発表論文 2004年

[2004_01]

Effects of Pd addition on electrochemical properties of MgNi

Tiejun Ma, Yuji Hatano, Takayuki Abe, Kuniaki Watanabe

Hydrogen Isotope Research Center, Toyama University, Gofuku 3190, Toyama 930-8555, Japan

Abstract

   Two kinds of Pd-modified MgNi were prepared and effects of Pd addition on the electrochemical properties of MgNi were investigated. Sample I was prepared by ball-milling amorphous MgNi with Pd (1, 6 and 10 mol%) for 10 min, 2 and 10h, and sample II was obtained by ball-milling Mg2Ni and Ni with 10 mol% Pd for 80h. The effects of Pd-modification for sample I depended on both Pd ratio and time of ball-milling. During the ball-milling, Pd became amorphous and distributed rather uniformly not only on the surface but also in the bulk of MgNi powder. At 6 and 10 mol% Pd, the degradation of discharge capacity of MgNi was significantly decreased. As for sample II, the cycle life was remarkably improved by the Pd-modification. Analyses of the roles of Pd on the behavior of MgNi showed that the improvements of MgNi properties by both Pd-modifications were not due to the increase in hydrogen absorption ability but caused by the suppression of Mg(OH)2 formation.

[2004_02]

Kinetics of dissociative absorption of hydrogen through Nb surface covered by oxygen

Y. Hatanoa, A. Livshitsa,d, A. Busnyuka,d, M. Noruraa, K. Hashizumeb, M. Sugisakib, Y. Nakamurac, N. Ohyabuc, K. Watanabea

aHydrogen Isotope Research Center, Toyama University, Gofuku 3190, Toyama 930-8555, Japan

bDepartment of Advanced Energy Engineering Science, Kyushu University, Hakozaki 812-8581, Japan

cNational Institute for Fusion Science, Toki 509-5292, Japan

dPermanent address: Bonch-Bruyevich University, 61 Moika, St. Petersburg 191186, Russia

Abstract

    The sticking coefficient of H2, α, on the surface of polycrystalline Nb containing 0.1 at% of O was examined by means of performance experiments in a wide temperature range between 510 and 1260 K. The temperature dependence of surface coverage of O was measured by Auger electron spectroscopy. Arrhenius plots of α showed a clear bend at around 900 K. The activation energy was examined to be 5 kJ•mol-1 in the low temperature region and 44 kJ•mol-1 in the high temperature region. On the other hand, the surface coverage of O, θox, was almost independent of the temperature below 900 K, but it decreased with increasing temperature above 900 K. Therefore, it was concluded that the activation energy of 5 kJ•mol-1, obtained in the lower temperature region at constant θox, corresponded to the potential barrier against H2 dissociation, Ec, while the value of 44 kJ•mol-1, obtained in the higher temperature region, was an apparent activation energy determined by the combination of Ec and the heat of segregation of O controlling the temperature dependence of θox. The obtained value of Ec was comparable to that on a clean Nb surface, although the dissociation of H2 was radically impeded by the presence of O. These observations indicate that the surface of the polycrystalline Nb covered O was not homogeneous: a majority of surface sites was poisoned by O, while a small portion kept the intrinsic activity for H2 dissociation.

[2004_03 ]

Barrier effect against hydrogen ingress by Ti segregating to surface of V-Ti alloy

R. Hayakawa, Y. Hatano, A. Pisarev, K. Watanabe

Hydrogen Isotope Research Center, Toyama University, Gofuku 3190, Toyama 930-8555, Japan

Abstract

    Specimens of V-4Ti alloy with Ti-enriched surface were prepared by heating in vacuo, and the influence of segregating Ti on H2 absorption was examined at temperatures from 473 to 1023 K under the presence of water vapor of 10-5 Pa. The rate of H2 absorption was significantly reduced by surface segregation of Ti in the temperature range examined. Such reduction in the absorption rate was ascribed to the increase in surface coverage of oxygen caused by oxidation of Ti by water vapor. It was concluded that Ti segregating to the surfaces provides a favorable barrier effect against the ingress of hydrogen isotopes.

