Incorporation of boron into metakaolin-based geopolymers for radionuclide immobilisation and neutron capture potential

Niu, X.*; Elakneswaran, Y.*; Li, A.*; Seralathan, S.*; Kikuchi, Ryosuke*; Hiraki, Yoshihisa; Sato, Junya; Osugi, Takeshi; Walkley, B.*

Cement and Concrete Research, 190, p.107814_1 - 107814_17, 2025/04

https://doi.org/10.1016/j.cemconres.2025.107814

Difference in expansion and dehydration behaviors between NH- and K-montmorillonite

Kawakita, Ryohei; Saito, Akito*; Sakuma, Hiroshi*; Anraku, Sohtaro; Kikuchi, Ryosuke*; Otake, Tsubasa*; Sato, Tsutomu*

Applied Clay Science, 231, p.106722_1 - 106722_7, 2023/01

https://doi.org/10.1016/j.clay.2022.106722

Origin of magnetovolume effect in a cobaltite

Miao, P.*; Tan, Z.*; Lee, S. H.*; Ishikawa, Yoshihisa*; Torii, Shuki*; Yonemura, Masao*; Koda, Akihiro*; Komatsu, Kazuki*; Machida, Shinichi*; Sano, Asami; et al.

Physical Review B, 103(9), p.094302_1 - 094302_18, 2021/03

https://doi.org/10.1103/PhysRevB.103.094302

The layered perovskite PrBaCoO demonstrates a strong negative thermal expansion (NTE) which holds potential for being fabricated into composites with zero thermal expansion. The NTE was found to be intimately associated with the spontaneous magnetic ordering, known as magneto-volume effect (MVE). Here we report with compelling evidences that the continuous-like MVE in PrBaCoO is intrinsically of discontinuous character, originating from an magnetoelectric transition from an antiferromagnetic insulating large-volume (AFILV) phase to a ferromagnetic less-insulating small-volume (FLISV) phase. Furthermore, the magnetoelectric effect (ME) shows high sensitivity to multiple external stimuli such as temperature, carrier doping, hydrostatic pressure, magnetic field etc. In contrast to the well-known ME such as colossal magnetoresistance and multi-ferroic effect which involve symmetry breaking of crystal structure, the ME in the cobaltite is purely isostructural. Our discovery provides a new path way to realizing the ME as well as the NTE, which may find applications in new techniques.

Cesium adsorption/desorption behavior of clay minerals considering actual contamination conditions in Fukushima

Mukai, Hiroki*; Hirose, Atsushi*; Motai, Satoko*; Kikuchi, Ryosuke*; Tanoi, Keitaro*; Nakanishi, Tomoko*; Yaita, Tsuyoshi; Kogure, Toshihiro*

Scientific Reports (Internet), 6, p.21543_1 - 21543_7, 2016/02

https://doi.org/10.1038/srep21543

Suppression of time-reversal symmetry breaking superconductivity in Pr(OsRu)Sb and PrLaOsSb

Shu, L.*; Higemoto, Wataru; Aoki, Yuji*; Hillier, A. D.*; Oishi, Kazuki*; Ishida, Kenji*; Kadono, Ryosuke*; Koda, Akihiro*; Bernal, O. O.*; MacLaughlin, D. E.*; et al.

Physical Review B, 83(10), p.100504_1 - 100504_4, 2011/03

https://doi.org/10.1103/PhysRevB.83.100504

Zero-field muon spin relaxation experiments have been carried out in the Pr(OsRu)Sb and PrLaOsSb alloy systems to investigate broken time-reversal symmetry (TRS) in the superconducting state, signaled by the onset of a spontaneous static local magnetic field B. In both alloy series B initially decreases linearly with solute concentration. Ru doping is considerably more efficient than La doping, with a 50% faster initial decrease. The data suggest that broken TRS is suppressed for Ru concentration 0.6 but persists for essentially all La concentrations. Our data support a crystal-field excitonic cooper pairing mechanism for TRS-breaking superconductivity.

