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High Temperature Glass SealHigh Temperature Glass SealHigh Temperature Glass Seal

Y-S Chou, J.W. Stevenson, X. Li, G. Yang, and P. SinghK2-44, Materials Division

Pacific Northwest National Laboratory

Funded under the SECA Core Technology Program through US Department of Energy’s

National Energy Technology Laboratory

August 7-9, 2007, San Antonio, Texas

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OutlineOutlineOutline

Accomplishment of FY07Mechanical strength evaluation: plain crofer, aluminized, spinel-coated Electrical stability evaluation: aging under DC loading SummaryFuture work

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FY07 AccomplishmentFY07 AccomplishmentFY07 AccomplishmentCompleted seal strength evaluation of high-temperature glass. Evaluated pre-oxidation, aging, coating, and environmental effects on strength.Without coating, strength would degrade if a thick Cr2O3 oxide layer present or aged in air. No strength reduction if aged in reducing gas. Cause for strength degradation was SrCrO4formation.Alumina coating is effective in blocking Cr; however, the deposition process needs to be optimized to minimize overdose. Spinel coating showed best results with minimum strength reduction even aging in air.Tested conventional and high-temperature sealing glasses in SOFC environment and 0.7 V DC loading. Conventional glass showed severe Fe diffusion and rapid increase in conductivity (830oC/~80hr), while high-temperature glass showed excellent electrical stability over ~1200hr at 850oC.

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High-temperature sealing glass HighHigh--temperature sealing glass temperature sealing glass

800oC

850oC

950oC

1000oC

1. Increase contact bonding strength2. Increase thermal stability3. decrease interfacial reactions

Tseal

Toperation

Tseal

time

ΔT

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Mechanical strength evaluationMechanical strength evaluationMechanical strength evaluation

1. Effect of pre-oxidation: Cr2O3 layer thickness2. Effect of different protective coating: Al2O3,

(Mn,Co)3O4

3. Effect of environment: oxidizing, reducing4. Accelerated condition:

850oC/500h in air850oC/250h in 30%H2O, 70%(2.7%H2/Ar)

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Interfacial tensile testingInterfacial tensile testingInterfacial tensile testing P

Al grip fixture

epoxy glass crofer

R. T.0.5 mm/min cross-head speed5-7 samples tested for each conditionSelf-aligned grip fixture½”x½” sample size

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Pre-oxidized croferPrePre--oxidized croferoxidized crofer

1000oC/2h 1200oC/2h

To mimic long-term oxidation1200oC resulted in pores underneathOutside discrete and non-uniform (Mn,Cr) oxide, inside dense and continuousCr2O3-rich oxideT<0.5μm (800oC/2h)

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Effect of pre-oxidation on tensile strengthEffect of preEffect of pre--oxidation on tensile strengthoxidation on tensile strength

crofer/YSO75, pst/crofer, 1/2"x1/2" at RT

0

1

2

3

4

5

6

7

8

9

none 800C/2h 1000C/2h 1200C/2h

pre-oxidation conditions

aver

age

tens

ile s

tren

gth,

MPa

~1-2 μm ~6-10 μm

<0.5 μm

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Load-displacement curve showed typical brittle failure

LoadLoad--displacement curve showed displacement curve showed typical brittle failuretypical brittle failure

RT YSO75 Crofer-AR @ 0.5mm/min

0

100

200

300

400

500

600

700

800

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

displacement (mm)

load

(N)

All showed brittle failure: coating, aging, oxide layer thickness, environment

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As-received

1000oC/2hPre-oxidized

Mixed fracture

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Fracture initiated mostly from edge flaws

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Effect of aging and environmentEffect of aging and environmentEffect of aging and environment

effect of aging on strength, crofer/YSO75/crofer, 1/2"x1/2"

0

1

2

3

4

5

6

7

8

9

10

no aging 850C/500h air aged 850C/250h red.aged

aver

age

tens

ile s

tren

gth,

MPa

Air: 850oC/500hWet and reducing: 30%H2O, 70%(2.7H2/Ar) 850oC/250h

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Fracture surface of aged sampleFracture surface of aged sampleFracture surface of aged sample

Presence of substantial amount of SrCrO4

850oC/500h air 850oC/250h reducing gas

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Aluminized crofer showed no chromate formation

Aluminized crofer showed no Aluminized crofer showed no chromate formationchromate formation

Plain crofer Aluminized crofer

SrCrO4

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Tensile strength of aluminized croferfrom pack cementation

Tensile strength of aluminized Tensile strength of aluminized crofercroferfrom pack cementationfrom pack cementation

RT average strength, MPa

0

1

2

3

4

5

6

7

8

9

none 1000C/2h 1200C/2h

oxidation condition

aver

age

stre

ngth

, MPa

Pack cementation, followed by heat-treatment in air

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Sealing with aluminized crofer from vapor phase deposition

Sealing with aluminized Sealing with aluminized crofercrofer from vapor from vapor phase depositionphase deposition

Vapor phase deposition followed by heat-treatment at 1000oC/2h airAs-sealed coupons all fractured through glass.Glass bonded well to aluminized crofer coupons.

