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 !