富山大学水素同位体科学研究センター研究報告29 ･ 30 : 83‑88, 2010.

Deuterium Permeation Mechanism in Erbium Oxide Coatings
for Tritium Permeation Barrier

T. Chikada I, A. Suzuki I, T･ Tanaka 2, T･ Kobayashi 3, H･ Maier4, T･ Terai I, and TI Muroga 2
J school of Engineering, UniversityofTob)0, Too)0 113‑8656, Japan
2 National InstitutejTor Fusion Science, Glfu 509‑5292, LIapan

3 Institute of Physical and Chemical Research (RIKEN), Saitama 351‑01 98, LIapan
4 Max‑Planck‑Instilutfiir Plasmaphysik, D‑85 748 Garching, Germany

Development of tritium permeation barrier is considered one of prlnClpal

investlgations to build up a fuel cycle in afusion power plant･ For the practical application
as tritium permeation barrier, fabrication of erbium oxide coatings by metal‑Organic
decomposition method has been carried out on reduced activation ferritic/martensitic steelsI

The coated samples showed various surface states after the heat‑treatment process under

different conditions･ An oxide layer was generated between the erbium oxide coatlng andthe substrate when heat‑treated in high purlty argOn･ It is indicated that the oxide layer hascaused defects in the coating and resultedinthe degradation of the samples during
deuterium pemeation measurements･ The sample heat‑treated in high purity hydrogen withmoisture shows the thinner oxide layer and stable permeation nuxes during themeasurements･ A coatlng Of O･3 pm in thickness indicates a permeation reduction factor of
700‑loo° at 773‑973 K, which is a comparable level to the coating deposited by physicalvapor deposition technique perfb‑ed in the previous study･Keywords: tritium, hydrogen, pemeation ba汀ier, ceramic coating, erbium oxide

Ⅰ. Introductiom[ト7].

Recently erbium oxide (erbia, Er203)
Over the past few decades, investigations
coatlngS have been investigated as insulating
on a control oftritium have been pursued fわr thecoatings fわr self‑cooled lithium blankets [8,9]･ It

realization of prototype reactors (DEMO) andcommercial

凡ISionpower

plants･was clarified that the Er203 COatlngS SuppressedThe

deuterium permeation to a level similar todevelopment of suppresslng tritium permeation

AI‑based coatlngS Which have been investigatedthrough wall of ducts in a blanket system is one
chief一y in history [10, 11]. However, theof the essential tasks since structure materials

such as reduced activation ferritic/martensitic(RAFM) steels have high pemeability ofhydrogen isotopes in the operational temperature
range. Fabrication of thin ceramic coatlngS is apromlSlng SOlution for reducing tritium loss, andthereby tritium permeation barrier (TPB)

previous studies on the Er203 COatlng have
employed a physical vapor deposition (PVD)
which

is

not

suitablefわraplant‑scale

fabrication.

h our previous work [12], themetal‑Organic decomposition (MOD) method,which is capable to fabricate oxide coatlngS On

coatlngS have been studied fわr many years

tubes or other complex shape substrates by83

T･ Chikada, AI Suzuki, T･ Tanaka, T･ Kobayashi, H･ Maier, T. Terai and T. Muroga
Coating with the erbium metal solvent, wassolvent･ In this process, the solvent tums to a gel.

demonstrated to form the Er203 coating for the

Finally, to cIYStallize the Er203 COatlng, thefirst time on a SS3 16 plate substrate. However,sample is heat‑treated at 873‑973 K for 10‑30

Compositions and microstructures of substrate

min in argon (purity of 99.9999%, 02 < 0.05

materials are expected to affect coatingppm, H20 < 0･5 ppm) Or hydrogen (purity or

properties during the fabrication process.

99･9999%, 02 < 0.02 ppm, H20 < 0.5 ppm) with

Moreover, the microstructure analysts Or theabout 0.6% moisture by infrared image fumace.

coatlng lS needed to understand a fbmation

The now rate is 10120 ml/min and the rate ofmechanism orthe Er203 aS Well as a pemeation

temperature

behavior of hydrogen isotopes. Consequently, ln

Kノmin. The moisture is added in the hydrogen

thisby passlng through ice chilled water in order topaper,

the

Er203

COatlngS

have

been

increaseanddecrease

is

20‑30

fabricated on RAFM steels by MOD method,

control the moisture concentration in theand then analyses and deuterium pemeation

atmosphere by known saturated vapor pressures.

