Corrosion Protection of Cast Iron in Drinking Water withHarmlessTernary Inhibitor

 

M.Umarani1, T.Kasilingam2andC.Thangavelu3,*

1MunicipalHigher Secondary School,Karur,Tamilnadu,India.

2DepartmentofChemistry,TheivanaiAmmalCollegeforWomen,Villupuram,Tamilnadu,India.

3DepartmentofChemistry,Govt.ArtsCollegeforWomen,Nilakottai,Dindigul,Tamilnadu,India.*CorrespondingAuthorE-mail:thavankasi@gmail.com

 

ABSTRACT:

Theprotectionofcorrosionofcastironindrinkingwaterusingcurryleafextract(CLE),ZincionsandSodiumTartrate(ST)wasinvestigatedusingclassicalweight-lossmeasurement,TafelpolarizationandNyquistimpedancemethods.Inhibitionefficiencyofaboveternaryinhibitorreachesmaximumvaluesat85%.TheshapeofDCpolarizationprofilerevealedthenewternarysystemwhichactsasanodictypeinhibitor.ACimpedancespectroscopicstudiesindicatedtheformationofaprotectivefilmontothemetalsurfaceinthepresenceofinhibitors.AnalysesoftheprotectivefilmusingscanningelectronmicroscopeandenergydispersiveX-rayanalysis.

 

KEYWORDS:Curryleafextract,Tafelpolarization,Nyquistimpedancespectroscopy,classicalweight-losstechniquesandSEM-EDX.

 

 


INTRODUCTION:

Mechanicalpropertiesofcastironlikestrength,ductility,andmodulusofelasticitydependstronglyonstructureanddistributionofmicrostructuralconstituents.Physicalpropertiessuchasthermalconductivityanddampingcapacityarestronglyinfluencedbymicrostructure.Castironpopularitystemsfromanabilitytocastcomplexshapesatrelativelylowcostandthewiderangeofpropertiesthatcanbeachievedbycarefulcontrolovercompositionandcoolingratewithoutradicalchangesinproductionmethods.

 

Alloyingelementscanplayadominantroleinthesusceptibilityofcastirontocorrosionattack.Siliconisthemostimportantalloyingelementusedtoimprovethecorrosionresistanceofcastirons.

 

Siliconisgenerallynotconsideredanalloyingelementincastironsuntillevelsexceed3%.Siliconlevelsbetween3and14%offersomeincreaseincorrosionresistancetothealloy,butaboveabout14%Si,thecorrosionresistanceofthecastironincreasesdramatically[1].

 

Castironpipeshavebeenusedtotransportpotablewaterforover500years[2]andironpipecorrosionhasbeenaproblemforjustaslong.TheAmericanWaterWorksAssociation(AWWA)estimatesthatitwillcostUSwaterutilities$325billionoverthenext20yearstoupgradewaterdistributionsystems[3].ThisAWWAvalueisbuiltontheU.S.EnvironmentalProtectionAgency(USEPA)estimateof$77.2billionforserviceandreplacementoftransmissionanddistributionsystemlinesoverthenext20years[4].Themajorityofdistributionsystempipesarecomposedofironmaterial:castiron(38%),ductileiron(22%),andsteel(5%)[5].Moreover,a1997surveyofthe100largestAmericanWaterWorksAssociationResearchFoundation(AWWARF)memberutilitiesfoundthat“themostcommondistributionsystemproblemiscorrosionofcastironpipe”[6].

 

Corrosionisanaturalandthermodynamicallystableprocess.Theprocessofcorrosioncanbereducedbutitcannotbeprevented.Therearemanymethodsbywhichcorrosioncanbeinhibitedonesuchmethodistheuseofinhibitivemethod.Theseinhibitorswhenaddedissmallconcentration,decreasetherateofcorrosion.CorrosioninhibitorsusuallycontainpolargroupswithatomssuchasN,SandO.Correspondinglyinhibitorsincludeawidelistoforganicandinorganiccompounds[7].

 

Theobjectiveofthepresentstudyistoinvestigatetheinhibitoryeffectsofthecurryleafextract,sodiumtartrateandZn2+inthecorrosioninhibitionofcostironindrinkingwaterusingelectrochemicalmethodsandnon-electrochemicalmethod.Surfaceanalyticaltechniquewasalsousedtoinvestigatethenatureofthesurfacefilm.

