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Journal Articles

Effect of interlayer cations on montmorillonite swelling; Comparison between molecular dynamic simulations and experiments

Yotsuji, Kenji*; Tachi, Yukio; Sakuma, Hiroshi*; Kawamura, Katsuyuki*

Applied Clay Science, 204, p.106034_1 - 106034_13, 2021/04

 Times Cited Count:4 Percentile:97.52(Chemistry, Physical)

Journal Articles

Surface complexation of Ca and competitive sorption of divalent cations on montmorillonite under alkaline conditions

Sugiura, Yuki; Ishidera, Takamitsu; Tachi, Yukio

Applied Clay Science, 200, p.105910_1 - 105910_10, 2021/01

 Times Cited Count:2 Percentile:0.03(Chemistry, Physical)

Journal Articles

Pore distribution of compacted Ca-montmorillonite using NMR relaxometry and cryoporometry; Comparison with Na-montmorillonite

Okubo, Takahiro*; Yamazaki, Akio*; Fukatsu, Yuta; Tachi, Yukio

Microporous and Mesoporous Materials, 313, p.110841_1 - 110841_11, 2021/01

 Times Cited Count:1 Percentile:69.4(Chemistry, Applied)

Pore distributions in water-saturated Ca-montmorillonite were investigated using $$^{1}$$H NMR measurements under various dry densities (0.8 - 1.6 g/cm$$^{3}$$) and porewater salinity conditions (deionized water, 0.1 and 1 M CaCl$$_{2}$$), at the temperature range of 233 - 303 K. The volume fractions of the interlayer pore including two and three hydrated layers and the non-interlayer pore in compacted Ca-montmorillonite were quantified by NMR relaxometry including $$T1$$ and $$T1/T2$$ distribution analysis, and were compared with NMR cryoporometry and X-ray diffractometry. These analysis provided consistent pictures on the pore distributions in compacted Ca-montmorillonite, in contrast to Na-montmorillonite. The main factor affecting the pore distribution in compacted Ca- and Na-montmorillonite is the density, whereas the effect of porewater salinity is relatively smaller. The effect of interlayer cations is also relatively smaller at higher density, although the differences in the pore structures are significant at low density.

Journal Articles

Sorption behavior of selenide on montmorillonite

Sugiura, Yuki; Tomura, Tsutomu*; Ishidera, Takamitsu; Doi, Reisuke; Francisco, P. C. M.; Shiwaku, Hideaki; Kobayashi, Toru; Matsumura, Daiju; Takahashi, Yoshio*; Tachi, Yukio

Journal of Radioanalytical and Nuclear Chemistry, 324(2), p.615 - 622, 2020/05

 Times Cited Count:1 Percentile:0.01(Chemistry, Analytical)

Journal Articles

3D-microstructure analysis of compacted Na- and Cs-montmorillonites with nanofocus X-ray computed tomography and correlation with macroscopic transport properties

Takahashi, Hiroaki*; Tachi, Yukio

Applied Clay Science, 168, p.211 - 222, 2019/02

 Times Cited Count:8 Percentile:70.54(Chemistry, Physical)

Microstructural and mass transport properties of compacted Na- and Cs-montmorillonites with different swelling properties were investigated by combining 3D microstructure analysis using nanofocus X-ray CT and diffusion measurement of HDO. The X-ray CT observations indicated that macropores in the dry state of compacted Na-montmorillonite are filled with gel phases, and the grain sizes of clay particles shifted toward smaller values through the saturation and swelling processes. By contrast, no gel phase and no decrease in the grain and pore volumes were observed for saturated Cs-montmorillonite. The geometrical factors of the macropores including tortuosity and geometric constrictivity of saturated Cs-montmorillonite determined by the X-ray CT was consistent with the corresponding values derived in the HDO diffusion test. In the case of Na-montmorillonite, the larger differences between the geometric factors evaluated by the X-ray CT and the diffusion tests can be explained by the electrostatic constrictivity factor and the additional geometrical factors in gel phase and interlayer that are smaller than the detection limit of the X-ray CT.

