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Journal Articles

Defect equilibria and thermophysical properties of CeO$$_{2-x}$$ based on experimental data and density functional theory calculation result

Watanabe, Masashi; Nakamura, Hiroki; Suzuki, Kiichi; Machida, Masahiko; Kato, Masato

Journal of the American Ceramic Society, 105(3), p.2248 - 2257, 2022/03

 Times Cited Count:0 Percentile:0.01(Materials Science, Ceramics)

Properties of CeO$$_{2}$$ were evaluated by DFT simulation to determine band gap, Frenkel defect formation energy and defect migration energy. Band gap and Frenkel defect formation energy were used to analyze defect equilibria. Oxygen partial pressure dependence of defect equilibria was evaluated based on oxygen potential experimental data and DFT calculation, and a Brouwer diagram was derived. The defect formation energies, including Frenkel defect, electron-hole pair and so on, were determined and used to evaluate the properties, including oxygen diffusion coefficients, electrical conduction, heat capacity and thermal conductivity. Mechanisms of various properties were discussed for a deeper understanding based on defect chemistry, and the relationship among properties were systematically described.

Journal Articles

Temperature effects on local structure, phase transformation, and mechanical properties of calcium silicate hydrates

Im, S.*; Jee, H.*; Suh, H.*; Kanematsu, Manabu*; Morooka, Satoshi; Koyama, Taku*; Nishio, Yuhei*; Machida, Akihiko*; Kim, J.*; Bae, S.*

Journal of the American Ceramic Society, 104(9), p.4803 - 4818, 2021/09

 Times Cited Count:6 Percentile:68.28(Materials Science, Ceramics)

Journal Articles

Determination of atomistic deformation of tricalcium silicate paste with high-volume fly ash

Jee, H.*; Im, S.*; Kanematsu, Manabu*; Suzuki, Hiroshi; Morooka, Satoshi; Koyama, Taku*; Machida, Akihiko*; Bae, S.*

Journal of the American Ceramic Society, 103(12), p.7188 - 7201, 2020/12

 Times Cited Count:8 Percentile:57.51(Materials Science, Ceramics)

Journal Articles

Local structure investigations of accumulated damage in irradiated MgAl$$_{2}$$O$$_{4}$$

Yoshioka, Satoru*; Tsuruta, Konosuke*; Yamamoto, Tomokazu*; Yasuda, Kazuhiro*; Matsumura, Sho*; Sugiyama, Takeharu*; Oba, Yojiro; Ishikawa, Norito; Kobayashi, Eiichi*; Okudaira, Koji*

Journal of the American Ceramic Society, 103(8), p.4654 - 4663, 2020/08

 Times Cited Count:2 Percentile:16.09(Materials Science, Ceramics)

X-ray absorption near edge structure (XANES) and small-angle X-ray scattering (SAXS) reveal the damaged structures in MgAl$$_{2}$$O$$_{4}$$ spinel induced by swift heavy ions. SAXS indicates the formation of ion tracks with cylindrical shape with a diameter of 5 nm. XANES indicates the cationic disordering between tetrahedral and octahedral sites by the irradiation. Quantitative analysis of XANES also reveals that cations preferably occupy the octahedral sites at high fluence.

Journal Articles

On the hydrogen production of geopolymer wasteforms under irradiation

Cantarel, V.; Arisaka, Makoto; Yamagishi, Isao

Journal of the American Ceramic Society, 102(12), p.7553 - 7563, 2019/12

 Times Cited Count:6 Percentile:37.12(Materials Science, Ceramics)

The hydrogen gas (H$$_{2}$$) production of wasteforms is a major safety concern for encapsulating nuclear wastes. For geopolymers, the H$$_{2}$$ produced by radiolytic processes is a key factor because of the large amount of water present in their porous structure. Herein, the hydrogen production was measured under $$^{60}$$Co gamma irradiation. The effect of water saturation and sample size were studied for pure geopolymers, or using zeolites as an example waste. When geopolymer monolithic samples were large and saturated by water, the hydrogen released was measured up to two orders of magnitude lower with a 40 cm long cylinder samples (1.9$$times$$10$$^{-10}$$ mol/J) than a sample in powder form (2.2$$times$$10$$^{-8}$$ mol/J). To interpret results, a simple model was used, considering only hydrogen production, a potential recombination and its diffusion in the geopolymer matrix. Knowing the diffusion constant of the matrix, the model was able to reproduce the evolution of the hydrogen release as a function of the water saturation level and predict the evolution when sample size is increased up to 40 cm.

