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Journal Articles

Melting of Pb charge glass and simultaneous Pb-Cr charge transfer in PbCrO$$_{3}$$ as the origin of volume collapse

Yu, R.*; Hojo, Hajime*; Watanuki, Tetsu; Mizumaki, Masaichiro*; Mizokawa, Takashi*; Oka, Kengo*; Kim, H.*; Machida, Akihiko; Sakaki, Koji*; Nakamura, Yumiko*; et al.

Journal of the American Chemical Society, 137(39), p.12719 - 12728, 2015/10

 Times Cited Count:23 Percentile:65.97(Chemistry, Multidisciplinary)

no abstracts in English

Journal Articles

Hydrogenation of a TiFe-based alloy at high pressures and temperatures

Endo, Naruki*; Saita, Itoko*; Nakamura, Yumiko*; Saito, Hiroyuki; Machida, Akihiko

International Journal of Hydrogen Energy, 40(8), p.3283 - 3287, 2015/03

 Times Cited Count:11 Percentile:35.05(Chemistry, Physical)

Journal Articles

Observation of transient structural changes on hydrogen absorption process of LaNi$$_{4.75}$$Sn$$_{0.25}$$ by time resolved X-ray diffraction

Machida, Akihiko; Higuchi, Kensuke*; Katayama, Yoshinori; Sakaki, Koji*; Kim, H.*; Nakamura, Yumiko*

Nihon Kinzoku Gakkai-Shi, 79(3), p.124 - 130, 2015/03

 Times Cited Count:4 Percentile:28.87(Metallurgy & Metallurgical Engineering)

Structural changes on hydrogen absorption process of hydrogen absorbing alloy LaNi$$_{4.75}$$Sn$$_{0.25}$$ have been investigated by time-resolved X-ray diffraction measurements using synchrotron radiation source. We have found the transient intermediate phase between the solid solution and hydride phases of LaNi$$_{4.75}$$Sn$$_{0.25}$$ under non-equilibrium hydrogen pressure condition at room temperature. LaNi$$_{4.75}$$Sn$$_{0.25}$$ has transformed into the hydride through three phase co-existing state. The hydrogen content of the intermediate phase estimated from the unit cell volume is independent of the induced hydrogen gas pressure. The variation of lattice constants indicate that the hydrogen atoms are located at the La$$_{2}$$Ni$$_{2}$$(Ni,Sn)$$_{2}$$ octahedron and La$$_{2}$$(Ni,Sn)$$_{2}$$ tetrahedron in the intermediate phase.

Journal Articles

Compositional dependence of hydrogenation properties in Ti$$_{1+y}$$(Fe$$_{1-x}$$Mn$$_{x}$$)$$_{1-y}$$ ($$0.2 leq x leq 0.5$$, $$0 leq y leq 0.08$$)

Sakaki, Koji*; Kim, H.*; Machida, Akihiko; Watanuki, Tetsu; Nakamura, Yumiko*

Nihon Kinzoku Gakkai-Shi, 79(3), p.112 - 117, 2015/03

 Times Cited Count:2 Percentile:8.58(Metallurgy & Metallurgical Engineering)

no abstracts in English

Journal Articles

Effect of a quenching rate on hydrogen storage properties of V$$_{0.79}$$Ti$$_{0.2}$$Zr$$_{0.01}$$

Kim, H.*; Sakaki, Koji*; Asano, Kota*; Ikeda, Kazutaka*; Otomo, Toshiya*; Machida, Akihiko; Watanuki, Tetsu; Nakamura, Yumiko*

Nihon Kinzoku Gakkai-Shi, 79(3), p.131 - 136, 2015/03

 Times Cited Count:0 Percentile:0.01(Metallurgy & Metallurgical Engineering)

no abstracts in English

Journal Articles

Improvement of hydrogen storage properties of Mg$$_{1-x}$$Pr$$_{x}$$Ni$$_{4}$$ by Changing Mg/Pr ratio

