Sealing Materials and Joining Techniques
Transcript of Sealing Materials and Joining Techniques
Sealing Materials and Joining Techniques
Jochen Schilm, Andreas Pönicke, Axel Rost
h l l ll d d h l1st Joint European Summer School on Fuel Cell and Hydrogen Technology
22th August – 2th September 2011
Viterbo ItalyViterbo, Italy
© Fraunhofer IKTS
www.ikts.fraunhofer.de
Contents
Introduction to sealing of SOFC
Glass based seals
Basics on glassBasics on glass
Glass based seals for SOFC
Long term behaviour of glass based sealsg g
Metal based seals
Basics on brazing
Active metal brazing / Reactive air brazing
Metal based seals for SOFC
Long term behaviour of brazed sealsLong term behaviour of brazed seals
Other sealing techniques
© Fraunhofer IKTS
Contents
Introduction to sealing of SOFC
Glass based seals
Basics on glassBasics on glass
Glass based seals for SOFC
Long term behaviour of glass based sealsg g
Metal based seals
Basics on brazing
Active metal brazing / Reactive air brazing
Metal based seals for SOFC
Long term behaviour of brazed sealsLong term behaviour of brazed seals
Other sealing techniques
© Fraunhofer IKTS
Sealing and joining of SOFC
Function
( )ti ht ti f t k t(gas-)tight connection of stack parts
Examples
cell and interconnectcell and interconnect
passive parts of the interconnect
manifold seal between interconnects
Requirements
stability at operating temperature 700 - 850°C
electrical insulation (partly)
i f CTE i h (T l )attenuation of CTE mismatch (T-cycles)
source: Staxera
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source: Staxera
Sealing and joining – materials requirements
requirement why is it important in the stack? material parameter
gas stream avoid mixing of reactants – voltage degradation gas tightness,gas stream separation
avoid mixing of reactants voltage degradationmicro-combustion can lead to complete seal breakdown
gas tightness, minimum porosity
CTE matching allow stack materials with different CTE to release thermo mechanical stress d ring transient thermal
viscous flow,d ctilitthermo-mechanical stress during transient thermal
operating pointsductility
heat conduction
lateral heat conduction away from hot spots, heat transport from stack core to outer shell
thermal conductivity,thickness
electrical insulation
avoid short-circuit of 2 adjacent interconnects ohmic resistance
mechanical to maintain stack integrity under shock and peel adhesionmechanical robustness
to maintain stack integrity under shock and vibration, to allow a defined mechanical load path in a stack
peel adhesion,compression behaviour
chemical retains seal integrity even under harsh chemical resistance againstchemical stability
retains seal integrity even under harsh chemical attacks – one single seal failure can cause complete stack breakdown!
resistance against chemical and electro-chemical attack
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Sealing and joining possibilities
glass based seals brazed joints compound sealsg
Ba-Al-Si glasses and ceramics
wide range of
j
Ag-Ti and Ag-Oxide based materials
active metal /
p
hybrid materials: mica + binder / seal or elastic metal componentstechnologies
inexpensive, easy to manufacture
tl t i t t
reactive air brazing
thin, but expensive bonding
tl f i l
components
elastic, but more complicated
standard in somecurrently most important technology
currently for special purposes
standard in some compressed stack designs
sources: FZ Jülich (1)
© Fraunhofer IKTS
Contents
Introduction to sealing of SOFC
Glass based seals
Basics on glassBasics on glass
Glass based seals for SOFC
Long term behaviour of glass based sealsg g
Metal based seals
Basics on brazing
Active metal brazing / Reactive air brazing
Metal based seals for SOFC
Long term behaviour of brazed sealsLong term behaviour of brazed seals
Other sealing techniques
© Fraunhofer IKTS
Glass: a super cooled melt
crystalline SiO2 glassy SiO2
ume
Melt
Superc
ooled
elt
Spec
ific
Vol S
me
Glass
Crystal
S
TemperatureTg Ts
siliconoxygen
glass transition temperature Tg
viscosity = 1013 Pa s (for all glasses)scos ty 0 a s ( o a g asses)
molecules are frozen-in-state (equilibrium position)
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The glass transition at Tg
glass melt atglass melt at elevated temperatures
Like a traffic jam on the motorwayy
glass below Tg
decrease of temperature
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Constituents of glass
network formers: SiO2, B2O3, P2O5
