sealing materials and joining techniques - hysafe · 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


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)

© Fraunhofer IKTS

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)

© Fraunhofer IKTS

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

© Fraunhofer IKTS

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)

© 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)

© Fraunhofer IKTS

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

© Fraunhofer IKTS

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


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

© 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

© Fraunhofer IKTS

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


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

© 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

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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

© 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)

© Fraunhofer IKTS

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


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

© Fraunhofer IKTS

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

© Fraunhofer IKTS

( )

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�


© Fraunhofer IKTS www.ikts.fraunhofer.de

High temperature steels, Interconnection

Jochen Schilm, Viktar Sauchuk, Stefan Megel

1st Joint European Summer School on Fuel Cell and Hydrogen Technology

22thAugust –2thSeptember 2011 gp

Viterbo, Italy

© Fraunhofer IKTS


Contents

Interconnects for SOFC

High temperature steels and alloys for interconnects

Evaporation of Chromium and Poisoning of electrodes

Formationofoxidescalesoninterconnects Formation of oxide scales on interconnects

Protective coatings on interconnects

High Chromium und temperature alloys

© Fraunhofer IKTS

Temperaturerangesin SOFC modules

SOFC stacksCombinationmetal-ceramics

850°C

AfterburnerSiSiCCeramicfoam

1300 °C

850 °C

PreheaterSiC glow plug

1200°C

CPOxreformerCorderitecatalyticmonolith

950 °C

© Fraunhofer IKTS

1200 C

Application of High temperature-steels in the SOFC systems

Interconnect in theSOFC stack

Balanceofplant(BOP)intheSOFCmodule Balance ofplant (BOP) in theSOFC module

General requirements:

good thermo-mechanical stability

to guarantee a long life of the system

abilitytoformadenseoxidelayer ability to form a dense oxide layer

to prevent an accelerated oxidation of the material and evaporation of the steel components

chemicalstability chemical stability

to avoid phase and structural changes during the stack operation and thermocycling

excellentimpermeability excellent impermeability

to prevent the leakage of gases

© Fraunhofer IKTS

Stackassemblyofa 1kW CFY-basedSOFC stack

Top plateBiggestCFY Interconnect

130x150 mm

Bipolar plate

Protection-andcontactlayer

Cll Cell

Air

Nickel meshes

Glili

Activearea: 127 cm²

Glass-ceramicsealing

Bottomplatewithcurrentplug

MicaSealingFuel

© Fraunhofer IKTS

Sealing

Requirements to SOFC interconnect

high electronic and thermal conductivity

to reduce resistive losses

Pidittlitfthll Providing temperature alignment of the cell

ability to form a dense conducting oxide layer

to protect the interconnector from further oxidation and from evaporation fthtlttditil of the steel components, to reduce resistive losses

good mechanical stability and thermo-mechanical compatibility with other stack components

titithtkbtdbilitdiththli to maintain the stack robustnessand operability during the thermocyclingand mechanical loading

chemical stability/compatibility under both oxidising and reducing conditions conditions

to avoid the phase and structure changes during the stack operation and thermocycling

excellentimpermeability excellent impermeability

to prevent a mutual penetration of the gaseous species from separated media

© Fraunhofer IKTS

Contents







© Fraunhofer IKTS

Schematic classification and selected properties of steels andalloysforSOFCapplication and alloys for SOFC application

Fe, CrandNiasbasematerials

FeAlloyTEC30…800 °C[10-6K-1]

Chromium-10,0-11,0CTE increases

Austeniticalloys

es do

wn

Stre

ng

thg

based

Ferritic11,0-12,5

Austenitic18,0-20,0

Price go

e

go

esu

p

Iron-Nickel15,0-20,0

Nickel-based14,0-19,0

CrNi

source: S.Megel, Dissertation, Kathodische Kontaktierung in planaren Hochtemperatur-BrennstoffzellenStuttgart:IRBFhGVerlag2009p168

© Fraunhofer IKTS

HochtemperaturBrennstoffzellen, Stuttgart.: IRB FhG Verlag, 2009, p. 168.

