富山大学水素同位体科学研究センター研究報告29 ･ 30 : 55‑60, 2010.

Application ofPalladium Coating on Group 5 Metals for
Vacuum Permeator‑Possible Problems and Solutions‑

Teo Nozaki 1 ), Eriko Yamakawa2), Asuka Hachikawa2), Kazuyoshi Ichinose2), Masanori Haral )and Yuji Hatanol)

1) Hydrogen Isotope Research Center, UniversiO) ofToyama, Toyama 93018555, Japan
2) Faculo) of Human development, UniversiO, ofToyama, Toyama 930‑8555, Japan

Permeation of hydrogen through Pd‑Ta‑Pd composite membrane was measured at 500

and 600 0C to examine the feasibilityof the concept to use this type of membrane aspermeationwindow to recover tritium from liquid Pb‑Li alloy･ At 500 oC, the permeation
rate gradually decreased with increasmg operation time due to surface contamination bycarbon･ These obseⅣations indicated that partial pressures or residual hydrocarbons in

vacuum permeator have to be strictly controlled to avoid carbon deposition･ Nevertheless,permeability could be restored by removal or carbon through reaction with 02 gaS･
At 600 oC, however, permanent degradation took place due to development of open

porosityinPd layer and interdiffusion between Pd and Ta. Preparation of HfN intermediate
layer between Pd and Ta hindered the porosity development and interdiffusion.

Keywords: Tritium Recovery, Permeation, Tantalum, Palladium, Fusion Blanket

Ⅰ. INTRODUCTION

Tritium recovery by vacuum permeation is

adlayer through surface segregation付om thebulk･ Preparation of Pd coatlng lS COmmOn Way
to solve this type of problems.

proposedindual coolant Pb‑Li breeder blanket
concept l1]･ Group 5 metals (V, Nb and Ta) are

One or the biggest problems fわr such
Pd‑group

potential candidates of tube material because ofhigh permeability or hydrogen isotopes andsufficient compatibility with liquid Pb‑Li alloy.

5

metal composite membrane isstability ofPd layers at elevated temperatures･ In
dual coolant Pb‑Li breeder blanket cpncept, theexpected operation temperature of vacuum

It, however, is known that the permeability ofhydrogen isotopes is sensitively innuenced bysurface impurities. Terai et al. [2] have examined

the fTeasibilityof an Nb permeationwindow andpermeator is 700 oC ll]. It has been reported that

Pd layers prepared on V [6], Nb l719] and Ta[10] react with substrate metals at/below thistemperature･ In the previous study, the present

reported that permeation rate of deuterium wasmuch smaller than that expected from diffusivity
and solubility of deuterium in Nb due to theauthors fわund that high temperature stability of

Pd on Ta is superior to that ofNb lll], but
details have not been examined. From thesegrowth of oxide films on surfTaces. Hatano et al.

[3‑5] have reported that severe pemeability

viewpoints, hydrogen pemeation throughPd‑Ta‑Pd composite membrane was examined atdeterioration is possible even in ultrahighelevated temperatures in the present study･
vacuum without oxide growth at elevatedtemperatures due to the fわrmation of oxygen55

T. Nozaki, E. Yamakawa, A. Hachikawa, K. Ichinose, M. Hara and Y. Hatano

II. EXPERIMENTAL

for 1 h, the specimen was exposed toair at room

II.A. Permeation Experimenttemperature for I h. Then hydrogen absorpt10n

Both sides of disk‑type Ta specimens (20rate was examined at 300 ℃. The initial pressure

mm thickness) WereofH2 gas Was adjusted to be 13 Pa. Oxide film

polished with abrasive papers, and finishedwith

was recovered on the area where Ta wasdiamond powder (9 and 3トLm) and colloidal

appearlng On the surface, and the absorptlOnsilica (0.04um). Thin Pd layers (270 nm

took place only through Pd layer under the

thickness) Were prepared on both sides bypresent conditions. The exposure to air at room

magnetron sputterlng at 300 oC･ The specimen

temperature and the abso叩tlOn meaSurementS at

surface was cleaned by rf‑sputtering in the

300 ℃ were repeated a鮎r each heat treatment

sputterlng apparatus prlOr tO the preparation of

in vacuum at 400, 500 , 600 and 700 oC fわr I h.

Pd layers.