Journal Articles

Thermal and mechanical properties of CeO$$_{2}$$

Suzuki, Kiichi; Kato, Masato; Sunaoshi, Takeo*; Uno, Hiroki*; Carvajal-Nunez, U.*; Nelson, A. T.*; McClellan, K. J.*

Journal of the American Ceramic Society, 102(4), p.1994 - 2008, 2019/04

 Times Cited Count:26 Percentile:87.06(Materials Science, Ceramics)

The fundamental properties of CeO$$_{2}$$ were assessed using a range of experimental techniques. The oxygen potential of CeO$$_{2}$$ was measured by the thermogravimetric technique, and a numerical fit for the oxygen potential of CeO$$_{2}$$ is derived based on defect chemistry. Mechanical properties of CeO$$_{2}$$ were obtained using sound velocity measurement, resonant ultrasound spectroscopy and nanoindentation. The obtained mechanical properties of CeO$$_{2}$$ are then used to evaluate the Debye temperature and Gruneisen constant. The heat capacity and thermal conductivity of CeO$$_{2}$$ were also calculated using the Debye temperature and the Gruneisen constant. Finally, the thermal conductivity was calculated based upon laser flash analysis measurements. This result demonstrates that the thermal conductivity has strong dependence upon material purity.

Journal Articles

Pair distribution function analysis of nanostructural deformation of calcium silicate hydrate under compressive stress

Bae, S.*; Jee, H.*; Kanematsu, Manabu*; Shiro, Ayumi*; Machida, Akihiko*; Watanuki, Tetsu*; Shobu, Takahisa; Suzuki, Hiroshi

Journal of the American Ceramic Society, 101(1), p.408 - 418, 2018/01

 Times Cited Count:12 Percentile:58.09(Materials Science, Ceramics)

Despite enormous interest in calcium silicate hydrate (C-S-H), its detailed atomic structure and intrinsic deformation under an external load are lacking. This study demonstrates the nanostructural deformation process of C-S-H in tricalcium silicate (C$$_{3}$$S) paste as a function of applied stress by interpreting atomic pair distribution function (PDF) based on in situ X-ray scattering. Three different strains in C$$_{3}$$S paste under compression were compared using a strain gauge and the real and reciprocal space PDFs. PDF refinement revealed that the C-S-H phase mostly contributed to PDF from 0 to 20${AA}$ whereas crystalline phases dominated that beyond 20${AA}$. The short-range atomic strains exhibited two regions for C-S-H: I) plastic deformation (0-10 MPa) and II) linear elastic deformation ($$>$$10 MPa), whereas the long-range deformation beyond 20${AA}$ was similar to that of Ca(OH)$$_{2}$$. Below 10 MPa, the short-range strain was caused by the densification of C-S-H induced by the removal of interlayer or gel-pore water. The strain is likely to be recovered when the removed water returns to C-S-H.

Journal Articles

Characterization of ZrN, ZrO$$_{2}$$ and $$beta$$'-Zr$$_{7}$$O$$_{11}$$N$$_{2}$$ nanoparticles synthesized by pulsed wire discharge

Lam, Do Van*; Suematsu, Hisayuki*; Ogawa, Toru

Journal of the American Ceramic Society, 100(10), p.4884 - 4892, 2017/10

 Times Cited Count:1 Percentile:6.04(Materials Science, Ceramics)

Nanoparticles of ZrN, ZrO$$_{2}$$ and ZrN, $$beta$$'-Zr$$_{7}$$O$$_{11}$$N$$_{2}$$ were synthesized by pulsed wire discharge. Morphology and phase analyses were carried out by X-ray diffraction and field-emission transmission electron microscopy (FE-TEM). By bright field image observation, electron energy loss spectroscopy (EELS) and selected area electron diffraction (SAD) analyses, those nanoparticles were separately characterized.

