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Journal Articles

Oxygen chemical diffusion coefficients of (U, Pu)O$$_{2-x}$$

Watanabe, Masashi; Sunaoshi, Takeo*; Kato, Masato

Defect and Diffusion Forum, 375, p.84 - 90, 2017/05

The oxygen chemical diffusion coefficient in (U, Pu)O$$_{2-x}$$ was determined by thermo-gravimetry as functions of the Pu content, oxygen-to-metal ratio and temperature. The surface reaction was considered in the diffusion coefficient determination. The activation energy for the chemical diffusion coefficient was 60 kJ/mol and 65 kJ/mol, respectively, in (U$$_{0.8}$$Pu$$_{0.2}$$)O$$_{2-x}$$ and (U$$_{0.7}$$Pu$$_{0.3}$$)O$$_{2-x}$$.

Journal Articles

Defect chemistry and basic properties of non-stoichiometric PuO$$_{2}$$

Kato, Masato; Nakamura, Hiroki; Watanabe, Masashi; Matsumoto, Taku; Machida, Masahiko

Defect and Diffusion Forum, 375, p.57 - 70, 2017/05

The basic properties of PuO$$_{2-x}$$ were reviewed, and the equilibrium defects in PuO$$_{2-x}$$ were evaluated from the experimental data of the oxygen potential and electrical conductivity as well as the Ab-initio calculation results. Consistency among various properties was confirmed, and the mechanistic models for thermal property representations were derived.

Journal Articles

Separation in $$varepsilon$$-phase of BiPb alloy under mega-gravity

Okayasu, Satoru; Ono, Masao; Nishio, Taichiro*; Iguchi, Yusuke*; Mashimo, Tsutomu*

Defect and Diffusion Forum, 323-325, p.545 - 548, 2012/04

 Times Cited Count:0 Percentile:0.01

Atomic sedimentation in solid occurs under mega-gravity treatment. As the result, partially melt-growth in $$varepsilon$$-phase of BiPb-alloy occurs. Small difference of densities between fully hcp structure of Bi$$_{3}$$Pb$$_{7}$$ and that of partially defected Bi$$_{3}$$Pb$$_{(7-delta)}$$ are enhanced under mega-gravity, and cause the separation of the $$varepsilon$$-phase. Superconducting properties differs between the separated two phases.

Journal Articles

Evaluation of the system free energy in FG-HAZ of Mod.9Cr-1Mo steel for nuclear power plants

Iwata, Mitsunao*; Sugiyama, Yuichi*; Murata, Yoshinori*; Takaya, Shigeru

Defect and Diffusion Forum, 326-328, p.578 - 582, 2012/04

 Times Cited Count:0 Percentile:0.01

no abstracts in English

Journal Articles

Isotope fractionation due to sedimentation of atoms in centrifuged indium-lead alloy

Ono, Masao; Iguchi, Yusuke*; Okayasu, Satoru; Esaka, Fumitaka; Kobayashi, Katsura*; Hao, T.; Bagum, R.*; Osawa, Takahito; Fujii, Kimio; Nakamura, Eizo*; et al.

Defect and Diffusion Forum, 289-292, p.63 - 68, 2009/04

The atomic-scale graded structure of In-Pb alloy was formed by an ultracentrifuge experiment under conditions that a gravitational field of 0.81$$times$$10$$^{6}$$ G for 100 hours at 150 $$^{circ}$$C in solid state in our previous study. The isotope ratio measurements were performed on the centrifuged sample with secondary ion mass spectrometer (SIMS). $$^{206}$$Pb/$$^{208}$$Pb and $$^{207}$$Pb/$$^{208}$$Pb isotope ratio changed with negative gradient in the direction of centrifugal force approximately 1.5% and 0.8%, respectively. And three-isotope diagram of $$^{206}$$Pb/$$^{208}$$Pb versus $$^{207}$$Pb/$$^{208}$$Pb proved that the isotope fluctuation depends on isotopic mass difference. These results showed that the strong gravitational field not only affected on the inter-diffusion but also on self-diffusion in this alloy as causing isotope fractionation effect, and the isotope fractionation was dependent on mass-difference.

Journal Articles

Sedimentation of impurity atoms in InSb semiconductor under a strong gravitational field

Iguchi, Yusuke*; Ono, Masao; Okayasu, Satoru; Mashimo, Tsutomu

Defect and Diffusion Forum, 289-292, p.319 - 322, 2009/04

An atomic-scale graded structure has been formed by sedimentation of substitutional atoms under an ultra-strong gravitational field of 1 million G level in alloys and compounds. In this study, we investigate the sedimentation of impurity atoms in semiconductor materials under a strong gravitational field. High-temperature ultracentrifuge experiments (0.59$$times$$10$$^{6}$$ G, 400$$^{circ}$$C, 60 hours) have been performed on an InSb single crystal wafer which surface was coated with Ge by means of Physical Vapor Deposition (PVD). It was observed that the penetration depth of diffused Ge atoms under the gravitational field was several times larger than under terrestrial field at the same temperatures.

