発表論文 1999年

[1999_01]

Charge and discharge characteristics of sintered Mg2Ni

Kuniaki Watanabe, Wei Min Shu, Kenzo Mizukami, Kohji Kobayashi, Yuji Hatano, Shotaro Morozumi

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

Abstract

    The effects of sample preparation of a Mg2Ni anode for a nickel/metal hydride battery were studied with an open electrochemical cell. The discharge capacity of sintered Mg2Ni increased initially with the charge/discharge cycles. The cycle life (CL) for sintered samples was much greater than that of un-sintered samples, and the largest CL appeared at a sintering temperature of 550℃. It was also observed that slight pre-oxidation of the sample powder was effective in improving the CL.
    Those effects were examined through the changes in the specific surface area and the chemical composition. The sample sintered at 550℃ had the largest specific surface area, and the segregation of Mg over the outside layer of samples was confirmed for those sintered at temperature higher than 550℃. The degradation after charge/discharge cycling was investigated with X-ray diffraction and scanning electron microscopy. The XRD pattern showed a new phase of Mg(OH)2, besides the phase of Mg2Ni, after charge/discharge cycling. This indicates that the formation of Mg(OH)2 on the outside layer of the samples contributes to the degradation of the anode performance.

Keywords: Hydride; Battery; Mg2Ni; Cycle-life; Pretreatment

[1999_02]

Absorption of hydrogen isotopes by Pd-Pt alloys

T. Yasumatsu, J.L. Wan, M. Matsuyama, K. Watanabe

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

Abstract

    In the search for more profitable working materials for the recently developed gas chromatographic hydrogen isotope separation operated around room temperature without any replacement gas, thermodynamic properties of Pd-Pt alloys for hydrogen absorption and hydride formation were studied in the composition range 0-10 at. % Pt, the temperature range 273-493 K, and with a H/M from 2×10-4 to 0.65. The heat of absorption at infinite dilution and hydride formation were determined for H2 and D2. The results showed that both the heat of absorption and hydride formation decreased with increasing Pt content in the alloy and the isotope effect defined by the ratio of equilibrium pressures did not change much with alloy composition. It is implied that any alloy used in the present study could be selected as a working material depending on the required operation conditions without significant change in the separation efficiency.

Keywords: Pd-Pt alloy; Hydrogen; Isotope; Absorption; Separation

[1999_03]

Zr系ゲッターによる水素の吸着・吸収

渡辺国昭

[1999_04]

Recovery of Deuterium from Argon Carrier Gas by ZrNi Modified with Electroless Pd Coating

Kan Ashidaa, Wataru Nishidab, Jyun-ichi Nagatac, Yoshiaki Nishimurac, Kuniaki Watanabea

a Hydrogen Isotope Research Center, Toyama University, Toyama 930-8555, Japan

b Graduate Student, Toyama University

c Undergraduate Student, Toyama University

Abstract

    The effectiveness of Pd-coating on ZrNi against impurity gas exposure was examined. X-ray diffraction profiles revealed that the surfaces of plate and grain samples are readily covered with Pd by electroless plating. Mutual diffusion between the Pd-overlayer and the ZrNi substrate and PdZr formation took place by vacuum heating above 973 K. Deuterium recovery (DR) in a flowing argon carrier gas containing 5 ppm of impurity gases was examined using packed columns of bare ZrNi and Pd/ZrNi grains. Results indicate that the Pd-coating successfully extends the life time of ZrNi against impurity gases at low temperature below 473 K. Furthermore, no noticeable reduction in DR was found in Pd/ZrNi, whereas bare ZrNi loss its activity at 10 ks at 573 K.