Journal Articles

An Evaluation of the thermophysical properties of stoichiometric CeO$$_{2}$$ in comparison to UO$$_{2}$$ and PuO$$_{2}$$

Nelson, A. T.*; Rittman, D. R.*; White, J. T.*; Dunwoody, J. T.*; Kato, Masato; McClellan, K. J.*

Journal of the American Ceramic Society, 97(11), p.3652 - 3659, 2014/11

 Times Cited Count:47 Percentile:91.62(Materials Science, Ceramics)

Journal Articles

Application of ultrasonic measurement on small-sized ceramic sample

Serizawa, Hiroyuki; Kaji, Yoshiyuki

Journal of the American Ceramic Society, 97(4), p.1187 - 1193, 2014/04

 Times Cited Count:1 Percentile:7.24(Materials Science, Ceramics)

The longitudinal and transverse wave velocities of polycrystalline MgO were successfully measured simultaneously and five types of elastic moduli, the Debye temperature, and the Gruneisen parameter were evaluated as functions of temperature from 298 K to 1764 K. An aluminum foil was used as a couplant between the MgO specimen and waveguide. Both acoustic waves were successfully propagated into the specimen through the solid and liquid aluminum layers. In particular, no influence of melted aluminum foil on the acoustic wave velocities was observed. With increasing temperature, the Young's, shear, and bulk moduli decreased monotonically and the Gruneisen parameter and Poisson's ratio increased monotonically, which indicated a decrease in the ionic bonding strength. The Debye temperature decreased almost linearly with increasing temperature, which showed the effect of thermal expansion.

Journal Articles

Microstructures and positron annihilation spectroscopy of nearly stoichiometric ZrC coating layers for advanced high-temperature gas-cooled reactor fuel

Aihara, Jun; Maekawa, Masaki; Ueta, Shohei; Kawasuso, Atsuo; Sawa, Kazuhiro

Journal of the American Ceramic Society, 94(12), p.4516 - 4522, 2011/12

 Times Cited Count:6 Percentile:36.67(Materials Science, Ceramics)

Japan Atomic Energy Agency has started to study and develop zirconium carbide (ZrC)-coated fuel particles for advanced high temperature gas-cooled reactors. The ZrC coated particles have been fabricated at JAEA by bromide process and heat treated to investigate the effects of the sintering process of fuel compact. The remarkable ZrC crystal grain growth occurred in a batch (F-batch) but not another batch (G-batch) in spite of the same C/Zr ratio and ZrC density. TEM/STEM observation of the specimens before heat treatment clarified that much more free carbons or voids were distributed in ZrC layer in G-batch than F-batch. The difference between F- and G-batch, which could not be detected by the estimation of C/Zr ratio and the ZrC density, could be detected with positron annihilation spectroscopy (PAS). Then PAS might be suitable for the quality control method of the ZrC coated fuel particles. Characterization of the defects detected with PAS would be the next step.

Journal Articles

Oxygen potentials of pyrochlore-type Am$$_{2}$$Zr$$_{2}$$O$$_{7+y}$$

Otobe, Haruyoshi; Takano, Masahide; Hayashi, Hirokazu; Arai, Yasuo

Journal of the American Ceramic Society, 94(10), p.3596 - 3599, 2011/10

 Times Cited Count:2 Percentile:17.16(Materials Science, Ceramics)

The relations between the oxygen potentials and the oxygen-nonstoichiometry (${it y}$) of the pyrochlore-type Am$$_{2}$$Zr$$_{2}$$O$$_{7+y}$$ for 1333 K were measured by the electrochemical method using a zirconia solid electrolyte and the mass changes by the oxidation and reduction. It was found that the oxygen potential of Am$$_{2}$$Zr$$_{2}$$O$$_{7+y}$$ smoothly increased from -516.52 to 0 kJ/mol with increasing ${it y}$ from 0.0 to 0.56 at 1333K. The oxygen potentials of Am$$_{2}$$Zr$$_{2}$$O$$_{7+y}$$ were higher than those of AmO$$_{2-x}$$ at the corresponding O/M by approximately 130 kJ/mol. The difference of the oxygen potentials between Am$$_{2}$$Zr$$_{2}$$O$$_{7+y}$$ and AmO$$_{2-x}$$ was consistent with that between Pu$$_{2}$$Zr$$_{2}$$O$$_{7+y}$$ and PuO$$_{2-x}$$ considering the difference of the ionic radii between Am and Pu. This leads to the systematical understanding of the thermodynamic properties of the transuraniumm oxides.