 

MATERIALSANDMETHODS:

Materials:

Thespecimensofsize1.0cm×4.0cm×0.1cmwerepresscutfromthecastironsheet,weremachinedandabradedwithaseriesofemerypapers.Thiswasfollowedbyrinsinginacetoneandbidistilledwaterandfinallydriedinair.Beforeanyexperiment,thesubstratesweretreatedasdescribedandfreshlyusedwithnofurtherstorage.Theinhibitorcurryleafextractwasusedascollected.Astocksolutionof1000ppmofcurryleafwaspreparedinbidistilledwaterandthedesiredconcentrationwasobtainedbyappropriatedilution.Thestudywascarriedoutatroomtemperature.

 

Alltheweighingofthecastironspecimens,beforeandafterimmersion,weredoneusingaDenverbalance,TP214model,withareadabilityof0.1mgin210grange.Thisbalancehasreproducibility(standarddeviation)of0.1mgin210grangeandwassuppliedbyDenverinstruments,Germany.

 

Electrochemicalstudies:

Boththepotentiodynamicpolarizationstudiesandelectrochemicalimpedancespectroscopic(EIS)studieswerecarriedoutusingtheelectrochemicalworkstationmodelCHI-660AandCHI-760dandtheexperimentaldatawereanalysedbyusingtheelectrochemicalsoftware(Version:12.22.0.0).Themeasurementswereconductedinaconventionalthreeelectrodecylindricalglasscellwithplatinumelectrodeasauxiliaryelectrodeandsaturatedcalomelelectrodeasreferenceelectrode.

 

Theworkingelectrodewascastironembeddedinepoxyresinofpolytetrafluoroethylenesothattheflatsurfaceof1cm2wastheonlysurfaceexposedtotheelectrolyte.Thethreeelectrodessetupwasimmersedincontrolsolutionofvolume100mlbothintheabsenceandpresenceoftheinhibitorsformulationsandallowedtoattainastableopencircuitpotential(OCP).

 

Polarizationcurveswererecordedinthepotentialrangeof-750to-150mVwitharesolutionof2mV.Thecurveswererecordedinthedynamicscanmodewithascanrateof2mVS-1inthecurrentrangeof-20mAto+20mA.TheOhmicdropcompensationhasbeenmadeduringthestudies.Thecorrosionpotential(Ecorr),corrosioncurrent(Icorr),anodicTafelslope(βa)andcathodicTafelslope(βc)wereobtainedbyextrapolationofanodicandcathodicregionsoftheTafelplots.Theprotectionefficiency(IEp)valueswerecalculatedfromtheIcorrvaluesusingtheequation.

 

 

 

Where

IcorrandI’corrarethecorrosioncurrentdensitiesincaseofcontrolandinhibitedsolutionsrespectively.

 

ElectrochemicalimpedancespectraintheformofNyquistplotswererecordedatOCPinthefrequencyrangefrom60KHzto10MHzwith4to10stepsperdecade.Asinewave,with10mVamplitude,wasusedtoperturbthesystem.Theimpedanceparametersviz.,chargetransferresistance(Rct),doublelayercapacitance(Cdl)wereobtainedfromtheNyquistplots.Theprotectionefficiencies(IEim)werecalculatedusingtheequation,

 

 

 

Where

RctandR’ctarethechargetransferresistancevaluesintheabsenceandpresenceoftheinhibitorrespectively.

 

Scanningelectronmicroscope(SEM):

Thecastironwasimmersedintheabsenceofinhibitorandinthepresenceoftheinhibitor.After7days,thespecimensweretakenout,washedwithtripledistilledwaterandairdried.TheSEMimagesofthesurfacesofthespecimenswereobtainedusingVEGA3TESCANmodelintheCentralInstrumentFacility,NationalCollege,Trichy.

 

EnergydispersiveX-rayanalysis(EDX):

EDAX(Model:BRUKERNanoGermany)systemattachedwithScanningElectronMicroscopewasusedforelementalanalysisorchemicalcharacterizationofthefilmformedonthecarbonsteelsurface.Asatypeofspectroscopy,itreliesontheinvestigationofsamplethroughinteractionbetweenelectromagneticradiationandthematter.Sothat,adetectorwasusedtoconvertX-rayenergyintovoltagesignals.Thisinformationissenttoapulseprocessor,whichmeasuresthesignalsandpassedthemintoananalyzerfordatadisplayontheanalysis.

