner core with hcp-Fe$$_{0.95}$$Si$$_{0.05}$$Hx.

Journal Articles

Hydrogen occupation and hydrogen-induced volume expansion in Fe$$_{0.9}$$Ni$$_{0.1}$$D$$_x$$ at high $$P-T$$ conditions

Shito, Chikara*; Kagi, Hiroyuki*; Kakizawa, Sho*; Aoki, Katsutoshi*; Komatsu, Kazuki*; Iizuka, Riko*; Abe, Jun*; Saito, Hiroyuki*; Sano, Asami; Hattori, Takanori

American Mineralogist, 108(4), p.659 - 666, 2023/04

 Times Cited Count:3 Percentile:71.64(Geochemistry & Geophysics)

The phase relation and crystal structure of Fe$$_{0.9}$$Ni$$_{0.1}$$H$$_x$$ (D$$_x$$) at high pressures and temperatures up to 12 GPa and 1000 K were clarified by in-situ X-ray and neutron diffraction measurements. Under $$P-T$$ conditions of the present study, no deuterium atoms occupied tetragonal ($$T$$) sites of face-centered cubic (fcc) Fe$$_{0.9}$$Ni$$_{0.1}$$D$$_x$$ unlike fcc FeH$$_x$$(D$$_x$$). The deuterium-induced volume expansion per deuterium $$v_mathrm{D}$$ was determined as 2.45(4) $AA$^3$$ and 3.31(6) $AA$^3$$ for fcc and hcp phases, respectively, which were significantly larger than the corresponding values for FeD$$_x$$. The $$v_mathrm{D}$$ value slightly increased with increasing temperature. This study suggests that only 10% of nickel in iron drastically changes the behaviors of hydrogen in metal. Assuming that $$v_mathrm{D}$$ is constant regardless of pressure, the maximum hydrogen content in the Earth's inner core is estimated to be one to two times the amount of hydrogen in the oceans.

Journal Articles

sparse-ir; Optimal compression and sparse sampling of many-body propagators

Wallerberger, M.*; Badr, S.*; Hoshino, Shintaro*; Huber, S.*; Kakizawa, Fumiya*; Koretsune, Takashi*; Nagai, Yuki; Nogaki, Kosuke*; Nomoto, Takuya*; Mori, Hitoshi*; et al.

Software X (Internet), 21, p.101266_1 - 101266_7, 2023/02

 Times Cited Count:17 Percentile:91.98(Computer Science, Software Engineering)

no abstracts in English

Journal Articles

Neutron imaging of generated water inside polymer electrolyte fuel cell using newly-developed gas diffusion layer with gas flow channels during power generation

Nasu, Mitsunori*; Yanai, Hiroshi*; Hirayama, Naoki*; Adachi, Hironori*; Kakizawa, Yu*; Shirase, Yuto*; Nishiyama, Hiromichi*; Kawamoto, Teppei*; Inukai, Junji*; Shinohara, Takenao; et al.

Journal of Power Sources, 530, p.231251_1 - 231251_11, 2022/05

 Times Cited Count:23 Percentile:88.13(Chemistry, Physical)

Journal Articles

High-pressure and high-temperature neutron-diffraction experiments using Kawai-type multi-anvil assemblies

Sano, Asami; Kakizawa, Sho*; Shito, Chikara*; Hattori, Takanori; Machida, Shinichi*; Abe, Jun*; Funakoshi, Kenichi*; Kagi, Hiroyuki*

High Pressure Research, 41(1), p.65 - 74, 2021/03

 Times Cited Count:4 Percentile:42.98(Physics, Multidisciplinary)

We applied Kawai-type multi-anvil assemblies (MA6-8) for time-of-flight neutron-diffraction experiments to achieve high pressures and high temperatures simultaneously. To achieve sufficient signal intensities, the angular access to the sample was enlarged using slits and tapers on the first-stage anvils. Using SiC-binder sintered diamond for the second-stage anvils that transmits neutrons, sufficient signal intensities were achieved at a high-pressure of $$sim$$23.1 GPa. A high-temperature experiment was also conducted at 16.2 GPa and 973 K, validating the use of tungsten carbide for the second-stage anvils. The present study reveals the capability of the MA6-8 cells in neutron-diffraction experiments to attain pressures and temperatures beyond the limits of the conventional MA6-6 cells used in the high-pressure neutron diffractometer PLANET at the MLF, J-PARC.

Journal Articles

Neutron diffraction study of hydrogen site occupancy in Fe$$_{0.95}$$Si$$_{0.05}$$ at 14.7 GPa and 800 K

Mori, Yuichiro*; Kagi, Hiroyuki*; Kakizawa, Sho*; Komatsu, Kazuki*; Shito, Chikara*; Iizuka, Riko*; Aoki, Katsutoshi*; Hattori, Takanori; Sano, Asami; Funakoshi, Kenichi*; et al.

Journal of Mineralogical and Petrological Sciences, 116(6), p.309 - 313, 2021/00

 Times Cited Count:2 Percentile:13.89(Mineralogy)

The Earth's core is believed to contain some light elements because it is 10% less dense than pure Fe under the corresponding pressure and temperature conditions. Hydrogen, a promising candidate among light elements, has phase relations and physical properties that have been investigated mainly for the Fe-H system. This study specifically examined an Fe-Si-H system using in-situ neutron diffraction experiments to investigate the site occupancy of deuterium of hcp-Fez$$_{0.95}$$Si$$_{0.05}$$ hydride at 14.7 GPa and 800 K. Results of Rietveld refinement indicate hcp-Fe$$_{0.95}$$Si$$_{0.05}$$ hydride as having deuterium (D) occupancy of 0.24(2) exclusively at the interstitial octahedral site in the hcp lattice. The effect on the site occupancy of D by addition of 2.6 wt% Si into Fe (Fe$$_{0.95}$$Si$$_{0.05}$$) was negligible compared to results obtained from an earlier study of an Fe-D system (Machida et al., 2019).

Oral presentation

Recent developments in neutron diffraction experiments at high pressure and high temperature and application to Earth science

Sano, Asami; Kakizawa, Sho*; Mori, Yuichiro*; Kagi, Hiroyuki*; Abe, Jun*; Funakoshi, Kenichi*; Hattori, Takanori

no journal, , 

Neutron scattering with high sensitivity to hydrogen can be a powerful tool in the investigation of hydrogen in the Earth's material. In the high-pressure neutron diffractometer PLANET at MLF in J-PARC, a large volume 6-axis multi-anvil press, and precise optics have enabled stable neutron diffraction experiments at high pressure and high temperature. This sample environment has promoted unique research, as exemplified by determining the amount of hydrogen in the iron alloys that form the Earth's core. In this presentation, recent results of neutron experiments at PLANET will be presented, as well as the on-going developments.

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