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Raj Singh-2006
INNOVATIVE SEALS FOR SOLID OXIDE
FUEL CELLS (SOFC)-SOFT SEALS
Raj N. Singh
Department of Chemical and Materials EngineeringUniversity of Cincinnati, Cincinnati
OH 45221-0012
Supported by DOE-SECA Program (Drs. Mani Mannvanan and TravisShultz, Project Managers) and University of Cincinnati
SECA Workshop, Philadelphia, September 12-14, 2006
Raj Singh-2006
INTRODUCTION
Requirements of Seals for SOFC
Electrochemical-insulating to avoid shorting
Lowest possible thermomechanical stresses upon processing, duringheatup, cooldown, and in steady state/transient operations
Long life (5,000-40,000h) under electrochemical and oxidizing/reducingenvironments at high temperatures ~600-850°C
Low cost
Type of Seals
Ceramic-Ceramic (Electrolyte-Ceramic Insulator)
Ceramic-Metal
Metal-Metal
Rigid and/or Compliant
Chemical/Mechanical/Liquid
Raj Singh-2006
PROGRAM OBJECTIVES AND
ACCOMPLISHMENTS
Phase-ISelect self-healing glasses for functionality as seals for SOFCs
Demonstrate functionality of the self-healing seals by leak tests
Measure stability of the self-healing glass in SOFC environments
Develop approaches to toughening self-healing glasses as seals for SOFs
Survey commercial glasses suitable for making seals for SOFCs
AccomplishmentsDeveloped glasses displaying self-healing ability
Demonstrated ability of self-healing glasses in sealing components through leaktests overa range of temperatures between 25-800°C
Achieved 300 thermal cycles between 25-800°C without leak of seals andaccumulated 3000 hours of hermetic seal performance at 800°C
These results provide great promise towards meeting SECA goals of seals forSOFC.
Raj Singh-2006
SEALS FOR PLANAR SOFC
Metal-Ceramic and Metal-Metal Seals Must Work at 650-850°C in Corrosive
Environments of Fuel and Air
Ceramic Spacer
Metal Interconnect
Metal Interconnect
Metal Frame
Metal Endplate
Fuel Air Air Fuel
Metal-Metal Seal
Ceramic-Metal SealElectrolyte
Raj Singh-2006
MATERIALS FOR CELL COMPONENTS
Electrolyte: YSZ, 10-30 μm, dense
Anode: Ni-YSZ Cermet, 25-600 μm, porous
Cathode: Doped La-Perovskite, 25-2000 μm, porous
IC (Interconnect): Doped Chromites/Alloys, 30 μm -5mils, dense
Seals: Insulating Ceramics/Glasses, dense
Manifolds: Heat Resistant Alloys
Operating Temperature: 650-850°C
Fuels: Reformed PNG, Propane, Diesel etc.
• Highly incompatible materials require seals
Raj Singh-2006
POSSIBLE APPROACHES TO SEALS FOR SOFC
Rigid SealsGlass-Metal, Ceramic Polymer-Ceramic/Metal, Brazes: require stableglasses, brazes, preceramic polymers
Low leak rates but susceptible to failures due to stresses
Feedback to materials and seal concept modifications to reduce stressbuildup and avoid failure
Compliant SealsBellows, Viscous Glass, Wet-Seals (MCFC): require flexible seal designs,stable glasses with appropriate viscosity over a range of temperature, wet-sealing materials and their containment
Moderate leak rate, some concepts may require pressure
Our Approaches for SealsSelf-Healing Glass Seals
Reinforced-Glass Seals
Layered Composite Seals
Raj Singh-2006
A SELF-HEALING SEALING CONCEPT
FOR SOFC
Rationale: A glass of appropriate characteristics can self-heal the cracks createdupon thermal cycling and/or stresses created during SOFC operation. In addition,thermomechnical incompatibilities between ceramic and metallic materialsrequiring seals/joining can be alleviated using a self-healing glass seal.
Advantages: Materials with dramatically different expansions can potentially beused for seals because this approach can alleviate/minimize thermomechanicalstresses and chemical reactions. The leaks developed upon SOFC operation andthermal cycling can be repaired in situ by the self-healing concept.
Challenges: Develop appropriate glasses which satisfy thermomechanical andthermochemical compatibilities, remain stable for long-time, and maintain self-healing capability.
Approach: Thermophysical and thermochemical property measurements andoptimization,self-healing ability, and leak testing to demonstrate self-healing seals.
