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[1999_01]
Journal of Alloys and Compounds, 293-295 (1999) 626-631
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 °C. 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 °C 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 °C. 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]
Journal of Alloys and Compounds, 293-295 (1999) 900-907
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] *The text is Japanese.
[1999_04]
Materials Transactions, JIM, 40(9) (1999) 851-854
Recovery of Deuterium from Argon Carrier Gas by
ZrNi Modified with Electroless Pd Coating
Kan Ashida, Wataru Nishida*, Jyun-ichi Nagata**, Yoshiaki Nishimura** and Kuniaki Watanabe
Hydrogen Isotope Research Center, Toyama University, Toyama 930-8555, Japan
*Graduate Student, Toyama University
**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]
Materials Transactions, JIM, 40(9) (1999) 919-922
Effect of Surface Modification by Heating in Argon
on Charge/Discharge Characteristics of Mg2Ni Electrode
Yuji Hatano, Tomoyuki Tachikawa 2, Koji Kobayashi 2,
Katsunori Mori 3, Kuniaki Watanabe, Shotaro Morozumi
Hydrogen Isotope Research Center, Toyama University, Toyama 930-8555, Japan
2 Graduate Student, Toyama University
3 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 °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]
Journal of Nuclear Materials, 266-269 (1999) 434-439
Release of hydrogen molecules from hydrogen-containing carbon film deposited on molybdenum
K. Ashida a, K. Watanabe a, I. Kitamura b, S. Ikeno b
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]
Journal of Nuclear Materials, 274 (1999) 320-328
Deposition of lithium on a plasma edge probe in TFTR
-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.