Sakaki, Koji*; Terashita, Naoyoshi*; Kim, H.*; Majzoub, E. H.*; Proffen, T.*; Machida, Akihiko; Watanuki, Tetsu; Tsunokake, Shigeru*; Nakamura, Yumiko*; Akiba, Etsuo*

Sumato Purosesu Gakkai-Shi, 3(6), p.359 - 366, 2014/11

no abstracts in English

JAEA Reports

Improvement of the environment for the diffusion experiment using granite samples and results of pore physicality measurement and mineralogical test

Yamashita, Riyo; Hama, Katsuhiro; Takeuchi, Ryuji; Morikawa, Keita*; Hosoya, Shinichi*; Nakamura, Toshiaki*; Tanaka, Yumiko*

JAEA-Technology 2014-029, 118 Pages, 2014/09

JAEA-Technology-2014-029.pdf:25.16MB

This study is to gain a better understanding of mass transfer phenomena in the geological environment as well as to develop technologies for: measurement of the solute transport parameters, model construction, numerical analysis and validation of all those technologies based on the existing information. As part of solute transport study, laboratory experiments were planned to understand the influence of the geological characteristics of fracture on the solute transport parameters, also understand the differences in test results by the different sizes of the samples used for an experiment, and moreover to validate the parameters obtained by numerical analysis.

Journal Articles

Reduction and unusual recovery in the reversible hydrogen storage capacity of V$$_{1-x}$$Ti$$_x$$ during hydrogen cycling

Kim, H.*; Sakaki, Koji*; Saita, Itoko*; Enoki, Hirotoshi*; Noguchi, Kazuo*; Machida, Akihiko; Watanuki, Tetsu; Nakamura, Yumiko*

International Journal of Hydrogen Energy, 39(20), p.10546 - 10551, 2014/07

 Times Cited Count:10 Percentile:30.26(Chemistry, Physical)

The effect of the vanadium content on the cyclic stability of V-Ti binary alloys was investigated. V$$_{1-x}$$Ti$$_x$$, $$x=$$ 0.2 and 0.5 samples were hydrogenated and dehydrogenated at 410 K and 553 K respectively, for more than 100 times. During hydrogen cycling, reduction in the reversible hydrogen storage capacity was clearly observed from both samples. In addition, the shape of the pressure-composition-isotherm curves was significantly altered over the testing cycle period; the absorption and desorption plateaus got markedly inclined and the hysteresis became evidently smaller. We found that even after the hydrogen storage capacity of V$$_{1-x}$$Ti$$_x$$ was significantly reduced, at low enough temperature V$$_{1-x}$$Ti$$_x$$ was able to absorb hydrogen as much as it did at the first cycle.

Journal Articles

Degradation mechanism against hydrogenation cycles in Mg$$_{2-x}$$Pr$$_x$$Ni$$_4$$ ($$x$$ = 0.6 and 1.0)

Sakaki, Koji*; Terashita, Naoyoshi*; Kim, H.*; Majzoub, E. H.*; Machida, Akihiko; Watanuki, Tetsu; Tsunokake, Shigeru*; Nakamura, Yumiko*; Akiba, Etsuo*

Journal of Physical Chemistry C, 118(13), p.6697 - 6705, 2014/04

 Times Cited Count:13 Percentile:44.39(Chemistry, Physical)

We present an investigation of the degradation mechanism against hydrogenation cycles in Mg$$_{2-x}$$Pr$$_x$$Ni$$_4$$ ($$x$$ = 0.6 and 1.0). Mg$$_{1.0}$$Pr$$_{1.0}$$Ni$$_{4}$$ shows significant degradation and loss of capacity after only a few cycles, while Mg$$_{1.4}$$Pr$$_{0.6}$$Ni$$_{4}$$ did not show any reduction of hydrogen storage capacity until 100 cycles. The peak broadening of X-ray diffraction patterns and accumulation of lattice strain were observed concomitantly with an increase of hydrogenation cycles only in Mg$$_{1.0}$$Pr$$_{1.0}$$Ni$$_{4}$$. These changes were not observed in Mg$$_{1.4}$$Pr$$_{0.6}$$Ni$$_{4}$$. In pair distribution function patterns, $$r$$-dependent peak broadening was observed and it became significant with an increasing number of cycles in Mg$$_{1.0}$$Pr$$_{1.0}$$Ni$$_{4}$$, suggesting an increase of the dislocation density. Mg$$_{1.4}$$Pr$$_{0.6}$$Ni$$_{4}$$ showed higher hardness and more pulverization upon hydrogenation than Mg$$_{1.0}$$Pr$$_{1.0}$$Ni$$_{4}$$.