Interconnect alloys –compositions and effects of components

CrNiCMnSiAlMinor

1.474217-190.030.121.00.7-1.40.7-1.4S

ZMG232220.330.020.50.40.19Zr, N

Crofer22APU22-240.16<0.03<0.8<0.5<0.5Ti, La

1.484524-2619-22<0.08<2<1-Mo,P

ITM26--<0.1<0.05<0.05Ti, Y2O3

Microstructure

TEC

Oxidescalecomposition

Oxide scale compositionPrecipitation

Adhesion

Inneroxidescale OxidescalecompositionInneroxidescale

Major components determine properties of the alloys

Minor components affect the formation of oxisescales on the surface Long term stability & Chromium evaporation

© Fraunhofer IKTS

Comparison of the thermal expansion of materials forSOFCcomponents SOFC components

238YSZITM

19

21

m/K

ZMG232Crofer221.47421.4845

Cr 24, Ni 19

15

17

CTE

/ppm,

11

13

C

902004006008001000

Temperature/ °C p

CeramicYSZ-materialsforelectrolytedeterminerequirementsofSOFC-steels

© Fraunhofer IKTS

Contents







© Fraunhofer IKTS

Evaporation of the Cr-species from the steel in air

) ( ) ( 5. 1 ) ( 23 2 2s O Cr g O s Cr

) ( 2 ) ( 5. 1 ) (3 2 3 2g CrO g O s O Cr

in humid air:

) ( ) ( 2 ) ( 2 ) ( 5. 1 ) (2 2 2 2 3 2g OH CrO g O H g O s O Cr

) )( ( 2 ) ( ) ( ) (g OH CrO g O H g O s O Cr) )( ( 2 ) ( ) ( ) (2 2 2 3 2g OH CrO g O H g O s O Cr

PoisoningofcathodesduetoreactionswithChromiumoxidesandhydroxides Poisoning of cathodes due to reactions with Chromium oxides and hydroxides

Clogging of pores in electrodes due to deposition of Chromium oxides and hydroxides

M.Stanislowski, Schriften FZJ, Energietechnik. V54 (2006), S18.

Degradation of steel by continuous evaporation of Chromium

© Fraunhofer IKTS

g

Hier noch 1 bis 2 Folien zum Thema Cr-Abdampfungaus denDissertationenrausarbeiten: den Dissertationen rausarbeiten:-Stanilowski: Seite 19 Dampfdrücke von Cr-O-OH-Spezies p

© Fraunhofer IKTS

Degradation of Stacks performance by passivationof the thddtChitifitt cathode due to Chromium-evaporation from interconnect

Deposition ofChromiumoxideinsidetheporousCathodemicrostructure

S. Megel, KathodischeKontaktierungin planarenHochtemperaturbrennstoffzellen, Ph.D. Thesis, ISBN978-3-8396-0066-5Band6SchriftenreiheKompetenzeninKeramikFraunhoferVerlagStuttgartGermany2009

PoisoningofthetriplepointsforthereductionofO2

© Fraunhofer IKTS

ISBN9783839600665,Band6SchriftenreiheKompetenzeninKeramik,FraunhoferVerlag,Stuttgart,Germany,2009

Contents







© Fraunhofer IKTS

Exampleofthe„time-resolved“ oxidationin thesteelat800 °C

1101001000

Logarithmictime scale/ h

Formation ofmultiple oxidelayerwithdifferent properties

source:SDunningJMOhandJCRawersinAlternativeAlloysforEnvironmentalResistanceTMS

Spallingofoxidefromthesurface

DepletionofsteelbyChromiumandManagnese

© Fraunhofer IKTS

source: S. Dunning, J.M. Oh, and J.C. Rawers, in Alternative Alloys for Environmental Resistance, TMS.