Journal Articles

Molecular dynamics simulations of physical properties of water and cations in montmorillonite interlayer; Application to diffusion model

Yotsuji, Kenji*; Tachi, Yukio; Kawamura, Katsuyuki*; Arima, Tatsumi*; Sakuma, Hiroshi*

Nendo Kagaku, 58(1), p.8 - 25, 2019/00

Molecular dynamics (MD) simulations were conducted to investigate physical properties of water and cations in montmorillonite interlayer nanopores. The swelling behaviors and hydration states were firstly evaluated as functions of interlayer cations and layer charge. The diffusion coefficients of water and cations in interlayer nanopores were decreased in comparison with those in bulk water and came closer to those in bulk water when basal spacing increased. The viscosity coefficients of interlayer water estimated indicated a significant effect of viscoelectricity at 1- and 2-layer hydration states and higher layer charge of montmorillonite. These trends from MD calculations were confirmed to be consistent with existing measured data and previous MD simulation. In addition, model and parameter related to viscoelectric effect used in the diffusion model was refined based on comparative discussion between MD simulations and measurements. The series of MD calculations could provide atomic level understanding for the developments and improvements of the diffusion model for compacted montmorillonite.

Journal Articles

Diffusion and adsorption of uranyl ion in clays; Molecular dynamics study

Arima, Tatsumi*; Idemitsu, Kazuya*; Inagaki, Yaohiro*; Kawamura, Katsuyuki*; Tachi, Yukio; Yotsuji, Kenji

Progress in Nuclear Energy, 92, p.286 - 297, 2016/09

 Times Cited Count:6 Percentile:61.4(Nuclear Science & Technology)

Diffusion and adsorption behavior of uranyl (UO$$_2^{2+}$$) species is important for the performance assessment of radioactive waste disposal. The diffusion behaviors of UO$$_2^{2+}$$, K$$^{+}$$, CO$$_3^{2-}$$ and Cl$$^{-}$$ and H$$_{2}$$O in the aqueous solutions were evaluated by molecular dynamics (MD) calculations. The diffusion coefficient (De) of UO$$_2^{2+}$$ is the smallest and is 26% less than the self-diffusion coefficient of H$$_{2}$$O. For the aqueous solution with high concentration of carbonate ions, uranyl carbonate complexes: UO$$_{2}$$CO$$_{3}$$ and UO$$_{2}$$(CO$$_{3}$$)$$^{2-}$$ can be observed. For the clay (montmorillonite or illite)-aqueous solution systems, the adsorption and diffusion behaviors of UO$$_2^{2+}$$ and K$$^{+}$$ were evaluated by MD calculations. The distribution coefficients (Kd) increase with the layer charge of clay, and Kd of UO$$_2^{2+}$$ might be smaller than that of K$$^{+}$$. Further, their two-dimensional diffusion coefficients were relatively small in the adsorption layer and were extremely small for illite with higher layer charge.

Journal Articles

Effects of OH$$^{-}$$ activity and temperature on the dissolution rate of compacted montmorillonite under highly alkaline conditions

Sawaguchi, Takuma; Tsukada, Manabu; Yamaguchi, Tetsuji; Mukai, Masayuki

Clay Minerals, 51(2), p.267 - 278, 2016/05

 Times Cited Count:5 Percentile:26.06(Chemistry, Physical)

The dependences of the dissolution rate of compacted montmorillonite on activity of OH$$^{-}$$ (a$$_{rm OH}$$-) and temperature (T) were investigated. The dissolution rate of montmorillonite ($$R_{rm A}$$) in compacted pure montmorillonite, which was formulized as $$R_{rm A}$$ = 10$$^{4.5}$$ (a$$_{rm OH}$$-)$$^{1.3}$$ e$$^{-55000/RT}$$, was higher than that in the compacted sand-bentonite mixtures: $$R_{rm A}$$ = 3500 (a$$_{rm OH}$$-)$$^{1.4}$$ e$$^{-51000/RT}$$. The difference can be explained by considering the decrease in a$$_{rm OH}$$- in the mixtures accompanied by dissolution of accessory minerals such as quartz and chalcedony. The dissolution rate model developed for pure montmorillonite is expected to be applied to bentonite mixtures if quantification of the decrease in a$$_{rm OH}$$- is achieved somehow.

