Selenide [Se(-II)] immobilization in anoxic, Fe(II)-rich environments; Coprecipitation and behavior during phase transformations

Francisco, P. C. M.; Matsumura, Daiju; Kikuchi, Ryosuke*; Ishidera, Takamitsu; Tachi, Yukio

Environmental Science & Technology, 56(5), p.3011 - 3020, 2022/03

https://doi.org/10.1021/acs.est.1c04216

Mineralogical characterization of radioactive particles from Fukushima soil using -XRD with synchrotron radiation

Motai, Satoko*; Mukai, Hiroki*; Watanuki, Tetsu; Owada, Kenji; Fukuda, Tatsuo; Machida, Akihiko; Kuramata, Chisaki*; Kikuchi, Ryosuke*; Yaita, Tsuyoshi; Kogure, Toshihiro*

Journal of Mineralogical and Petrological Sciences, 111(5), p.305 - 312, 2016/10

https://doi.org/10.2465/jmps.150722

no abstracts in English

Proximity factor on transformation from subsurface to surface flaw

Hasegawa, Kunio*; Li, Y.; Serizawa, Ryosuke*; Kikuchi, Masanori*; Lacroix, V.*

Procedia Materials Science, 12, p.36 - 41, 2016/00

https://doi.org/10.1016/j.mspro.2016.03.007

If subsurface flaws are detected that are close to component free surfaces, flaw-to-surface proximity rule is used to determine whether the flaws should be treated as subsurface flaws as is, or transformed to surface flaws. However, specific factors for the proximity rules on transforming subsurface to surface flaws differ among fitness-for-service codes. The objective of the paper is to reveal the proximity factor from the stress intensity factor interaction between the subsurface flaw and the free surface.

Novel features in filled skutterudites containing rare-earth elements with a plural number of 4f-electrons

Sato, Hideyuki*; Aoki, Yuji*; Kikuchi, Daisuke*; Sugawara, Hitoshi*; Higemoto, Wataru; Oishi, Kazuki; Ito, Takashi; Heffner, R. H.; Saha, S. R.*; Koda, Akihiro*; et al.

Physica B; Condensed Matter, 404(5-7), p.749 - 753, 2009/04

https://doi.org/10.1016/j.physb.2008.11.182

Wide varieties of strongly correlated electron phenomena are performed on the stage of a filled skutterudite structure. Especially when one of the players contains a plural number of 4f electrons, the orbital degrees of freedom play a major role as a new type of nonmagnetic and/or weak-magnetic phenomena. Several examples found in Pr- and Sm-based filled skutterudites are introduced in relation to muon spin relaxation experiments.

Knight shift measurements in the superconducting state of PrLaOsSb (X=0.4) probed by SR

Higemoto, Wataru; Aoki, Yuji*; Oishi, Kazuki; Ito, Takashi; Heffner, R. H.; Saha, S. R.*; Koda, Akihiro*; Sato, Hideyuki*; Kadono, Ryosuke*; Kikuchi, Daisuke*; et al.

Journal of Magnetism and Magnetic Materials, 310(2, Part1), p.620 - 622, 2007/03

no abstracts in English

Time reversal symmetry breaking in superconducting (Pr,La)OsSb and Pr(Os,Ru)Sb

Shu, L.*; Higemoto, Wataru; Aoki, Yuji*; Frederick, N. A.*; Yuhasz, W. M.*; Heffner, R. H.; Oishi, Kazuki; Ishida, Kenji*; Kadono, Ryosuke*; Koda, Akihiro*; et al.

Journal of Magnetism and Magnetic Materials, 310(2, Part1), p.551 - 553, 2006/11

Natural evidence for the cementation in bentonite buffer based on transmission electron microscopy observation of bentonite ores

Kikuchi, Ryosuke*; Horiuchi, Misato*; Saito, Masaki*; Ishiwata, Tobimaru*; Nishiki, Yuto*; Sato, Tsutomu*; Takayama, Yusuke; Mitsui, Seiichiro

no journal, , 

In geological disposal of high-level radioactive wastes, the use of swelling clay is intrinsic as a buffer around waste packages. In order to achieve long-term safety, longevity of montmorillonite, a major constituent of bentonite buffer, under disposal related conditions is important. One of the alteration processes of concern is cementation of clay layers due to precipitation of secondary minerals such as silica. In this study, we examined natural bentonite ores that could serve as natural analogues for the cementation process, especially focusing on microstructure of consolidated bentonite. Bentonite ores were collected from the Tsukinuno Mine in Yamagata Prefecture, Japan. This bentonite is thought to have been formed by the diagenesis of volcanic ash. A dry polishing technique was used to form a smooth surface that well shows the original microstructure of bentonite ores, allowing petrographic discussion as in the observation of non-clayey rocks. Besides coarse quartz (probably pyroclastic origin), fine silica with grain sizes ranging from a few microns to submicron is widely observed in bentonite ores. The distribution of fine silica is characterized by discrete grains or short chains or small clusters in the fine-grained montmorillonite matrix, suggesting that they formed in closed system diagenesis and a low mobility of silica in clay matrix. Thin foils including fine silica and montmorillonite were extracted from polished sections using a focused ion beam apparatus and observed by transmission electron microscopy (TEM). TEM observations demonstrated a microstructure where montmorillonite edge is directly bonded to the fine silica particles. The microstructure as seen in this study, is interpreted to be formed by the authigenic silica precipitation during diagenesis, not by a physical mixture. The silica coating of montmorillonite edge could prevent water access to its interlayer space and free swelling, which leads to a decrease in swelling pressure.