富山大学水素同位体科学研究センター研究報告 33：9-19，2013.

論文
ZrNi-H 系の磁気特性
赤丸悟士、岡﨑圭祐、原正憲、波多野雄治、松山政夫

富山大学水素同位体科学研究センター〒930-8555 富山市五福 3190

Magnetic properties of ZrNi-H systems
Satoshi Akamaru, Keisuke Okazaki, Masanori Hara, Yuji Hatano,and Masao Matsuyama
Hydrogen Isotope Research Center, University of Toyama, Gofuku 3190,
Toyama 930-8555, Japan(Received December 20, 2013; Accepted May 23, 2014 )Abstract
We estimate the amount of hydrogen isotope gas stored in getter materials without using adesorption process and by measuring the magnetic susceptibility of ZrNi–H systems. The magnetic
susceptibility of ZrNiHx increased with an increase in the hydrogen content, x, reaching a maximum
value at x  0.5. As x > 0.5, the magnetic susceptibility began to decrease and reached a minimum
value at x = 2.7. The behavior of magnetic susceptibility could be qualitatively modeled using themolar fractions of the ZrNi, monohydride, and trihydride phases observed using X-ray diffraction
analysis.

1. Introduction
The hydrogen storage properties of a ZrNi getter, such as low equilibrium pressure,resistance to disproportion via hydrogen uptake, and relatively low desorbing
temperatures are favorable for the safe storage and supply of hydrogen isotope gas [1].

9

赤丸悟士・岡﨑圭祐・原正憲・波多野雄治・松山政夫

Therefore, a ZrNi getter is one of the candidates for tritium storage getter in futurenuclear fusion reactors [2-4].
Estimating the amount of tritium gas stored in a ZrNi getter is important for
managing the tritium gas inventory. In general, this amount is estimated using a
volumetric method: gas pressure and volume are measured after desorption of tritium
gas from a ZrNi getter. In ordinary managements, estimating the stored tritium amount
via desorption techniques is difficult because there is a possibility of tritium leakage
during the measurement process. A calorimetric method is a reliable candidate formeasuring the stored tritium amount without a desorption process. In this method, theamount of tritium is estimated based on the decay heat [5-12]. This method isadvantageous over the volumetric method, but an accurate estimation with thecalorimetric method requires a measurement time of ~24 h.
The magnetic properties of a getter material can be utilized to estimate the amount ofhydrogen isotope gas stored in a getter without a desorption process; this is because themagnetic properties often depend on the amount of absorbing hydrogen isotope gas. For
example, the magnetic susceptibility for the Pd–H systems is proportional to the amountof hydrogen in Pd [13]. The estimation method using the magnetic susceptibility of agetter has a few advantages over other methods: the measurement is performed withkeeping hydrogen isotope gas in the getter, and the measurement time is short.
Therefore, this method could be applicable to the regular monitoring of hydrogenisotopes stored in a getter material. To apply this method to a ZrNi getter, the magnetic
properties of ZrNi–H systems should be investigated.
In this work, the dependence of the magnetic susceptibility on the stored hydrogenamount in a ZrNi getter at room temperature was investigated. In addition, the behavior

10

ZrNi-H 系の磁気特性

of the magnetic susceptibility relative to the stored hydrogen amount was discussed
based on the molar fractions of the crystallographic phases formed in ZrNi–H systems.

