National Energy Technology Laboratory

SOFC Interconnect Work at NETL

Paul Jablonski and

David E. Alman

National Energy Technology Laboratory

Office of Fossil Energy

RE Surface Treatment Results

• Oxidation resistance of Crofer improved by 3x (800C/3% water/4,000h)− Appears to minimize internal silica layer formation

• Improved ASR (800C/500h)− Button cell tests underway

• Oxidation resistance of type 430 vastly improved− Eliminated spall (800C/3% water/4,000h)

• Effectively makes 12 Cr alloys perform as 22 Cr

Improving Oxidation Resistance with Rare Earths

• Well established that small amounts RE improve oxidation resistance (RE: Ce, La, Y)

• Melt addition+Elements added during ingot production (single

manufacturing step)−Difficulty in melting (react with crucibles)−Surface concentration limited by solubility and diffusivity

• Surface treatments+Rare Earth concentrated where needed (at surface and

have most benefit)− “Extra” manufacturing step.? Long term effectiveness (as with any coating or surface

treatment)

Research Goal• Investigate rare earth surface treatment for improving

oxidation resistance of alloys for SOFC applications.• Two different surface treatments investigated

−Developed at NETL• Similar to pack cementation: coated with a powder mixture containing

CeO2 or CeN and halide activator followed by heating in a controlled atmosphere (900oC-12 hrs), after which residual “pack” coating is washed off the surface.

• Patent application filed with USPTO in September, 2005.• Applied to over 50 alloys of interest to FE.

−Described in a paper by P.Y. Hou and J. Stringer (H/S)• J. Electrochem Soc., Vol 134, No. 7, July 1987, pp. 1836-1849• Coupons heated to 200oC were coated with a cerium-nitrate slurry

(10w/o nitrate adjusted with HNO3 to pH=2), followed heating in air at 400oC to decompose to CeO2

Surface Treatments to Improve Oxidation• As part of NETL-Albany’s SOFC research effort, we

have utilized surface treatments to incorporate reactive elements (Ce, La, Pr) into the surface of metallic alloys for development of metallic interconnects.

Crofer 22APU: 800oC-Air+3%H2O

Time (hrs)0 1000 2000 3000 4000 5000

Spec

ific

Mas

s C

hang

e (g

/cm

2 )

0.0000

0.0002

0.0004

0.0006

0.0008

0.0010

0.0012

0.0014

Crofer22APU - As received Crofer 22APU + ARC RE AdditionCrofer 22APU + RE Addition via method described by Hou and Stringer (1987)

800oC-Air+3%H2O-500hrs

Binding Energy (eV)

01002003004005006007008009001000

Rel

ativ

e In

tens

ity

0

2000

4000

6000

8000

Mn 3p

Crofer 22APUCrofer 22APU+Ce (ARC process)Crofer 22APU+Ce (Hou and Stringer process)

Cr 3s

Si 2s

Ce 4p3

Si 2p / Ce 4d

C 1s

Ti 2p

O 1s

Ti 2sC

r 2p

Mn 2pC

e 3d5C

e 3d3

Mn 2s

Cr 2S

Fe 2p

Thermal Treatment (TC) Only is Ineffective

Repeatable Behavior

800oC-Air+3%H2O

Time (hrs)

0 1000 2000 3000 4000 5000

Spec

ific

Mas

s C

hang

e (g

/cm

2 )

0.0000

0.0005

0.0010

0.0015

#1, Nov 04#2, Nov 04#3, Nov 04#4, Mar 05#5, Nov 05#6, Nov 05

#1, Nov 04#2, Nov 04#3, Nov 04 #4, Mar 05 #5, Nov 05 #6, Nov 05

Crofer 22APU+Ce

Crofer 22APU

Crofer 22APU

Crofer 22APU+Ce

Effect of Ce Treatment: Fe-Ce-0.5Mn-1Ti

800oC-Air+3%H2O

Time (hrs)

0 200 400 600 800 1000 1200 1400 1600 1800

Spec

ific

Mas

s C

hang

e (g

/cm

2 )

0.000

0.001

0.002

0.003

F9 (12Cr)F10 (18Cr)F11 (22Cr)F9+Ce (12Cr)F10+Ce (18Cr)F11+Ce (22Cr)

Fe-Cr-0.5Mn-1.0Ti base

Fe-12Cr + Ce alloy superior

performance to an Fe-22Cr alloy

In Melt Additions of RE

Fe-22Cr-0.5Mn-0.1Ti800oC Air+3% H2O

Time (hrs)

0 500 1000 1500 2000

Spec

ific

Mas

s C

hang

e (g

/cm

2 )

0.0000

0.0002

0.0004

0.0006

0.0008

0.0010

0.0012

0.0014

0.0016F1 (0 mischmetal)F2 (0.05 mischmetal)F3 (0.1 mischmetal) F4 (1.0 mischmetal) Crofer 22APU (0.1 La)

