outline of the report relevance of the topic experimental limitations and our solutions results on...
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![Page 1: Outline of the report Relevance of the topic Experimental limitations and our solutions Results on permeation measurements of Be coated Eurofer samples](https://reader034.vdocuments.us/reader034/viewer/2022051819/5514e645550346b0478b59e0/html5/thumbnails/1.jpg)
Outline of the report
• Relevance of the topic
• Experimental limitations and our solutions
• Results on permeation measurements of Be coated
Eurofer samples
• Conclusions and further plans
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Activities of the Vacuum lab in relation to hydrogen /
deuterium gas interaction on ITER grade: stainelss
steel, Be and W
Study of hydrogen diffusivity, solubility and surface
parameters which deteremine the kinetics, by using:
1) infusion / outgassing techniques (until 2009)
or (and)
2) membrane techniques (from late 2009)
Any of them requires a careful selection of all experimental
details to get reliable results. Measurements consist of
time consumtion, failures, non-reproducible runs etc...
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Processes involved in the hydrogen isotope retention and recycling in fusion reactor plasma-facing materials.
R. A. CAUSEY, J. Nucl. Mater., 300, p.91 (2002).
Relevance of permeation of H/D/T in fusion reactors
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Experimental setup
permeation method using H2 or D2 (3 UHV chambers)
kovar glass and alumina thimbles:
infusion / outgassing techniques
(2 UHV chambers)
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Instead of applying the more common
dynamic method, where the ion current of a characteristic
mass number applying mass spectrometer is recorded
we improved
the static method (gas accumulation), pressure recorded by
non-ionizing gauges in a small volume followed by
precise mass spectrometry
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Classical permeation experiment using hydrogen or deuterium
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2 CM heads:
1 mbar &
0.05 mbar FS pmin = 310-11 mbar
inverted
magnetron
All metal UHV system:- pressure rise measurement (vol. 0.5L)
- inert gauges
- post MS1 bar CM head
Vacuum system for permeation measurements using gas accumulation method
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Membrane technique [permeation]• determine coefficients like
– permeability (P), solubility (S), diffusivity (D) etc.– what is the limiting step for hydrogen migration
• samples investigated in 2010:– Eurofer steel (40mm diam, 0.5mm thick) dr.R.Lindau, IMF-FZK
– Be coated Eurofer by TVA at NILPRP (dr.Lungu)– W coated Eurofer at NILPRP (dr.Ruset) High-Z
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Conventional permeation cell to test a membrane in the
form of a disc
Vacuum side
High pressure side
Au gasket
40 mm O.D. membrane
Massive flanges guarantee uniform load of the seal and seems obvious
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Thin-walled permeation cell low background H contribution
Vacuum side – pLO
High pressure side – pHI, H2
Au gasket
40 mm O.D. membrane
Thin-walled inset ~ 0.3 mm,
A ~ 66 cm2
Flanges are
not a part of
the UHV
All permeation measurements have been performed at 400°C.
Be / W coated surface is facing the high pressure (upstream) side.
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External outlook of the permeation cell
Thin-walled inset – downstream side
Upstream side
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Results on the cell testing A comparative test was done by two identical AISI316
membranes, 2 h to 400 °C and further heating at 400 °C for 72
hours. QMS analysis of accumulated gases done occasionally.
Conventional cell with massive flangesd = 12 mm thick area & A1 15 cm2;
d = 0.3 mm thin area & A2 20 cm2,
d = 0.5 mm membrane & A2 8.5 cm2
Thin-walled celld = 0.3 mm thin area & A2 66 cm2,
d = 0.5 mm membrane & A2 8.5 cm2
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0.E+00
1.E-05
2.E-05
3.E-05
4.E-05
5.E-05
6.E-05
0 10000 20000 30000 40000 50000 60000 70000 80000 90000
t / s
mb
ar L
/s
thick wall
thin wall
Comparison of the conventional with the thin-walled cell
Outgassing rate at 400°C in the first 24 h
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Comparison of the conventional with the thin-walled cell
Outgassing rate at 400°C in 5 - 24 h
30000 40000 50000 60000 70000 80000 900001E-8
1E-7
1E-6
1E-5
30000 40000 50000 60000 70000 80000 900001E-8
1E-7
1E-6
1E-5
thick wall cell
thin wall cell
q / m
ba
r L
/s
t / s
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Comparison between conventional and improved cell
• Sensitivity of the setup increased, approx. 380 times
much lower permeation fluxes could be recorded.• Preparation time of the cell to achieve this value was
substantially shorter, 3 days instead of several weeks.
