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[2000_01]
Journal of Nuclear Materials, 283-287 (2000) 868-871
Yuji Hatano, Yoshiyasu Nanjo, Ryo Hayakawa, Kuniaki Watanabe
Hydrogen Isotope Research Center, Toyama University, Gofuku 3190, Toyama 930-8555, Japan
Abstract
Hydrogen permeation through vanadium was examined under helium ion irradiation. The upstream surface of a vanadium membrane was exposed to hydrogen gas at 673K and 640 Pa, and the downstream surface was irradiated with 5 keV helium ions. No significant variation in the permeation rate was observed in the initial stage of irradiation. The permeation rate, however, started to decrease at a helium ion dose of 1021 m-2 with further irradiation. In this region, the permeation rate dropped immediately by intermission of irradiation and shot up by resumption. These results were successfully explained with a model that helium bubbles act as trapping sites of hydrogen and detrapping is enhanced under irradiation.
[2000_02]
Materials Transactions, JIM, Vol. 41, No. 9, (2000) pp. 1146-1149
Masanori Hara, Ryo Hayakawa*2 and Kuniaki Watanabe
Hydrogen Isotope Research Center, Toyama University, Toyama 930-8555, Japan
*2 Graduate Student, Toyama University
Abstract
The kinetics of hydrogen-induced disproportionation
of Zr2Co was studied by the conventional constant volume method
in a temperature range of 773 to 873 K. It was found that Zr2Co
disproportionated as 2Zr2Co + 3H2--> 3ZrH2
+ ZrCo2 through a two-step mechanism as 1) Zr2Co
+ H2--> ZrH2 + ZrCo and 2) 2ZrCo + H2--> ZrH2 + ZrCo2. The first step was very fast and completed
within only 100s at 773K. The rate, however, decreased with increases in
temperature. The apparent rate constant for the first step disproportionation
was determined to be k= 2.0×10-2 exp [15.0×103
(J/mol)/RT], where the kinetics could be explained by nucleation and one-dimensional
growth model. The kinetics of the second step disproportionation could
be explained by nucleation and three-dimensional growth model.
Keywords: disproportionation, hydrogen, kinetics,
hydrogen absorbing alloy, zirconium-based alloy, Zr2Co, ZrCo
[2000_03]
Fusion Engineering and Design, 49-50 (2000) 885-891
Masao Matsuyama, Satoshi Ueda, Kuniaki Watanabe
Hydrogen Isotope Research Center, Toyama University,
Gofuku 3190, Toyama 930-8555, Japan
Abstract
A newly developed technique, β-ray induced X-ray
spectrometry (BIXS), was applied to in situ and real-time measurements
of depth profiles of tritium in palladium and zirconium. Two distinct spectra
were detected by BIXS, one due to the characteristics X-rays giving rise
to a sharp intense peak; and the other due to the bremsstrahlung X-rays
leading to a broad weak peak. The intensities of these peaks for palladium
decreased with time at room temperature, while they were almost constant
for the Zr-sample at room temperature. Heating the Zr-sample, however,
caused similar changes in the spectra as those for palladium at room temperature.
It was found that these phenomena are due to the diffusion of tritium into
the bulk regions, causing a reduction of the tritium concentration in the
sub-surface layers of the samples. All of the observed beta-ray induced
X-ray spectra could be reproduced well by computer simulation by assuming
respective depth profiles of tritium in the samples. It was confirmed that
BIXS in quite useful to analyze the dynamic transport behavior of tritium
in materials.
Keywords: Tritium interaction; β-Ray; X-Ray
spectrometry; Depth profiles; In situ measurement
[2000_04]
Fusion Engineering and Design, 49-50 (2000) 831-838
Masanori Hara a, Toshio Okabe b, Katsunori Mori
c, Kuniaki Watanabe a
a Hydrogen Isotope Research Center, Toyama
University, Gofuku 3190, Toyama 930-8555, Japan
b Faculty of Science, Toyama University, Gofuku 3190, Toyama 930-8555, Japan
c Faculty of Engineering, Toyama University, Gofuku 3190, Toyama 930-8555, Japan
Abstract
The kinetics and mechanism of the hydrogen-induced
disproportionation of ZrCo was studied experimentally. In general, the
time dependence of the disproportionation has a sigmoidal shape. The disproportionation
rate increased with increasing initial hydrogen pressure and showed a 3/2-power
dependence on the pressure. As for the temperature dependence, the rate
increased with temperature only up to 815 K and then decreased at higher
temperatures. Namely, a volcano-type pattern was observed in the Arrhenius
plot of the rate constant. In addition, a fairly large isotope effect was
observed for the rate of disproportionation between hydrogen and deuterium.
These results were explained well by a nucleation and nuclei growth model,
in which hydrogen solubility in the ZrCo phase was assumed to play an important role.
Keywords: ZrCo; Kinetics; Mechanism; Hydrogen-induced disproportionation