provide skeletal structure of glass as an irregular, 3-dimensional network
structural integrity
network modifiers: Na2O, CaO, MgO, Y2O3
breaking of network and forming of t i t d b diterminated oxygen-bondings
modification of glass networkstrong influence on glass properties
intermediate oxides: Al2O3, PbO, Bi2O3
depending on their fraction and the glass composition these oxides can act ascomposition these oxides can act as network formers and network modifiers
stabilization of glass structure
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Influence of various constituents on glass properties
lowering of viscosity
reduction of thermal
B2O3SOFC sealing glass with decreased viscosity for better reduction of thermal
expansioncoefficient
increase of mechanical24 Al O
yprocessing
increase of mechanical strength
decrease of tendency ofcrystallisation16
20
24
Pa
s
pure SiO2 glass
Al2O3
crystallisation
lowering of viscosity
decrease of chemical d bilit
8
12
16
og /
log
P p 2 g
Li2O, Na2O
durability
raising of chemical resistance
increase of thermal expansion0
4SOFC sealing glasslo
MgO, CaO
BaOcoefficient
reduction of processingtemperatures
600 800 1000 1200 1400 1600temperature / °C
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Optical dilatometry
shades of cylindrical specimen are photographed
analysis of marked areas with digital image processing
measure for specimen volume
detection of form changes
applicationsapplications
deduction of sintering profiles
wettability angles
measurement of probe viscosity through form changes
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Characteristically change of specimen form
deduction of working temperatures and sintering profiles
start of end of softening half ball viscous flow sintering sintering point point (around 45°)
109 Pa·s 107 Pa·s 105-6 Pa·s 103-4 Pa·s 102.2 Pa·s0 a s 0 a s 0 a s 0 a s 0 a s
after: M.J. Pascual. L. Pascual & A. Durán, Phys. Chem. Glasses, 2001, 42 (1), 61-66
© Fraunhofer IKTS
y
Contents
Introduction to sealing of SOFC
Glass based seals
Basics on glassBasics on glass
Glass based seals for SOFC
Long term behaviour of glass based sealsg g
Metal based seals
Basics on brazing
Active metal brazing / Reactive air brazing
Metal based seals for SOFC
Long term behaviour of brazed sealsLong term behaviour of brazed seals
Other sealing techniques
© Fraunhofer IKTS
Glass based seals
requirements to the glass
stable up to 850 °C but still low melting (stack manufacturing!)
adjusted coefficient of thermal expansion (CTE) adjusted viscosityadjusted coefficient of thermal expansion (CTE), adjusted viscosity
chemically stable against oxidation (air) and reduction (H2/ CO/ CO2 /H2O(g))
gas tight, mechanically stable, robust against cycling
cost effective, easy to manufacture
typical solutions
glass is applied as paste or tape
some % of crystal phase for mechanical stability and optimised viscosity
additional materials to stabilize matrix: ceramic mats ceramic powdersadditional materials to stabilize matrix: ceramic mats, ceramic powders
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Glass based seals – manufacturingdirect route
melting in Pt crucible,quenching in water
ball milling(D50 < 3 μm)
paste or slurrypreparation
dispensing on substrate
glass tape route
tape casting laminating hot isostatic pressing stamping to shape
source: FZ Jülich (1)
© Fraunhofer IKTS
Partial crystalline glass ceramics as sealing materials
Gl t SiO Al O B O (B O Z O) B Si O t lli hGlass system: SiO2– Al2O3 – BaO (B2O3– ZnO) - BaSi2O5 as crystalline phase
Requirements :
Long term stabiliyt up to 850 °C
SiO2(1713o )
1600
Cristobalite
1700
SiO2
Long term stabiliyt up to 850 °C
hemetic Metal-Metal- and Metal-ceramic joints
1600
1700
BaSi2 O514001470o
Tridymite 1296o
Mullite
1554o
n-Ce lis ian
1122o
BaSi2O5
Good redox stability
Electrical Isolation
b l h l l d ( h )
Al6Si2 O1 3
2000
1900
1800
B3SB2 S
BSB2 S3
B5 S8B3 S5
2 5(1426o )
BaA l 2
S i 2O 8
(1760
o )1590
o
150013
001 359
o
Sanb
ornite
Corundum
-Ce lsia n-C
H LBaSi2O5
Crofer 22
Stability againt mechanical load (Pressure; sheer)
Accomplishable by:
0 100Wt %BaO
Al2 O3
20
BA6BAB3A 60BaO Al2O3
CTE after cristallisation > 9,5·10-6 K-1
Viscosity after sealing at 850°C 108 Pa·s
N ti t PbO Bi O
Glass ceramic
No reactive components as PbO, Bi2O3…
Spezific resistivity > 20 k cm-1 (at 850°C)(No alkali oxides)
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Mechanical behaviour of glass seal material
glass remains viscous at all stack ti i t !
