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

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Contents


Glass based seals




Metal based seals

Basics on brazing





© 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

© Fraunhofer IKTS

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)

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Contents


Glass based seals




Metal based seals

Basics on brazing





© 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

© Fraunhofer IKTS

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


Glass based seals




Metal based seals

Basics on brazing





© 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)

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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

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, , , 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


Glass based seals




Metal based seals

Basics on brazing





© 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

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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

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Contents


Glass based seals




Metal based seals

Basics on brazing





© 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

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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

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Contents


Glass based seals




Metal based seals

Basics on brazing





© 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

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, 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

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, ( ), ,

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


Glass based seals




Metal based seals

Basics on brazing





© 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


Glass based seals




Metal based seals

Basics on brazing





© 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

© Fraunhofer IKTS

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

© Fraunhofer IKTS

Contents


� lass based seals


� lass based seals for SOFC


Metal based seals

Basics on brazing

Active metal brazing / �eactive air brazing



Other sealing techni�ues

© Fraunhofer IKTS

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

© Fraunhofer IKTS

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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sealing materials and joining techniques

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