• Error due to the permeation of H2 to the air not observed
even at p = 0.1 mbar.• Minimum detectable flux j = 1.7×10-9 mbar L/(s cm2) or
4×1010 H2/(s cm2)
V.Nemanic, B.Zajec, M. Zumer, JVST A, 28(4) (2010) 578
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Permeation measurements through Be coated
Eurofer membranes prepared by TVAIdea and motivation• Bulk Be sample tiles tested at JET successfully • Inconel coated Be tiles tested successfully • Similar tiles may be applied at ITER
What is the permeation rate of hydrogen H2/D2/T2 through such
Be films? Published bulk data scattered!
If porous, they may increase the tritium retention in Inconel
since both neutral gas and plasma enter its surface easier
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JET ITER-like wall experiment
ITER
100m2 Tungsten • Low erosion • high melting T • Negligible T retention
Optimise lifetime & T- retentionBut high Z & melting
700m2 Beryllium first wall• low Z• Oxygen getter
Optimise plasma performanceBut large erosion & melting
50 m2 Graphite CFC • Lowish Z• No melting in transients• Superior heat shock behaviour
Optimise heat flux resistanceBut large erosion & T retention
W
CFC
JET
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Published data on solubility and diffusivityfor hydrogen (H,D,T) in beryllium
• published data on diffusivity and solubility very
scattered and almost useless for prediction of results
(A.A. Pisarev, Fusion Techn., 28, (1995) 1262)
• no data about hydrogen amount in our samples available
• a few reports on the same Be quality found as a rough
guidance for scheduled measurements
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Published data on solubility and diffusivity
A. Nikroo, H.W. et al, Fusion Science and Technology, 51, 4 (2007) 553-555
The only report we could
find on Be films
reveals that Be shells
are porous
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Permeation of Be/Eurofer prepared by TVA (SEM)
As received Slightly polished by alumina
(1 m, 300 nm, 60 nm grains)
Be thickness 8 m, Eurofer 500 m
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Permeation of Be/Eurofer prepared by TVA (AFM)
As received
RMS = 140 nm
Polished by alumina
RMS = 2 nm – 6 nm
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Permeation of Be/Eurofer - fluxes
Sample flux, q PRF
H2/(s cm2)
1 3.21012 140
2 2.11011 2184 ?
3 2.81013 16
4 3.11013 15
5 9.01012 50
Results at 1 bar upstream pressure and 400 °C obtained
a short period after hydrogen was introduced
(5 of 8 samples displayed, 3 were too rough or failed)
Is there any reason for great scattering of the flux values?
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Additional 2 samples with Ag interlayer below Be:
• Be coated membranes troublesome for permeation measurements:– Au gasket did not tightly seal the membrane fine polishing
– Sealing improved but not leak-tight (~10-5 mbarL/s) Be film is porous
for He between Be and Au. Is it porous for H2 too?
UHV [high pressure side]
UHV UHV
UHV [high pressure side]
Ag film
much better, but still leak
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Permeation of 2 additional samples Ag film+Be
Sample flux, q PRF
H2/(s cm2)
6 9.01012 50
7 5.11012 83
Results at 1 bar upstream pressure and 400 °C
Is there any general reason for scattering of the flux values
for 8 µm Be prepared by TVA at the same bias?
The behaviour also different from bare membranes!?
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Eurofer coated with Be:
at t = 0
pHI 0 1 bar
time / s
j /
10
-7 m
bar
H2 c
m-2 s
-1
Permeation reductionfactor (PRF) of steadyfluxes
coated
bare
j
jPRF
Permeation rate vs. time for 4 Be coated membranes (first exposure to 1 bar H2)
PRF=13
PRF=22
PRF=42
PRF=110
• Large scatter in kinetics (shape of curves) & PRF among identical samples.
• Subsequent H2 exposures more consistent but still large variations among samples. Steady flux for bare membrane achieved in 10s
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Eurofer coated with Be:
10 20 30 400
1x10-7
2x10-7
3x10-7
4x10-7
92
188
437
724
1086
1294
pHI
0.5 / mbar0.5
j /
mol
H2 c
m-2 s
-1
permeation is limited by diffusionDiffusion limited regime (DLR)
HIpj mbar
mbar
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Eurofer coated with Be:
porosity leak cannot be completely eliminated small air leak always present air could oxidize Be layer
Intentional oxidation by 1 bar of air (10min) increases the permeation rate for 2-5 times.
XPS profile of polished & oxidized Be sample
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Eurofer coated with Be: could there be small holes (pinholes) in Be film ?
Low-angle (2°)polishing wedge
Imperfections doexist, but difficultto find.
Sample has ~cm2
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TC29
Non-loaded
SEM by FZJ-IEF sent by dr.Lungu
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Eurofer coated with Be: what can be deduced from permeation meas.?
PRF = ~10 - 100
Assume Be film is homogenous and dense (no holes) & DLR:
d1
P1
d2
P2
H
Pd
dPPRF
dddP
d
P
d
P
d
2
2
212
2
1
1 ,
P-1 R from electr.Similar to parallel resistorsand parallel insulation layers.However: H conc. is not continious
Permeation coef. P:
Time lag L:
0 500 1000 1500times0
10
20
30
40
50
60
pOL
Single layer:
Two layers:
Ash, Barrer, Palmer; Brit. J. Appl. Phys., 1965, VOL. 16, p.873
L
j must monotonically increase tothe steady state value
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Eurofer coated with Be: what can be deduced from permeation meas.?