Huczkowski: Seite 18 Abhängigkeit der Massenzunahme von Additiven in Cr-Fe-Legierungen

© Fraunhofer IKTS

Oxidation behaviour of HT steels

2020 OuterOxideScale

Formation of outer and inner oxidations

OuterOxideScale

0

20

0

20 OuterOxideScaleOuterOxide Scale

-40

-20

-40

-20

Inner Oxide Scale ness in m

idl

-80

-60

-80

-60 ZMG232 ThicknInnerOxide Scale

01600320048006400-100

-80

-100

-80

Tiih

20 m

Time inh

© Fraunhofer IKTS

Oxidation behaviour of HT steels

016003200480064002020 OuterOxideScale


idl01600320048006400

0

20

0

20 OuterOxideScaleOuterOxide Scale

-40

-20

-40

-20


InnerOxide Scale

80

-60

80

-60 ZMG232 Thickn

CroFer22APUBaseMaterial

01600320048006400-100

-80

-100

-80

Tiih

CroFer22APU20 m Base Material

Time inh

© Fraunhofer IKTS

Oxidation behaviourofHT steels

01600320048006400 016003200480064002020 OuterOxideScale


01600320048006400 01600320048006400

0

20

0

20 OuterOxideScale

InnerOxideScale

OuterOxide Scale

-40

-20

-40

-20


InnerOxide Scale

80

-60

80

-60 ZMG232 Thickn

CroFer22APU

Base Material

01600320048006400-100

-80

-100

-80

Tiih

CroFer22APU ITM14

20 m

Time inh

© Fraunhofer IKTS

Oxidation behaviourofHT steelsSteel XSFC-1C44Mo20 (Sandvik)

after 800 h oxidationafter 12000 h oxidation

© Fraunhofer IKTS


Breakawayoxidation(ZMG232L @ 850°C)

6400h12000h 3200h

12000h20000h

nCrforZMG232L; Crofer22APU < 15 wt. %

© Fraunhofer IKTS

Cr;

Contents







© Fraunhofer IKTS

Oxidation behaviourofHT steelsCoatedvs. uncoated

Increaseofouteroxidescaleafter oxidationin airat850 oC

40Crofer22APUuncoated

30

Crofer22APU uncoatedITMLC uncoatedZMG232L uncoatedCrofer22APU coatedITMLC coated ess

/ m

20

ZMG232L coated

aleth

ickne

10

Oxid

e sca

040008000120000

Thickness of oxide scales : ZMG232 > CroFer22APU > ITM14

Time / h

© Fraunhofer IKTS

Oxidation behaviourofHT steelscoatedvs. uncoatedWeightgainafteroxidationat850°Cinair Weight gain after oxidation at 850 C in air

15Crofer22APU uncoatedITMLCd

10 cm-2

ITMLC uncoatedZMG232L uncoatedCrofer22APU coatedITMLC coatedZMG232Ltd 10

ain/ m

g cZMG232L coated

5

Weig

ht

ga

04000800012000

0

W

Weight gain: ZMG232>CroFer22APU>ITM14

04000800012000Time / h

© Fraunhofer IKTS


ComparisonWeightgainandScalethicknessforZMG232L ComparisonWeightgainandScalethicknessforZMG232L

1540 WeightGainScaleThickness

Oxide scale thickness

10

30

g/cm 2

ess/ μm

10

20

ghtGain

/ mg

Scale

Thickne

5

10 Weig

Oxide S

800h3200h6400h12000h

Realoxidation: idli

04000800012000

0

04000800012000

0

Time / h

x=kt1/2x=ktn

Real oxidation: No parabolic progression:

Oxide scale gainTheory (Wagner’s law):

© Fraunhofer IKTS

Problem solution: Protective coatings

In situ formationfromthebasematerial oran additional layer

Requirements:

•dense

Result:

