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Alman, D. E.

Jablonski, P. D.

UNT Digital Library

Surface Modifications for Oxidation Resistance National Energy Technology Laboratory8th Annual SECA Workshop – San Antonio, TX, August 7-9, 2007 David E. AlmanPaul D. JablonskiOffice of Research & Development8th Annual SECA Workshop – San Antonio, TX, August 7-9, 2007 Accomplishments• Surface treatment developed at NETL based on CeO2− Applied to over 50 commercial and experimental alloys including; T430, T441, Crofer22APU− For comparative purposes applied other RE surface treatment that are described in the literature.− RE Treatments are effective in enhancing oxidation resistance.• Initiated long term testing to determine effectiveness.− ASR measurements and single-cell test indicate surface treatment can enhance SOFC performance.− Modified NETL treatment to use La2O3• Investigated influence of Si levels on behavior of interconnect alloys−Oxidation as a function of Si level in T430 (objective is to determine critical Si-level).8th Annual SECA Workshop – San Antonio, TX, August 7-9, 2007 Reactive Element  (RE) Effect• Well known that the addition of small amounts of RE (Ce, La, Y, etc) improves oxidation resistance• Characteristics¾ Reduction in the oxidation rate• Change in scale growth mechanisms• cation transport Æ anion transport• Modification of scale microstructure• large columnar grains Æ small equiaxial grains¾ Stabilize Cr2O3 scales at lower Cr levels¾ Improvement in scale adhesionminor: Mn, Ni, Zr, La22.0BalZMG2320.06 La--0.08--0.522.0BalCrofer22APULaAlTiSiMnCrFeAlloy8th Annual SECA Workshop – San Antonio, TX, August 7-9, 2007 RE Surface Additions• Surface treatments+ Rare Earth concentrated where needed (at surface)+ Applied to any alloy − ($) “Extra” manufacturing step.? Long term effectiveness (as with any coating or surface treatment)La-rich particles- Most commercial ferriticstainless steels do not contain RE ($)• Melt addition+ Elements added during ingot production (single manufacturing step)− Difficulty in melting (react with crucibles)− Surface concentration limited by solubility and diffusivity8th Annual SECA Workshop – San Antonio, TX, August 7-9, 2007 Effect of RE on Oxidation800oC-Air+3%H2OTime (hrs)0 500 1000 1500 2000Specific Mass Change (g/cm2)0.00000.00020.00040.00060.00080.00100.00120.00140.0016F1 F2=F1+0.05 mischmetalF3=F1+0.1 mischmetalCrofer 22APU (0.1 La)w/ NETL-Ce surface treatment~50-60%reduction in massgain w/ surfacetreatmentF1=Fe-22Cr-0.5Mn-0.1Ti   Mischmetal is a combination of Ce, La and other RE8th Annual SECA Workshop – San Antonio, TX, August 7-9, 2007 Cerium Surface Treatments• Developed a combination of  pack cementation and superficially applied coating technique  (NETL).¾Coat surface with a slurry mixture: CeO2 and halide (NaCl) activator. ¾Heat (900oC) in a controlled atmosphere (x10-3Torr)¾Residual “pack” coating is washed off the surface. • Applied treatment described by Hou & Stringer (H/S).¾J. Electrochem. Soc., Vol 134, No. 7, July 1987, pp. 1836-1849.¾Coupons heated to 200oC were coated with a cerium-nitrateslurry (10w/o nitrate adjusted with HNO3 to pH=2), followed by heating in air at 400oC to decompose to CeO2.