sealing materials for solid oxide fuel cells · 2014. 7. 31. · seca ctp meeting, 10/25/05 (1)...

SECA CTP Meeting, 10/25/05 (1) R.K. Brow, [email protected] University of Missouri-Rolla

Sealing Materials forSealing Materials forSolid Oxide Fuel CellsSolid Oxide Fuel Cells

Richard K. Brow

Materials Science & Engineering DepartmentUniversity of Missouri-Rolla

Rolla, MO 65409

SECA Core Technology ProgramPeer Review Meeting

Lakewood, COOctober 25-26, 2005


AcknowledgementsAcknowledgementsThis research was performed primarily by• Dr. Signo Reis and Mr. Teng Zhang (UMR)

Thanks also go to• Xiao Dong Zhou, Harlan Anderson, Clarissa Vierrether

(UMR)• Raj Singh (U. Cincinnati)• Ron Loehman (Sandia National Labs),• Matt Chou (PNNL)• Matt Seabaugh (NexTech)

The financial support of the Department of Energy (SECA project NT42221/Travis Schultz program manager) is gratefully acknowledged.


OutlineOutline

Goal: Develop stable, resilient sealing materials for SOFCs

• Reviewing the problem; initial glass development research

• Progress over the past six months– Glasses with greater CTE’s– Developing composite materials

• Summarizing our program


The sealing problem is a challengeThe sealing problem is a challenge

1. Challenging compositional design problem

• Uncommon combination of properties

• Investigate uncommon families of glasses

2. Glass-ceramics are a likely option

• Crystallization studies- seal processing and long-term material stability

3. Interfacial chemistry• Glass-metal reactions• Material stability/volatility

• Thermochemical stability


200 400 600 8000.0

0.2

0.4

0.6

0.8

1.0

CTERT-600=8.4x10-6/ 0C

CTERT-600=11.4x10-6/ 0CG36

G27

LG38

"As made glasses"

% L

inea

r Cha

nge

Temperature ( 0C )

ZnO/(SrO+CaO)=0.00ZnO/(SrO+CaO)=0.35ZnO/(SrO+CaO)=1.00

Glass forming system under study:•Alkaline earth/zinc pyrosilicates

•35-50 SiO2•30-50 RO (R=Mg, Ca, Sr, Zn; no Ba)•0-10 B2O3, Al2O3, TiO2, etc.

Design targets include:•10<CTE<13 ppm/ºC•800ºC<Tseal< 900ºC•Thermochemical and thermomechanicalstability

Sealing glass propertiesSealing glass propertiesdepend on compositiondepend on composition


200 400 600 8000.0

0.2

0.4

0.6

0.8

1.0

1.2

CTERT-600=10.0x10-6/ 0CG27

CTERT-600=5.5x10-6/ 0CLG38

CTERT-600=12.4x10-6/ 0CG36

"As sealed glasses"

% L

inea

r Cha

nge

Temperature ( 0C )

ZnO/(SrO+CaO)=0.00ZnO/(SrO+CaO)=0.35ZnO/(SrO+CaO)=1.00

Sealing glass propertiesSealing glass propertiesdepend on compositiondepend on composition

Glass forming system under study:•Alkaline earth/zinc pyrosilicates

•35-50 SiO2•30-50 RO (R=Mg, Ca, Sr, Zn; no Ba)•0-10 B2O3, Al2O3, TiO2, etc.

Design targets include:•10<CTE<13 ppm/ºC•800ºC<Tseal< 900ºC•Thermochemical and thermomechanicalstability


Thermal properties of sealing glasses are Thermal properties of sealing glasses are controlled by the controlled by the ZnOZnO/RO ratio/RO ratio

20 40 60 80 100

(2) - CaSrAl2Si2O7

(1) - Ca2ZnSi2O7

(2)(2)(1)

(1,2)

(1,2)

(1,2)

2θ ( degree)

As-sealed G27

As-sealed G36, 750C for 10 days

As-sealed LG38

ZnO/(SrO+CaO)=0.00CTE=12.4 ppm/ºC




Representative crystalline phasesRepresentative crystalline phasesin the UMR glassin the UMR glass--ceramicsceramics

• Pyrosilicates– CaSrAl2SiO7, Ca2ZnSi2O7

• Orthosilicates– Sr2SiO4, Zn2SiO4

• Composition is most important parameter for final phase distribution.

