富山大学研究推進機構水素同位体科学研究センター研究報告 37：11－18，2017.

論文

水素により制御可能な開閉器の実験的検証
赤丸 悟士，村井 美佳子，原 正憲

富山大学研究推進機構水素同位体科学研究センター〒930-8555 富山市五福 3190

Experimental study of a hydrogen-controllable switch of electric circuits
Satoshi Akamaru, Mikako Murai, Masanori Hara
Hydrogen Isotope Research Center, Organization for Promotion of Research, University ofToyama
Gofuku 3190, Toyama 930-8555, Japan(Received January 12, 2018; accepted June 22, 2018)
Abstract
In this paper, the hydrogen-controllable switch of electric circuits was proposed. The concept of the switch
is based upon hydrogen gas pressure controlling the switch condition, either opened or closed, without any
electrical supports. The switch has been designed so that it is closed in an atmosphere that does sot containhydrogen. To study its switching behaviors, the switch was placed in the argon gas flow. When flowing gas
was changed to a gas mixture containing 9% H2 – 91%Ar, the switch was open after 201 s. However, whenthe mixture was replaced by argon gas, the switch was closed again. In addition, we determined that thethreshold for hydrogen concentration while turning the switch on could be adjusted by an arranging amagnet in the switch.

1. Introduction
Safe handling of hydrogen (H2) gas is a critical issue in the supply network of large11

赤丸悟士・村井美佳子・原正憲

amounts of H2 gas. The H2 gas is flammable in air at concentration levels of 4-75%, which isa wider range compared to methane and gasoline [1]. Therefore H2 concentration levels must
be monitored at all times in order to maintain safety levels while handling the H2 gas. Ingeneral, if the H2 concentration in the atmosphere reaches above 1%, all ignition sourcesmust be removed as soon as possible. One of the main ignition sources are electric circuits.
As the ignition energy for a mixture of air and hydrogen is relatively low, a small electric
spark can ignite the mixture [1]. Thus all electrical equipment in the work space must be
turned off when a H2 leak is detected.
Almost all safety devices operating in the hydrogen-containing air atmosphere require
electrical supply, and the safety device can also ignite the mixture. Therefore safety devices
without an electrical supply are favorable to maintain safety while H2 handling. A uniqueswitching device, namely, a magnetic switch controlled by hydrogen gas, is described in thispaper. A typical magnetic switch is operated by the change in the external magnetic field. The
magnetic field is generated from either an electrical current or a permanent magnet. The
switch described in this paper can be controlled by not magnetic field but by H2 gas within acertain pressure. The switch does not require electrical supply to control it; only H2 gas cancontrol the switch. Consequently, this switch provides a safe mechanism for using inhydrogenous environment.
In this paper, we explain the basic mechanisms of the hydrogen-controllable switch ofelectric circuits, how the test switch was constructed, and the methods in which thecharacteristics of the switch relative to H2 gas were verified.

2. Experimental
2.1. Principle of operation of the hydrogen-controllable switch12水素により制御可能な開閉器の実験的検証

Fig. 1. Basic mechanisms of the hydrogen-controllable switch.
The basic mechanisms of the hydrogen-controllable switch are depicted in Fig. 1. The plate in
the switch contains ferromagnetic hydrogen absorbing alloy PdCo. The plate is movable, andthe permanent magnet can control both opening and closing of the electrical circuit. Initially,
without the permanent magnet the plate is set to open the switch (Fig. 1a). The permanent
magnet is placed near the PdCo-containing plate, and the plate contacts a terminal, turning
thus the switch on (Fig. 1b).
When hydrogen appears in the surrounding atmosphere, PdCo absorbs hydrogen and themagnetization of PdCo is reduced [2]. As the results, attractive force between the magnet andthe PdCo-containing plate is reduced, and the plate leaves from the terminal turning thus theswitch off (Fig. 1c).
If hydrogen gas leaves the surrounding atmosphere, PdCo desorbs hydrogen, and thePdCo-containing plate contacts the terminal again. This switch can be used repeatedly, andthus works as the hydrogen-controllable switch.