¾Surface also cleaned in water after treatment.8th Annual SECA Workshop – San Antonio, TX, August 7-9, 2007 Surface After Treating (CeO2-NETL)• The surface treatment pre-oxides the surface. Ce-rich oxide forms at the gas-substrate surface.  A Cr-Mnoxide forms underneath the Ce-rich oxide.Crofer+Ce (NETL)8th Annual SECA Workshop – San Antonio, TX, August 7-9, 2007 ThermodynamicsCeO2 reacts with Crduring treatment to form CeCrO30.10.20.30.40.50.60.70.80.90.10.20.30.40.50.60.70.80.90.10.20.30.40.50.60.70.80.9CeO2Mn Femole fractions /(CeO2+Fe+Mn)Cr(s) + Fe(s) + Ce2O3(s) + Mn(s2) + CeCrO3(s)MnO(s) + Fe(s) + Ce2O3(s) + Mn(s2) + CeCrO3(s)MnO(s) + Fe(s) + Ce2O3(s) + Ce18O31(s) + CeCrO3(s)Ce18O31(s) + Fe(s) + Ce6O11(s) + Monoxide1 + CeCrO3(s)CeO2 - Fe - Mn - Cr800oC,  mole Cr/(CeO2+Fe+Mn) = 0.25/4/2007N:\myfiles\Months\2007\April 2007\David CeO2 Coating\May 4\CeO2-Fe-Mn-20Cr.emfFe(s), CeCrO3, Ce6O11, Ce18O31, MnO8th Annual SECA Workshop – San Antonio, TX, August 7-9, 2007 Surfaces After Treating CeN-based (H/S: 400oC)CeO2-based (NETL:900oC)Ce-oxideCe-oxideFe-Cr8th Annual SECA Workshop – San Antonio, TX, August 7-9, 2007 Surfaces After Treating (Prior to Oxidation)Crofer+Ce (NETL) Crofer+Ce (H/S)CeO2-BasedMax Temp 900oCCeN -BasedMax Temp 400oC68Fe-20Cr-0Mn-1.2 Ce-8.7O*29Fe-10Cr-0Mn-16Ce-43O*76Fe-23Cr-1Mn*not accurate due to edge effect (rounding of edge during sample preparation), however, indicates Ce is present at the surface.Oxide Layer8th Annual SECA Workshop – San Antonio, TX, August 7-9, 2007 800oC-Air+3%H2OTime (hrs)0 1000 2000 3000 4000Specific Mass Change (mg/cm2)0.000.200.400.600.801.001.201.40Influence of Surface Treatment on OxidationCroferCrofer +Ce (NETL)Crofer +Ce (H/S)~2-3x reductionin weight gain8th Annual SECA Workshop – San Antonio, TX, August 7-9, 2007 Total Oxidation NETL Ce-Surface TreatmentCrofer 22APU:800oC-Air+3%H2OTime (hours)0 500 1000 1500 2000 2500Specific Mass  Change (mg/cm2)0.000.200.400.600.801.00Crofer 22APU Crofer 22APU+Ce Crofer 22APU+Ce  total weight gain (treatment+oxidation)8th Annual SECA Workshop – San Antonio, TX, August 7-9, 2007 Influence of Surface Treatment on OxidationDiffraction Angle (2 Theta)15 20 25 30 35 40 45 50 55 60 65 70Relative Intensity05001000150020002500S1E RCS1S2ES1ES1S2ES1FeRCES1S1ER S2E CS1EECroferCrofer+Ce (NETL)Crofer + Ce (H/S)S1=(Mn,Cr,Fe)3O4E=Cr2O3R=TiO2S2=(Mn,Cr,Fe)2O3Fe=Fe-Cr alloyC=CeO24000 hrs-800oC-Air+3%H2O8th Annual SECA Workshop – San Antonio, TX, August 7-9, 2007 Oxide Scale FormationDiffraction Angle (2Theta)25 30 35 40 45 50Relative Intensity0102030405060Crofer+Ce (NETL) 4000 h:800oC-Air+3%H2OFeCS1S1ES1MOEMOECS1ERS1=(Mn,Cr,Fe)3O4E=Cr2O3MO=(Mn,Cr,Fe)2O3O1=CrCeO3R=TiO2C=CeO2Fe=Fe-Cr alloyCrofer+Ce (NETL) – 0 hrsO1 O18th Annual SECA Workshop – San Antonio, TX, August 7-9, 2007 Influence of Surface Treatment on OxidationDetailed scale microstructures can be found in  D.E. Alman and P.D. Jablonski, “Effect of Minor Elements and a Cerium Surface Treatment on the Oxidation Behavior of an Fe-22Cr-0.5Mn (Crofer 22APU) Ferritic Stainless Steel, International Journal of Hydrogen Energy, accepted for publication (2006),  currently available on line at  www.sciencedirect.com.thinner oxide scales with surface