In Melt + Surface Treatment

800oC Moist Air (Fe-22Cr-0.5Mn-0.1Ti)

Time (hrs)

0 500 1000 1500 2000

Spec

ific

Mas

s C

hang

e (g

/cm

2 )

0.0000

0.0002

0.0004

0.0006

0.0008

0.0010

0.0012

F3+Ce F3 Crofer Crofer+Ce

Minor Element Effect

800oC-Air+3%H2O

Time (hrs)

0 400 800 1200 1600 2000 2400

Spec

ific

Mas

s C

hang

e (g

/cm

2 )

0.0000

0.0002

0.0004

0.0006

0.0008

0.0010

0.0012

0.0014

Crofer-J

Crofer-10Crofer-20 Crofer 22APU

Haynes 230

differencedue to Al,Si and Ocontent

Ce Surface Treatment on Crofer 22APU

800oC-Air+3%H2O

Time (hrs)

0 400 800 1200 1600 2000 2400

Spec

ific

Mas

s C

hang

e (g

/cm

2 )

0.0000

0.0002

0.0004

0.0006

0.0008

0.0010

0.0012

0.0014

Crofer-J

Crofer-10Crofer-20

Crofer 22APU+ Ce

Crofer 22APU

Haynes 230

Ce surfacetreatmentreduced weight gain~ 3 times

CROFERCROFER--1010

CROFERCROFER--10+Ce10+Ce

TYPE-430

spalling

Surface: Type-430800oC-4000hrs-Air+3%H2O

430430 430+Ce (ARC)430+Ce (ARC) 430+Ce (H/S)430+Ce (H/S)

Surface: Type-430800oC-4000hrs-Air+3%H2O

Type 430 Type 430 + CeO(NETL)

Type 430 + CeO(H/S)

Stainless Steel Alloys

430-A 430-B 430-C 430-D 430-std Crofer22APU

Fe Bal Bal Bal Bal Bal

16.6

<0.001

0.016

0.37

0.42

0.06

Bal

Cr 16.85 17.03 17.13 17.11 22.42

Ti <0.001 <0.001 <0.001 0.080 0.092

Al <0.001 <0.001 <0.001 <0.001 0.13

Si <0.01 <0.01 <0.01 <0.01 0.12

Mn 0.44 0.47 0.49 0.52 0.45

C 0.005 0.05 0.1 0.01 0.02

Alloys 430A-D were melted and fabricated at NETL

Low Si 430 Alloys

800oC-Air+3%H2O

Time (hrs)

0 100 200 300 400

Spec

ific

Mas

s C

hang

e (m

g/cm

2 )

0.0

0.1

0.2

0.3

0.4

Crofer 22APU (Fe-22Cr-0.45Mn-0.09Ti-0.12Si)430-commercial (Fe-16.7Cr-0.41Mn-0.37Si) 430-A (Fe-16.9Cr-0.44Mn-0.01Si)430-B (Fe-17.0Cr-0.47Mn-0.01Si)430-C (Fe-17.1Cr-0.49Mn-0.01Si)430-D (Fe-17.1Cr-0.52Mn-0.08Ti-0.01Si)

Surface Treated Low Si 430 Alloys

800oC-Air+3%H2O

Time (hrs)

0 100 200 300 400

Spec

ific

Mas

s C

hang

e (m

g/cm

2 )

0.00

0.10

0.20

0.30

0.40

430 (commercial) 430-A 430-B 430-C 430-D

closed symbols Ce surface treated

Summary

• Oxidation results of a simple surface treatment have been presented.

• The Cerium surface treatment improves the oxidation performance of type 430.

• The Cerium surface treatment improves the oxidation performance of RE containing alloys such as Crofer 22 APU.

• Improved ASR results have been achieved with RE treated Crofer 22 APU.

Acknowledgements

• Gordon Xia and Z. Gary Yang from PNNL for performing the ASR measurements.

• Chris Johnson from NETL-Morgantown for assistance with initial SOFC button cell testing.

• W.J. Quadakkers from Forschungszentrum Jülich for supplying the “Crofer J” material.

• Ed Argetsinger, Marisa Arnold, Richard Chinn, Keith Collins, Paul Danielson, Dan Davis, Neal Duttlinger, Mike Hayes, Al Hunt, Steve Matthes, and Dave Smith from NETL-Albany for assistance with experiments.

• Margaret Zoimek-Moroz, Tom Adler, Omer Dogan, Gordon Holcomb, Karol Schrems, Rick Wilson, John Dunning and Paul King from NETL-Albany for contributions to the SOFC effort at Albany.

Experimental Alloys and RE Surface Treated Materials Available For Evaluation by SECA

Participants

Contact: Paul D. Jablonski: 541.967.5982 orDavid E. Alman: 541.967.5885