Muon spin relaxation and hyperfine-enhanced Pr nuclear spin dynamics in Pr(Os,Ru)Sb and (Pr,La)OsSb

Shu, L.*; MacLaughlin, D. E.*; Aoki, Yuji*; Tsunashima, Yoshino*; Yonezawa, Yuki*; Sanada, Shotaro*; Kikuchi, Daisuke*; Sato, Hideyuki*; Heffner, R. H.; Higemoto, Wataru; et al.

Physical Review B, 76(1), p.014527_1 - 014527_8, 2007/07

https://doi.org/10.1103/PhysRevB.76.014527

Introduction to plasma fusion energy

Takamura, Shuichi*; Kado, Shinichiro*; Fujii, Takashi*; Fujiyama, Hiroshi*; Takabe, Hideaki*; Adachi, Kazuo*; Morimiya, Osamu*; Fujimori, Naoji*; Watanabe, Takayuki*; Hayashi, Yasuaki*; et al.

Kara Zukai, Purazuma Enerugi No Subete, P. 164, 2007/03

no abstracts in English

Se(-II, IV) interactions with Fe(II) species and phases under anoxic and reducing conditions

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

no journal, , 

Relationship between petrographic texture and swelling property in cemented bentonite ores

Ishiwata, Tobimaru*; Kikuchi, Ryosuke*; Otake, Tsubasa*; Sato, Tsutomu*; Kawakita, Ryohei; Takayama, Yusuke; Mitsui, Seiichiro

no journal, , 

It is known that the cementation of bentontie may cause the reduction of swelling pressure. However, fundamental mechanism of this reducing swelling pressure has not been well understood. To understand the mechanism, it is essential to identify the cementitious materials and observe the changes in microstructure associated with cementation. In this study, the microstructural observation and swelling tests were conducted on several bentonite ores collected from Tsukinuno Mine in Yamagata Prefecture, Japan, as natural analog of cementation, and the relationship between petrographic texture and swelling pressure was discussed. Thin sections of bentonite ores were prepared by dry polishing technique to observe flat surfaces in micro scales. Scanning electron microscopy (SEM) demonstrated the widespread distribution of authigenic, a few micron silica in the matrix of montmorillonite. Transmission electron microscopy (TEM) revealed that the micro silica minerals (commonly quartz and less commonly amorphous silica) adhered to the edge of montmorillonite grains. These observations suggest that the adherence of these cementitious materials to montmorillonite prevents water access to the interlayer of montmorillonite and swelling, resulting in a decrease in swelling pressure. While these microstructures were observed commonly in all samples collected from several bentonite beds, the relative abundance of montmorillonite and micro silica minerals varied among different beds. It is possible that the swelling pressure in the cemented bentonite is affected by the relative abundance of montmorillonite and cementitious materials.

Quantitative investigation of factors contributing to swelling pressure decrease of bentonite by cementation based on image processing

Ishiwata, Tobimaru*; Kikuchi, Ryosuke*; Otake, Tsubasa*; Sato, Tsutomu*; Kawakita, Ryohei; Takayama, Yusuke; Mitsui, Seiichiro

no journal, , 

Bentonite clay is planned to be used as a buffer material in the geological disposal of high-level radioactive wastes. The swelling property of bentonite is expected to keep low permeability and control the migration of radionuclides thereby ensuring the safety of geological disposal. In the long-term, however, cementation of bentonite may degrade the swelling property where secondary minerals precipitate and adhere to the montmorillonite component of bentonite. In the present study, natural bentonite ores were investigated as analogues to cementation of bentonite in geological disposal. The images of SEM and EPMA were integrated into "mineral map", which could visually illustrate the distributions of individual mineral grains including fine cementitious minerals. Finally, multi regression analysis (MRA) was used to investigate correlation between petrographic parameters and swelling pressure. MRA showed swelling pressure of bentonite increases with the content of montmorillonite, and decreases with the total perimeter of accessary minerals. This suggests that the presence of secondary minerals can inhibit the swelling of montmorillonite and the area of contact between montmorillonite and secondary minerals might be a key parameter.