20 40 60 80

0

500

1000

1500

2000

2500

CP

S

As-sealed(850°C/4 hrs)

CaSrAl2SiO7Ca2ZnSi2O7

20 40 60 80

0

400

800

120028 days/750°C

Crofer APU22/G#27750ºC/100 hrs


Glass#27 possesses a good CTEGlass#27 possesses a good CTE--match with YSZ match with YSZ

200 400 600 800 1000-0.04

0.00

0.04

0.08

0.12

As sealed

3 days/750oC

7 days/750oC

14 days/750oC

28 days/750oC

ΔCTE

(gla

ss-Y

SZ)

Temperature(oC)

Glass #27

Expansion of residual glass

CTE match below 650ºC


Greater Greater CTECTE’’ss are neededare neededfor some SOFC designsfor some SOFC designs

• Compositional modifications include– Replacing ZnO with CaO and SrO– Reducing Al2O3 content– Modifying relative SiO2 and B2O3 contents

• About fifteen new compositions prepared this past reporting period


Glass #36 may be more appropriateGlass #36 may be more appropriatefor some SOFC designsfor some SOFC designs

200 400 600 800 10000.0

0.2

0.4

0.6

0.8

1.0

1.2

750

% L

inea

r Cha

nge

Temperature ( 0C )

αRT-800=119x10-7/ 0C

αRT-800=100x10-7/ 0C

E-briteCroferYSZ (Y-Stabilized Zirconia)G#36, 850oC for 2hrs


0 10 20 30 40 50 60 70 80

20

40

60

80

100

Res

idua

l gla

ss (%

)

days

Held at 750ºC/airHeld at 800ºC/air

Crystallization Kinetics of Glass#36/DTA AnalysesCrystallization Kinetics of Glass#36/DTA Analyses


The CTE of glass#36 changes at 800The CTE of glass#36 changes at 800ººCC

100 200 300 400 500 600 700 800 9004

5

6

7

8

9

10

11

12

13

14

15

16

As sealed (890oC2h)

800oC 1 week

CTE

(10

-6 /

o C)

Temperature ( 0C )

‘as sealed’- 890ºC/2hrs

After one week at 800ºC

12.3 ppm/ºC11.4 ppm/ºC

Long term (1000 hrs) are underway


CaCa--silicate phases form on crystallizationsilicate phases form on crystallization

‘as sealed’, 890ºC(1)- CaSiO3(2)- CaSrSiO4

800ºC, one week (1)- CaSiO3(2)- CaSrSiO4


Crofer-Glass(UMR-36) sealAnnealed at 800ºC, tested at RT

Raj Singh- U. Cincinnati

0

200

400

600

800

1000

1200

1400

0 100 200 300 400 500 600

Time (Minutes)

Pres

sure

(Tor

r)

As MadeAfter annealing 50 hoursAfter annealing 100 hoursAfter annealing 500 hours

Leaker/500 hrs

Initial Hermeticity TestsInitial Hermeticity Tests-- Mixed ResultsMixed Results


0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

0.05

0.055

0.06

500 600 700 800 900 1000 1100Temperature (C)

delta

Tem

p.

2-5 um30-50 um

We use DTA to characterizeWe use DTA to characterizeprocessing effects on propertiesprocessing effects on properties

Finer particles crystallize more readily


-12

-11.8

-11.6

-11.4

-11.2

-11

-10.8

-10.6

-10.4

0.78 0.79 0.8 0.81 0.82 0.83

1000/T (K-1)

ln(β

/T2 )

Kissinger analysis: DTA heating rates

We use DTA to characterizeWe use DTA to characterizeprocessing effects on propertiesprocessing effects on properties

FineParticles,

355 kJ/mole

CoarseParticles,

346 kJ/mole


0

0.2

0.4

0.6

0.8

1

1.2

100 300 500 700 900

Temperature (C)