 

RESULTSANDDISCUSSION:

ClassicalWeight-lossmethod:

Thevaluesofinhibitionefficiencyandcorrosionrate(mmy-1)obtainedfromweightlossmethodatdifferentconcentrationaresummarizedinTable1.Itisobservedfromthatinhibitionefficiencyincreaseswithincreasingtheprotectorconcentrationindrinkingwaterandshowsasharpincreaseintheprotection,whichreacheditsmaximumvalueatconcentrationof5ppmZn2++100ppmST+250ppmCLEandfurtherincreaseintheprotectorconcentrationdoesnotshowanyappreciablechangeintheinhibitionefficiency.Thisindicatesthattheprotectiveeffectofinhibitorisnotsolelyduetotheirreactivitywiththedrinkingwater.Theprotectorybehaviouroftheternaryinhibitoragainstcorrosionofcastironcanbeattributedtotheadsorptionofinhibitoronthecastironsurface,whichlimitsthedissolutionofthecastironbyblockingofitscorrosionsitesandhencedecreasingthecorrosionratefrom139.2to22.2mmy-1.

 

Table1.Non-electrochemicalparametersofcastironindrinkingwaterintheabsenceandpresenceofCurryleafextract+Zn2++ST

Concentration(ppm)

Corrosionrate(mmy-1)

Inhibitionefficiency(%)

CLE

Zn2+

ST

Control

-

100

139.2

-

10

5

100

82.1

41

50

5

100

72.3

48

100

5

100

64.0

54

150

5

100

45.9

67

200

5

100

34.8

75

250

5

100

22.2

84

 

Impedancespectra:

Nyquistimpedance(EIS)spectraofcastironunderourstudyareshowninFig.1.Nyquistparameters,namelythechargetransferresistance(Rct)andthedoublelayercapacitance(Cdl)aregiveninTable2.Whencastironisimmersedindrinkingwater,theRctisfoundtobe213.1Ωcm2andtheCdlvalueis7.8693×10-6F/cm2.Whenpresenceofternaryinhibitor(5ppmZn2++100ppmST+250ppmCLE),theRctvalueshasincreasedtremendouslyfrom213.1Ωcm2to1467.6Ωcm2andCdlvaluesdecreases7.8693×10-6F/cm2to0.1507×10-6F/cm2.TheincreasedRctanddecreasedCdlvaluesobtainedfromimpedancestudiesjustifythegoodperformanceofacompoundasaninhibitorindrinkingwater[8].Thisbehaviourshowsthatthefilmobtainedactsasabarriertothecorrosionprocessthatobviouslyprovestheexistenceandformationoftheinhibitivefilm.

 

 

Figure1.Nyquistplotsofcastironintheabsenceandpresenceofternaryinhibitor

 

Table2.ElectrochemicalNyquistparametersforthecastironindrinkingwaterinthepresenceandabsenceofinhibitor

Conc.ofCLE(ppm)

Conc.ofST(ppm)

Conc.ofZn2+(ppm)

Rctohm.cm2

CdlF.cm-2×10-6

%IEim

Blank

-

-

213.1

7.8693

-

250

100

5

1467.6

0.1507

85

 

PolarizationTechnique:

TheTafelparametersobtainedfromelectrochemicalmeasurementssuchascorrosionpotential(Ecorr),corrosioncurrent(Icorr),anodicandcathodicTafelslopes(βaandβc)andinhibitionefficiencyaregiveninTable3.

 

 

Figure2.Tafelcurvesofcastironintheabsenceandpresenceofternaryinhibitor

 

TheobservedEcorrvaluesdolargechangeinaregularmannerfromtheblankvalue.Thisindicatesthattheinhibitorworksthroughanodicmodeofinhibition.ItisobviousfromFigure2,thatTafelcurvesareshiftedmarkedlytolowercorrosioncurrentdensityinthepresenceofinhibitor(5ppmZn2++100ppmST+250ppmCLE).TheIcorrvaluedecreasefromtheblankvalue(7.450to1.314),thisdecreaseinIcorrisanindicationofincreasedinhibitionefficiency(82).