109 Massive Proben nicht kristallisiert Folie kristallisiert Folie nicht kristallisiert
massive glass block, not crystallizedtape, crystallizedtape, not crystallized
operating points!
107
108
Pa s
Pa s
p y
106
10
skos
ität /
Psc
osity
/ P
drastic increase in i i b B Si O
700 750 800 850 900 950 1000104
105Vi
vis
BaSi2O5-crystallite glass matrixviscosity by BaSi2O5-crystallite formation –what we need! crystallite formation is thermo-
dynamically favoured and occurs at h fi h700 750 800 850 900 950 1000
Temperatur / °Ctemperature / °Cthe first heat up
sealing process
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Adaption of Viscosity and CTE by crystallisation of BaSi2O5
Amorphous melt
1,0x10-5
1,2x10-5
K-1
Crystalline microstructure
107
109
1011/ P
a s
Amorphous melt Crystallized tape Crystallized powder compacts
6,0x10-6
8,0x10-6
Amorphous glass
CTE
/ K
1
103
105
10
Vis
cosi
ty /
200 400 600 800
Temperature / °C
700 800 900 1000 1100101
Temperature / °C
S ffi i t ti d T t i d f liSufficient time- and Temperature window for sealing processAngepasstes Kristallisationsverhalten
800
400
600
800
per
atu
r / °
C
Example for aSealing profile 1.
2. 3.1. Debindering
2. Sealing of glass to metal
0 5 10 15 20 25 30 350
200
Tem
p
Zeit / h
g p
3. Crystallisation
© Fraunhofer IKTS
Zeit / h
Glass seals in SOFCBaO MgO CaO SrO La2O3 B2O3 Al2O3 SiO2 Additives
Argonne National Lab.
24,56 20,13 40,29 6,92 8,11
PNNL 36,9 10,5 52,6
PNNL 30,0 10,0 20,0 10,0 30,0
FZ Jülich 38 0 5 0 10 0 45 0 2 0 ZrOFZ Jülich 38,0 5,0 10,0 45,0 2,0 ZrO2
FZ Jülich 45,0 5,0 5,0 45,0
Pascual et. al. 27,0 10-18 5-20 40-55 PbO, ZnO
Smeacetto et al. 24-26 6-8 53-58 10-12 Na2O
Saswati Gosh 35-58 8-15 0-5,5 28-44 B2O3, La2O3, ZnO
Sources: P.A. Lessing, J. Mater. Sci. 42 (10), 2007, 3465-3476M.J. Pascual, A. Guillet, A. Duran, J. Pow. Sour. 169 (2007) 40–46Saswati Ghosh, A. Das Sharma, P. Kundu, S. Mahanty, R.N. Basu, J. Non-Cryst. Solids 354 (2008), 4081–4088F. Smeacetto, M. Salvo, M. Ferraris, V. Casalegno, P. Asinari, A. Chrysanthou c, J. Eur. Cer. Soc., 28 (2008), 2521-2527
© Fraunhofer IKTS
, , , g , , y , , ( ),
Crystallinity of glass ceramics seals
High crystalline glass ceramics
Stable against excessive heatingEffect of self healing
Mechanical stability of SOFC-Stacks
Density Porosity (Self healing of cracks ?)( g )
Amorphous or partial crytsalline 20N at 750°Cmicrostructure
Viskosity decreases at high temperatures
Healing of cracks is possible
20N at 750°C4-Point Bending
Healing of cracks is possible
Hermetic density, good adhesion
Can stand only less mechanical loadViscous flow of the glass melt
W.N. Liu, X. Sun, B. Koeppel & M. Khaleel, Experimental study of the aging and self-healing of the glass/ceramic sealant used in SOFC, Int. J. Appl. Ceram. Technol., 7 [1], 22-29 (2010)
© Fraunhofer IKTS
used in SOFC, Int. J. Appl. Ceram. Technol., 7 [1], 22 29 (2010)
Contents
Introduction to sealing of SOFC
Glass based seals
Basics on glassBasics on glass
Glass based seals for SOFC
Long term behaviour of glass based sealsg g
Metal based seals
Basics on brazing
Active metal brazing / Reactive air brazing
Metal based seals for SOFC
Long term behaviour of brazed sealsLong term behaviour of brazed seals
Other sealing techniques
© Fraunhofer IKTS
Long term performance of glass seals in a stack context