2.2. Experimental test of operation of the hydrogen-controllable switch
The schematic view of the experimental system is illustrated in Fig. 2. The switch wasassembled from two Cu rods, a 0.01 mm thick Cu plate with the Pd0.9Co0.1 alloy powder
deposited on the back side, an NdFeB magnet, and a glass cell. The opposite sections of each13

赤丸悟士・村井美佳子・原正憲

copper rod were machined in such away that they were flat surface facing

outletNdFeB Magnet

inleteach other across a small gap. The Cu
plate (with Pd0.9Co0.1 alloy on the backCu rodside) was put on one flat surface andCu rod

Glass Cell

Cu plate

PdCo powder

was bound with Cu wire. A terminal ofthe plate was bent into a triangular

Mass flow controller
H2Ar

outletshape, perpendicular to the upper Curod. The apparatus described above
was covered by the glass cell, and theNdFeB magnet was placed outside of100 ΩSource meterFig. 2. Schematic view of the basic components
to show switching behaviors.

the cell. The position of the NdFeB magnet was adjusted so that the Cu plate touched theupper Cu rod.
The switch was connected to the low voltage SourceMeter instrument, Keithley 2401. A
100 Ω resistor was set parallel to the switch. The direct electrical current of 100 mA,
supported by the SourceMeter instruments, flowed constantly through an electrical circuit,and the changes in the voltage were continuously monitored as measurements wereperformed. H2 and Ar gases were supplied to each mass flow controller, making a mixture
with a certain H2 concentration. The mixture flowed into the cell with flow rate of 100
ml/min.

3. Results and discussion
Figure 3 illustrates the typical experimental result for the hydrogen-controllable switch.
The distance between the cell and the magnet dsw-mag was 0.7 cm. The voltage Eall showedalmost 0 V under Ar gas flow at time t less than 0 second, indicating that the switch was14水素により制御可能な開閉器の実験的検証

voltage, Eall / V

dsw-mag : 0.7 cm
ArH concentration 9% in Ar
21000ONOFFON400

800

1200

1600time, t / s

2000

2400

28003200

Fig. 3. Typical switching behavior of the hydrogen-controllable switch. H2 was added toAr at t = 0 s, and H2 addition to Ar was stopped at 1800 seconds. The H2 concentration inthe H2-Ar mixture and the distance between the cell and the magnet were fixed at 9% and
0.7 cm, correspondingly.
closed, namely, the Cu plate maintained contact with the upper Cu rod. The gas that flowed
into the cell was changed at t = 0 s to the mixture of H2 and Ar with H2 concentration of 9%.
At t = 206 s, the Eall quickly changed to 10 V, indicating that the switch was turned off,
namely, the Cu plate was no longer in contact with the upper Cu rod. The switch was heldopen during the H2-Ar mixture flow. The flowing gas in the cell was changed to Ar at t =1800 s. After 904 seconds from thedsw-mag : 0.7 cm

Voltage, Eall / V10H concentration 9%0210
H concentration 2%20

H concentration 1%20400800
1200time, t / sof

theflowinggas(corresponding to t = 2704 s), the Eall
became almost 0 V again. Changing theEall to 0 V implied that the switch wasturned on, namely, the Cu plate made100change

1600

Fig. 4. Switching behavior for various H2concentration in the H2-Ar gas mixture. The
distance between the cell and the magnet was0.7 cm.

contact with the upper Cu rod. Theseresults

indicatethattheswitch,

constructed in this study, is controlled byusing a mixture of 9% H2 in Ar.
Figure 4 illustrates the switching15

