Watanabe, Masashi; Nakamura, Hiroki; Suzuki, Kiichi; Machida, Masahiko; Kato, Masato
Journal of the American Ceramic Society, 105(3), p.2248 - 2257, 2022/03
Properties of CeO 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.
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
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
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
X-ray absorption near edge structure (XANES) and small-angle X-ray scattering (SAXS) reveal the damaged structures in MgAlO 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.
Cantarel, V.; Arisaka, Makoto; Yamagishi, Isao
Journal of the American Ceramic Society, 102(12), p.7553 - 7563, 2019/12
The hydrogen gas (H) production of wasteforms is a major safety concern for encapsulating nuclear wastes. For geopolymers, the H 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 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 (1.910 mol/J) than a sample in powder form (2.210 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.
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
The fundamental properties of CeO were assessed using a range of experimental techniques. The oxygen potential of CeO was measured by the thermogravimetric technique, and a numerical fit for the oxygen potential of CeO is derived based on defect chemistry. Mechanical properties of CeO were obtained using sound velocity measurement, resonant ultrasound spectroscopy and nanoindentation. The obtained mechanical properties of CeO are then used to evaluate the Debye temperature and Gruneisen constant. The heat capacity and thermal conductivity of CeO 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.
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
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 (CS) 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 CS 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 whereas crystalline phases dominated that beyond 20. 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 was similar to that of Ca(OH). 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.
Lam, Do Van*; Suematsu, Hisayuki*; Ogawa, Toru
Journal of the American Ceramic Society, 100(10), p.4884 - 4892, 2017/10
Nanoparticles of ZrN, ZrO and ZrN, '-ZrON 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.
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
Serizawa, Hiroyuki; Kaji, Yoshiyuki
Journal of the American Ceramic Society, 97(4), p.1187 - 1193, 2014/04
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.
Aihara, Jun; Maekawa, Masaki; Ueta, Shohei; Kawasuso, Atsuo; Sawa, Kazuhiro
Journal of the American Ceramic Society, 94(12), p.4516 - 4522, 2011/12
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.
Otobe, Haruyoshi; Takano, Masahide; Hayashi, Hirokazu; Arai, Yasuo
Journal of the American Ceramic Society, 94(10), p.3596 - 3599, 2011/10
The relations between the oxygen potentials and the oxygen-nonstoichiometry () of the pyrochlore-type AmZrO 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 AmZrO smoothly increased from -516.52 to 0 kJ/mol with increasing from 0.0 to 0.56 at 1333K. The oxygen potentials of AmZrO were higher than those of AmO at the corresponding O/M by approximately 130 kJ/mol. The difference of the oxygen potentials between AmZrO and AmO was consistent with that between PuZrO and PuO 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 of the American Ceramic Society, 93(9), p.2487 - 2490, 2010/09
Molten glass containing RuO 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 rods in the primary aggregate, and applying Bruggeman's effective medium approximation for the higher aggregates and their clusters.
Igawa, Naoki; Taguchi, Tomitsugu; Fukazawa, Hiroshi; Yamauchi, Hiroki; Utsumi, Wataru
Journal of the American Ceramic Society, 93(8), p.2144 - 2146, 2010/08
The neutron powder diffraction measurement of LiCoNiMnO 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: a -3 space group, with Li and O mainly occupying the 3 and 6 sites, and Co, Ni and Mn randomly occupying the 3 site. Approximately 4% of the Li and Ni atoms exchanged their original sites (3 and 3) to occupy 3 and 3, 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 3-9-3 sites on those planes.
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
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
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).
Otobe, Haruyoshi; Akabori, Mitsuo; Arai, Yasuo; Minato, Kazuo
Journal of the American Ceramic Society, 92(1), p.174 - 178, 2009/01
The oxygen potentials of the oxygen-deficient fluorite-type oxide AmPuO 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 0.25. The oxygen potentials were -93.63 and -440.18 kJmol for = 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 range of 0.02 0.243. The temperature dependence was almost linear over the and temperature ranges concerned.
Otobe, Haruyoshi; Akabori, Mitsuo; Minato, Kazuo
Journal of the American Ceramic Society, 91(6), p.1981 - 1985, 2008/06
The oxygen potentials of AmO were measured in the 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 =0.01 and -319.1 kJ/mol for =0.485, which were higher than those of CeO by approximately 200 kJ/mol for the corresponding values. From the dependence of the oxygen potentials on and temperature, a tentative phase diagram of Am-O system was proposed, which suggested the presence of the intermediate phases of AmO and AmO in the Am-O system.
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.
Yasukawa, Katsumasa*; Nishimura, Michiaki*; Nishihata, Yasuo; Mizuki, Junichiro
Journal of the American Ceramic Society, 90(4), p.1107 - 1111, 2007/04Patent publication (In Japanese)
no abstracts in English