positive result negative result
over firing large pores
fuelair
dense and crystallized g g p
burn marks
cracks
dense and crystallized
only small pores
no constrictionsproducts of corrosion reactions
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Degradation of sealing glasses in SOFC-stacks
T t f l h b T i d bilit f l tTemperature of glassphase above Tg increased mobility of glass components
Viscous glass + electrical Field + Metallic sealing parts
= Electrochemical systemy
Interfacial reactions with metallic sealing partners
ElectricCathode 1 - metal
Redox reactions of Metallic inclusions
Electricfield
Evaporation of
Glass i
Diffusion of glass componentsAir Fuel
Chromates
glass & metalp
glass components
ceramicEvaporation of metal (e.g. Cr)
Formation & growth of pores
New crystalline phases
conc. E-Field
Anode 2 - metal Leaching of metal/alloy components
y
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Experimental setup for long term testing under SOFC operating conditions - Dual atmosphere test rigconditions - Dual atmosphere test rig
T = 850 °C
U 0 7 30 VU = 0,7 – 30 V
Fuel gas in vol%: 30 H2, 60 N2, 7 CO2, 3 H2O
4x
Top view of model sealing 30 x 60 mm²
© Fraunhofer IKTS
Acceleration of testing by rising the voltage
100M
U = 0,7 VU = 30 V
Same resistivity after 300 h
10M
U = 30 V
y /
cm
Stronger decrease at 30 V
Much lower resistivity after 1000 h
680 k1M
Res
istiv
ity
Implies much stronger d d
680 k cm
88 k cm
0 200 400 600 800 1000
100k
Time / h
degradation at 30 V
Proven by Helium leak rate
88 k cm
Voltage in V 0,7 30 Helium leak Rate < 1 10-10 3 5 10-2Helium leak Rate
in mbar l s-1 cm-1
< 1 10-10 3,5 10-2
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Effect of higher voltages – microstructure of glass-metal interfaces
CathodeCathode
U = 0,7 V U = 5 V U = 30 VAnodeAnode
Interfacial layers
Porosity
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Interfacial reactions with…
glass seal glass seal
interconnector YSZ electrolyte
glass seal
SiO2
BaCrO4
glass sealBaSi2O5
SiO2
steel Mex(MnCr)3-xO4 YSZBa-Zr-Si-O
degraded microstructure with local changes of glass composition
BaCrO4
formation of SiO2
changes of properties at interfaces
© Fraunhofer IKTS
Contents
Introduction to sealing of SOFC
Glass based seals
Basics on glassBasics on glass
Glass based seals for SOFC
Long term behaviour of glass based sealsg g
Metal based seals
Basics on brazing
Active metal brazing / Reactive air brazing
Metal based seals for SOFC
Long term behaviour of brazed sealsLong term behaviour of brazed seals
Other sealing techniques
© Fraunhofer IKTS
Basics on brazing of metals and ceramics
required condition
wettability between surface and molten braze
description by Young‘s equationLV
SV = SL + LV cosSL
SV
> 90°, non-wetting
< 90°, wetting of surface
20° d tti b i ibl< 20°, good wetting, brazing possible
sources: L.Y. Ljungberg, Br. Ceram. Trans. 100 (5), 2001, 218-228M.G. Nicholas, Br. Ceram. Trans. J. 85 (4), 1986, 144-146
© Fraunhofer IKTS
Brazing methods for metals and ceramics
route A
brazing ofbrazing of metallised ceramics
braze
metal
?route B
active metal brazing
ceramic? g
under inert gas / vacuum
Croute C
reactive air b ibrazing
© Fraunhofer IKTS
Contents
Introduction to sealing of SOFC
Glass based seals
Basics on glassBasics on glass
Glass based seals for SOFC