The detailed procedure is described in Refs. [8]mm diameter and 0.5

Pemeation rate of hydrogen through theand l9].

specimen was measured at 500 and 600 0C with

The specimen surfaces before and after thea vacuum device evacuated to 10‑6 pa by aheat treatments in vacuum were analyzed withturbomolecular pump and an oil‑sealed rotary

Auger electron spectroscopy (AES), scanningpump. The device was separated into twoelectron microscopy (SEM) combined withchambers, i.e. up‑ and downstream chambers, byenergy dispersive X‑ray spectroscopy (EDS) andthe specimen sealed with metal gaskets

X‑ray diffractometry (XRD), and those after the(U‑Tightseal, Usui Kokusai Sangyo Kaisha,permeation experiments were examined by

Japan). The pressure of hydrogen in the

SEM‑EDS.

upstream chamber was kept at I.0 Torr (0.13kPa), and that of hydrogen pemeating throughIII. RESULTS AND DISCUSSION

the specimen into the downstream chamber wasFig. I (a) shows SEM image or themeasured by a calibrated quadrupole mass

specimen under the as‑prepared conditions･ It isanalyzer and capacitance manometer. The

shown that polycrystalline Pd layer was fbmedpressure in the downstream chamber was

on Ta and grain size was aboutmaintained to be sufficiently low in comparison

Palladium was a sole element detected by EDS

with the upstream by continuous pumplng at

as shown in Fig. 1 (b). The X‑ray diffhction

known pumplng speed. The permeation nux was

pattem under the as‑prepared conditions is

calculated with the pumplng Speed and pressure.

shown in Fig. 2. Peaks of Pd and Ta were

300

nm.

obseⅣed, and there was no visible peak of

II.B Surface Characterization

impurlty Or Second phase.

The change in reaction rate or hydrogen on

The change in permeation rate at 500 ℃

the specimen surface with heat treatments waswith time is plotted in Fig. 3. Initial value of

examined by abso叩tlOn experiments at 300 oC･

permeation rate was 5xl0‑8 moI H2 m‑1S‑Ipa‑1/2･Sheet‑type Ta specimens with Pd layer (270 nm)

This value is smaller than the permeation rate

on one side was prepared斤om the same plate as

evaluatedfrom the equation proposed by Lasser

the specimens f♭r permeation experiments, and[11]from data on hydrogen diffusivity andinstalled in a quartz tube attached to a different

solubility in Ta (1.3×10 7 moI H2 m ls lpa 1′2),

vacuum apparatus evacuated to lOl6 pa by abut the difference is small. The permeation rateturbomolecular pump and an oil‑sealed rotary

gradually decreased with time, and it reached apump. After heat treatment in vacuum at 300 oC

halfof initial value after operation for 30 h.

56Application of Palladium Coating on Group 5 Metals for Vacuum Permeator"VJ･T. S･. u･TOuI810I/Q'21tu O!DuCa JedTH

02 †eatment

5

10

15

20

25

30

35

40

45

time, ∫/hFig. 3 Change in pe‑eability ofH2 fわr
3 て｣ つ山 l ･ l

pd/Tan)d at 500 oC.

S‑亡コOU
LJ 'て⊃ ､､ LlJ

Z IO [⊥】 迄80Fig. I (a)SEM image and (b)EDS spectrum
or Pd/Ta specimen as‑prepared.

200

400

600

800 1000

Kinetic energy (eV)Fig. 4 AES spectrum for Pd/Ta after heating
at600 oC f♭r 5 h.

sputterlng tO remove Carbon･●pd■

In order to understand the effect of carbon.nLtZJk!SuaT

パリっ0

in the pemeation experiments, 02■●

introduced in both of up‑

gaS Wasand downstream

chambers to 13 Pa, and the specimen was heated● ■at 400 oC f♭r 1 h. As shown in Fig. 3, thepe…eability was restored completely by this
40

60

80

100

120

treatment in 02 gaS･ Hence, 1t Was COnCluded

28 /de喜Fig. 2 XRD diffraction patternof Pd/Ta

that the reduction in permeability shown in Fig･
3 was due to contamination by carbon, andspecimen as‑prepared.

removal of carbon as CO or CO2 led to

In the absorptlOn experiments, significant

restoration of permeability･ The source of carbon

reduction in surface reaction rate was observed

is considered to be hydrocarbons present in theafter heating the specimen at 600 oC fわr 5 h･ The

devices as residual gases. These observations

analysis by AES showed that the surface of Pd

indicate that partial pressures of residual

layer was severely contaminated by carbon ashydrocarbons in vacuum permeator have to beshown in Fig. 4. The surface reaction rate wasstrictly controlled to avoid deterioration inrecovered for certain extent after gentle

permeability･ This type of degradation, however,57

T. Nozaki, E. Yamakawa, A. Hachikawa, K. Ichinose, M. Hara and Y. Hatano㌔d･TI S･[̲ Lul .us10tJQ'31VJu.!1Pau Cdゴ

5432‑00

0

0

0.2

0.3

0.4

0.5

0.6

time,∫/hFig･ 5 Change in permeability ofH2 for Fig･ 7 SEM image ofPdrra after heating at
Pd/Ta at 600oC.