Journal Articles

Formation of amorphous graded structure in Bi$$_{3}$$Pb$$_{7}$$ intermetallic compounds under strong gravitational field

Mashimo, Tsutomu; Iguchi, Yusuke*; Bagum, R.*; Sano, Tomokazu*; Takeda, Shingo*; Kimura, Shigeru*; Sakata, Osami*; Ono, Masao; Okayasu, Satoru; Tsurui, Takao*; et al.

Defect and Diffusion Forum, 289-292, p.357 - 360, 2009/04

A visible four-layers structure with anomalous nano-sturucture was formed from a homogeneous e-phase Bi$$_{3}$$Pb$$_{7}$$ intermetallic compound under a strong gravitational field (1.02$$times$$10$$^{6}$$ G, 130$$^{circ}$$C, 100 hours). In the 4th layer (lowest-gravity region), pure Bi particles precipitate. In the 2nd 3rd layers, composition graded structures, where Pb content increased along the gravity direction, were formed. It was found that the very broad XRD peak appeared in the 2nd layer, which indicated that an amorphous structure was contained.

Journal Articles

Strong-gravity effect on twinned Y$$_{1}$$Ba$$_{2}$$Cu$$_{3}$$O$$_{7-x}$$ single crystal

Bagum, R.*; Okayasu, Satoru; Iguchi, Yusuke*; Ono, Masao; Mashimo, Tsutomu

Defect and Diffusion Forum, 289-292, p.517 - 521, 2009/04

Ultracentrifuge experiments were performed on the twinned Y$$_{1}$$Ba$$_{2}$$Cu$$_{3}$$O$$_{7-x}$$ (Y123) single crystal at much lower temperatures than the melting point. Two layers structure with slightly different compositions was observed in the sample ultracentrifuged at 250 $$^{circ}$$C (380,000 G), which might be due to the sedimentation of atoms. In the strong gravity layer, it was found that the Y123 phase disappeared, and unknown XRD peaks appeared. Decomposition occurred in the sample ultracentrifuged at 400 $$^{circ}$$C.

Journal Articles

Diffusion of $$^{8}$$Li short-lived radiotracer in Li ionic conductors of NaTl-type intermetallic compounds

Sugai, Hiroyuki; Sataka, Masao; Okayasu, Satoru; Ichikawa, Shinichi; Nishio, Katsuhisa; Mitsuoka, Shinichi; Nakanoya, Takamitsu; Osa, Akihiko; Sato, Tetsuya; Hashimoto, Takashi; et al.

Defect and Diffusion Forum, 273-276, p.667 - 672, 2008/00

Journal Articles

Sedimentation of substitutional solute atoms in intermetallic compound of Bi-Pb system under ultra-strong gravitational field

Ono, Masao; Huang, X.*; Kinoshita, Takahiro*; Ueno, Hideto*; Osakabe, Toyotaka; Mashimo, Tsutomu

Defect and Diffusion Forum, 237-240(2), p.1101 - 1104, 2005/00

Ultra-strong gravitational field can induce sedimentation of even atoms in condensed matter. We had realized sedimentation of substitutional solute atoms in some miscible alloys. How about in the other alloys? So, In this study, the ultra-centrifuge experiments were performed on an intermetallic compound of Bi-Pb system (Bi$$_{3}$$Pb$$_{7}$$) by changing time duration of experiment time (experimental conditions; maximum centrifugal force: 1.0$$times$$10$$^{6}$$g level, temperature: 130-150 $$^{circ}$$C, duration: 30-150h, state: solid). Composition changes were observed in the centrifuged samples. And, it was found that the Bi phase appeared from starting state of Bi$$_{3}$$Pb$$_{7}$$ around the weak gravitational field region of the sample. These results showed that sedimentation of substitutional solute atoms occurred, and induced the structure change in intermetallic compounds.

Journal Articles

Sedimentation of substitutional solute atoms in condensed matter; New type of diffusion

Mashimo, Tsutomu

Defect and Diffusion Forum, 237-240(1), p.30 - 37, 2005/00

Mega-gravity field realizes the sedimentation of even atoms, and is expected to create a nonequilibrium crystal-chemical state in condensed matter. We presented a self-consistent diffusion equation for sedimentation of atoms in condensed matter. Next, we developed an ultracentrifuge to generate strong acceleration field of over 1 million g, and, recently, succeeded in realization of the sedimentation of substitutional solute atoms in some alloys. The diffusion coefficients of sedimentation on Bi-Sb alloy were estimated to be much greater than those of conventional one. It is suggested that the sedimentation of substitutional atoms in solids or liquids can be included in a new type of diffusion, where the diffusion mechanism was yet unknown. In this article, the recent progress in the investigation of sedimentation of atoms under mega-gravity field is reviewed, and the diffusion mechanism is discussed. The application of the mega-gravity field is also discussed.

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