Keywords: hydrogen storage alloy; surface modification; zirconium nickel; palladium coating; electroless plating; hydrogen recovery

[1999_05]

Effect of Surface Modification by Heating in Argon on Charge/Discharge Characteristics of Mg2Ni Electrode

Yuji Hatanoa, Tomoyuki Tachikawab, Koji Kobayashib, Katsunori Moric, Kuniaki Watanabea, Shotaro Morozumia

a Hydrogen Isotope Research Center, Toyama University, Toyama 930-8555, Japan

b Graduate Student, Toyama University

c Material Systems Engineering and Life Science, Faculty of Engineering, Toyama University

Abstract

    Charge/discharge characteristics of Mg2Ni electrodes were examined by focussing attention on the influence of surface modification by heating in argon. The initial activation was significantly easier for the electrodes heated at 550゚C than un-heated ones. The surfaces of electrodes became porous by the heating because of the evaporation of magnesium. A MgO layer was formed during the heating. The improvement of charge/discharge characteristics by the heating was ascribed to the increase in the specific surface area and the porosity of the oxide film, and to the formation of MgNi2 and nickel phases which should act as the local reaction sites for hydrogen during the change and discharge processes.

Keywords: Mg2Ni; magnesium; surface property; initial activation; evaporation; oxidation; porous metal; electrode; nickel/metal hydride battery

[1999_06]

Release of hydrogen molecules from hydrogen-containing carbon film deposited on molybdenum

K. Ashidaa, K. Watanabea, I. Kitamurab, S. Ikenob

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

b Materials Science and Engineering, Faculty of Engineering, Toyama University, Gofuku 3190, Toyama 930-8555, Japan

Abstract

    Molybdenum (Mo) plates covered with a hydrogen-containing carbon film, C(H)/Mo, were prepared as a model system to simulate carbon-metal mixed materials. The C(H)/Mo samples annealed at given temperatures and times in vacuum were analyzed by means of X-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), thermal desorption spectroscopy (TDS) along with X-ray diffraction measurements (XRD). The XPS measurements revealed that the samples surface was covered with a carbon film containing hydrogen and a small amount of oxygen below 773 K. The Mo 3d 5/2 peak appeared only after annealing at 873 K for 600 s, indicating that carbon atoms diffused to the bulk of Mo. The XRD measurements showed that Mo2 formed in the surface layer after annealing at 1073 K for 600 s. In addition, it was observed with TDS that hydrogen molecules desorbed from the sample above 873 K. All of the above observations indicated that solid state chemical reactions take place at relatively low temperatures to cause Mo2C formation and H2 release in the subsurface layer or out of the C(H)/Mo system.

Keywords: Molybdenum; Carbon deposition; Material mixing

[1999_07]

Deposition of lithium on a plasma edge probe in TFTR.
Behavior of lithium-painted walls interacting with edge plasmas

Behavior of lithium-painted walls interacting with edge plasmas

Y. Hirookaa, K. Ashidab, H. Kugelc, D. Walshd, W. Wamplerd, M. Bellc, R. Conna, M. Harab, S. Luckhardta, M. Matsuyamab, D. Mansfieldc, D. Muellerc, C. Skinnerc, T. Waltersc, K. Watanabeb

a University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0417, USA

b Toyama University, Gofuku 3190, Toyama 930, Japan

c Princeton University, P. O. Box 451, Princeton, NJ 08543, USA

d Sandia National Laboratories, Albuquerque, NM 87185-5800, USA

Abstract

    Recent observations have indicated that lithium pellet injection wall conditioning plays an important role in achieving the enhanced supershot regime in TFTR (the tokamak test fusion reactor). However, little is understood about the behavior of lithium-coated limiter alls, interacting with edge plasmas. In the final campaign of TFTR, a cylindrical carbon fiber composite probe was inserted into the boundary plasma region and exposed to ohmically heated deuterium discharges with lithium pellet injection. The ion-drift probe surface exhibits a sign of codeposition of lithium, carbon, oxygen, and deuterium, whereas the electron side essentially indicates high-temperature erosion. It is found that lithium is incorporated in these codeposits in the form of oxide at the concentration of a few percent. In the electron side, lithium has been found to penetrate deeply into the probe material, presumably via rapid diffusion through interplane spaces in the graphite crystalline. Though it is not conclusive, materials mixing in the carbon and lithium system appears to be a key process to successful lithium wall conditioning.