measurements of the coating have been

II. B. Analysis
perf♭med to evaluate the microstructure of thecoating and its properties as a TPB.

As for the analysis of the coatlng, the surfaceof the coating is examined uslng a laser

ⅠⅠ. Experimental

microscope･ The crystal structure of the coating

II･ A. Sample Preparation

is analyzed using X‑ray diffraction (XRD). The

The MOD method is qulte Similar to thecross‑section of the coating lS examined using
field emission scannlng electron microscopy

sol‑gel method in coating procedure: l) Coating
a liquid precursor on a substrate by spln‑COatlng(FEISEM)･ The composition‑reflected images
are achieved with this equlpment by detecting

or dip‑coating, 2) drying for solidification, andthen 3) heat‑treating to cIYStallize the coating as

backscattering electrons. The chemical analysts
uslng energy dispersive X‑ray spectroscopy

an erbium oxide･ In the present work, thespln‑COatlng technique was employed tofabricate uniform coatlngS On Plate substrates.

The RAFM steels F82H (8Cr‑2W, Heat No.

9753 42W‑4) and JLF‑1 (9Cr‑2W) are used as
substrates･ Square‑shaped plates of 25 mm on a

(EDX) is also available.
The deuterium pemeation equlpment andthe experimental procedure are described indetailin[11]. To brieny explain the scheme, twoparts of the apparatus divided by the sample are

separately evacuated up to about 10‑6 pa, andside and O･5 mm in thickness are mirror polished･Firstly, the erbium organic solvent (Kojundothen deuterium (purity of 99.995%) of 104‑105
Pa is introduced into one side (called upstream)

Chemical Laboratory Co., Ltd. Er‑03⑧) whichcontains 2･7‑3･3 wt% erbium carboxylic acid iswith a leak valve. The sample is mounted withthe coatlng facing the upstream f♭r avoiding

put on the substrate and homogenized by asuぬce oxidation on uncoated side of the sample

spln‑COater･ The spln‑COater Was Operated at theby contamination molecules. A nux ofdeuterium

rate of500叩m fわr 10 s and then 2000叩m fわr

20 s to remove supernuous droplets and spreadthe solvent to the substrate･ This drop andpemeation through the sample to another part(called downstream) is measured by quadrupole

mass spectrometer (qMS). The downstream

rotating process is repeated f♭r 5 times to obtaina nat surface. Secondly, the sample is put on a

hot plate set at 393 K for lOmin to dry thechamber is continuously pumped during theexperiments and the qMS works within therange of lO 10‑10 5 mol/m2s for D2 in this84

Deuterium Permeation Mechanism in Erbium Oxide Coatings for Tritium Permeation Barrier
method with secondalY electron multiplier.

(a)(Fe,C｢203/ lWhen the pemeation f一ux at the downstream hasreached steady state, the deuterium is added up
to the next pressure. The temperature or the(.m=)A)!sua)ul(b) lsample during measurements is set at 773‑973 K
to increase the permeation rate to a detectable(C) llevel.

When diffusion limits gas permeation(d)/Er203 l

through a sample rather than surface reactions,the permeation nux istypically represented byfollowing equation l13]:

20

30

J‑PpO5/d

40

50

60

D冊action angle 2β (degree)where Jis the permeation nux (mol m 2 S‑1), p is

Fig. L XRD spectra of the samples heat‑treatednamed permeability (mol m一㌧I pa 05) which isin high purity argon under various conditions:intrinsic parameter fTor the sample, p is the(a) heat‑treated at 873 K f♭r 60 min, (b) at 973 K

driving pressure (Pa), and d is the thickness offor 30 min, (C) at 973 K for 20 min, and (d) at

the sample (m).

973 K fわr 10 min. The rates or temperature
increase and decrease was 20 K min‑1 fわr sample

III. Results and DisctISSion(a) and (b), 30 K min . for sample (C) and (d),III. A. Heat‑treatment in Ar

respectively.

