High Temperature Oxidation and Corrosion of Metals PDF
Preview High Temperature Oxidation and Corrosion of Metals
High Temperature Oxidation and Corrosion of Metals Second Edition David J. Young School of Materials Science and Engineering, University of New South Wales, Sydney AMSTERDAMlBOSTONlHEIDELBERGl LONDONlNEWYORKlOXFORD PARISlSANDIEGOl SANFRANCISCOlSINGAPORElSYDNEYlTOKYO Elsevier Radarweg29,POBox211,1000AEAmsterdam,Netherlands TheBoulevard,LangfordLane,Kidlington,OxfordOX51GB,UK 50HampshireStreet,5thFloor,Cambridge,MA02139,USA Copyright(cid:1)2016,2008ElsevierLtd.Allrightsreserved. Nopartofthispublicationmaybereproducedortransmittedinanyformorbyanymeans, electronicormechanical,includingphotocopying,recording,oranyinformationstorage andretrievalsystem,withoutpermissioninwritingfromthepublisher.Detailsonhowtoseek permission,furtherinformationaboutthePublisher’spermissionspoliciesandourarrangements withorganizationssuchastheCopyrightClearanceCenterandtheCopyrightLicensingAgency, canbefoundatourwebsite:www.elsevier.com/permissions. 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BritishLibraryCataloguinginPublicationData AcataloguerecordforthisbookisavailablefromtheBritishLibrary LibraryofCongressCataloging-in-PublicationData AcatalogrecordforthisbookisavailablefromtheLibraryofCongress ISBN:978-0-08-100101-1 ForinformationonallElsevierpublications visitourwebsiteathttps://www.elsevier.com/ Publisher:JohnFedor AcquisitionEditor:KostasMarinakis EditorialProjectManager:SarahWatson ProductionProjectManager:AnithaSivaraj Designer:MariaInesCruz TypesetbyTNQBooksandJournals Coverimage:Burnerrigtestsinbothheatingandcoolingpositionsethermalbarriercoatedsuper alloyhot.CourtesyoftheNationalAeronauticsandSpaceAdministration,JohnH.Glenn ResearchCenteratLewisField(NASAIdentifierGRC-C-1999-2487). Foreword The depletion of the first edition print run and an enormous increase in pub- lished research on high-temperature corrosion have combined to make a second edition of this book desirable. Recent work on mass transport in alumina and, more generally, on oxide grain boundary diffusion has contrib- uted improved clarity to our understanding of how protective alumina and chromiascalesbehave.Similarly,newinvestigationsintowatervapoureffects on scaling processes have expanded and refined our knowledge, although a simple, coherent picture remains elusive. These contributions, and several others, have been drawn upon in updating the original text. Two new topics have been added, reflecting the large body of published research now available and the technological developments which drove that work.Chapter10treatscorrosionbycarbondioxide,animportantissueifCO 2 is to be captured from combustion gas streams. In addition, the thermal properties of carbon dioxide, along with its pressure-volume-temperature characteristics,makeitattractiveasaheattransferandworkingfluid.Forthese reasons, it is a candidate for use in nuclear reactors and concentrated solar thermal power generation. Unfortunately, it is also corrosive to a variety of alloys. AnewChapter12,CorrosioninComplexEnvironments,isconcernedwith the corrosion phenomena arising from the presence of ionic melts and vola- tilising halides. Interest in these topics has arisen out of the much increased use of both biomass and municipal waste as fuels for thermal power genera- tion. The resulting flue gases and deposits can be remarkably corrosive, and boiler operating temperatures are strictly limited as a result. As in the first edition, I have tried to acknowledge important contributions to our understanding made by many researchers, and I apologise for any omissions.Thesecondeditionhasbenefitedfromcolleaguesaroundtheworld who have offered hospitality and/or generously gave expert commentary: Brian Gleeson (University of Pittsburgh), Daniel Monceau (INPT-CIRIMAT, Toulouse), Bruce Pint (Oak Ridge National Laboratory), Joe Quadakkers (Forschungszentrum, Ju¨lich), Michael Schutze (Dechema, Frankfurt) and Jim Smialek (NASA, Lewis). Rectifying an important omission from the first edi- tion,Ithankmywifeandfamilyfortheirsupportandremarkableforbearance. David J. Young December 2015 xiii Preface