Table3.ElectrochemicalTafelparametersforthecastironindrinkingwaterinthepresenceandabsenceofinhibitor

Conc.ofCLE(ppm)

Conc.ofST(ppm)

Conc.ofZn2+(ppm)

Tafelparameters

IEp

(%)

EcorrmVvsSCE

IcorrAµ/cm2

βamV/decade

βcmV/decade

Blank

 

-

-741

7.450

151.4

122.6

-

250

100

5

-575

1.314

210.1

182.7

82

 

Scanning Electron Microscope:

 

Figure 3. SEM micrographs of cast iron a) Polished surface    b) Absence of inhibitor   c) Presence of ternary inhibitor

 


SEMmicrographsforcastironinabsenceandpresenceofinhibitorsystemhavebeenpresentedinFig.3.Themorphologyofthecastironspecimenintheabsenceofinhibitorisveryroughandthesurfacewasdamagedduetometaldissolution.Polishedcastironsurface(Fig.3a)isgoodsurfacepropertiesascomparedtotheblankmaterial(Fig.3b).At5ppmZn2++100ppmST+250ppmCLE,ithasbeenfoundthatthesmoothnessofthesurfaceimprovedremarkablyandthemetalsurfaceisalmostfreefromcorrosionduetothebettercoverageofthemetalsurface(Fig.3c).

 

EnergyDispersivex-rayAnalysis:

ThecompositionofprotectivefilmformedonthecastironsurfacewasanalyzedusingEDXasshowninFig.4.(a-c).TheEDXspectrumofpolishedcastironsampleinFig.4ashowsaunityofsurfacecompositionproperties,whilethespectrumincaseofcastironsampleimmersedinabsenceofinhibitormoleculeswasfailedbecauseitisseverelyweakenedduetothecorrosionasshowninFig.4b.byadding5ppmZn2++100ppmST+250ppmCLEthedecreaseofironpeakandappearanceofcarbon,heteroatomandzincpeakwasobservedduetotheformationofastrongprotectivefilmoftheinhibitormoleculesonthesurfaceofcastironsampleshowninFig.4c.Theactionofinhibitorisrelatedtoadsorptionandformationofabarrierfilmontheelectrodesurface.TheformationofsuchabarrierfilmisconfirmedbySEMandEDXexaminationofcastironsurface.

 



Figure4.EDXspectraofcastirona)Polishedsurfaceb)Drinkingwater(blank)c)Presenceofternaryinhibitor


CONCLUSION:

Thefollowingmainconclusionsaredrawnfromthepresentinvestigation.

1      Ternaryinhibitorformulationhasgoodinhibitionefficiencyforthecorrosionofcastironindrinkingwater.

2      Tafelcurvesshowedthattheinvestigatedternaryinhibitorformulationactsasananodictypeinhibitoroncastironindrinkingwater.

3 Allresultsobtainedfromweightlosstechnique,polarizationtechniqueandelectrochemicalimpedancespectroscopyareinreasonablygoodagreementandshowsincreasedinhibitionefficiencywithincreasinginhibitorconcentration.

4      Surfaceanalysisusingscanningelectronmicroscope(SEM)andEnergydispersivex-rayanalysisshowedasignificantmorphologicalimprovementonthecastironsurface.

 

REFERENCES:

1.   I.SekineandY.Hirakwa,Corrosion,42,(1986)276.

2. G.Gedge,CorrosionofCastIroninPotableWaterService.Proc.CorrosionandRelatedAspectsofMaterialsforPotableWaterSupplies,ProceedingsoftheInstituteofMaterialsConference.London,UK(1992).

3.   AWWA.AWWAReport:$325billionforPipes.AWWAMainstream,February:3(1999).

4.   C.Davies,D.L.Fraser,P.C.Hertzler,&R.T.Jones,USEPA'sInfrastructureNeedsSurvey.JournalAWWA,89:12:30(1997).

5.   AmericanWaterWorksAssociation.WATER:\STATS1996Survey.(1996).

6.   Bray,A.V.Personalcommunication.(1997).

7.   C.Thangavelu,R.Sudhakaran,M.Sekar,T.AsokanandT.Kasilingam,J.Chem.Bio.Phy.Sci.Sec.B,;5(1),(2015)63-71.

8.   ChinnaiyanThangaveluandThavanKasilingam,ChemSciRevLett,3(9),(2014)10-17

 

 

 

 

 

 

Receivedon04.01.2018Modifiedon28.02.2018

Acceptedon20.04.2018©AJRCAllrightreserved

AsianJ.ResearchChem.2018;11(3):580-584.

DOI:10.5958/0974-4150.2018.00103.7