•Inhibitionofoxidescalegrowth

•Good adhesion

•Thermalstablility

•PreventionofCrevaporation

ElilbThermal stablility

•chemical compatibility withother SOFC stack components

•Electricalcontactbetweenstackcomponents

•High electronic conductivity

© Fraunhofer IKTS

Influence of protective layers on interconnect properties

PorousperovskiteLSMC roll-coatinglayer

Crofer22APU

after 12000h oxidationZMG232L

after12000hoxidation after 12000h oxidation

Breakawayoxidationwith& withoutprotectivelayer

ZMG232Lafter12000hat850oCwith4thermalcycles

© Fraunhofer IKTS

ZMG232L after 12000 h at 850 C with 4 thermal cycles

Contents







© Fraunhofer IKTS

SchematicclassificationandselectedpropertiesofthesteelsforSOFC application

FeCTE increases

AlloyCTE30…800 °C[10-6K-1]

Chromium-based(CFY)

10,0 …11,0

Fii110125

Austeniticalloys

es do

wn

Stre

ng

thg

Ferritic11,0…12,5

Austenitic18,0…20,0

Iron-Nickel15,0…20,0 Price go

e

go

esu

p

Nickel-based14,0…19,0

CrNi

Higheroperationtemperaturesupto900°C

source: S.Megel, Dissertation, KathodischeKontaktierungin planarenHochtemperatur-BrennstoffzellenStuttgart:IRBFhGVerlag2009p168

Higher operation temperatures up to 900C

Longer operating lifes> 20.000h

© Fraunhofer IKTS

Brennstoffzellen, Stuttgart.: IRB FhGVerlag, 2009, p. 168.

Schema von Plannseezur pulvermetallurgischen HtllCFYMtilfhlth Herstellung von CFY-Material fehlt noch

© Fraunhofer IKTS

Advantages of SOFC stacks assembled with

CFYinterconnect+ESCcellsvsferriticinterconnect+ASCcells

Long lifetime and robustness in Reduction-Oxidation-and thermal-cyclings

CFY interconnect + ESC cells vs. ferriticinterconnect + ASC cells

Thermal expansion of ESC (8YSZ, 10SCSZ) fits to CFY interconnect

Wide range in operating temperatures (Tmax= 900…920°C)

LttditdthihthldtiitfCFYll Lower temperature gradient due to higher thermal conductivity of CFY-alloy

Lower cost due to economics of scale

© Fraunhofer IKTSQuelle: Plansee

Cost reduction of CFY-based interconnect production

Powdermetallurgicalproductionprocess

CFY/ICpieces CFYICCosts

-Powder metallurgical production process

-Near net shaping Low cost post-processing

100,0

1E+09 120

CFY/ICpieces(number of pcs.)

CFY-IC-Costs(arbitrary units)

1 Bio.

150 Mio.

4-5 GWSOFC

100,0

10000000

100000000

80

100

10 Mio.

100 Mio.

15 Mio.

40-50 MWSOFC

400-500 MWSOFC

Interconnects designed by

50,0

100000

1000000

40

604-5 MWSOFC

100,000

1 Mio.

150,000

1.5 Mio.

25,0

12,56,03,0

1000

10000

0

2010,000

1,500

15,000

1000 020042006200820112015> 2020

1000

Tenfold increase of pieces of interconnect

© Fraunhofer IKTS

p

cost reduction of 50%

Conclusions

Formation and growth of the oxide scale during operation at elevated temperatures is the main process for the degradation and long-term stabilityofhighchromiumferriticalloysinSOFCstacks stability of high chromium ferriticalloys in SOFC stacks

Even simple porous protection layers inhibit remarkably the oxidation processoftheinterconnectmaterial process of the interconnect material

Spinelsare most suitable materials for effective low-cost protection layerswhichcanbealsousedascontactintermediateatthecathodesideofthe which can be also used as contact intermediate at the cathode side of the cell

Optimally matched combination of interconnect and protection pyplayer materials is decisive factor to guarantee the long-term operation of the SOFC stack

Ferriticsteelslimited operationtemperature(850°C) andlifetime(<20.000h)

Cr-basedalloyHigher operationtemperatureandlifetime>20.000h

© Fraunhofer IKTS

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