The su血ce obseⅣation was perf♭med f♭rfour samples heat‑treated under different

Therefわre, it is proved that the rough surface has

been resulted斤om the (Fe, Cr)203 phase.

conditions. The sample (a), which has been
Figure 2 illustrates the cross‑section image
heat‑treated at 873 K f♭r 60 min with the rate of

temperature increase and decrease of 20 K min‑1,
shows a rough surface of the coatlng On F82H

substrate. When heat‑treated at 973 K fTor 30 minof the sample (a) by FE‑SEM. tt is clearly seenthat the coating has famed a fわur‑layer structure

which has consisted in sequence of the F82H
substrate, the Fe‑Cト0 layer, the dense Er203,

as the sample (b), the coating also shows a roughand the uncrystallized reglOn. The substantial
suぬce and some holes･ Meanwhile the sample

thickness of the Er203 COatlng is found to be(C) and (d) show relatively smooth surfaces
0.2‑0.3

LLm. Besides, gaps are seen in thewhen treated at 973 K fわr 10‑20 min with therate of temperature increase and decrease of 30

Fe‑Cr‑0 layer. In the refTerence l14], it issuggested that the oxide layer oHLトl substrate

良 min 1.

XRD patterns of the coatlngS are indicatedin Fig･ L The peak at 29.4o deriving from Er203

has caused peeling of the Er203

COating

deposited at 973 K by a PVD method. ln thesame way, lt is expected that the gaps in the(222) are seen in every sample. However, thepeak is broad and the diffraction intenslty lS
qulte low, which means the coatlngS have notoxide layer have caused the rough surface of thecoatlng. Deuterium pemeabilities of theuncoated F82H substrate, the sample (a), (b),been cIYStallized su用ciently. In addition, theand (C) as afunction of the inverse of the test
peaks representing (Fe, Cr)203 are Seen in thetemperature are shown in Fig. 3. As fわr the

sample (a) and (b) at around 24, 33, and 35.50,

sample (a) and (b), values or pemeation
while they are weak in the sample (C) and (d).

reduction factor (PRF) which is obtained by85

T･ Chikada, A･ Suzuki, T･ Tanaka, T･ Kobayashi, HI Maier, T･ Terai and T. Muroga
shown in Fig. 3 has indicated similar outcome tothe sample (C). In our previous work 【12], theoptlmized heat treatment condition fわr thecoating on the 316 stainless steel substrate wasat 973 K f♭r 60 min with the rate ortemperature
increase and decrease or20 Kノmin in high purlty
argon･ By comparlng the results, it is fわund that

the RAFM substrates are liable to be oxidized
more strongly than the 3 16 stainless steel during

Fig･ 2･ A cross‑section FE‑SEM image or thethe heat treatment･ Therefore, a quicker andsample (a).

more moderate heat‑treatment condition isnecessary tofulfiH crystallization of the Er203
dividing the permeability or the bare sample byWith avoiding strong oxidation of the RAFM

that of the coated one are less than 5 at 773 andsubstrates.

873 KI The result suggests that the rough surfaceof the coatlng has caused generation of holes orIII. B. Heat‑treatment in H2with H20

cracks reaching the substrate, and thus
deuterium has passed through the defTects asshortcut･ On the other hand, the sample (C) has

To reduce the oxide layer of the substrate,
the heat treatment in high purity hydrogen with

about O･6% moisture has been performed･ The
shown

a

PRF

value

of

200

in

the

first

measurement at 873 K･ However, the pemeation
suppression efficiency has degraded to a PRF of
30 as the measurements have run･ It is expectedthat the crystallized coating has damaged during
temperature change because of theinhomogeneous oxide layer･ In addition, thesamples were heat‑treated at 973 K fわr 10 min

with the rate of temperature increase anddecrease of 30 Kminll. The sample (f) was
coated 3 times uslng the same process. Bothcoatings are uniform and nomicron‑size holes
and cracks are seen from the surface observation

using SEM.
pemeability of the sample (d) which is not

XRD spectra of the samples are illustrated
in Fig. 4. The peaks of (Fe, Cr)203 are not

T(K)
873

(9㌔d＼SJujJ10LU)Al!I qea∈)￠d

[

773

鳴

673

573

椿椿辻ﾒﾒﾒﾒﾒﾒﾒﾒﾒ剪%clearly seen in the sample (e), though the peaksRof Er203 is weak･ On the other hand, the sharp

i r‑Ll r一.l妻u o ､LJ ･O
こ=iil:上し‥peak at 29.40 deriving from Er203 (222) is seen剪‑in the sample (i)･ In addition, other peaks of

Er203 (400) (440), and (622) are also seen at 34,‑‑

一一一一一＼‑.ト‑‑ 劒(
‑

ｸ

ﾂ 把
蔘

76 ﾗ

49, and 580, respectively. It is indicated that the

6 ﾖbｒ 剪6 ﾗ

剿VｶR " ﾆR

heat treatment in high purityhydrogenwith
moisture is an effective atmosphere to avoid
formation of the (Fe, Cr)203 layer and crystamze

一号
1.0

1.2

1.4

1.6

1.8

1000汀(1/K)

the Er203 COatlng･ Moreover, thicker coatings
can be produced by repeatlng the coating

Fig. 3. Arrhenius plots of deuterium

procedure.