treatments800oC-2000h-Air+3%H2OCrofer+Ce (NETL) Crofer+Ce (H/S)Crofer2µm36Cr-0.5Mn (Cr2O3)20Cr-20Mn26Cr-13MnSiO2Ce-rich oxide17Cr-16Mn25Cr-12Mn36Cr-0.5MnAl-rich oxideCe-rich oxide38Cr-1Mn25Cr-13MnCrofer+Ce (H/S)8th Annual SECA Workshop – San Antonio, TX, August 7-9, 2007 Influence of Surface Treatment on Oxidation800oC-4000hrs-Air+3%H2OMinimize internal oxidationCrofer + Ce(NETL)Crofer + Ce (H/S)Crofer8th Annual SECA Workshop – San Antonio, TX, August 7-9, 2007 Surface Treatments• Slows scale growth − Scale microstructures were similar with NETL and H/S treatment methods.• Minimizes  internal oxidation.− Indicates slows oxygen diffusion through the scale.• Ce at surface modifies initial stages of transient oxidation Æ alters the subsequent growth of the scaleÆ enhanced oxidation resistance.− formation of CeCrO3 – type oxide during transient oxidation.− Pre-oxidation during NETL treatment • (initial oxidation of H/S?)• Why?− Scale microstructure is changed• (high diffusivity columnar to low diffusivity equiaxed)− Ce in oxide changes diffusion through oxide.− NETL-ORD  IAES project at CMU to investigate influence of RE on transient oxidation.8th Annual SECA Workshop – San Antonio, TX, August 7-9, 2007 coatingJ. Rakowski, 20062 to 3 timesreductionwith Ce-surface treatmentCe-surface treated at NETL Tested at AlleghenyT430=Fe-17Cr-0.5Mn8th Annual SECA Workshop – San Antonio, TX, August 7-9, 2007 Long Term Exposure800oC-Air+3%H2OTime (hrs)0 1000 2000 3000 4000 5000 6000Specific Mass Change (mg/cm2)0.000.501.001.502.002.50Crofer 430-A 430-B 430-C 430-D 0.13<0.01<0.01<0.01<0.01Al0.120.0920.4522.42BalCrofer<0.010.0800.5217.11Bal430-D<0.01<0.010.4917.13Bal430-C<0.01<0.010.4717.03Bal430-B<0.01<0.010.4416.85Bal430-ASiTiMnCrFebare alloys430 alloys produced at NETLOxidation test in progress8th Annual SECA Workshop – San Antonio, TX, August 7-9, 2007 Long Term Exposure800oC-Air+3%H2OTime (hrs)0 1000 2000 3000 4000 5000 6000Specific Mass Change (mg/cm2)0.000.501.001.502.002.50Crofer 430-A 430-B 430-C 430-D 0.13<0.01<0.01<0.01<0.01Al0.120.0920.4522.42BalCrofer<0.010.0800.5217.11Bal430-D<0.01<0.010.4917.13Bal430-C<0.01<0.010.4717.03Bal430-B<0.01<0.010.4416.85Bal430-ASiTiMnCrFebare alloysCe-treated (NETL)430 alloys produced at NETLOxidation test in progress8th Annual SECA Workshop – San Antonio, TX, August 7-9, 2007 Influnence of Si Content: T430Testing is in progress8th Annual SECA Workshop – San Antonio, TX, August 7-9, 2007 Time at 800oC, hrs0 100 200 300 400 500ASR (mOhms-cm-2)56789Electrical PerformanceCrofer 22APULower ASR 9 for SOFC interconnectCroferMeasurements made by G. Xia & Z.G.Yang, PNNLCrofer 22APU+CeSamples pre-oxidized at 800oC for100 hours prior to testing8th Annual SECA Workshop – San Antonio, TX, August 7-9, 2007 Electrical Performance05101520250 200 400 600 800 1000Time, hASR, mOhm.cm2 Ce-treated T-441 (by NETL)Bare T-441ASR Measurements performed by PNNL (Z.G. Yang)800oC, air; LSM cathode//LSM contact//interconnect8th Annual SECA Workshop – San Antonio, TX, August 7-9, 2007 Laboratory Scale Testing• “Button” cell test frames in Morgantown• Fe-22Cr-0.5Mn steel current collector was attached to the cathode with Pt paste (a Pt mesh placed between interconnect and cathode).