% L

inea

r Cha

nge 'as sealed', 10.3 ppm/C

2 weeks at 750C, 11.1 ppm/C

4 weeks at 750C, 11.5 ppm/C

Glass#51 has promisingGlass#51 has promisingdilatometricdilatometric characteristicscharacteristics


10 20 30 40 50 60 70 80 900

200

400

600

800

(2) - SrSiO3

2 2

2

2

2

2

22

2 22

2

2

21

1 1

1

11 1 1

(1) - Sr2Al2SiO7

Cou

nts

Cou

nts

2θ (degree)

As-sealed G#51, 750oC 2 weeks

0

200

400

600

800

(2) - SrSiO3

1

1

1

1

11

(1) - Sr2Al2SiO7As-sealed G#51

As sealed G#51

Two weeks at 750ºC

SrSr--silicate phases form on crystallizationsilicate phases form on crystallization

(1) – Sr2Al2SiO7(2) - SrSiO3

(1) – Sr2Al2SiO7(2) - SrSiO3


0 2 4 6 8 10 12 14 1610-5

10-4

10-3

G#36

G#52G#51

G#27

ΔWei

ghta

t 800

ºC (g

/cm

2 )(w

et fo

rmin

g ga

s)

days

Glass stability in wet forming gas (800Glass stability in wet forming gas (800ººC)C)

More stable materials have•Less residual glass•Lower B2O3-contents


GlassGlass--metal adhesion strength measured metal adhesion strength measured by pinby pin--pull testpull test

Romulus adhesion testing machine- Quad Group Inc.

~300μm glass coatings on interconnect substrates; ‘as sealed’and after heat treatments

G#27/430 SS

G51/430SS- ‘as sealed’ 20.9±6.9 MPa

G51/430SS- 750ºC/700hrs 20.7±10.2 MPa

G52/430SS- ‘as sealed’ 19.8±3.8 MPa

G52/430SS- 750ºC/700hrs 18.9±2.6 MPa


Sealing materials can be Sealing materials can be modified by adding fillersmodified by adding fillers

• Tailor CTE• Control crystallization• Affect interfacial reactions• Relieve thermal stresses

– Controlled cracking in glass matrix; healing by viscous flow of residual glass• Design CTE and elastic mismatches


Composite OverviewComposite OverviewMaterial CTE

(ppm/ºC)Elastic Modulus (GPa)

Notes

G36 12.1 80

Ni 13.3 207

Mo 5.1 324

316SS 17 193

Ti-Ni 34-83 Phase transition

WC 5.2 669

SiC 4.3 483

ZrO2 7.0→10.5 138-210 Phase transition

Quartz 7.0→13.3 Phase transition


0

0.2

0.4

0.6

0.8

1

1.2

100 300 500 700 900 1100

Temperature (C)

% L

inea

r Cha

nge

G36, 864C 1h90%G36/10%Ni90%G36/10%SiC90%G36/10%SS

DilatometricDilatometric characteristics depend on fillercharacteristics depend on filler


0.015

0.02

0.025

0.03

0.035

0.04

0.045

0.05

0.055

0.06

0.065

500 600 700 800 900 1000 1100

Temperature (C)

delta

Tem

p.

G36/10%SiCG36(53um)

Composite crystallization behaviorComposite crystallization behaviorwill be characterized by DTAwill be characterized by DTA


Experiments UnderwayExperiments Underway

• Composite processing– Dense seals using tape-casting techniques

• Composite properties– Tailoring CTE– Induced cracking?

• Composite reactivity– Filler/matrix compatibility’– SOFC interfaces


SOFC Seal SummarySOFC Seal Summary• SOFC seals offer an interesting materials challenge• RO- polysilicate compositions have promising

combinations of properties– Polysilicate glass-ceramics can be designed with

thermal and chemical properties desired for some SOFC seal designs.

– Thermo-chemical and thermo-mechanical stabilities are critical for long-term applications.

• Composite seals based on RO-polysilicate glasses– Reduce stresses due to thermal cycling?

Thank you for your attention!Thank you for your attention!

sealing materials for solid oxide fuel cells · 2014. 7. 31. · seca ctp meeting, 10/25/05 (1)...

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