700oC fわr 1 h.
一

AA

ﾇ

B

●■Ta
▲pd.IT丘.つd＼Lt!suaTl

0

A.‑.I

●▲

20

40

60

80

1 00

1 20

28 /°eg

Fig･ 8 XRD diffraction pattem ofPd/Ta after
heating at700oC fわr 1 h･tt

く卜!

value is slightly smaller than the permeation rateevaluated from the equation proposed by Lasser[12](9.3×10 8 moI H2 m ls 1pa ‑/2). The reductionin permeation rate was obseⅣed also at 600 0C

as shown in this figure. In order to examine

whether restoration ofpemeability is possible atthis temperature, air was introduced to up‑ and
2.00

4.00

6.00

8.00 10.00

keV

downstream chambers to 10‑2 pa with keeplng

specimen temperature at 600 oC･ This treatment,
however, resulted in irreversible change in

Fig･ 6 (a) SEM image and (b) EDS spectrumof downstream side for Pd/Ta/Pd
a触r hydrogen permeation at 600 oC･

surface state. Namely, the color of surfacechanged from shiny metallic gray to black･ Fig･

6 (a) shows SEM image of downstream side

is reversible and the permeability can besurface a氏er this treatment as an example. This

restored by heat treatment in 02 gaS･

figure indicates increase in surface roughness･ In

Fig･ 5 shows the change in permeability

with time at 600 oC･ Initial value of pemeation
rate was 4×10‑8 moI H2 mlls‑Ipa‑1/2, and this58

the X‑ray spectrum, large peak of Ta was
obseⅣed together with that or 0 in addition to
Pd as shown in Fig. 6 (b). These obseⅣations

Application of Palladium Coating on Group 5 Metals for Vacuum Permeator
prepared arc‑plasma gun (ULVAC Co., Japan)
under

0.3

Pa

N2

gaS

70

nm. Blisters (2 ‑ 20トLm

thickness was

atmosphere,

and

its

diameter) Were found on the surface after theheat treatment at 700 0C as shown in this figure･

Nevertheless, development of open poroslty Was
notobseⅣed.

ln

addition,intermetallc

compound was not detected in XRD analysts.

The pe‑eation experiments with the specimens

having Hm intermediate layer is currently ln
Fig.9 SEM image of Pd/HfN/Ta aRer heating

preparation, and results will be reported infuture.

at 700oC fわr 1 h.

suggest that Ta oxides were fbmed on thespecimen surface.

ⅠV SUMMARY

The pe‑eation of hydrogen throughIn order to understand the mechanism

underlying Ta oxides fb‑ation, the specimen
heated in vacuum at

700

0C fわr 1 h was

examined by SEM‑EDX and XRD. As shown in
Fig･ 7, porous structure was developed by theheat treatments. Fo…ation of intermetallic

compound (Pd3Ta) was also indicated by XRD
analysis (Fig. 8). These obseⅣations suggestthat Ta appeared on the surface during

Pd‑Ta‑Pd composite membrane was examined atelevated temperatures to understand theapplicability or this type of composite

membrane to tritium recovery from liquid Pb‑Li
alloy･ The composite membrane was degraded

during operation by two different mechanisms:
reversible degradation by carbon deposition, andirreversible degradation by interdiffusion andopen porosity development. In the fbmer case,permeation experiment at 600 0C due to open

the pe‑eation rate could be restored by removal

poroslty development and interdimlSion, andof carbon through the reaction with oxygen. In

reacted with oxygen during the above一mentioned
treatment in 10 2

the case of latter, however, degradation waspa air. It was therefわrepermanent. It was shown that the preparation of

concluded that Pd layer in several hundreds nm

thickness cannot keep its coatlng effects atthin HfN inte‑ediate layer hinders open

porosity development and interdiffusion.

operation temperature of vacuum pern1eatOr.

One of the ideas to solve this type ofproblems is to increase the thickness of Pd layer
drastically, but it should be accompanied by
sign捕cant increase in the cost and di用culties infabrication･ Reduction in operation temperature
led to poor thermal efficiency of the reactor.