赤丸悟士・村井美佳子・原正憲

behavior with different H2 concentrations in the H2-Ar gas mixture. The experimentalconditions, except H2 concentration, were the same as in Fig. 3. With H2 concentrations of
9% and 2%, the switch was turned off at t = 206 s and 606 s, respectively. However, theswitch remained closed at the H2 concentration of 1% in the H2-Ar gas mixture. It appearedthat there was the threshold of H2 concentration to turn the switch off. In addition, the time toturn the switch off at the H2 concentration of 2% was three times longer than at the H2concentration of 9%. These facts can be explained by the following reasons. The switch wasturned off when the attractive force between the magnet and the PdCo alloy was smaller than
the gravity and/or the elastic force of the Cu plate. The attractive force is generally governedby a magnetization of the PdCo alloy and the distance between the switch and the magnet.
Note that the magnetization of PdCo becomes smaller as higher H2 partial pressure [2], andthe magnetization is proportional to the square root of H2 partial pressure [3]. In thisexperimental condition, the magnetization of the PdCo alloy under the H2 concentration of
1% was larger than threshold magnetization Mth. This is the value required to keep
equilibrium between the magnetization-induced attractive force on the one hand, and teh
gravity and the elastic force of the Cu plate on the other hand. The rate of hydrogen
absorption is higher at higher H2

dsw-mag : 0.9 cm

partial pressure, so the magnetization

under higher H2 partial pressure.
Figure 5 shows the switching
behaviorwithaslightly

longerdistance between the cell and themagnet, dsw-mag, which was set to 0.9cm. The switch was turned off with the16voltage, Eall / Vof the PdCo alloy reaches Mth faster10H concentration 9%2010

H concentration 1%
200400800
1200time, t / s

1600Fig. 5. Switching behavior after changing thedistance between the cell and the magnet to0.9 cm.

水素により制御可能な開閉器の実験的検証

H2 concentration of 9% at t = 101 s. This time was shorter than for dsw-mag = 0.7 cm. At the H2concentration of 1%, the switch was turned off at t = 322 s. These results demonstratequalitatively that the attractive force between the magnet and the PdCo alloy becomes weakerwith longer distance dsw-mag. Consequently, it indicated that the threshold of the H2concentration to turn the switch off could be adjusted by the distance between the magnet andthe PdCo alloy.
A significant problem emerged from this experiment is an instability of the electriccontact between the Cu plate and the upper Cu rod. We observed that Eall did not change toalmost 0 V whereas the Cu plate seemed to be attached to the upper plate. There are two
reasons for this instability. The first reason is a weakness of the attractive force without H2gas, and the other reason was the surface condition at the contact point. The former reason
can be solved by the development of a high performance ferromagnetic hydrogen absorbing
alloy, which is favorable in demonstrating a large change of magnetization by hydrogenabsorption. The solution for the latter reason is coating the plate with less oxidation materials
such as Pt, it is possible to improve the contact. In future we will try to improve the switch.

4. Conclusions
The hydrogen-controllable switch was demonstrated through an experiment. The switch
was similar to a conventional reed switch but was characterized using ferromagnetichydrogen absorbing alloy PdCo with one side of contact. The switch was generally closed byusing the permanent magnet taking advantage of the attractive force between the magnet andthe PdCo alloy. The switch spontaneously opened in the presence of hydrogen gas due to adecrease in magnetization of the PdCo alloy occurring in the presence of hydrogen gas. Whilethe basic behaviors mentioned above have been confirmed, some improvements are necessary
in order to obtain a stable hydrogen-controllable switch.

17赤丸悟士・村井美佳子・原正憲

Acknowledgement
This study was supported by the future technology research fund, University of Toyama.

References[1] H. Fayaz, R. Saidur, N. Razali, F. S. Anuar, A. R. Saleman, M. R. Islam, Renewable andSustainable Energy Reviews 16 (2012) 5511-5528.
[2] S. Akamaru, T. Matsumoto, M. Hara, K. Nishimura, N. Nunomura, M. Matsuyama,
Journal of Alloys and Compounds 580 (2013) S102-S104.
[3] N. Nunomura, M. Hara, S. Akamaru, Proceedings in PRICM8: Pacific Rim International
Congress on Advanced Materials and Processing (2013) 1837-1841.

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