Journal Articles

In situ synchrotron $$^{57}$$Fe M$"o$ssbauer spectroscopy of RFe$$_{2}$$ (R = Y, Gd) hydrides synthesized under ultra-high-pressure hydrogen

Mitsui, Takaya; Masuda, Ryo*; Seto, Makoto; Hirao, Naohisa*; Matsuoka, Takehiro*; Nakamura, Yumiko*; Sakaki, Koji*; Enoki, Hirotoshi*

Journal of Alloys and Compounds, 580(Suppl.1), p.S264 - S267, 2013/12

 Times Cited Count:4 Percentile:31.72(Chemistry, Physical)

Journal Articles

Origin of degradation in the reversible hydrogen storage capacity of V$$_{1-x}$$Ti$$_{x}$$ alloys from the atomic pair distribution function analysis

Kim, H.*; Sakaki, Koji*; Ogawa, Hiroshi*; Nakamura, Yumiko*; Nakamura, Jin*; Akiba, Etsuo*; Machida, Akihiko; Watanuki, Tetsu; Proffen, T.*

Journal of Physical Chemistry C, 117(50), p.26543 - 26550, 2013/12

 Times Cited Count:30 Percentile:72.62(Chemistry, Physical)

Reduction in reversible hydrogen storage capacity with increasing hydrogenation and dehydrogenation cycle number is observed in numerous hydrogen storage materials, but the mechanism behind this unfavorable change has not been elucidated yet. In this study, we have investigated the development of structural defects or disorders in V$$_{1-x}$$Ti$$_x$$H$$_2$$, $$x$$ = 0, 0.2, and 0.5, during the first 15 hydrogen absorption and desorption cycles using the atomic pair distribution function (PDF) analysis of synchrotron X-ray total scattering data to find out the possible structural origin of the poor cyclic stability of V$$_{1-x}$$Ti$$_x$$ alloys.

Journal Articles

An in situ M$"{o}$ssbauer study using synchrotron radiation

Masuda, Ryo; Mitsui, Takaya; Ito, Keiji*; Sakaki, Koji*; Enoki, Hirotoshi*; Nakamura, Yumiko*; Seto, Makoto

Hyperfine Interactions, 204(1-3), p.139 - 142, 2012/03

 Times Cited Count:2 Percentile:79.02

We have been developing a system for in situ M$"{o}$ssbauer studies using synchrotron radiation (SR) to elucidate the mechanism of hydrogenation processes. In the system, samples reacts in an atmosphere chamber and SR-based M$"{o}$ssbauer spectra using variable-frequency nuclear monochromator and energy spectra of inelastic nuclear resonant scattering (NRS) of SR are measured. As a feasibility study, the temperature dependence of the M$"{o}$ssbauer and inelastic NRS spectra of $$^{57}$$Fe in $$c$$-GdFe$$_2$$H$$_3$$ under vacuum were measured. In both spectra, clear differences were observed between 373 K and 573 K. These differences can be interpreted by the change of microscopic environment around Fe at the dehydrogenation. Thus, it is confirmed that this system works well enough to perform the in-situ M$"{o}$ssbauer study on the dehydrogenation of $$c$$-GdFe$$_2$$H$$_3$$.