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Appreciable amount of Al diffusionAppreciable amount of Al diffusionAppreciable amount of Al diffusion

Fe

Cr

Al 15%10%

5%

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Issue of overdosing AlIssue of overdosing AlIssue of overdosing Al

as-received and aluminized crofer22APU

0.00E+00

2.00E-03

4.00E-03

6.00E-03

8.00E-03

1.00E-02

1.20E-02

1.40E-02

1.60E-02

0 200 400 600 800 1000

Temp (ºC)

Line

ar E

xpan

sion

Aluminizing by vapor phase deposition followed by heat-treatment at 1000-1100oC/2h air

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RT seal strength of spinel-coated crofer/YSO75 glass

RT seal strength of spinelRT seal strength of spinel--coated coated crofer/YSO75 glasscrofer/YSO75 glass

RT average tensile strength (spinel coating)

0

1

2

3

4

5

6

7

8

9

10

plain as-sealed coated as-sealed

coated air aged coated red. aged

aver

age

stre

ngth

, MPa

(Mn,Co)3O4 coated crofer22APU

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Fracture surface of as-sealedMn1.5Co1.5O4-coated crofer22APU

Fracture surface ofFracture surface of asas--sealedsealedMnMn1.51.5CoCo1.51.5OO44--coated crofer22APUcoated crofer22APU

Fracture through glass, not at the interface. YSO75 not fully coverageAll 8 samples showed edge flaw

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Fracture surface of air agedMn1.5Co1.5O4-coated crofer22APU

Fracture surface ofFracture surface of air agedair agedMnMn1.51.5CoCo1.51.5OO44--coated crofer22APUcoated crofer22APU

850oC/500 h air

Suggest 5 μm coating was not enough

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Setup for resistivity measurementSetup for Setup for resistivityresistivity measurementmeasurement

air side

fuel sidehybridmica seal

alumina supportpipe

Inconel pressingfixture

crofer

crofer crofer

compressive loading

glass glass

VV

Power supply

+

+

-

-

resistor

sense

sense

out

out

air side

fuel sidehybridmica seal

alumina supportpipe

Inconel pressingfixture

crofer

crofer crofer

compressive loading

glass glass

VV

Power supply

+

+

-

-

resistor

sense

sense

out

out

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Good electrical stability for HT glass on plain crofer22APU

Good electrical stability for HT glass on Good electrical stability for HT glass on plain crofer22APUplain crofer22APU

YSO75 @0.7V & 20%H2O, 2.7%H2/Ar (t<432hrs), 80%H2 (t>432hrs)power outage @ ~700 h

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

0 200 400 600 800 1000 1200

hrs at elevated temperatures

ohm

-mCrofer(as-received)/glass/crofer(as-received) @ 0.7V

G18 @830oC

YSO75 @ 850oC

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EDS showed substantial Fe diffusionEDS showed substantial Fe diffusionEDS showed substantial Fe diffusion

G18 near air side after electrical stability test

1

2

point O% Al% Si% Ca% Cr% Fe% Ba%1 43 1 1 50 4 12 44 27 16 1 123 43 20 24 1 124 47 3 16 6 7 215 44 1 5 2 11 28 9

34

5

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Good electrical stability for HT glass on (Mn,Co)3O4-coated crofer22APU

Good electrical stability for HT glass on Good electrical stability for HT glass on (Mn,Co)(Mn,Co)33OO44--coated crofer22APUcoated crofer22APU

YSO75 spinel coated 0.7V (30%H2O, 70% (2.7%H2/Ar))

1.00E+00

1.00E+01

1.00E+02

1.00E+03

1.00E+04

1.00E+05

0 100 200 300 400 500 600

hrs @ 850C

ohm

-m

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Materials set evaluation in 2”x2” singelcell test @ 800oC

Materials set evaluation in 2Materials set evaluation in 2””x2x2”” singelsingelcell test @ 800cell test @ 800ooCC

INDEC cell, SS441, spinel coating, LSM contact paste, aluminizing

SS441, YSO77x1, spinel, LSM, H-micax4, 97%H2 450 sccm,air 900 sccm

0

0.1

0.2

0.3

0.4

0.5

0.6

0 20 40 60 80 100 120 140 160 180 200

hrs @ 800C

pow

er d

ensi

ty, W

/cm

^2

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Summary FY07Summary FY07Summary FY07

Mechanical strength tests of M/G/M coupons showed strength degradation for uncoated crofer22APU only if aged in air or started with thick Cr2O3 surface layer.Aluminizing is effective in blocking Cr; however, overdosing would increase CTE for thin samples and leads to seal failure.(Mn,Co)3O4-coated crofer showed similar initial seal strength as plain crofer or aluminized ones. Minimal strength degradation when aged in air.HT glass showed very good electrical stability in SOFC and DC loading at 850oC up to ~1200h.Successful demonstration of 2”x2” single cell test at 800oC with candidate materials set: HT glass, spinel coating, SS441, and LSM contact paste.

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Future workFuture workFuture workMaterials set validation with single cell (2”x2”) stack testing and standardize the design:

1. Sealing glass: high-temperature, self-healing and composite.

2. Metallic interconnect: SS441 (standard or low Si), crofer22APU

3. Protective coating: (Mn,Co)3O4, aluminaShort-term (200-500h) performance test at 800-850oCShort-term thermal cycling test (800oC/24h, cool to RT)x10Collaboration with modeling workStrengthening of candidate high-temperature glass with reinforcement