2. Experimental
Zr and Ni grains, the initial materials used for preparing a ZrNi getter, werepurchased from Furuuchi Chemical Co. Ltd. and Kojyundo Kagaku K.K., respectively.
The purities were 99.7% and 99.9% for Zr and Ni, respectively. The grains were
weighed to yield an atomic ratio of 1:1, and they were then compounded into a ZrNi
ingot by using an arc furnace under argon atmosphere. To remove residual oxygen in theargon atmosphere, a titanium ingot was melted in advance. The ZrNi powder was
obtained using the following process: the ZrNi ingot was cut into cubes ~10 10 10mm3, and the cubes were inserted into a quartz cell attached to a vacuum system. The
cell was set at 510−5 Pa, and a heat treatment at a temperature of 873 K was thenperformed as an activation process. Hydrogen gas at a pressure of 105 Pa wasintroduced into the cell at room temperature. Because the hydrogen gas pressure
gradually decreased with hydrogen uptake, hydrogen gas was repetitively added tomaintain the gas pressure. After a week, the ZrNi ingot was completely pulverized fromthe hydrogen uptake. The ZrNi hydride powder was taken out to air, and ~0.25 g of thepowder was transferred to a quartz measurement cell. The measurement cell was
evacuated to 510−5 Pa, followed by the annealing of the cell with the ZrNi powder at
873 K for 3 h to completely desorb hydrogen from the ZrNi hydride.
The magnetic susceptibility and amount of hydrogen stored in the ZrNi powder were
measured by a self-made, pressure-composition isotherm measurement system equippedwith an alternative magnetic susceptibility measurement system. The details of the11

赤丸悟士・岡﨑圭祐・原正憲・波多野雄治・松山政夫

system were already described in a previous paper [13]. The measurement process was
as follows: hydrogen gas at a certain pressure was exposed to the ZrNi powder, and thepressure decreased with hydrogen uptake. Once the pressure became constant, thehydrogen pressure in the gas phase and stored hydrogen amount had reachedequilibrium. The hydrogen content at equilibrium, which corresponds to the storedhydrogen amount in the ZrNi powder, was calculated based on the pressure drop. Next,
the alternating magnetic susceptibility at equilibrium was measured. This process was
repeated until the equilibrium pressure reached ~100 kPa. All measurements were
performed at room temperature. X-ray diffraction (XRD) patterns were measured using
the X’pert system (Panalytical) using Cu-K x-rays. The acceleration voltage was 40
kV, and the range of the diffraction angle was 25°–50°.

3. Results and discussion
Figure 1 shows the dependence of magnetic susceptibility on the hydrogen content

magnetic

susceptibility of ZrNi powder withouthydrogen was 22.010−9 m3/kg, which
agreed with previously reported data
[14].

The

magnetic

susceptibility

gradually increases with increasinghydrogen content and has a maximum
value of 23.110−9 m3/kg at ahydrogen content of ~0.5. For the

12

25

3

The

-9

temperature.

Magnetic susceptibility,  / 10 m /kg

for the ZrNi–H systems at room

20
15
10
5

ZrNiH

x

0
0

0.5
1
1.5
2
2.5
Hydrogen content, x / -3

Figure 1. Magnetic susceptibilities of the ZrNi–H
systems at room temperature. The open andclosed symbols indicate corresponding results
obtained in the first and second cycles ofmeasurements.

ZrNi-H 系の磁気特性

hydrogen content above 0.5, the magnetic susceptibility decreased linearly withincreasing hydrogen content. In this study, the ZrNiH2.7 system with the maximum
hydrogen content has a minimum magnetic susceptibility of 16.610−9 m3/kg. To
confirm the reproducibility of the magnetic susceptibility dependence on the hydrogencontent, the magnetic susceptibility for the ZrNi–H systems was measured as a functionof hydrogen content the second time after the desorption of all the hydrogen absorbed in
the first cycle of the measurement (Fig. 1). Results obtained in the second cycle ofmeasurement were consistent with those from the first cycle, indicating the magnetic
susceptibility values to be quantitatively reproducible.
The peak structure in the magnetic susceptibility is possibly because of changes in the
crystallographic phases upon hydrogen uptake. ZrNi hydride is characterized by two
crystallographic phases, namely monohydride and trihydride phases [15]. The pressurecomposition isotherm reported previously [16] indicated that the ZrNi and monohydride
phases coexist at the hydrogen contents lower than 1.0, and the monohydride andtrihydride phases coexist in the hydrogen content range between 1.0 and 2.7.
To confirm changes in the crystallographic phase of the ZrNi–H systems based onhydrogen content, four samples with different hydrogen contents were prepared, and the
XRD measurements of these samples were performed. Figure 2 shows the XRD patternsof the ZrNiH0.0, ZrNiH0.5, ZrNiH1.0, and ZrNiH2.7 systems (ZrNi hydride with hydrogencontent in the ratio [H]/[ZrNi] = x is denoted as ZrNiHx).
The XRD pattern of the ZrNiH0.0 system clearly shows peaks related to the ZrNi
phase. A minor peak related to the trihydride phase is also observed, and the appearanceof this peak can be explained by the capture of residual hydrogen during pulverizationof the ZrNi ingot.