Journal Articles

Percolation in radioactive-waste glass melt with RuO$$_2$$

Ogawa, Toru

Journal of the American Ceramic Society, 93(9), p.2487 - 2490, 2010/09

 Times Cited Count:1 Percentile:10.17(Materials Science, Ceramics)

Molten glass containing RuO$$_2$$ particles develops electronic conduction, which causes unstable operation of the joule-heated melter for the radioactive waste vitrification. Percolation behavior of molten glass-ruthenium oxide composites was examined by noting hierarchical formation process with four length scales. A low percolation threshold less than 1 vol% was reasonably reproduced by assuming the packing of soft RuO$$_2$$ rods in the primary aggregate, and applying Bruggeman's effective medium approximation for the higher aggregates and their clusters.

Journal Articles

Crystal structure and nuclear density distribution of LiCo$$_{1/3}$$Ni$$_{1/3}$$Mn$$_{1/3}$$O$$_{2}$$ analyzed by Rietveld/maximum entropy method

Igawa, Naoki; Taguchi, Tomitsugu; Fukazawa, Hiroshi; Yamauchi, Hiroki; Utsumi, Wataru

Journal of the American Ceramic Society, 93(8), p.2144 - 2146, 2010/08

 Times Cited Count:15 Percentile:61.31(Materials Science, Ceramics)

The neutron powder diffraction measurement of LiCo$$_{1/3}$$Ni$$_{1/3}$$Mn$$_{1/3}$$O$$_{2}$$ was carried out and the crystal structure and scattering density distribution were analyzed by Rietveld refinement and the maximum entropy method to estimate the Li diffusing pathway. Rietveld refinement showed that the structure was basically the same as LiCoO$$_{2}$$: a ${it R}$-3${it m}$ space group, with Li and O mainly occupying the 3${it a}$ and 6${it c}$ sites, and Co, Ni and Mn randomly occupying the 3${it b}$ site. Approximately 4% of the Li and Ni atoms exchanged their original sites (3${it a}$ and 3${it b}$) to occupy 3${it b}$ and 3${it a}$, respectively. Based on maximum entropy method analyses, we surmise that Li atoms moved on the (001), (003) and (00-3) planes and diffused through the 3${it a}$-9${it e}$-3${it a}$ sites on those planes.

Journal Articles

Formation of continuous pore structures in Si-C-O fibers by adjusting the melt spinning condition of a polycarbosilane - polysiloxane polymer blend

Kita, Kenichiro; Narisawa, Masaki*; Mabuchi, Hiroshi*; Ito, Masayoshi*; Sugimoto, Masaki; Yoshikawa, Masahito

Journal of the American Ceramic Society, 92(6), p.1192 - 1197, 2009/06

 Times Cited Count:11 Percentile:54.88(Materials Science, Ceramics)

Journal Articles

TEM/STEM observation of ZrC coating layer for advanced high-temperature gas-cooled reactor fuel, Part II

Aihara, Jun; Ueta, Shohei; Yasuda, Atsushi; Ishibashi, Hideharu; Mozumi, Yasuhiro; Sawa, Kazuhiro; Motohashi, Yoshinobu*

Journal of the American Ceramic Society, 92(1), p.197 - 203, 2009/01

 Times Cited Count:7 Percentile:43.55(Materials Science, Ceramics)

The ZrC coating layer was fabricated with bromide process at JAEA. In a later stage of the project, we have successfully kept nominal deposition temperature almost constant. Microstructures of the ZrC layers, of which nominal deposition temperatures were able to measure, were characterized by means of TEM and STEM and the results were compared and discussed with those obtained for different batches including those reported in a previous study. The ZrC grains were oriented in the ZrC layers deposited at about 1630 K. This feature was rather different from that reported in the previous study. The formation of fairly different PyC structures was found on the PyC/ZrC boundary as well as around the pores existing near the boundary. Fibrous carbons were observed on the PyC/ZrC boundary produced in a batch deposited at a higher temperature (nominal temperature was 1769 K); no such fibrous carbons were found in a batch deposited at a lower temperature (nominal temperature was 1632 K).