Long term behaviour of glass based sealsg g
Metal based seals
Basics on brazing
Active metal brazing / Reactive air brazing
Metal based seals for SOFC
Long term behaviour of brazed sealsLong term behaviour of brazed seals
Other sealing techniques
© Fraunhofer IKTS
Active metal brazing
(re-) active metal brazing
brazes contain surface-active elements (Ti, Zr, Hf, Nb)
brazing mechanism:
1. increased diffusion of active metal to interface braze ceramic (> 800 °C)interface braze-ceramic (> 800 C)
2. reaction between active metal and ceramic
3. formation of reactive layer e.g. TiO2, TiN
requirements
pO2 < 10-4 – 10-5 mbary g 2,
4. wetting of reaction layer by liquid braze
5. bonding
pO2 0 0 ba
p 30 MPa
source: M.G. Nicholas, Int. Conf. Joining Glass, Ceramics and Metal, Bad Nauheim, 1989, 3-16
© Fraunhofer IKTS
, g , , , ,
Microstructure of a braze after sealing
Active metal braze
96% A 4% Ti
reaction zone 1
3YSZ96% Ag, 4% Ti
(TiOx + Fe + Cr)
seal (mostly Ag)
reaction zone 2 (TiOx)steel
( x)
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Reactive air brazing
brazing mechanism for Ag-CuO
1 i it id ti f C t C O1. in-situ oxidation of Cu to CuO
2. solution of CuO in Ag decreases the melting temperature
3. eutectic mixture at 932 °C and 1,4 mol.% CuO
4. wetting of ceramic by molten braze possible
5. solidification of braze and joining
source: J.Y. Kim et al., J. Electrochem. Soc. 152 (6), 2005, J52-J58
© Fraunhofer IKTS
, ( ), ,
Wettability of pure silver and Ag-CuO
1,0 wt.% CuO + 99,0 wt.% Agpure silver
on YSZ: TS = 939 °C, = 75,5°on YSZ: TS = 949 °C, = 96,7°
on steel: TS = 933 °C, = 70,4°on steel: TS = 943 °C, = 79,7°
© Fraunhofer IKTS
Phase diagram of Ag-CuO in air
Immiscibility gap
source: ACerS-NIST, Phase Equilibria Diagrams
© Fraunhofer IKTS
, q g
Contents
Introduction to sealing of SOFC
Glass based seals
Basics on glassBasics on glass
Glass based seals for SOFC
Long term behaviour of glass based sealsg g
Metal based seals
Basics on brazing
Active metal brazing / Reactive air brazing
Metal based seals for SOFC
Long term behaviour of brazed sealsLong term behaviour of brazed seals
Other sealing techniques
© Fraunhofer IKTS
Typical application of metal and glass seals in a stack context
glass or metal
glass seal for
for cell bonding
electrical isolation
source: FZ Jülich
© Fraunhofer IKTS
source: FZ Jülich
Active metal brazing of cells in interconnects
problems of active metal brazing
ll b kli
ESC cell brazed in metal frame under inert gas atmosphere cell bucklinginert gas atmosphere
reduction of anode during brazing
© Fraunhofer IKTS
Sealing SOFC by reactive air brazing
PNNL FZ Jülich
Ag-1CuO, Ag-2CuO, Ag-4CuO, Ag-8CuO (+ 0,5TiH2)
different paste systems
Ag-4CuO, Ag-8CuO,Ag-8CuO-0,5TiH2
dispenser pastep y
patented brazes: Ag-CuO, Ag-V2O5, Pt-Nb2O5
brazing temperature between980 - 1050°C
IKTS
Ag 4CuO Ag 10CuO pastes
BMWNi based brazing foils with TiAg-4CuO … Ag-10CuO-pastes Ni-based brazing foils with Ti
sources: WO 03/059843 A1, K.S. Weil et al., Method of joining ceramic and metal partsD. Federmann et al., 7th European SOFC Forum, Luzern, 2006, P0425T. Koppitz et al., 8th Int. Conf. Brazing, High Temperature Brazing and Diffusion Welding, Aachen, 2007, 124-129S. Zuegner et al., 8th Int. Conf. Brazing, High Temperature Brazing and Diffusion Welding, Aachen, 2007, 122-123
