J. Plasma Fusion Res. SERIES, Vol. 10 (2013)

Solubility of hydrogen isotopes in zirconia ceramics
Kenichi HASHIZUME1), Kosuke OGATA1), Satoshi AKAMARU2), and Yuji HATANO2)
1) Interdisciplinary Graduate School of Science and Engineering, Kyushu University, Hakozaki 6-10-1, Fukuoka 812-8581,Japan.
2) Hydrogen Isotope Research Center, University of Toyama, Gofuku 3190, Toyama 930-8555, Japan.
(Received: 25 May 2012 / Accepted: 5 October 2012)

The hydrogen solubility in zirconia (yttria stabilized zirconia, YSZ) using a tritium imaging plate (IP) technique
has been measured in a temperature region ranging from 673K to 973K. The tritium distribution in the zirconia
specimens was nearly uniform suggesting an equilibrated dissolution. The hydrogen solubility in specimens wererather low (around ppm or below) and showed Arrhenius type temperature dependence, while it seemed to be
independent of Y contents.
Keywords:

Zirconia, YSZ, Tritium Gas Exposure, Imaging Plate Technique, Hydrogen Solubility

the disks exceeded 95 % of theoretical ones for all grades.
The crystal structure of the disk specimens characterizedby X-ray diffraction was tetragonal for TZ-3Y, themixture of tetragonal and cubic for TZ-4Y, and cubic for
TZ- 6Y, 8Y and 10Y as shown in Fig.1. The single- andpoly-crystalline specimens were heated at 873 K for 1 h ina vacuum to remove an initially dissolved hydrogen, andthen exposed to 133 Pa of tritium-deuterium gas mixture(T/(T+D)~ 0.17) at temperatures ranging from 673 to 973
K for 1-5 h. No apparent pressure change was observed
during the tritium gas exposure. After that, the specimens

1. Introduction

Oxide materials are used in fusion reactors as plasma
diagnosis windows, electric insulators and tritium
permeation barriers [1-7]. Tritium dissolution andpermeation in the oxide materials are a significant issue
from a stand point of tritium retention and leakage.
However, compared with metals and alloys, tritium(hydrogen) solubilities in oxides have not been studied
well, because very low hydrogen solubility in oxides madedifficult to detect hydrogen in them [8].
In this study, we have tried to examine thehydrogen solubility in Y2O3 stabilized ZrO2(YSZ) using arather high concentration tritium gas and an imaging plate(IP) technique. The single- and poly-crystalline YSZ
specimens were used in order to clarify the influences ofgrain boundary and Y content on hydrogen solubility.

Intensity (arbitrary uint)

3000

2. Experimental

Mirror polished single crystal plates (1050.5mm3) of cubic zirconia (13%Y2O3-ZrO2(100)) from Dalian
Keri Optoelectronic Technology Co. Ltd. were used as
specimens. Polycrystalline specimens were prepared withconventional sintering process using PSZ powders
manufactured by Toso Co. Ltd (grades: TZ-3Y, TZ-4Y,TZ-6Y, TZ-8Y and TZ-10Y, Y contents of which ranged
from 6 % (TZ-3Y) to 20 % (TZ-10Y)). The each grade
powder was die-pressed into disks and then isostaticallypressed at 200 MPa. The disks were sintered at 1773 K
for 20 h. The size of the disk specimens was about 8mm in diameter and 1 mm in thickness. The densities ofTZ-10Y

2500
2000

TZ-8Y

1500

TZ-6Y

1000

TZ-4Y

500
TZ-3Y

02030

40

50

60

7080

2 theta (degree)

Fig.1 XRD spectra of polycrystalline specimens

author’s e-mail:hashi@nucl.kyushu-u.ac.jp33©2013 by The Japan Society of Plasma
Science and Nuclear Fusion Research

K. Hashizume et al., Solubility of Hydrogen Isotopes in Zirconia Ceramics(tritium activities) seemed to be rather uniform except formuch intense parts which should be surface contaminations,particularly in specimen edges where were not polished.
Since the high PSL intensity area was limited around theedges, these PSD data were omitted. The errors without
the contaminations were estimated to be r30 % for allspecimens. The PSL images of the cross sections suggested
an equilibrated dissolution of tritium.
Figure 3 shows the tritium activities (hydrogensurface densities) on the specimens exposed to the tritiumgas. The amount of tritium uptaken on the specimen
surface increased with increasing temperature up to 2105
Bq/cm2 (equivalently ~1015 H/cm2) and almost saturated at
873 K. At 973 K the tritium density on the single
crystalline surface decreased, where tritium desorption
should be more dominated than its adsorption. In any
case, no clear difference appeared among the specimens.
Figure 4 shows the tritium activities in the singleand poly-crystalline specimens which increase with theexposure temperature, which appear to be very similar tothat of its surface density. Figure 5 also shows the tritium
activities in poly-crystalline specimens against an oxygen
deficiency x which was simply calculated from Y contentsof YSZ. No clear difference in tritium activities appeared
for the single- and poly-crystalline specimens. Several
studies previously suggested that the hydrogen solubility ingrain boundary was high, compared with the oxide grain
inside. Unfortunately, the spatial resolution of IP technique
is not high enough to detect tritium only in the grainboundary. The influence of grain boundary would be
examined in the future study. In any case, it should besafely concluded that no clear influence of grain boundaryand O deficiency (Y content) in the present experimentalcondition.