13

赤丸悟士・岡﨑圭祐・原正憲・波多野雄治・松山政夫

(131)

200

because the relative peak intensity between
these three phases changed in the four samples.
We attempted to estimate the molar fraction for
the three phases by calculating the peak area of
each phase in the XRD patterns. The peakareas of the selected peaks corresponding toeach phase (the selected peaks are indicated by

ZrNi

(002)

ZrNiH3(130)?

ZrNi

(111)

ZrNiH0.0

800

(041)

(130)

1000
(021)

system also changed with hydrogen uptake

1200
Intensity, I / cps

molar fraction of each phase in the ZrNi–H

0
1400

?

600
400
200

?

?

ZrNiH3

XRD measurements also point out that the

ZrNiH

0.5
(assigned by ZrNiH)

(131)

400

?

(002)

600

1.0

(130)?
ZrNi

(111)

1000

ZrNiH3

Intensity, I / cps

1200

800

ZrNiH

ZrNi

400

0
1400

system shows only the trihydride phase. These

ZrNi–H systems change with hydrogen uptake.

600

200

have grown. The XRD pattern of the ZrNiH2.7

results reveal that the crystallographic phases of

800

ZrNiH3(021), (110), ZrNi

addition to this, the trihydride phase appears to

1000(021), (110), ZrNiof the ZrNi and monohydride phases, and in

Intensity, I / cps

1200

ZrNiH3, ZrNi

(111)

0
1400

The ZrNiH1.0 system is also mainly composed

ZrNiH3200

ZrNiH3
ZrNiH3
ZrNi
(002)

400

(041)

600

ZrNi, ZrNiH3

composed of ZrNi and monohydride phases.

2.7

800

ZrNiH3

ZrNiH0.5 system, indicating that this system is

1000

ZrNiH

(021)

clearly appear in the XRD pattern of theIntensity, I / cps

1200

(130)

(111), (040)

1400

ZrNiH3

New peaks related to the monohydride phase

0
25

30
35
40
45
Diffraction angle, 2 / degree

50

Figure 2. XRD patterns of four ZrNi
hydrides with different hydrogen content.
The gray areas indicate the analyzed
peaks of the molar fractions shown in
Figure 3; the gray areas around 34°, 35°,
and 45° correspond to the (040) and (111)
peaks related to the trihydride phase, the(111) peak related to the monohydride
phase, and the (131) peak related to the
ZrNi phase, respectively.

gray areas in Figure 2) can be calculated using peaks reproduced by a Gaussian function.
The molar fraction of the ZrNi, monohydride, and trihydride phases in each sample wasdetermined using the following method. The ZrNiH2.7 system only comprises the14