© Fraunhofer IKTS
window sheetReactive air brazing of cells in stack
braze: Ag-8CuO
steel: Crofer 22 APU
cell with
steel: Crofer 22 APU
cell: ASC with YSZ electrolyte
cell withbrazingsolderwindow sheet
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brazed unit
brazed jointcell
source: D. Federmann et al., 7th European SOFC Forum, Luzern, 2006, P0425
cell
© Fraunhofer IKTS
Reactive air brazing of cells in stack
anode substrate: YSZ and NiO
electrolyte layer: YSZ
braze
source: D. Federmann et al., 7th European SOFC Forum, Luzern, 2006, P0425
window sheet: Crofer 22 APU
© Fraunhofer IKTS
, p , , ,
Contents
Introduction to sealing of SOFC
Glass based seals
Basics on glassBasics on glass
Glass based seals for SOFC
Long term behaviour of glass based sealsg g
Metal based seals
Basics on brazing
Active metal brazing / Reactive air brazing
Metal based seals for SOFC
Long term behaviour of brazed sealsLong term behaviour of brazed seals
Other sealing techniques
© Fraunhofer IKTS
Structural degradation of Ag in H2 und O2
degradation of Ag at T > 500 °C in H2 + 3% H2O
diffusion of O and H formation of H O embrittlement of Agdiffusion of O2 and H2 formation of H2O(g) embrittlement of Ag
source: P. Singh et al., J. Mater. Eng. Perform. 13 (3), 2004, 287-294
© Fraunhofer IKTS
g , g ( ), ,
Methods and ExperimentalWork station for induction brazing
Medium-frequency generatorWork station for induction brazing
Heating rates up to 250 K/min
Contact less temperature control1
Sample, Holder and Inductor Reactive Air Brazing
Ag-CuO-Pastes
CuO-fraction between 4 and 10 Vol.-%
Screenprinting of pastesScreenprinting of pastes
Joining partners3 YSZ with
- Crofer 22 APUCrofer 22 APU- ITM/LC (Plansee)
Temperaturecontroller
Pyrometer
© Fraunhofer IKTS
Comparison of bending strength of inductive- and furnace brazed 3YSZ-Crofer22APU-samples
200Ag 4CuO Ag 8CuO Ag 8CuO 0,5TiH2
200
150
a
K K K M K K K M K M150
/ MPa
100
tigkeitinMPa
100tren
gth
/
50
Biegefest
end
ing
st
NNL
MME
NNL
KTS
NNL
MME
NNL
KTS
ZJ;376
MPa
NNL
KTS
ZJ;295
MPa
50
50
B
PN DM PN IK PN DM PN IK FZ PN IK FZ
0
Inductive brazed 3YSZ-Crofer22APU compounds (IKTS)
0
© Fraunhofer IKTS
Inductive brazed 3YSZ Crofer22APU compounds (IKTS)
Comparison of induction brazed samples ofC f 22 APU d ITM LCCrofer 22 APU and ITM-LCSamples with Crofer 22 APU
1 m thin interfacial layer
Samples with ITM-LC
Similar thickness of interfacial layer1 m thin interfacial layer
Layer composition: Cr-Mn-Cu oxide
Solid inclusions of CuO in the braze
Similar thickness of interfacial layer
Layer composition: Cr-Fe-Cu oxide
Manganese is a very reactive layer forming component of Crofer 22 APU.
Ag-4CuO brazeAg-4CuO braze Ag 4CuO brazeAg 4CuO braze
ITM-LC10 m
Crofer 22 APU10 m
© Fraunhofer IKTS
Annealin� of induction brazed samples in air at ��� �C
Thickness of reaction layer on Crofer 22 APU and ITM-LC brazed � ith Ag-4CuO after annealing in air.
Samples sho� ed a hermetic
10
12
ayer
in
m
pdensity (helium leak rates belo� 10-� mbar.l.s-1.cm-1)
Interfacial layers gro� and
�
�
eact
ion
La y g
change their composition during annealing
� ro� th of layers according
2
4
ckn
ess
of
�
Crofer 22 APUITM-LC
to a saturation mechanism
Maximum layer thickness about 10 m
0 200 400 �00 �000
Thic
Annealing Time in h
ITM LC
Interfacial layers remained dense and gro� th is saturated.
