JAEA-Review-2010-065.pdf:15.99MB - 日本原子力研究開発機構

4-05
Synergy Effects in Electron/Ion Irradiation and
Alkaline Pretreatment on Hydriding Property of
Hydrogen Storage Alloys
H. Abe a) , M. Kishimoto b) , H. Uchida c) and T. Ohshima a)
a) Environment and Industrial Material Research Division, QuBS, JAEA,
b) Course of Applied Science, Graduate School of Engineering, Tokai University,
c) Department of Energy Science and Engineering, School of Engineering, Tokai University
1, 2)
In previous studies , we reported that the alkaline
pretreatment of the alloy surface using LiOH, NaOH or
KOH accelerates the initial rate of hydrogen absorption of
hydrogen storage alloys. Electron/ion beam irradiation is
known to produce a high density of vacancy type defects in
the surface region of materials and to be quite useful
3, 4)
methods for the surface modification .
In this study, we examined the synergy effects of both the
electron/ion irradiation and alkaline pretreatment on the
Mm-Ni based alloy surface. We aimed to fabricate alloys
with a higher performance of the hydrogen absorption rate
by the surface modification of the alloys using electron/ion
irradiation in this report. The electron/ion beam
modifications are effective methods to improve the
hydrogen absorption rate in metals. We also analyzed the
chemical compositions at the surface of the
irradiated/un-irradiated Mm-Ni based alloys, their crystal
structures, and the phases of bulk. The samples used in
this study were MmNi3.48Co 0.73Mn 0.45Al 0.34 (Mm =
La 0.35Ce 0.65) alloys. The samples were irradiated with
either e - at an acceleration energy of 2 MeV with a dose
from 5 × 1016 to 1 × 1017 /cm 2 using the 2 MV Cockcroft-
Walton electron accelerator in JAEA-Takasaki. The
hydrogen absorption rate measurements were performed for
the irradiated and un-irradiated Mm-Ni based alloys using
the electrochemical apparatus method. An alkaline
treatment was made by heating a sample at 398 K for 30 min
JAEA-Review 2010-065
in a 6 M-KOH solution. This treatment introduces K ions
3, 4)
in the surface oxide layers of the alloy . The hydrogen
absorption rate of Mm-Ni based alloy was measured
electrochemically in the 6 M-KOH with an open cell as the
current density at a constant potential of -0.93 V at room
temperature, from 0 to 120 minutes. These were measured
after the combined with and without 6 M-KOH alkaline
pretreatment respectively.
Figure 1 shows hydriding curves for samples with and
without electron irradiation before electrochemical process.
Samples with electron irradiations in the air exhibit much
higher hydriding rates than that of a sample without
irradiation. As known, electron irradiation induces
vacancy type defects in the surface region of the alloy.
These defects may act as hydrogen trapping sites, and
increase hydrogen concentration in the surface region.
This may enhance the initial hydriding rate, which was
similarly observed for other metals pretreated by various
5)
charged ions .
Figure 2 shows hydriding curves for samples with and
without electron irradiation. After the electron irradiations
in air, samples were treated in an alkaline solution of
6 M-KOH. Samples with electron irradiations show higher
- 129 -
reaction rates than that of a sample without irradiation.
The reaction rates for samples with both the irradiation and
the alkaline treatment are much higher than those for
samples only with electron irradiations (Fig. 1). After the
irradiation, samples were exposed to air before the
measurement of electrochemical hydriding rate. In this
step, the surface oxidation of samples surely took place.
Therefore, the additional alkaline treatment was effective to
enhance the rate, because the alkaline treatment induces the
K atoms in the surface oxides, and reduces the work
function of electron of the surface to facilitate the
dissociation of H2O and the subsequent hydriding rate 1, 2) .
Electron irradiation onto the surface of the Mm based
hydrogen storage alloy was found very effective.
Additional alkaline treatment was found also to contribute to
the enhancement of the hydriding rate. These effects can
be interpreted in terms of the induced vacancy defects by
electron irradiation, and the surface oxidation of the alloy
surface.
H/MmNi 3.48 Mn 0.73 Co 0.45 Al 0.34
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0 20 40 60 80 100 120
H/MmNi 3.48 Mn 0.73 Co 0.45 Al 0.34
3.0
2.5
2.0
1.5
1.0
0.5
Tim e [m in]
No irradiation
2MeV 1x10 17 /cm 2
2MeV 5x10 16 /cm 2
Fig. 1 Hydriding curves for samples with and
without electron irradiation.
c
b
a
No irradiation
2MeV 1x10 17 /cm 2
2MeV 5x10 16 /cm 2
0.0
0 20 40 60
Time [min]
80 100 120
Fig. 2 Hydriding curves (a) for a sample without
electron irradiation and with alkaline treatment,
and (b) and (c) for samples with electron
References
1) H. Uchida et al., J. Alloy Comp. 662 (2002) 330-332.
2) H. Uchida et al., J. Alloy Comp. 751 (1999) 293-295.
3) H. Abe et al., J. Alloy Comp. 288 (2005) 404-406.
4) H. Abe et al., J. Alloy Comp. 348 (2006) 408-412.
5) H. Abe et al., Nucl. Instrum. Meth. B, 206 (2003) 224.
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b:
c:
a:
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irradiations and alkaline treatment.
c
b
a