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Journal Articles

Local coordination about La$$^{3+}$$ in molten LaCl$$_3$$ and its mixtures with alkali chlorides

Okamoto, Yoshihiro; Suzuki, Shinichi; Shiwaku, Hideaki; Ikeda, Atsushi; Yaita, Tsuyoshi; Madden, P. A.*

Journal of Physical Chemistry A, 114(13), p.4664 - 4671, 2010/03

 Times Cited Count:51 Percentile:85.84(Chemistry, Physical)

The local structure around the La$$^{3+}$$ ions in molten LaCl$$_{3}$$ and its mixtures with alkali and alkaline earth chlorides has been investigated by using extended X-ray absorption fine structure (XAFS) and molecular dynamics (MD) techniques. New experimental methods allow observations at the La K-absorption edge at the high temperatures of interest and the ability of the technique to obtain reliable information even at very low La$$^{3+}$$ concentrations in multi-component mixtures is demonstrated. Both the mean La-Cl interionic separation and the mean La$$^{3+}$$ coordination number are found to decrease as the concentration of La$$^{3+}$$ in the mixture decreases. In dilute mixtures with such cations La$$^{3+}$$ is able to adopt a very stable octahedral coordination geometry but this is inhibited by the presence of more strongly coordinating cations like Li$$^{+}$$ and Mg$$^{2+}$$.

JAEA Reports

Study on mixing behavior of rare earth chloride in molten alkali chloride by molecular dynamics (MD) calculation

Numakura, Masahiko; Yaita, Tsuyoshi; Shiwaku, Hideaki; Suzuki, Shinichi; Kobayashi, Toru*; Akutsu, Kazuhiro; Madden, P. A.*; Okamoto, Yoshihiro

JAEA-Research 2009-003, 26 Pages, 2009/04

JAEA-Research-2009-003.pdf:4.29MB

We investigated the mixing behavior of molten TbCl$$_3$$ in LiCl-KCl eutectuic melt by MD simulation. Also, simulation of molten YCl$$_3$$ and LaCl$$_3$$ systems were performed to elucidate the difference of the structural change by the difference in cation size (Y$$^{3+}$$$$<$$Tb$$^{3+}$$$$<$$La$$^{3+}$$). The coordination number of the molten pure YCl$$_3$$, TbCl$$_3$$ and LaCl$$_3$$ are mainly 6, 7 and 8 respectively. We consider that, in the molten pure state, the coordination number is influenced by the cation size. However, independent of cation size, the molten MCl$$_3$$ tend to be formed the stable 6-fold structure by the mixing with LiCl-KCl eutectic. And, MD simulations on MCl$$_3$$-LiCl and MCl$$_3$$-KCl systems revealed that the mixing effect was different between LiCl and KCl.

JAEA Reports

Molecular dynamics simulation study on behavior of metallic ion in molten salt mixture bath

Okamoto, Yoshihiro; Tsuruoka, Takuya*; Yaita, Tsuyoshi; Madden, P. A.*

JAEA-Research 2007-005, 25 Pages, 2007/03

JAEA-Research-2007-005.pdf:1.8MB

Behavior of very small amount of metallic ion in molten alkali chloride mixture melt is very important information in pyrochemical reprocessing of spent nuclear fuels. In the present work, mixing behavior of molten LaCl$$_3$$ in LiCl-KCl eutectic melt was simulated by molecular dynamics simulations. It has been reported that molten pure LaCl$$_3$$ has an 8-fold (LaCl$$_8$$)$$^{5-}$$ structure. The coordination number decreases by mixing with LiCl-KCl eutectic mixture melt and indicates a value close to 6 less than 31%LaCl$$_3$$ composition. It suggests that molten LaCl$$_3$$ has an octahedral coordination structure in the mixture, as shown in molten YCl$$_3$$ systems. In the MD simulation, the mixing effect was different between LiCl and KCl. It is due to high number density of Cl$$^-$$ ion in molten LiCl comparable to molten LaCl$$^3$$ and strong Coulomb force introduced by a small Li$$^+$$ ion.