Journal Articles

Pore distribution of water-saturated compacted clay using NMR relaxometry and freezing temperature depression; Effects of density and salt concentration

Okubo, Takahiro*; Ibaraki, Moe*; Tachi, Yukio; Iwadate, Yasuhiko*

Applied Clay Science, 123, p.148 - 155, 2016/04

 Times Cited Count:19 Percentile:73.19(Chemistry, Physical)

The pore distribution of water-saturated compacted clay (Na-montmorillonite at 0.8 and 1.4 g/cm$$^{3}$$ saturated by three salt concentrations) was evaluated using $$^{1}$$H NMR relaxometry and freezing point depression. The populations of interlayer water with four hydrated state and non-interlayer water were calculated from the assumed thresholds. The sample with lower density exhibits higher population of non-interlayer water up to 55%. Low-temperature $$^{1}$$H NMR experiments in view of freezing point depression indicated that mesopore water in approximately 4 nm space observed in the calorimetric study was considered as non-interlayer water and the threshold temperature. The result showed that population of non-interlayer water by expected from freezing point depression agreed with $$^{1}$$H NMR relaxometry within 10%. Correlation experiments between longitudinal ($$T_{1}$$) and transverse relation times ($$T_{2}$$) at -10$$^{circ}$$C suggested that high-mobility bulk-like water molecules existed at a clay density of 1.4 g/cm$$^{3}$$.

Journal Articles

Sorption of Eu$$^{3+}$$ on Na-montmorillonite studied by time-resolved laser fluorescence spectroscopy and surface complexation modeling

Sasaki, Takayuki*; Ueda, Kenyo*; Saito, Takumi; Aoyagi, Noboru; Kobayashi, Taishi*; Takagi, Ikuji*; Kimura, Takaumi; Tachi, Yukio

Journal of Nuclear Science and Technology, 53(4), p.592 - 601, 2016/04

 Times Cited Count:9 Percentile:75.69(Nuclear Science & Technology)

The influences of pH and the concentrations of Eu$$^{3+}$$ and NaNO$$_{3}$$ on the sorption of Eu$$^{3+}$$ to Na-montmorillonite were investigated through batch sorption measurements and time-resolved laser fluorescence spectroscopy (TRLFS). The pH had a little effect on the distribution coefficients (Kd) in 0.01 M NaNO$$_{3}$$, whereas the Kd strongly depended on pH at 1 M NaNO$$_{3}$$. A cation exchange model combined with a one-site non-electrostatic surface complexation model was successfully applied to the measured Kd. The TRLFS spectra of Eu$$^{3+}$$ sorbed were processed by parallel factor analysis (PARAFAC), which corresponded to one outer-sphere (factor A) and two inner-sphere (factor B and C) complexes. It turned out that factors A and B correspond to Eu$$^{3+}$$ sorbed by ion exchange sites and inner-sphere complexation with hydroxyl groups of the edge faces, respectively. Factor C became dominant at relatively high pH and ionic strength and likely correspond to the precipitation of Eu(OH)$$_{3}$$ on the surface.

Journal Articles

Local structure around cesium in montmorillonite, vermiculite and zeolite under wet condition

Tsuji, Takuya; Matsumura, Daiju; Kobayashi, Toru; Suzuki, Shinichi; Yoshii, Kenji; Nishihata, Yasuo; Yaita, Tsuyoshi

Clay Science, 18(4), p.93 - 97, 2014/12

Journal Articles

Experimental and modeling study on long-term alteration of compacted bentonite with alkaline groundwater

Yamaguchi, Tetsuji; Sakamoto, Yoshifumi; Akai, Masanobu; Takazawa, Mayumi; Iida, Yoshihisa; Tanaka, Tadao; Nakayama, Shinichi

Physics and Chemistry of the Earth, 32(1-7), p.298 - 310, 2007/00

 Times Cited Count:39 Percentile:73.73(Geosciences, Multidisciplinary)

Dissolution rate of montmorillonite, diffusivity of hydroxide ion and permeability coefficient in compacted sand-bentonite mixtures were experimentally determined and formulated. A coupled mass-transport/chemical-reaction code was developed to predict variation in permeability of engineered bentonite barrier with alkaline fluid by using the formulae.