[2004_04]

Characteristics of a promising tritium process monitor detecting bremsstrahlung X-rays

W.M. Shua, M. Matsuyamab, T. Suzukia, M.F. Nishia

aTritium Engineering Laboratory, Japan Atomic Energy Research Institute, Tokai-mura, Naka-gun, Ibaraki-ken 319-1195, Japan

bHydrogen Isotope Research Center, Toyama University, Gofuku 3190, Toyama 930-8555, Japan

Abstract

    The characteristics of a tritium process detecting bremsstrahlung X-rays with a NaI(Tl) scintillation counter were examined with pure tritium in a concentration range of 102–108 GBq/m3. The measurement principle of this type of tritium process monitor is observing the bremsstrahlung X-rays generated by the interaction between beta particles from tritium and a gold film coated on the inner surfaces of a small measuring cell. A linear relationship between the counting rate of bremsstrahlung X-rays and the tritium concentration was observed for the concentration range of 102–106 GBq/m3, and the sensitivity of the monitor was determined to be about 0.5 GBq/m3/cpm in this concentration range. A linear response of this monitor was also observed for a tritium mixture diluted with deuterium. In addition, as an example of its practical use, this monitor was confirmed to be applicable to tracing 3He release from a uranium bed during heating. These results show that this type of tritium monitor is very promising as a process monitor for the fuel processing system of fusion reactors.

[2004_05]

Influence of heat treatment on hydrogen ingress into V-4Cr-4Ti alloy

R. Hayakawaa, Y. Hatanoa, K. Fukumotob, H. Matsuib, K. Watanabea

aHydrogen Isotope Research Center, Toyama University, Gofuku 3190, Toyama 930-8555, Japan

bInstitute of Materials Research, Tohoku University, Sendai 980-8577, Japan

Abstract

    Speciments of V-4Cr-4Ti alloy were heated at 1273 K in vacuum, and the influence of this heat treatment on H2 absorption was examined at temperatures from 523 to 1023 K under the presence of water vapor of 10-5 Pa. The rate of H2 absorption was significantly reduced by the heat treatment in the temperature range examined. Such reduction in the absorption rate was ascribed to the surface segregation of Ti and increase in surface oxygen coverage caused by preferential oxidation of segregating Ti by water vapor. Comparison with data reported by other researchers [J. Nucl. Mater. 233-237 (1996) 376; Fusion Technol. 34 (1998) 868; J. Nucl. Mater. 233-237 (1996) 510] indicated the strong barrier effect of Ti oxide against hydrogen ingress.

[2004_06]

Effects of heat treatment on trapping and release of tritium from He pre-irradiated tungsten

M. Matsuyamaa, S. Nakagawaa, M. Enyamaa, K. Watanabea, H. Iwakirib, N. Yoshidab

aHydrogen Isotope Research Center, Toyama University, Gofuku 3190, Toyama 930-8555, Japan

bResearch Institute for Applied Mechanics, Kyushu University, Kasuga, Fukuoka 816-8580, Japan

Abstract

    The effects of heating on retention of tritium implanted into tungsten pre-irradiated with helium have been examined by β-ray-induced X-ray spectrometry (BIXS), which gives information about changes in the amount and depth profile of tritium retained on/in materials. Tritium implantation and isochronal heating of the helium pre-irradiated and unirradiated tungsten samples were repeated as a series of experiments, and changes in the X-ray spectra were measured in each heating cycle. Quite different decreasing behavior between Ar(Kα) and W(Mα) X-ray intensities for both samples was observed in the heating process, and it was seen that the majority of tritium implanted into the helium pre-irradiation sample was trapped by the radiation defects rather than in helium bubbles.

[2004_07]

Behavior of tritium release from thin boron films deposited on SS316

S. Nakagawaa, M. Matsuyamaa, H. Kodamab, Y. Oyac, K. Okunob, A. Sagarad, N. Nodad, K. Watanabea

aHydrogen Isotope Research Center, Toyama University, Gofuku 3190, Toyama 930-8555, Japan

bRadiochemistry Research Laboratory, Faculty of Science, Shizuoka University, Ohya 836, Shizuoka 422-8259, Japan

cRadioisotope Center, The University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan

dNational Institute for Fusion Science, Oroshi-cho 322-6, Toki 509-5292, Japan

Abstract

    Release and diffusion behavior of tritium implanted into thin boron films were examined by isochronal and isothermal heating. For comparison, a polycrystal boron plate was also employed for the same examinations. Changes in the residual amount of tritium with heating were measured by β-ray-induced X-ray spectrometry (BIXS). Most of the tritium desorbed at room temperature was in HTO form, and the residual amount decreased to 20-30% of the initial amount loaded at 773 K. The time-course of the tritium reduction was well represented by an exponential function, suggesting that the tritium release obeys first order reaction kinetics and the rate-determining step is a diffusion process. The apparent activation energy of diffusion was determined to be 0.17 eV. Both the depth profiles calculated from a diffusion equation and determined by computer simulation of X-ray spectra agreed quite well for polycrystal boron.