• Pt mesh attached to anode.• Ag current cables and voltage taps spot welded to current collectorselectrolytecathodeanodeinterconnectPt meshPt pasteAg current cablesAg voltage taps8th Annual SECA Workshop – San Antonio, TX, August 7-9, 2007 Time (hrs)0 20 40 60 80 100 120Power Density (W/cm2)0.100.150.200.250.30Crofer (as polished surface) F5+CeLaboratory Scale Cell Performance0.7V/800oC; Fuel: H2+3%H2O; Oxidant: Air +3% H2OLSM Cathode/Fe-22Cr-0.5Mn Interconnectinitial oxide on surfaceCr poisoningResults published: D.E. Alman, C.D. Johnson, W.K. Collins, and P.D.Jablonski, “The Effect of Cerium Surface Treated Ferritic Stainless Steel Current Collectors on the Performance of Solid Oxide Fuel Cells (SOFC),” Journal of Power Sources, Vol 168, 2007, pp. 351-355.8th Annual SECA Workshop – San Antonio, TX, August 7-9, 2007 Pre-Oxidized Current Collectors• S.P. Simner, Anderson, Xia, Yang, Pederson, Stevenson, J. Electrochemical Soc., vol 154 (4), pp. A740-A745, 2005Behavior of cell with Ce-treated interconnect (previous slide) similar to behavior of cells with pre-oxidized interconnects. 8th Annual SECA Workshop – San Antonio, TX, August 7-9, 2007 NETL Treatment with La2O3composition is at%CeN-based (H/S: 400oC)CeO2-based (NETL:900oC)La2O3-based (NETL:900oC)Ce-oxideCe-oxideFe-CrLa-oxide8th Annual SECA Workshop – San Antonio, TX, August 7-9, 2007 800C-Moist AirTime (hrs)0 200 400 600 800 1000 1200 1400Specific Mass Change (mg/cm2)0.000.200.400.600.801.00Crofer Crofer +Ce (NETL)Crofer+La (NETL) Effect of Rare Earth 8th Annual SECA Workshop – San Antonio, TX, August 7-9, 2007 Initial Conductivity: ASR Experimental SetupFurnace at 800°CCurrentSource200 mA/cm2VAlloyAlloyLSM CompactLSM PasteLSM PastePlatinum LeadsSample under load8th Annual SECA Workshop – San Antonio, TX, August 7-9, 2007 Electrical PerformanceTime at 800oC, (hrs)0 200 400 600 800ASR, (mΩ-cm2)01020304050Crofer+LaCrofer + CeCrofer+CeCrofer+La8th Annual SECA Workshop – San Antonio, TX, August 7-9, 2007 Summary• RE surface treatments effective in improving oxidation resistance.−Applied to ferritic stainless steels for interconnect application (Crofer and Type 430).−Both Ce-based methods (NETL and H/S) were effective.−La modification to the NETL method was effective. • ASR measurements indicate that slower scale growth will enhance SOFC performance.8th Annual SECA Workshop – San Antonio, TX, August 7-9, 2007 On-Going and Future Work• Continue long term exposures on Ce- and La-treated samples− to determine if and when breaks-down occurs−accelerated tests −Analyze long term ASR (or cell tests)• Continue investigation influence of Si content−Determine critical Si level−Low cost production of low Si steels using recycled scrap (develop innovative slag additives to getter Si during metling).8th Annual SECA Workshop – San Antonio, TX, August 7-9, 2007 Experimental Alloys and RE Surface Treated Materials Available For Evaluation by SECA ParticipantsContact: Paul D. Jablonski: 541.967.5982 orDavid E. Alman: 541.967.5885

Surface Modifications for Oxidation Resistance

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Surface Modifications for Oxidation Resistance

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