© Fraunhofer IKTS
Morp�olo�� of a�ed interfacial la�ers after ��� � in air t ��� �Cat ��� �C
Crofer 22 APU
1 2 thi C id l t bli h d
ITM-LC
I iti ll f d l d1 - 2 m thin Cr oxide scale established after 200 h at the metal surface
Second thicker layer: Cr-Mn-Cu oxide
Initially formed layer gro� s and becomes enriched by Ag
Additional 2nd phase: Cr-oxide particles at the metal surface� ro� th of pores on metal surface particles at the metal surface(no dense layer)
Ag-4CuO brazeAg-4CuO braze Ag 4CuO brazeAg 4CuO braze
ITM-LC10 m
Crofer 22 APU10 m
© Fraunhofer IKTS
Interfacial la�ers bet� een Crofer22APU and �A� brazes � it� �ar�in� Cu� -contents after ���� at ����C in air
Ag-4CuO Lot Ag-�.5CuO Lot
C f 22 APU 10 m C f 22 APU 10 mCrofer 22 APU 10 m Crofer 22 APU 10 m
Microstructure of interfacial la�ers after a�in�
Cr-Mn-Cu- and Cr-Fe-Cu-Oxide layers
Pores on the metall surface
Comparable thicknesses of interfacial layers
� o effect of increased CuO-contents in the braze on theformation of the interfacial layers
Co pa ab e t c esses o te ac a aye s
© Fraunhofer IKTS
� ro� t� of interfacial la�ers until saturation
� ire�tl� afteri� � � �ti�e � ra�i� �
After ��� h � ��� �C � air e�pos� re
B
3YSZ� igh solubility and mobility of oxygen in silver diffusion of oxygen
50
m
Braze of oxygen
CuO content is not
O2
25 - CuO-content is not
the limiting component for thegro� th of the oxide layer
Oxide layer
oxide layer
gro� th is limited by the diffusion of
Metal
by the diffusion of Chromium and Manganese from steel
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Interface bet� een �� �� and braze of induction brazed lsamples
� ire�tl� after � ra�i� �A � 5C O b
� o interfacial layers
Sometimes CuO inclusions at the ceramic surface
Ag-�.5CuO braze
After a� � eali� � i� air at ��� �C3YSZ ceramic10 m
� o changes of microstructure
� o gro� th of interfacial layersAg-�.5CuO braze
Sample after inductive brazing
� o interfacial layers can be found. CuO facilitates � etting of braze on ceramic.
Sample after �00 h / �50 �C / air exposure
3YSZ ceramic10 m
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Contents
Introduction to sealing of SOFC
� lass based seals
Basics on glassBasics on glass
� lass based seals for SOFC
Long term behaviour of glass based sealsg g
Metal based seals
Basics on brazing
Active metal brazing / �eactive air brazing
Metal based seals for SOFC
Long term behaviour of brazed sealsLong term behaviour of brazed seals
Other sealing techni�ues
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Compressi�e seals
plai� mi�a seals
h t f
h�� ri� mi�a seals
h t f hl it b t thisheets ofphlogopite KMg3(AlSi3O10)(O� )2or muscovite KAl2(AlSi3O10)(O� )2
sheets of phlogopite bet� een thin glass or silver layers to seal uneven mica surface
sources: S. Le et al.� �. Po� er Sources 1�� (2)� 200�� 44�-452Y.-S. Chou et al.� �. Am. Ceram. Soc. �� (�)� 2003� 1003-100�Y.-S. Chou et al.� �. Po� er Sources 112 (1)� 2002� 130-13�
cross section of muscovite mica
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Compressi�e mica seals � properties
re�uires high compressive loads
major leakpath
high leak rates
0�02 sscm cm-1
interface reactions
� 2O loss (2��4 � ) causes degradationdegradation
poor thermal cycle stability
minorleakpath
stability
Tmax �00 �C
sources: Y.-S. Chou et al., J. Power Sources 157 (6), 2006, 260-270, WO 2005/024280, Y.-S. Chou et al., Method for making and using advanced mica-based seal for high-temperature applications
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g g g p pp
� t�er compressi�e seals
corrugated metal sand� ich arrange ment plain mica papercorrugated metalsheet filled � ithmica paste
leak rate:
sand� ich arrange-ment of mica paper and metal sheet
leak rate: not
plain mica paper
leak rate:very high
i dleak rate:� 1 � 10 4 mbar l/s�mm
re�uired compression force: 5 MPa
leak rate: not detectable
re�uired compression force: 0�� MPa
re�uired compressionforce: � 15 MPa
force: 5 MPa
source: M. Bram et al.� �. Po� er Sources 13� (1-2)� 2004� 111-11�
force: 0�� MPa
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If we knew what it was we were doing, it would g,not be called research, would it?Albert Einstein
T�an� �ou �er� muc� for �our attention�
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