[2004_08]

Implanted hydrogen isotope retention and chemical behavior in boron thin films for wall conditioning

Y. Oyaa, H. Kodamab, M. Oyaidzub, Y. Morimotob, M. Matsuyamac, A. Sagarad, N. Nodad, K. Okunob

aRadioisotope Center, The University of Tokyo, 2-11-16, Yayoi, Bunkyo-ku, Tokyo 133-0032, Japan

bRadiochemistry Research Laboratory, Faculty of Science, Shizuoka University, 836, Oya, Shizuoka-shi, Shizuoka 422-8529, Japan

cHydrogen Isotope Research Center, Toyama University, 3190 Gofuku, Toyama 930-8555, Japan

dNational Institute for Fusion Science, 322-6, Oroshi-cho, Toki, Gifu 509-5292, Japan

Abstract

    The behavior of hydrogen isotopes in boron was studied by XPS and TDS. The samples used were boron polycrystals and boron thin films produced by plasma CVD using decaborane (B10H14) diluted by He gas. The 1.0 keV deuterium ions were implanted into the samples up to fluence of 5.4 × 1021 Dm-2 at various temperatures. It was found that deuterium retention at 573 K was decreased less than 35% compared to that at room temperature. The activation energies for B-D-B and B-D bonds were estimated to be 1.11±0.21 and 2.17±0.36 eV for the boron thin films, and 1.36±0.20 and 2.27±0.45 eV for the boron polycrystal, respectively. The B-H distance and the activation energy for the B-H bond were also calculated by the Gaussian 03 code and these were consistent with the experimental values.

[2004_09]

Studies on structural and chemical characterization for boron coating films deposited by PCVD

H. Kodamaa, M. Oyaidzua, M. Sasakia, H. Kimuraa, Y. Morimotoa, Y. Oyab, M. Matsuyamac, A. Sagarad, N. Nodad, K. Okunoa

aRadiochemistry Research Laboratory, Faculty of Science, Shizuoka University, 836, Oya, Shizuoka-shi, Shizuoka 422-8529, Japan

bRadioisotope Center, The University of Tokyo, 2-11-16, Yayoi, Bunkyo-ku, Tokyo 133-0032, Japan

cHydrogen Isotope Research Center, Toyama University, 3190 Gofuku, Toyama 930-8555, Japan

dNational Institute for Fusion Science, 322-6, Oroshi-cho, Toki, Gifu 509-5292, Japan

Abstract

    Characterization of the structure and the chemical state of boron coating films were performed by XRD and TDS measurements. The structure of the boron coating films was shown to be amorphous by XRD measurement. By changing the total pressure, the discharge power, and the substrate temperature, the growth rate of the boron coating films and the hydrogen retention were evaluated. It was found that the growth rate decreased as the total pressure increased, and increased with an increase in the discharge power. For the substrate temperature dependence, the hydrogen retention decreased as the substrate temperature increased. However, the growth rate remained constant, although the hydrogen retention decreased as the substrate increased. This indicates that the growth rates are not controlled by the chemical form of B-H bond, but by that of B-B bond. In the TDS analysis, hydrogen atoms released from B-H-B and B-H bonds were observed.