Journal Articles

Cross-machine benchmarking for ITER of neoclassical tearing mode stabilization by electron cyclotron current drive

La Haye, R. J.*; Prater, R.*; Buttery, R. J.*; Hayashi, Nobuhiko; Isayama, Akihiko; Maraschek, M. E.*; Urso, L.*; Zohm, H.*

Nuclear Fusion, 46(4), p.451 - 461, 2006/04

 Times Cited Count:140 Percentile:97.92(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Suppression of neoclassical tearing modes towards stationary high-beta plasmas in JT-60U

Isayama, Akihiko; JT-60 Team

Plasma Science and Technology, 8(1), p.36 - 40, 2006/01

 Times Cited Count:3 Percentile:11.73(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Role of anomalous transport in onset and evolution of neoclassical tearing modes

Konovalov, S. V.; Mikhailovskii, A. B.*; Ozeki, Takahisa; Takizuka, Tomonori; Shirokov, M. S.*; Hayashi, Nobuhiko

Plasma Physics and Controlled Fusion, 47(12B), p.B223 - B236, 2005/12

 Times Cited Count:7 Percentile:26.36(Physics, Fluids & Plasmas)

Neoclassical Tearing Modes, NTMs, are known to limit the maximum attainable plasma pressure, degrade confinement and, at worst, culminate in disruption of the tokamak discharges. Key role in NTM evolution belongs to the radial profiles of the plasma flow, temperature and density which are determined by the conjunction of the longitudinal and cross-filed transport arising from thermal conduction, particle diffusion, and viscosity. In this report the influence of anomalous perpendicular heat transport and anomalous ion perpendicular viscosity on early stage of the NTM evolution is studied theoretically.

Journal Articles

Development and contribution of RF heating and current drive systems to long pulse, high performance experiments in JT-60U

Moriyama, Shinichi; Seki, Masami; Terakado, Masayuki; Shimono, Mitsugu; Ide, Shunsuke; Isayama, Akihiko; Suzuki, Takahiro; Fujii, Tsuneyuki; JT-60 Team

Fusion Engineering and Design, 74(1-4), p.343 - 349, 2005/11

 Times Cited Count:7 Percentile:47.08(Nuclear Science & Technology)

no abstracts in English

Journal Articles

The "Hybrid" scenario in JET; Towards its validation for ITER

Joffrin, E.*; Sips, A. C. C.*; Artaud, J. F.*; Becoulet, A.*; Bertalot, L.*; Budny, R.*; Buratti, P.*; Belo, P.*; Challis, C. D.*; Crisanti, F.*; et al.

Nuclear Fusion, 45(7), p.626 - 634, 2005/07

 Times Cited Count:86 Percentile:93.32(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Steady-state sustainment of high-$$beta$$ plasmas through stability control in Japan Atomic Energy Research Institute tokamak-60 upgrade

Isayama, Akihiko; JT-60 Team

Physics of Plasmas, 12(5), p.056117_1 - 056117_10, 2005/05

 Times Cited Count:28 Percentile:68.34(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Application of micro-PIXE to quantitative analysis of heavy elements sorbed on minerals

Kozai, Naofumi; Mitamura, Hisayoshi; Onuki, Toshihiko; Sakai, Takuro; Sato, Takahiro; Oikawa, Masakazu*

Nuclear Instruments and Methods in Physics Research B, 231(1-4), p.530 - 535, 2005/04

 Times Cited Count:9 Percentile:57.47(Instruments & Instrumentation)

Applicability of micro-PIXE analysis to quantitative evaluation of heavy elements sorbed on minerals was investigated to get better understanding of sorption and distribution of heavy elements onto mixture of minerals in soil. For this, external standards, that is, heavy element-sorbing minerals of uniform shape and size, were analyzed by micro-PIXE. It was found that such external standards were available to quantitative evaluation by micro-PIXE though their applicability may be limited.

Journal Articles

Monte-Carlo simulation of electron cyclotron current drive in NTM magnetic islands

Hamamatsu, Kiyotaka; Takizuka, Tomonori; Hayashi, Nobuhiko; Ozeki, Takahisa

Europhysics Conference Abstracts (CD-ROM), 29C, 4 Pages, 2005/00

no abstracts in English

45 (Records 1-20 displayed on this page)