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CORROSIVEDAMAGECORROSIVEDAMAGEINMATERIALS&ITSINMATERIALS&ITSPREVENTIONPREVENTIONDr.T.K.G.NAMBOODHIRIDr.T.K.G.NAMBOODHIRIProfessorofMetallurgyProfessorofMetallurgy(Retired)(Retired)INTRODUCTIONINTRODUCTION•Definition:CorrosionDefinition:Corrosionisthedegenerationisthedegenerationofmaterialsbyofmaterialsbyreactionwithreactionwithenvironment.environment.Examples:RustingofExamples:Rustingofautomobiles,automobiles,buildingsandbuildingsandbridges,Foggingofbridges,Foggingofsilverware,Patinasilverware,Patinaformationoncopper.formationoncopper.UNIVERSALITYOFUNIVERSALITYOFCORROSIONCORROSION•Notonlymetals,butnon-metalslikeNotonlymetals,butnon-metalslikeplastics,rubber,ceramicsarealsoplastics,rubber,ceramicsarealsosubjecttoenvironmentaldegradationsubjecttoenvironmentaldegradation•EvenlivingtissuesinthehumanbodyEvenlivingtissuesinthehumanbodyarepronetoenvironmentaldamagearepronetoenvironmentaldamagebyfreeradicals-Oxidativestress-byfreeradicals-Oxidativestress-leadingtodegenerativediseaseslikeleadingtodegenerativediseaseslikecancer,cardio-vasculardiseaseandcancer,cardio-vasculardiseaseanddiabetes.diabetes.CORROSIONDAMAGECORROSIONDAMAGE•DisfigurationorlossofappearanceDisfigurationorlossofappearance•LossofmaterialLossofmaterial•MaintenancecostMaintenancecost•Extractivemetallurgyinreverse-LossExtractivemetallurgyinreverse-Lossofpreciousminerals,power,waterofpreciousminerals,power,waterandman-powerandman-power•Lossinreliability&safetyLossinreliability&safety•Plantshutdown,contaminationofPlantshutdown,contaminationofproductetcproductetcCOSTOFCORROSIONCOSTOFCORROSION•AnnuallossduetocorrosionisestimatedtoAnnuallossduetocorrosionisestimatedtobe3to5%ofGNP,aboutRs.700000croresbe3to5%ofGNP,aboutRs.700000crores•Direct&IndirectlossesDirect&Indirectlosses•Directloss:Materialcost,maintenanceDirectloss:Materialcost,maintenancecost,over-design,useofcostlymaterialcost,over-design,useofcostlymaterial•Indirectlosses:Plantshutdown&lossofIndirectlosses:Plantshutdown&lossofproduction,contaminationofproducts,lossproduction,contaminationofproducts,lossofvaluableproductsduetoleakageetc,ofvaluableproductsduetoleakageetc,liabilityinaccidentsliabilityinaccidentsWHYDOMETALSWHYDOMETALSCORRODE?CORRODE?•AnyspontaneousreactionintheAnyspontaneousreactionintheuniverseisassociatedwithauniverseisassociatedwithaloweringinthefreeenergyoftheloweringinthefreeenergyofthesystem.i.e.anegativefreeenergysystem.i.e.anegativefreeenergychangechange•AllmetalsexceptthenoblemetalsAllmetalsexceptthenoblemetalshavefreeenergiesgreaterthanhavefreeenergiesgreaterthantheircompounds.Sotheytendtotheircompounds.SotheytendtobecometheircompoundsthroughbecometheircompoundsthroughtheprocessofcorrosiontheprocessofcorrosionELECTROCHEMICALELECTROCHEMICALNATURENATURE•AllmetalliccorrosionareAllmetalliccorrosionareelectrochemicalreactionsi.e.metaliselectrochemicalreactionsi.e.metalisconvertedtoitscompoundwithaconvertedtoitscompoundwithatransferofelectronstransferofelectrons•TheoverallreactionmaybesplitintoTheoverallreactionmaybesplitintooxidation(anodic)andreductionoxidation(anodic)andreduction(cathodic)partialreactions(cathodic)partialreactions•NextslideshowstheelectrochemicalNextslideshowstheelectrochemicalreactionsinthecorrosionofZninreactionsinthecorrosionofZninhydrochloricacidhydrochloricacidELECTROCHEMICALREACTIONSELECTROCHEMICALR...