[2004_10]

Tritium uptake by SS316 and its decontamination

Y. Torikai, R.-D. Penzhorn, M. Matsuyama, K. Watanabe

Hydrogen Isotope Research Centre, Toyama University, Gofuku 3190, Toyama 930-8555, Japan

Abstract

    As-received and highly polished SS316 specimens were loaded with HT at 473-473 K. The uptake by polished samples was found to be up to five times that of as-received ones, when loading was performed immediately after polishing. This disparity vanished when polished specimens were subjected to a prolonged exposure to air prior to loading. The tritium loss from tritium-loaded SS316 specimens was examined by chemical etching and by thermal release in a flow system using various carrier gases at several temperatures. While at moderate temperatures the type of carrier has an impact on the tritium release rate, at higher ones this effect disappears. Moisture in the carrier gas has little influence on the loss rate of bulk tritium. Etching depth profiles of specimens previously heat-treated in the presence of air or Ar + H2 and of untreated specimens are given. Evidence for chronic tritium liberation from SS316 at 298 K is provided.

[2004_11]

Surface modification of Al2O3 ceramic grains using a new RF sputtering system developed for powdery materials

Takayuki Abe, Satoshi Akamaru, Kuniaki Watanabe

Hydrogen Isotope Research Center, Toyama University, Gofuku 3190, Toyama 930-8555, Japan

Abstract

    A new RF sputtering system installed with a hexagonal-barrel was developed for modifying the surfaces of powdery materials. The validity of this system was examined for surface coating of three kinds of Al2O3 powders with different grain shapes and sizes. It was found that the surfaces of powder grains could be uniformly coated with Pt layers, regardless of their shapes and sizes. It should be noticed that the hexagonal barrel made it possible to form a uniform Pt layer over a Al2O3 grain of 20 μ diameter, whereas a cylindrical barrel failed to made a uniform layer on the same sample. Cyclic voltammograms (CVs) of the Pt-coated Al2O3 samples prepared by use of the hexagonal barrel gave the same CV of bulky Pt, indicating that electrochemical characteristics of the Pt films are identical with those of Pt metal.

[2004_12]

Study of PEFCs by AC impedance, current interrupt, and dew point measurements
I. Effect of humidity in oxygen gas

Takayuki Abea, Hiroyuki Shimaa, Kuniaki Watanabea, Yukio Itob

aHydrogen Isotope Research Center, Toyama University, Toyama 930-8555, Japan

bToyo Corporation, Tokyo 103-8284, Japan

Abstract

    The effect of humidity in oxygen gases on the performance of a polymer electrolyte fuel cell (PEFC) was examined by using linear current sweep (current-voltage), current interrupt, and ac impedance methods in combination with temperature variations of cathode humidifiers. The total resistance of the membrane increased about 3.4 mΩ by the temperature change of the cathode humidifier from 80 to 35°C. The results of electrochemical analysis showed that one-third of the total resistance change was due to the membrane resistance and almost the same amount could be attributed to the charge-transfer resistance. The measurements of dew points in hydrogen and oxgen gases at the entrance and the exit of the fuel cell made it clear that the water transport was sensitively affected by the temperatures of humidifiers of the cathode side. In the case of equal temperatures, water migrated from the cathode side to anode side, while the water movement in the reverse direction took place at the cathode humidifier temperature lower than the anode.

[2004_07]

Behavior of tritium release from thin boron films deposited on SS316

S. Nakagawaa, M. Matsuyamaa, H. Kodamab, Y. Oyac, K. Okunob, A. Sagarad, N. Nodad, K. Watanabea

aHydrogen Isotope Research Center, Toyama University, Gofuku 3190, Toyama 930-8555, Japan

bRadiochemistry Research Laboratory, Faculty of Science, Shizuoka University, Ohya 836, Shizuoka 422-8259, Japan

cRadioisotope Center, The University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan

dNational Institute for Fusion Science, Oroshi-cho 322-6, Toki 509-5292, Japan

Abstract

    Release and diffusion behavior of tritium implanted into thin boron films were examined by isochronal and isothermal heating. For comparison, a polycrystal boron plate was also employed for the same examinations. Changes in the residual amount of tritium with heating were measured by β-ray-induced X-ray spectrometry (BIXS). Most of the tritium desorbed at room temperature was in HTO form, and the residual amount decreased to 20-30% of the initial amount loaded at 773 K. The time-course of the tritium reduction was well represented by an exponential function, suggesting that the tritium release obeys first order reaction kinetics and the rate-determining step is a diffusion process. The apparent activation energy of diffusion was determined to be 0.17 eV. Both the depth profiles calculated from a diffusion equation and determined by computer simulation of X-ray spectra agreed quite well for polycrystal boron.