Almostallmetalsandalloysoftechnologicalinterestoxidiseandcorrodeathigh temperatures. However, the nature of their reaction products and the rates at whichmetalsurfacesaredegradedvarywidely,andacapacityforpredictionis highlydesirable.Thisbookisconcernedwithprovidingafundamentalbasisfor understanding the alloy-gas oxidation and corrosion reactions observed in practiceandinthelaboratory.Itspurposeistoenablethepredictionofreaction morphology,kineticsandrateasafunctionoftemperatureandthecomposition ofbothalloyandgas. The term ‘oxidation’ is used in a generic sense for any chemical reaction which increases the metal oxidation state by forming a compound such as an oxide,sulphide,carbide,etc.Alloy oxidationreactionscanbeconceived ofas occurringinthreestages.Initially,allreactivecomponentsofanalloyincontact with a hot gas are likely to react simultaneously. Subsequently, more thermo- dynamically stable compounds replace less stable ones, and a state of near equilibriumislocallyapproached.Thereactingsystemcanthenbemodelledasa seriesofspatiallyadjacentlocalequilibriumstateswhichvaryincrementallyin reactant chemical potentials. During this stage, the reaction morphology and compositiondistributionareinvariantwithtime.Ultimately,this‘steadystate’is lost,andallreactivealloycomponentsareconsumedinafinalbreakdownstage. Successfulalloysarethosewhichevidencelengthyperiodsofslow,steady- statereaction.Forthisreason,considerableemphasisisplacedonanalysingthe underlyinglocalequilibriumconditionandtestingitsapplicabilitytoparticular metaloralloy-oxidantsystems.Whenanalloy-gasreactionisatasteadystate, the constant composition profile developed through the reaction zone can be mappedontotherelevantsystemphasediagramasa‘diffusionpath’.Frequent useismadeofthesepathsinunderstandingreactionproductdistributionsandin predicting,oratleastrationalising,reactionoutcomes. Analysis of the alloy oxidation problem requires a multidisciplinary approach.Physicalmetallurgy,materialsscienceandphysicalchemistryprovide the tools with which to dissect alloy phase constitutions and their trans- formations, oxide properties and chemical kinetics. Deliberate emphasis is placedontheuseofchemicalthermodynamicsinpredictingoxidationproducts anddescribingsolidsolutionphases.Equalattentionispaidtothedetailedun- derstandingofdefect-baseddiffusionprocessesincrystallinesolids.Theintro- ductoryChapter1indicateshowthesevariousdisciplinescancontributetothe xv xvi Preface analysis. The lengthy Chapter 2 reviews the thermodynamic, kinetic and mechanicaltheoriesusedinthisbook.Italsocontainstabulateddataandrefers toAppendicesonalloycompositionanddiffusion. After these preliminaries, the book is arranged in a sequence of chapters reflectingincreasingcomplexity,whichequateswithgreatersystemcomponent multiplicity.Ananalysisofthereactionbetweenpuremetalsandsingleoxidant gasesis followedby a discussion ofmetal reactionswith mixedoxidant gases and then, in Chapters 5e7, an examination of alloy reactions with a single oxidant. Much of this discussion is based on the early work of Carl Wagner, whichstillprovidesagoodconceptualframeworkand,inseveralcases,auseful analytical basis for quantitative prediction. However, as will be shown, increasing system complexity is accompanied by a weakening in theoretical completeness. The problems arise from multicomponent effects and from microstructuralcomplexity. Consider first the effect of increasing the number of alloy components. A steady-statereactingsystemconsistingofabinaryalloyandasingleoxidantcan be modelled in a two coordinate description of both thermodynamics and diffusion kinetics, provided that temperature and pressure are constant. Sub- stantialthermodynamicanddiffusiondata isavailable formanysuchsystems, andthisisusedindevelopingdiffusionpathdescriptions.Increasingthenumber of alloy components leads, however, to chemical and structural interactions among them, rendering the experimental problem much less tractable, and diagrammaticrepresentation impossible. In the absenceof the requisiteexten- sive thermodynamic and diffusion data, the Wagner theory cannot be applied. Instead, higher order alloys are discussed from the point of view of dilute additioneffectsonthebehaviourofbinaries. Wagner’s