were quenched down to fix tritium distribution. After thespecimen surfaces were exposed to IP (TR2025, GE HealthCare Co.) for 15 min in order to measure surface tritium
densities, the specimens were cut in halves with a diamondsaw, and the cross sections of the specimens were exposed
to IP for 15 h. The details of this procedure were describedin elsewhere [7]. Photo-stimulated luminescence (PSL)
intensities were obtained from IP Reader (FLS7000,Fujifilm). The PLS values were converted to tritium
activities by calibration with a tritium standard sample(ART 123A, American Radiolabeled Chemicals, Inc.).
Hydrogen surface density and solubility were evaluatedfrom the tritium activity and isotope abundance ratio.
3. Results and Discussion
Figure 2 shows the examples of the PSL images ofspecimen surface and cross section. The PSL intensities
High T

Low T
5mmFig. 2 PSL images of surface and cross section.
Single crystal plate (left) and polycrystalline disk(right) exposed to D-T gas at 873 K for 1 h.
53h exposure151h exposure

Tritium activity (MBq/cm3)

H surface density (H/cm2)

105h exposure

5x10

T surface activity (Bq/cm2)

T/(T+D)~0.17

10T /͠

51x10

5x104
144

<T1J$SEO

1.0

1.1

1.2

1.3

2x10
1.4

10210

110

0

1000/T (1/K)

40013mol%Y O YSZ(single crystal)
233mol%Y O YSZ(polycrystal)
236mol%Y O YSZ(polycrystal)
2310mol%Y O YSZ(polycrystal)

101.5

500

600

2-1

1.0

1.1

1.2

3

1.3

1.4

1.5

1.6

1000/T (1/K)

Fig. 3 Hydrogen isotope surface density (Tsurface activity) on single crystal specimen.

Fig. 4 Tritium activities in single- and polycrystalline specimens (5 h exposure to D-T gas).

34

K. Hashizume et al., Solubility of Hydrogen Isotopes in Zirconia Ceramics

crystal structures of zirconia (monoclinic, tetragonal andcubic) and hydrogen containing gas species (H2 or H2O).
The present study focused on the solubility ofhydrogen in zirconia ceramics. The dependence ofhydrogen amounts uptaken on surface and bulk in theoxides becomes clear using the IP technique. This also
indicates that the IP technique was a useful tool to study
the kinetics of hydrogen dissolution and hydrogensolubility in various oxides.

The color of the specimens after the tritium gas
exposure slightly changed to be brownish. Not only thecharacteristics of surface but that of bulk might beinfluenced by the reductive reaction. However, the effect of
this reaction is not discussed here because the adsorption
reaction of hydrogen is too complicated to make aquantitative analysis.

Tritium activity (MBq/cm3㪀102873K773K673K

101

100-1

100

0.02

0.04

0.06

0.08

0.1

4.

Summary
Using an imaging plate (IP) technique and highconcentration tritium gas (T/(T+D)~0.17), tritium
solubility in zirconia ceramics (YSZ) was measured in atemperature region ranging from 673 K to 973 K. The
surface activity of tritium on the specimens increased withincreasing temperature and almost saturated at 873 K,
which reached 2105 Bq/cm2 (equivalently ~1015 H/cm2).
The hydrogen solubility in the oxides also increased
with increasing temperature. No clear difference in thesolubility appeared between single crystal andpolycrystalline specimens and among the specimens withvarious Y contents.

0.12x in Zr(Y)O2-x

H mol / 1 mol ZrO2 at 133Pa

Fig. 5 Tritium activities vs O deficiency x inpoly-crystalline specimens.
10-410-510-610-75.

Acknowledgements
The present study was partly supported by theusage/research program of the Hydrogen Isotope ResearchCenter, University of Toyama (HRC2010-04) and by theSohoko Research Program of National Institute for Fusion
Science (NIFS11KUR014) .

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present study (c-ZrO2 in H2)
Yamanaka (m-ZrO 2 in H2O)
Wagner (c-ZrO2 in H2O)

10-8

0.4

Park (t-ZrO2 in H2)

0.6

0.8

1

1.2

1000/T (1/K)

1.4

1.6

Fig. 6 Comparison of hydrogen solubility in zirconia(5h-exposed single-crystal for the present data).
The present data on hydrogen solubility are comparedwith literature data [9-12] in Fig. 6. The all literature data
have been converted to those at a pressure of 133 Pa ofhydrogen containing gases (H2 or H2O), based on relationss v p1H/ 22 and s v p1H/ 22O . As shown in Fig. 6, thevalues of solubility and its temperature dependence arerather scattered. Reasons of the scattering are not clear atpresent stage, but might be attributed to differences inexperimental conditions such as dissolution temperatures,35