Journal Articles

Structural study of molten lanthanum halides by X-ray diffraction and computer simulation techniques

Okamoto, Yoshihiro; Madden, P. A.*

Journal of Physics and Chemistry of Solids, 66(1), p.448 - 451, 2005/01

The local structure of molten LaCl$$_3$$ has been characterized by the octahedral coordination (LaCl$$_6$$)$$^{3-}$$. It is based on X-ray diffraction (XRD) and Raman spectroscopy results. On the other hand, a different structural image was proposed in the neutron diffraction (ND) and the molecular dynamics (MD) studies. These ND and MD works concluded that a coordination behavior changes with cation size in molten rare earth trichlorides. Thus, they reported the coordination number of Cl$$^-$$ ions around La$$^{3+}$$ ion is 8.2 in the ND work and 7.9 in the MD work. In the present work, XRD measurements of molten LaCl$$_3$$ were performed to investigate the local structure. The coordination number of the 1st La$$^{3+}$$-Cl$$^-$$ pair in molten LaCl$$_3$$ was 7.1 from analysis of the correlation function G(r). The structural change by increasing anion size was examined by the XRD measurement of molten LaBr$$_3$$. The XRD data were nicely reproduced by the MD simulations with polarizable ionic model.

Oral presentation

Mixing behavior of rare earth - alkali chlorides probed by XAFS and MD simulation

Okamoto, Yoshihiro; Yaita, Tsuyoshi; Shiwaku, Hideaki; Matsuura, Haruaki*; Madden, P. A.*

no journal, , 

Mixing behavior of rare earth trichlorides (RECl$$_3$$) with LiCl-KCl eutectic melt was studied by using an X-ray absorption fine structure (XAFS) and a molecular dynamics (MD) simulation techniques. We had confirmed that the local structure of pure RECl$$_3$$ melt changed corresponding to size of RE$$^{3+}$$ ion. On the other hand, it can be concluded that many mixtures show stabilized 6-fold coordination (RECl$$_6$$)$$^{3-}$$ structure in diluted compositions. It suggests that molten RECl$$_3$$ has a simular local structure in diluted composition.

Oral presentation

On the local structural change in molten LaCl$$_3$$ mixtures by the difference of the solvent salt

Okamoto, Yoshihiro; Shiwaku, Hideaki; Ikeda, Atsushi; Suzuki, Shinichi; Akutsu, Kazuhiro; Kobayashi, Toru; Yaita, Tsuyoshi; Madden, P. A.*

no journal, , 

The solvent dependency of the local structure in molten LaCl$$_3$$ was examined by using the X-ray absorption fine structure (XAFS) and molecular dynamics (MD) techniques. An octahedral coordination structure (LaCl$$_6$$)$$^{3-}$$ is not formed and stabilized by the mixing with LiCl and MgCl$$_2$$, but with KCl. It suggests that a cation having smaller size and higher electric charge obstructs the stabilization of the coordination structure.

Oral presentation

High energy XAFS study of molten DyCl$$_3$$ systems

Okamoto, Yoshihiro; Shiwaku, Hideaki; Suzuki, Shinichi; Akutsu, Kazuhiro; Kobayashi, Toru; Yaita, Tsuyoshi; Madden, P. A.*

no journal, , 

X-ray absorption fine structure (XAFS) measurement of molten DyCl$$_3$$ and mixture with LiCl-KCl eutectic were performed by using Dy K-absorption edge. The local structures of solid and molten DyCl$$_3$$ and molten 5%DyCl$$_3$$-(LiCl-KCl eutectic) were almost the same except fluctuation factors such as the Debye-Waller factor. It can be estimated that Dy$$^{2+}$$ ion generated from the disproportional reaction between Dy$$^{3+}$$ ion and Dy metal is partially dissolved in the mixture melt.

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