ZrNi-H 系の磁気特性

trihydride phase, and the sums of the (111) and (040) peak areas related to the trihydride
phase in each sample were normalized assuming that the molar fraction of the trihydride
phase, Ctri, in the ZrNiH2.7 system was 100%. Because the ZrNiH0.0 system comprises
the ZrNi and trihydride phases, the molar fraction of the ZrNi phase in this system wasdetermined by the subtraction of the trihydride phase fraction; the result was 99%. The
molar fractions of the ZrNi phase, CZrNi, in ZrNiH0.5 and ZrNiH1.0 systems were
determined by comparing the corresponding ZrNi (131) peak areas with the ZrNi peakarea for the ZrNiH0.0 system, and they were 41% and 24% for ZrNiH0.5 and ZrNiH1.0,
respectively. Finally, the molar fractions of the monohydride phase, Cmono, in the
ZrNiH0.5 and ZrNiH1.0 systems were determined by subtracting the fractions of the ZrNi
and trihydride phases, and they were 57% and 66% for ZrNiH0.5 and ZrNiH1.0,
respectively. The molar fractions of the ZrNi, monohydride, and trihydride phases for
1amount of hydrogen stored in each sample

0.8

can therefore be calculated based on thephase fraction (Figure 3). These results are

Molar fraction / -each sample are plotted in Figure 3. The

ZrNi
monohydride
trihydride

0.6
0.4

summarized in Table I. The calculated

0.2hydrogen contents in each sample are almost

00

consistent with the actual hydrogen contents,
proving that the phase fractions can be wellestimated from the XRD patterns.

0.5

1
1.5
2
2.5
Hydrogen content, x / -3

Figure 3. The estimated molar fraction ofeach phase using the typical X-ray
diffraction peaks for each phase as indicatedin Figure 2.

The magnetic susceptibility of these four samples can be estimated using the molar
fractions (Figure 3). First, the magnetic susceptibility of each single phase wasdetermined. Because the ZrNiH2.7 system comprises a single trihydride phase, the15

赤丸悟士・岡﨑圭祐・原正憲・波多野雄治・松山政夫

Table I. The calculated hydrogen content and magnetic susceptibility for each ZrNi-H system.
The magnetic susceptibility of the ZrNi phase is estimated to be 22.1 × 10-9 m3/kg and that of themonohydride phase is assumed to be 23.1 × 10−9 m3/kg.

Calculatedhydrogen content
ZrNiH0.0
ZrNiH0.5
ZrNiH1.0
ZrNiH2.7

0.03
0.63
0.93
2.71

Magnetic susceptibility / 10−9 m3kg−1

calMeasured value

22.0
22.4
22.1
16.6

22.0
23.1
22.1
16.6

magnetic susceptibility of the ZrNiH2.7 system, measured as 16.610−9 m3/kg, can be
assigned to the trihydride phase,tri. The ZrNiH0.0 system includes a small amount of
the trihydride phase; therefore, the magnetic susceptibility of the ZrNi phase, ZrNi, isslightly larger than that of the ZrNiH0.0 system and is estimated to be 22.110−9 m3/kg.
Because the magnetic susceptibility of the ZrNi–H systems has a maximum at ahydrogen content of ~0.5 (Figure 1), the magnetic susceptibility of the monohydride
phase is expected to be larger than that of the ZrNi phase. We assume the magnetic
susceptibility of the monohydride phase,mono, to be 23.110−9 m3/kg. The totalmagnetic susceptibility, cal, of each system was calculated as;

calCZrNi ZrNi + Cmono mono + Ctritri.
The cal values for the four ZrNi–H systems are summarized in Table I. The cal values
are almost the same as the experimentally measured values for the magnetic
susceptibility, indicating that the magnetic susceptibilities for the ZrNi–H systems canbe qualitatively understood based on the molar fraction of the ZrNi, monohydride, andtrihydride phases. Notably, the cal of the ZrNiH0.5 system is smaller than the one
measured. This is mainly because of the uncertain molar fraction estimated from the
XRD patterns. More accurate determination of the fractions of these three phases ineach sample will be required to quantitatively determine the magnetic susceptibility.