Oral presentation

Development of time resolved X-ray diffraction measurement system for studying hydrogenation and dehydrogenation processes

Higuchi, Kensuke; Machida, Akihiko; Katayama, Yoshinori; Sakaki, Koji*; Nakamura, Yumiko*

no journal, , 

no abstracts in English

Oral presentation

High speed X-ray diffraction measurements of hydrogen storage alloy on hydrogen absorption and desorption processes

Higuchi, Kensuke; Machida, Akihiko; Katayama, Yoshinori; Sakaki, Koji*; Nakamura, Yumiko*

no journal, , 

no abstracts in English

Oral presentation

M$"{o}$ssbauer study on the hydrides of C15 RFe$$_2$$ (R=Sm,Gd) compounds

Masuda, Ryo; Mitsui, Takaya; Ito, Keiji*; Sakaki, Koji*; Enoki, Hirotoshi*; Nakamura, Yumiko*; Kobayashi, Yasuhiro*; Kitao, Shinji*; Seto, Makoto

no journal, , 

Oral presentation

Time resolved X-ray diffraction measurement of LaNi$$_{4.5}$$Al$$_{0.5}$$ alloy on hydrogen absorption process

Higuchi, Kensuke; Machida, Akihiko; Katayama, Yoshinori; Sakaki, Koji*; Kim, H.*; Nakamura, Yumiko*

no journal, , 

no abstracts in English

Oral presentation

Transient structural change of LaNi$$_{4.5}$$Al$$_{0.5}$$ alloy on hydrogen absorbing process

Higuchi, Kensuke; Machida, Akihiko; Katayama, Yoshinori; Sakaki, Koji*; Kim, H.*; Nakamura, Yumiko*

no journal, , 

no abstracts in English

Oral presentation

Time resolved X-ray diffraction measurements on hydrogen absorption/desorption processes of hydrogen absorbing alloys

Machida, Akihiko; Higuchi, Kensuke*; Katayama, Yoshinori; Sakaki, Koji*; Kim, H.*; Nakamura, Yumiko*

no journal, , 

We have investigated the structural properties of the hydrogen absorbing alloys on the hydrogen absorbing process. In-situ measurements are essential to elucidate the mechanism of the hydrogen storage because the hydrogen absorbing state usually keeps under the pressurized hydrogen gas environment. And then, the time-resolved measurements are one of the powerful tools for studying the gas-solid reaction processes. We have constructed the time-resolved X-ray diffraction system at BL22XU, SPring-8 in order to measure the X-ray diffraction patterns with higher time-resolution and higher quality. To demonstrate the performance of the constructed system, we have performed the time-resolved X-rays diffraction experiments for La(Ni,Al)$$_{5}$$. We have found the formation of the transient intermediate phase on hydrogen absorbing reaction process from solid solution phase to known hydride phase.

Oral presentation

Formation of a novel TiFe hydride and estimation of its hydrogen content at high pressures and temperatures

Endo, Naruki; Matsumoto, Itoko*; Nakamura, Yumiko*; Saito, Hiroyuki; Machida, Akihiko; Katayama, Yoshinori

no journal, , 

Oral presentation

In-situ and time-resolved measurement on hydrogen absorption/desorption processes of hydorgen absorbing alloys using synchrotron radiation X-rays

Machida, Akihiko; Watanuki, Tetsu; Katayama, Yoshinori; Kim, H.*; Sakaki, Koji*; Nakamura, Yumiko*

no journal, , 

Hydrogen absorbing alloys are widely investigated as potential hydrogen storage materials for several applications including fuel cell vehicles as well as stationary energy storage system. In order to investigate the structural changes during the hydrogen absorption/desorption processes, we have developed an in-situ X-ray diffraction measurement setup at the Japan Atomic Energy Agency Beamline BL22XU in SPring-8. The in-situ X-ray diffraction measurement has been performed for the several hydrigen absorbing alloys under equilibrium and non-equilibrium pressure of hydrogen gas. In addition, by using a large area detector and high energy X-ray about 70 keV, we are capable of performing X-ray total scattering experiments to obtain the atomic pair distribution function. In this presentation, we will intorduce our measurement setup and show some preliminary results.

27 (Records 1-20 displayed on this page)