theory is based on lattice diffusion. However, the transport properties of slow-growing oxides are largely determined by their grain boundaries and, in some cases perhaps, microporosity. Additional alloy com- ponentscanaffectboththeoxidegrainsizeandthediffusionpropertiesofthe grain boundaries. A description of these phenomena is, at this stage, largely empirical. Thelatterpartofthebookisconcernedwiththeeffectsofothercorrodents and temperature variations. Chapters 8 and 9 deal with sulphur and carbon- bearing gases.Theveryrapiddiffusionrates involvedinsulphidationandcar- burisationmakesthempotentiallythreateningcorrosionprocessesinanumber ofindustrialtechnologies.Offundamentalinterestarethecomplicationsarising outofthecomplexgas-phasechemistriesandthesometimesslowhomogeneous gas-phasereactions.Itbecomesnecessaryindiscussingthebehaviourofthese gasmixturestoconsidertheroleofcatalysts,includingthealloysinquestionand theircorrosionproducts.Itemergesthatnotonlythegasphase,butalsothegas- solidinterfacecanbefarremovedfromlocalequilibrium.Inparticular,analysis of the catastrophic ‘metal dusting’ corrosion caused by carbon-supersaturated gasescallsfortheuseofnonequilibriummodels. Preface xvii The effects of water vapour on oxidation are discussed in Chapter 10. In many respects this is the least well understood aspect of high-temperature corrosion. The reason for the difficulty is to be found in the multiple ways in which water molecules can interact with oxides. Preferential adsorption, hydrogen uptake, lattice defect changes, grain boundary transport property changes, gas generation withinoxideporesandscale andscale-alloy interface mechanicalpropertychangesneedalltobeconsidered. Finally, the effects of temperature cycling on oxide scale growth are considered in Chapter 11. A combination of diffusion modelling with a rather empiricalscalespallationdescriptionisfoundtoprovideareasonablysuccessful way of extrapolating data for particular alloys. However, there is a need for developmentofmorepredictivedescriptionsoftherelationshipbetweenspall- ationpropensity,alloypropertiesandexposureconditions. Discussion is focused throughout on developing an understanding of the fundamentals of high-temperature oxidation. Frequent use is made of experi- mental informationon real alloysinorder toillustrate the principles involved. However,noattemptismadetosurveytheveryextensiveliteraturewhichexists for alloy oxidation. Thus most examples considered concern either iron- or nickel-base alloys, whereas cobalt-base alloys are largely ignored. Nickel alu- minidesarediscussed,butotherintermetallicsareseldommentioned.Thescope of the book is further limited by the exclusion of some particular topics. Examplesinclude‘pesting’(disintegrationbygrainboundaryattack)ofsilicides, andextensiveoxygendissolutionbymetalssuchastitaniumandzirconium.No bookofmanageableproportionscaneverbecomplete,orevenfullyuptodate. Itisremarkablethatsincetheearly,verysubstantialprogressmadebyCarl Wagner and associates in understanding oxidation phenomena, the research effort has nonetheless continued to expand. The reason, of course, is the continuing need to operate equipment at ever higher temperatures to achieve greaterefficienciesandreducedemissions.Theneedtodevelopsuitablemate- rialscanbeexpectedtodriveevenmoreresearchinyearstocome. Writingthisbookhasbeenalargetask,anditscontentinevitablyreflectsmy own experience, as well as the ideas and results of others. I have tried to acknowledge important contributions to our understanding made by many researchers,andapologiseforanyomissions.Myownresearchinthisareahas benefited from interaction with many talented students, research fellows and colleagues, all acknowledged bydirectreference. Ithasalsobeensustainedin largepartbytheAustralianResearchCouncil,abodytobecommendedforits willingness to support fundamental research. This book has benefited from colleagues from around the world who offered hospitality and/or generously gaveexpertcommentaryasIwrote:BrianGleeson(IowaStateUniversity),Jack Kirkaldy (McMaster University), Daniel Monceau (CIRIMAT, Toulouse), Toshio Narita (Hokkaido University), Joe Quadakkers (Forschungzentrum, Julich),JimSmialek(NASA,Lewis)andPeterTortorelli(OakRidgeNational Laboratory). xviii Preface Finally,Iacknowledgewithgratitudeandaffectiontheinspirationprovided by my mentors and friends at McMaster University, Walt Smeltzer and Jack Kirkaldy. DavidJ.Young August2007 Abbreviations and Acronyms APT Atom probe tomography CTGA Continuous thermogravimetric analysis CVD Chemical vapour deposition EBSD Electron back scattered diffraction EDAX Energy dispersive analysis of X-rays EELS Electron energy loss spectroscopy EPMA Electron probe microanalysis FIB Focused ion beam IGCC Integrated gasification combined cycle ppm Parts per million (unit of relative concentration) ppma Parts per million by atoms ppmm Parts per million by mass PVD Physical vapour deposition SAD Selected area diffraction SCC Supercritical CO 2 SEM Secondary electron microscope SIMS Secondary ion mass spectrometry TBC Thermal barrier coating TEM Transmission electron microscope TGA Thermogravimetric analysis TGO Thermally grown oxide XPS X-ray photoelectron spectroscopy XRD X-ray diffraction YSZ Yttria-stabilized zirconia xix Symbols GREEK SYMBOLS a Coefficientofthermalexpansion a Enrichmentfactorformetalininternaloxidationzone d Thicknessofgasphaseboundarylayer d Deviationfromstoichiometryinoxide h Electrochemicalpotentialofcomponenti i h Viscosityofgas g g Surfacetension,freeenergyperunitsurfacearea g Activitycoefficientofcomponenti i l Interplanardistance,jumpdistance l x=t12,forparametricsolutionstoFick’sequation m Chemicalpotentialofcomponenti i n Stoichiometriccoefficientinchemicalreactionorcompound vg Kinematicviscosityofgas n Kineticfrequencyterm iv vP Poisson’sratio j Electrostaticpotential r Density s Mechanicalstress q Fractionofsurfacesites x Extentofreaction x MolefractionofoxideBOinsolidsolutionA1(cid:1)xBxO εc Criticalstrainformechanicalfailureofscaleorscale-alloyinterface ε Wagnerinteractioncoefficientsforsolutecompoundsiandk ik ε Mechanicalstraininoxide OX SYMBOLS A Surfaceareaofoxidisingmetal ai Chemicalactivityofcomponenti a0;a00 Boundaryvaluesofoxygenactivityatmetal-scaleandscale-gas o o interfaces Bi Mobilityofspeciesi Ci Concentrationofcomponenti C0,C00 Boundaryvaluesofconcentrationatmetal-scaleandscale-gasinterfaces. D Diffusioncoefficient d Grainboundarywidth DA IntrinsicdiffusioncoefficientforspeciesA DA* Tracerorself-diffusioncoefficientofspeciesA Dij Diffusioncoefficientrelatingfluxofcomponentitoconcentration gradientincomponentj xxi xxii Symbols e D Chemical(orinter)diffusioncoefficient Do Diffusioncoefficientforsoluteoxygeninalloy Do,i Diffusioncoefficientforoxygenalonganinterface E Electricfield EOX Elasticmodulusofoxide EA Activationenergy e0 Freeelectron F TheFaraday(96,500C) f Fraction fv Volumefraction G TotalormolarGibbsfreeenergy GOX Shearmodulusofoxide Gv Freeenergyperunitvolume gBO Volumefractionofinternallyprecipitatedoxide,BO H Totalormolarenthalpy hl Positivehole ijS Speciesiadsorbed(bound)tosurfacesite ioz Internaloxidationzone Ji Fluxofcomponenti K Chemicalequilibriumconstant k Rateconstant k Boltzmann’sconstant kc Parabolicrateconstantformetalconsumption,corrosionrateconstant kl Linearrateconstantforscalethickening km Gaseousmasstransfercoefficient ks Surfaceareafractionofoxidespalled kðiÞ Parabolicrateconstantforinternaloxidation p kp Parabolicrateconstantforscalethickening kw Parabolicrateconstantforscalingweightgain kv Vaporisationrate Kp Equilibriumconstantatfixedpressure Ksp Solubilityproduct KIC Fracturetoughness,criticalstressintensityfactor Lij Generalmobilitycoefficient,Onsagerphenomenologicalcoefficient L Lengthofmaterialoverwhichgasflows l Halfthicknessofalloysheet MW Molecularweight mi Molarconcentrationofcomponenti ml,m0 Numberofchargeunitsonlatticepointdefectspecies n Numberofmoles Ni Molefractionofcomponenti NAV Avogadro’snumber NM,i MolefractionofcomponentMatscale-alloyinterface NM,min MinimummolefractionofcomponentMrequiredtosupportgrowthof externalMOscale NðoÞ MolefractionofcomponentMoriginallypresentinalloy M NðsÞ Molefractionofdissolvedoxygenatalloysurface O P Pressure p DA/DB,ratioofmetalself-diffusioncoefficientsinternaryoxide pi Partialpressureofcomponenti
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