The cross‑section image of the sample (i) is

pe‑eability of the bare F82H and the coatedsamples heat‑treated in high purityargon.

86

shown in Fig. 5. ln this case, the thickness ortheDeuterium Permeation Mechanism in Erbium Oxide Coatings for Tritium Permeation Barrier

T (K)
(f)

('m2)A)!SualuL

973

873

773

I

鳴

l

673
｣

573
l

(㌔djSfulJ)O∈)書qpauJ ￠d
0000

1

(e) I
i≧

ラ
■∇0把

6 ﾒ 6 & H pーe( pletf 乏

定

∇
20

30

40

50

j io

60

20 (degree)iFig. 4. XRD pattems of the samples heat‑treated

1.0

1

2

1.4

1,6

1.8

1000汀(1/K)

at 973 K in high purity hydrogen with moisture.
The sample (e) and (f) were coated once and 3

Fig. 6. Arrhenius plots of deuterium

times, respectively.

pemeability or the bare F82H and the samples

heat‑treated in hydrogen with 0.6% moisture･

estimated. That means the thickness of thecoating can be increased by repeatlng thecoatlng procedure. Forthermore, the O･3

LLm‑thick coatlng aS Shown a comparable

reduction efrlCiency to the 1 llm‑thick one
fabricated by phusical vapor deposition･
Therefわre, the MOD coatlng lS promising fわr theFig.5. A cross‑section FE‑SEM image of thesample (りshown in Fig. 4. The layer structure

practical application as TPB･

IV. Summaryof the coatlng is derived from the repeatedCOatlng prOCeSSeS･

The Er203 COatlng has been fabricated on

the RAFM steels by the MOD method. The
Fe‑Cト0 layer is estimated approximately 50 nm,

samples heat‑treated in high purlty argon

which is much thinner than that in Fig. 2. It is

indicate the rough surface generated by theproved that the thick Fe‑Cr‑0 layer has caused

Fe‑Cr‑0 layer and degradation during deuterium

the rough surface of the coatlng and can bepermeation measurements at 773‑873 K･ The

avoided by the heat treatment in high purlty

unifわrm surfacehydrogen with moisture.

deuterium pemeation has achieved by thewith high sufficiency of

Figure 6 shows deuterium permeabilities ofheat‑treatment in high purity hydrogen withthe samples at 773‑973 K･ The measurements

moisture. The coating OfO.3 LLm in thickness has

have been repeated more than twice at eachshown reduction factors of 500‑700

temperature to confTlrm reprOducibility of the

reproducibility atdata with the variation of less than l0%. Bothcomparable efficiency to 1 LLm‑thick coatlngSsamples have shown stable pe‑eabilities andfabricated by physical vapor deposition.

no degradation have been seen･ From theAdditionally, it is expected that higher PRFs canviewpolnt Of PRf, values of 100 at the sample

be obtained by repeatlng the coatlng process On(e) and 500‑700 at the sample (f) were

the request of blanket systems･

773‑973and data

K, which is87

T. Chikada, A. Suzuki, T. Tanaka, T. Kobayashi, H. Maier, T. Terai and T. Muroga

Acknowledgements[8] B. A. Pint, P.F. Tortorelli, A. Jankowski, ∫.

Hayes,
This

work

was

supported

in

paれ

T.

Muroga,A.

Suzuki,0.Ⅰ.

by

KAKENHI (19055001), Ministry of Education,
Culture, Sports, Science and Technology, Japan

Yeliseyeva, V.M. Chemov, "Recent
progress in the development of electricallyinsulating coatlngS fわr a liquid lithium

and Research Fellowships of the Japan Society
for the Promotion of Science

blanket," J. Nucl. Mater., 3291333,

for Young

1 19‑124 (2004).
Scientists.
[9] T. Muroga, ∫.M. Chen, V.M. Chemov, K.

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