16

ZrNi-H 系の磁気特性

4. Conclusions
The magnetic susceptibilities for ZrNi–H systems with various hydrogen contents
were measured at room temperature. The magnetic susceptibility reached a maximum ata hydrogen content of ~0.5, and monotonically decreased with an increase in thehydrogen content above 0.5. The XRD measurements of four samples with differenthydrogen content indicated that several phases coexist in the samples. For example, theZrNiH1.0 system is composed of three phases: the ZrNi, monohydride, and trihydride
phase.
The behavior of magnetic susceptibility in ZrNi–H systems could be qualitatively
modeled using the molar fractions of the ZrNi, monohydride, and trihydride phases
observed by X-ray diffraction analysis. The molar fraction of each phase can be
estimated using the area of the diffraction peak assigned to this phase. The magnetic
susceptibility of each phase can be qualitatively determined by knowing theexperimentally measured magnetic susceptibilities and phase fractions for each ZrNi–H
system.
For the ZrNi–H systems, the magnetic susceptibility measurements can be used toestimate the amount of hydrogen stored in the ZrNi getter at higher hydrogen contents(above 0.5). To estimate the amount of hydrogen stored in a ZrNi getter at lower
hydrogen contents, suppressing the growth of the monohydride phase by alloying, i.e.,Zr(Ni1−xCox) is necessary.

Acknowledgement
This study was supported by Grant-in-Aid for Scientific Research on Prior Areas,
Tritium for Fusion (No 476) from MEXT, Japan.

17

赤丸悟士・岡﨑圭祐・原正憲・波多野雄治・松山政夫

References[1] G. G. Libowitz, H. F. Hayes, T. R. P. Gibb, Jr., Journal of Physical Chemistry 62(1958) 76-79.
[2] K. Watanabe, K. Tanaka, M. Matsuyama, K. Hasegawa, Fusion Engineering and
Design 18 (1991) 27-32.
[3] T. Kabutomori, Y. Wakisaka, K. Tsuchiya, H. Kawamura, Journal of Nuclear
Materials 258-263 (1998) 481-487.
[4] K. Tsuchiya, T. Kabutomori, H. Kawamura, Fusion Engineering and Design 58-59(2001) 401-405.
[5] J. L. Hemmerich, Fusion Technology 28 (1995) 1732-1736.
[6] A. Perevezentsev and J. Hemmerich, Fusion Science and Technology 41 (2002)
797-800.
[7] J. E. Klein, M. K. Mallory, and A. Nobile, Jr., Fusion Technology 21 (1992)
401-405.
[8] T. Hayashi, T. Suzuki, M. Yamada, and M. Nishi, Fusion Technology 34 (1998)
510-514.
[9] T. Hayashi, M. Yamada, T. Suzuki, Y. Matsuda, and K. Okuno, Fusion Technology
28 (1995) 1015-1019.
[10] T. Hayashi, T. Suzuki, M. Yamada, and K. Okuno, Fusion Technology 30 (1996)
931-935.
[11] T. Hayashi, T. Suzuki, M. Yamada, and M. Nishi, Fusion Science and Technology
48 (2005) 317-323.
[12] S O’hira, T. Hayashi, H. Nakamura, K. Kobayashi, T. Tadokoro, H. Nakamura, T.
Itoh, T. Yamanishi, Y. Kawamura, Y. Iwai, T. Arita, T. Maruyama, T. Kakuta, S. Konishi,

18

ZrNi-H 系の磁気特性

M. Enoeda, M. Yamada, T. Suzuki, M. Nishi, T. Nagashima, and M. Ohta, Nuclear
Fusion 40 (2000) 519-525.
[13] S. Akamaru, M. Hara, and M. Matsuyama, Review of Scientific Instruments 83(2012) 075102.
[14] E. M. Carvalho and I. R. Harris, Journal of Less Common Metals 106 (1985)
117-128.
[15] D. G. Westlake, Journal of the Less Common metals 75 (1980) 177-185.
[16] R. Kronski and T. Schober, Journal of Alloys and Compounds 205 (1994) 175-178.

19