Journal Articles

Oxygen potentials of (Am$$_{0.5}$$Np$$_{0.5}$$)O$$_{2-x}$$

Otobe, Haruyoshi; Akabori, Mitsuo; Arai, Yasuo; Minato, Kazuo

Journal of the American Ceramic Society, 92(1), p.174 - 178, 2009/01

 Times Cited Count:6 Percentile:39.81(Materials Science, Ceramics)

The oxygen potentials of the oxygen-deficient fluorite-type oxide Am$$_{0.5}$$Pu$$_{0.5}$$O$$_{2-x}$$ were measured by the electrochemical method with using a zirconia solid-electrolyte. The coulomb titration has been made for the sample at 1333 K over 0.02 $$<$$ ${it x}$ $$leq$$ 0.25. The oxygen potentials were -93.63 and -440.18 kJmol$$^{-1}$$ for ${it x}$ = 0.021 and 0.25 at 1333 K, respectively. The temperature dependence of the oxygen potentials was also measured between 1000 and 1333 K over the ${it x}$ range of 0.02 $$<$$ ${it x}$ $$leq$$ 0.243. The temperature dependence was almost linear over the ${it x}$ and temperature ranges concerned.

Journal Articles

Oxygen potential measurement of americium oxide by electromotive force method

Otobe, Haruyoshi; Akabori, Mitsuo; Minato, Kazuo

Journal of the American Ceramic Society, 91(6), p.1981 - 1985, 2008/06

 Times Cited Count:20 Percentile:71.74(Materials Science, Ceramics)

The oxygen potentials of AmO$$_{2-x}$$ were measured in the ${it x}$ range of 0.01 to 0.5 and the temperature range of 1000 to 1333 K by the electromotive force (EMF) method. The oxygen potentials at 1333 K were -19.83 kJ/mol for ${it x}$=0.01 and -319.1 kJ/mol for ${it x}$=0.485, which were higher than those of CeO$$_{2-x}$$ by approximately 200 kJ/mol for the corresponding ${it x}$ values. From the dependence of the oxygen potentials on ${it x}$ and temperature, a tentative phase diagram of Am-O system was proposed, which suggested the presence of the intermediate phases of Am$$_{7}$$O$$_{12}$$ and Am$$_{9}$$O$$_{16}$$ in the Am-O system.

Journal Articles

TEM/STEM observation of ZrC-coating layer for advanced high-temperature gas-cooled reactor fuel

Aihara, Jun; Ueta, Shohei; Yasuda, Atsushi; Ishibashi, Hideharu; Takayama, Tomoo; Sawa, Kazuhiro; Motohashi, Yoshinobu*

Journal of the American Ceramic Society, 90(12), p.3968 - 3972, 2007/12

Japan Atomic Energy Agency (JAEA) has started to study and develop ZrC coated fuel particles for advanced high temperature gas cooled reactors. This paper mainly focuses on the microstructures of the ZrC and isotropic dense pyrolytic carbon (PyC) coating layer produced in the early stage of the project. The structure of free carbon region in the ZrC coating layer appears to be such that c-plane was along with the ZrC grain boundary. It appears that the existence of the free carbon phase, especially with such structure, deteriorates the fission product (FP) retention performance in addition to the mechanical strength of ZrC. The PyC coating layer appears to be a medium-range ordered amorphous structure.

Journal Articles

Core-shell structure analysis of BaTiO$$_{3}$$ ceramics by synchrotron X-ray diffraction

Yasukawa, Katsumasa*; Nishimura, Michiaki*; Nishihata, Yasuo; Mizuki, Junichiro

Journal of the American Ceramic Society, 90(4), p.1107 - 1111, 2007/04

 Times Cited Count:37 Percentile:85.28(Materials Science, Ceramics)JP, H16-330250   Patent publication (In Japanese)

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47 (Records 1-20 displayed on this page)