PRF = ~10 - 100
Assume Be film is homogenous and dense (no holes) & DLR:
PRF=10 PBe = 3.0x10-14 mol H2 / m2 s Pa0.5
PRF=100 PBe = 2.7x10-15 mol H2 / m2 s Pa0.5
P = D × SD = ?, S = ?
Measured time-lag not reliable to obtain D.
Take solubility S from published data:
400°C
SBe ~ 0.002 mol H2 / cm3 Pa0.5
, DBe = 1.5x10-7 cm2/s, L2= 26s
, DBe = 1.4x10-8 cm2/s, L2= 96s
400°C
DB
e /
cm
2s
-1
1000/T / K-1
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Permeation results – conclusions and plans
• Permeation flux was measured on 10 samples
• Porosity on the microscopic scale was expressed as
intight seal (He) on Be/Au interface or in the bulk Be below Au
• The SEM evidence on porosity (pinholes) given (FZJ and JSI),
but confirmation that a low number of pinholes is indeed
responsible for the scattering in permeation flux could not be
given at this moment • W / Be films will be tested and compared to Be and W films • comparison to various models is already in progress
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Eurofer coated with Be: what can be deduced from permeation meas.?
PRF = ~10 - 100
Assume Be film is homogenous and dense (no holes) & DLR:
• Measured PRF are in agreement with published range of Be D and S
• Observed time lag is considerably longer than predicted (26-96 s)
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Eurofer coated with Be: what can be deduced from permeation meas.?
PRF = ~10 - 100
Assume Be film is impermeable, permeation occurs only through pinholes
H
d
,)18.11(
1
rdFPRF
r – pinhole radius
d – substrate thickness (500μm)F – fraction of free surface
W. Prins and J.J. Hermans, J. Phys. Chem., 63 (1959) p. 716
1
3.0/
F
rdpinhole
pinhole
pinhole
With known PRF we cannotdecouple r and pinhole area density n.
Pinholes with smaller radius coverlesser fraction of the membrane surface.
Equilibrium H concentration in the substrate at the bottom of the pinhole.
10-5 10-4 10-3 10-21
10
100
1000
small pinholes
PR
F
F
d/r = 100 d/r = 1000 d/r = 10000
large pinholes
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Permeation through clean Eurofer
Could the air leak, Be porosity and permeation results be related?
Eurofer membrane was oxidized in water vapor and subsequently
also in the air. Tested at 1 bar (air) & 400 °C.
Duration, conditions PRF
Clean Eurofer well outgassed 1
Oxid. H2O, 400°C ~25 mbar, satur. at 25°C,18h 13.6
Oxid.air 400°C 1 bar, 18 h 0.75
Porous iron oxide even increases the permeation flux,
but Cr rich oxide seems to suppress it.
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Permeation Be/Eurofer - searching for explanation
• A few Be coated Eurofer membranes were also oxidized in the air
at 1 bar and 400 °C.
• Results do not express so evident influence of the air, since all
samples have been previously (inevitably) exposed to air leaks
when a thin but dense oxides could be formed.
• The expected suppressing of hydrogen flux was not achieved as
expected since BeO should be even less permeable than Be
• It seems that Eurofer is exposed to the air in pinholes or voids in Be• Some facts should be verified by a new experiment.
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01002003004005006000
0.5
1
1.5
2
2.5
Binding Energy (eV)
Nor
mal
ized
Inte
nsity
-C
1s
-A
r2p
-B
e1s
-O
1s
-O
2s
-B
e1s
Surface
After sputtering,subsurface region
-O
1s
XPS survey spectra on polished Be sample
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104106108110112114116118120122124
0
0.5
1
1.5
2
2.5
x 104
Binding Energy (eV)
Inte
nsity
(c/s
)
dept
h
Be-oxide Be-metal
Be 1s
XPS depth profile of polished Be sample
0
10
20
30
40
50
60
70
80
90
100
0 20 40 60 80 100 120 140
Estimated depth (nm)
Co
nce
ntr
atio
n (
at.
%)
O
C
Be
Oxide film
non-zero O conc.:influence of roughness
XPS spectra Be 1s as a function of depth
X-ray photoelectron analysis -XPS• XPS: very surface sensitive technique
• XPS depth profiling (by Ar ion sputtering) => in-depth distribution of elements
Be covered by Be-oxide layer Be-oxide layer thickness ~ (35 ± 10) nm, native only 2-3 nm
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Permeation of oxidized Be/Eurofer (SEM)
Polished oxidized Be heavily oxidized Eurofer