Raj Singh-2006
OBJECTIVES
Demonstrate Self-Healing Behavior of Glass
Fabricate Seals Displaying Self-Healing Response
Describe Performance and Durability of the Self-Healing Seals Under SOFC Conditions
Fuel Environment
Dual Fuel-Air Environments
Thermal Cycles and Time
Raj Singh-2006
EXPERIMENTAL
MaterialsElectrolyte YSZ (Tape Casting and Sintering)
Metal (Crofer22 APU)
Sealant-Silicate Glass
Fabricate Seals Displaying Self-Healing BehaviorSelf-healing Behavior by Video Imaging
Performance and Durability of the Self-Healing SealsTesting at RT and High Temperatures
Effect of Pressure Drop Across The Seal
Effect of Thermal Cycling Between 25-800°C
Effect of Test Atmosphere Typical of SOFC
Effect of Time at 800°C on Seal Durability
Raj Singh-2006
A SEAL PERFORMANCE TEST SYSTEM
Continuous monitoring of leak test conditions
304
stainless
steel
Glass Seal
YSZ
Crofer
HighPressure
LowPressure
P
Furnace
Data
Acquisition
Raj Singh-2006
STUDY OF CRACK-HEALING BEHAVIOR OF
GLASS
Demonstration of self-healing of crack
Glass Glass
Unhealed Healed
Raj Singh-2006
LEAK PERFORMANCE OF SELF-HEALING SEAL
At 25°C
Hermetic response
0
200
400
600
800
1000
1200
1400
0 200 400 600 800 1000 1200
Time (Minutes)
Pre
ss
ure
(T
orr
)
P ~ 150 Torr
Seal (Crofer-Glass-YSZ)
Raj Singh-2006
LEAK PERFORMANCE OF SELF-HEALING SEAL
At High Temperatures
Hermetic behavior upon heating and cooling
0
200
400
600
800
1000
1200
1400
0 100 200 300 400 500
Time (Minutes)
Pre
ssu
re (
To
rr)
Crofer / Glass / YSZ Seal
Atmospheric Pressure= 730 Torr
Heating Cooling
First cycle
250C P= 50 Torr
5000C P= 50 Torr 7500C P= 50 Torr
7000C P= 50 Torr 500
0C P= 50 Torr
4000C P= 50 Torr
Raj Singh-2006
DEMONSTRATION OF SELF-HEALING
BEHAVIOR OF SEAL AT HIGH TEMPERATURES
Hermetic behavior after self-healing
0
200
400
600
800
1000
1200
1400
0 100 200 300 400 500
Time (Minutes)
Pre
ssu
re (
To
rr)
Crofer / Glass / YSZ Seal
Atmospheric Pressure= 740 Torr
Heating Cooling
Third cycle
Seal started leaking after 25
minutes at 8000C
5000C P= 40 Torr
7500C P= 40 Torr
8000C P= 40 Torr
7500C P= 40 Torr
5000C P= 40 Torr
4000C P= 40 Torr
Raj Singh-2006
DEMONSTRATION OF SEAL DURABILITY UPON
THERMAL CYCLING BETWEEN 25-800°C IN DRY
FUEL
Hermetic behavior after 217 cycles/1700 h
0 20 40 60 80 100 120 140
Time (Minutes)
Pre
ssu
re (
To
rr)
Cycle #216
Cycle #215
Cycle #214
Cycle #213
Cycle #212
Cycle #211
Cycle #210
Cycle #209
Cycle #208
Cycle #207
Cycle #206
Cycle #217
8000C 250C
Pressure inside the seal: 740 Torr. Atmospheric pressure 760 Torr.
Raj Singh-2006
DEMONSTRATION OF SEAL DURABILITY UPON
THERMAL CYCLING BETWEEN 25-800°C IN WET
FUEL
Hermetic behavior after 232 cycles/2100 h
0 20 40 60 80 100 120 140
Time (Minutes)
Pre
ssu
re (
To
rr)
Cycle #230
Cycle #229
Cycle #228
Cycle #227
Cycle #226
Cycle #225
Cycle #224
Cycle #223
Cycle #222
Cycle #221
Cycle #220
Cycle #219
Cycle #218
Cycle #232
Cycle #231
8000C 250C
Pressure inside the seal: 740 Torr. Atmospheric pressure 760 Torr.
Raj Singh-2006
DEMONSTRATION OF SELF-HEALING ABILITY
AND SEAL DURABILITY BETWEEN 25-800°C IN
DUAL ATMOSPHERE
Self-healing in 271 cycle of leak in 270 cycle/2900 h
0 20 40 60 80 100 120 140
Time (Minutes)
Pre
ssu
re (
To
rr)
Cycle #250
Cycle #245
Cycle #240
Cycle #237
8000C 250C
Cycle #270
Cycle #265
Cycle #260
Cycle #255
Cycle #271
Pressure inside the seal: 740 Torr. Atmospheric pressure 760 Torr.
Raj Singh-2006
SUMMARY
A self-healing sealing concept is developed for SOFC tosatisfy significant thermochemical and thermomechanicalincompatibilities among materials requiring hermetic seals.
Seals incorporating self-healing concept were fabricated andtested under conditions prototypical of a SOFC.
Performance of the self-healing seals for ~3000 hours and~300 thermal cycles was demonstrated via leak tests asfunctions of temperature, pressure, thermal cycling,environment, and in situ self-healing.
Long term leak test results demonstrated promise of the self-healing seals for potential applications in SOFC.
Raj Singh-2006
PROGRAM OBJECTIVES-Phase II
Develop additional sealing glasses and demonstrate long-termstability
Demonstrate toughening of glasses by fiber reinforcement
Demonstrate seal durability of self-healing and reinforced-glasses
Demonstrate and transition sealing technology to SECA team
Raj Singh-2006
ACKNOWLEDGMENTS
SECA Core Technology for Program Support
Mani Mannvanan and Travis Shultz for Program Management and Guidance onProject
Wayne Surdoval, Don Collins, and Lance Wilson for Discussions on Seals
S. Parihar for help with experiments
PNNL, Ceramatec, and University of Utah for Electrolyte Samples
Matt Chou, Jeff Stevenson, P. Singh, S. Elangovan and Anil Virkar
GE Power Systems, FuelCell Energy, and Delphi for Guidance andIndustry Perspective
N. Minh, Pinakin Patel, and Diane England
Raj Singh-2006
Thank You !