From these viewpoints, the inte‑ediate layer toprevent the reaction between Pd and Ta has beendeveloped by the present authors. Fig. 9 shows

the SEM image of the specimen with Pd layer(270 nm) prepared on HfN intemediate a氏er

Acknowledgments
The authors express their sincere thanks toProfessor A. L Livshits in The Bonch‑Bruevich
Saint‑Petersburg State Un iverslty Of
Telecommunications fわr fruitful discussion andhis advice･ This study has been. supported in partby Grant‑in‑Aid for Scientific Research on
Priorlty Areas, 476, Tritium Science andTechnology fわr Fusion Reactor fTrom MEXT,

Japan, and Grant‑in‑Aid for Scientific Research(B) from Japan Society for the Promotion ofheating at 700 oC fわr 1 h･ The HfN layer was59

T. Nozaki, E. Yamakawa, A. Hachikawa, K. Ichinose, M. Hara and Y. Hatano"Thermal Degradation of a Palladium

Science (19360313).

Coating on Hydrogen‑Tight Niobium

Membranes", Tech. Phys" 55, 1 17 (2010).

Refe re Acesl1] C. P. C. Wong, S. Malang, M. Sawan, M.

[8] Y Hatano, K. Ishiyama, H. Homma and K.

Dagher, S. Smolentsev et al., "An OveⅣiew

Watanabe, "Improvement in Ilighof Dual Coolant Pb‑17Li Breeder First

Temperature Stability of Pd Coating on Nb

Wall and Blanket Concept Development fわr

by Nb2C Intermediate Layer", Inl. J

the US TTER‑TBM Design", Fusion Eng.

Hydrogen Energy, 32, 61 5 (2007).

Design, 81, 461 (2006).

[91 Y Hatano, K. Ishiyama, H. Homma and K.

[2] T. Terai, A. Suzuki and T. Tanaka, "Tritium

Watanabe, "Improvement of High

Recovery from Li17‑Pb83 Liquid Breeder

Temperature Stability of Pd Coating on Nb

by Permeation Window Method", J Nucl.

by lntemediate Layer Comprising NbC andMatet:, 248, 159 (1997).

Nb2C", J. Alloys & Compounds, 4461447,[3] Y Hatano, K. Watanabe, A. Livshits, A.
Busnyuk, V. Alimov, Y. Nakamura and K.

[10] K. S. Rothenberger, B. H. Howard, R. P.

Hashizume, "Effects of Bulk Impurity

Killmeyer, A. V Cugini, R. M. Enick, F.

Concentration on the Reactivity of Metal

Bustamante, M. V Ciocco, B. D.

Surface: Sticking of Hydrogen Molecules

Morreale, 良. E. Buxbaum, "Evaluation

and Atoms to Polycrystalline Nbof, Tantalum‑Based Materials for

Contalnlng Oxygen'', J. Chem. Phys., 127,

Hydrogen Separation at Elevated204707 (2007).

Temperatures and Pressures", J[4] Y Hatano, A. Busnyuk, A. Livshits, H.
Homma and M. Matsuyama, "Co汀elation

Membrane Sci., 218, 19 (2003).
【11】Y. Hatano, K. Ishiyama, T. lnoue and T.

between Hydrogen Isotope Pemeation

Nozaki, "Stability of Pd Layers on Group 5

through Niobium and Bulk Oxygen

Metals", Extended Abstract of lOth Int.

Concentration:

Conf Inorganic Membranes, Aug, 18‑22,

Possible Innuence of

Oxygen on Tritium Recovery from Pb‑Li
by Vacuum Permeator", Fusion Sci.

[5] Y. Hatano, A. Busnyuk, V Alimov, A.

Livshits, Y. Nakamura and M. Matsuyama,"Influence of Oxygen on Permeation of
Hydrogen lsotopes through Group

2008, Too)0.
[12] R. Lasser, Tritium and Helium‑3 in Metals,
Springer‑Verlag Berlin Heidelberg, 1989, P.

Technol., 52, 990 (2007).

5

Metals", Fusion Sci. Technol., 54, 526(2008).

[6] D. Edlund and J. McCarthy, "The
Relationsh ip between lntermetal 1 ic

Diffusion and Flux Decline in Composite
Metal Membranes: Implications fわr

Achieving Long Membrane Lifetime", J.

Membrane Sci., 107, 147 (1995).
[7] A. 0. Busnyuk, M. E. Notkin, I. P.
Grigoriadi, V. N. Alimov and A. I. LifTshitz,

60

539 (2007).

39.