DSpace at VNU: Yttrium 3-(4-nitrophenyl)-2-propenoate used as inhibitor against copper alloy corrosion in 0.1 M NaCl solution

Many studieshaveconcentrated onimprovingthecorrosion resistanceof copper alloys viavarious methods suchas equal-channel angular pressing [11,12], dynamic plastic deformation [13],surface

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j o u r n a l h o m e p a g e :w w w e l s e v i e r c o m / l o c a t e / c o r s c i

Yttrium 3-(4-nitrophenyl)-2-propenoate used as inhibitor against

copper alloy corrosion in 0.1 M NaCl solution

Nguyen Dang Nama,∗, Vo Quoc Thangb, Nguyen To Hoaia, Pham Van Hienc,∗∗

a Petroleum Department, PetroVietnam University, 762 Cach Mang Thang Tam Street, Long Toan Ward, Ba Ria City, Ba Ria, Vung Tau Province, Vietnam

b Faculty of Fundamental Science, PetroVietnam University, 762 Cach Mang Thang Tam Street, Long Toan Ward, Ba Ria City, Ba Ria, Vung Tau Province,

Vietnam

c Department of Chemical Engineering, Ho Chi Minh City University of Technology, 268 Ly Thuong Kiet Street, District 10, Ho Chi Minh City, Vietnam

a r t i c l e i n f o

Article history:

Received 13 May 2016

Received in revised form 2 August 2016

Accepted 6 August 2016

Available online xxx

Keywords:

A Copper

B IR spectroscopy

B SEM

B Polarization

C Neutral inhibition

a b s t r a c t

Yttrium3-(4-nitrophenyl)-2-propenoatehasbeenstudiedasaneffectivecorrosioninhibitorforcopper alloyin0.1Mchloridesolution.Theresultsshowthatthesurfaceofcopperalloycouponsexposedto solu-tionscontaining0.45mMyttrium3-(4-nitrophenyl)-2-propenoatehadnosignsofcorrosionattackdue

toprotectivefilmformation,whereasthesurfaceofcopperalloycouponsexposedtonon-inhibitorand lowerconcentrationsofyttrium3-(4-nitrophenyl)-2-propenoatecontainingsolutionswereseverely cor-roded.Ahighinhibitionperformanceisattributedtotheformingprotectiveinhibitingdepositsthatslow downtheelectrochemicalcorrosionreactionsandmitigatecorrosionbypromotingrandomdistribution

ofminoranodes

©2016ElsevierLtd.Allrightsreserved

1 Introduction

Copperanditsalloysareidealmaterialsfortubecastingand

pipeproductsduetotheirgoodelectricalandthermalconducting

properties,corrosionresistance,antibacterialnature,weldability,

ductility,toughness,nonmagneticcharacteristics,andeasytoform

alloysalongwithrecyclablility[1–3].Duetotheseproperties,they

havebeenextensivelyappliedtostorepotablewaterinbuildings

andhomesaswellasformanydiversefluidsrangingfromoiland

chemicalprocessestomarineindustries[4–6].Importantly,

cop-peralloyshavehighcorrosionresistance,machinabilityandhigh

levelofheattransferwhichareamajorcriteriaforair-conditioning,

refrigerationsystems,firesprinklersystemsandfuelgas

distribu-tionsystems.Unfortunately,pittingofcopperalloysispromotedin

thepresenceofammonia,steamwithsufficientlevelsofCO2,NH3,

sulfides,chloridesinwaters,andironoxide[7–9]

Copperisa noblemetalandmorestable intheatmospheric

environment incomparison withzinc oriron During oxidation

processes,itcanlooseoneortwoelectronstoformtwotypesof

pos-itivelychargedions[10].Thesepositivelychargedionscanexiston

itsowninsolution,however,theycanalsoassociatewithnegatively

∗ Corresponding author.

∗∗ Corresponding author.

E-mail addresses: namnd@pvu.edu.vn , ndnam12a18@yahoo.com (N.D Nam),

phamvanhien240991@gmail.com (P.V Hien).

chargedionssuchashydroxide,chloride,carbonate,bicarbonate and sulphateions, aswellasorganiccompoundstoform solu-bleandsolidcomplexesinsolutions,whichisamajorcausefor seriouscorrosionproblemrelatedtocopperalloysinaggressive environmentsasexpectedduringoperationalprocesses.Therefore, improvingthecorrosionresistanceofcopperanditsalloysisan interestingtopicof studieswitha goalofmeetingtherequired corrosionresistance,whichisakeyforcopperanditsalloy appli-cations

Many studieshaveconcentrated onimprovingthecorrosion resistanceof copper alloys viavarious methods suchas equal-channel angular pressing [11,12], dynamic plastic deformation [13],surfacetreatments[14,15],coatings[16,17],alloyingelements [18,19]andcorrosioninhibitors[20–23].Amongthesemethods, theuseofcorrosioninhibitorssignificantlyinfluencesthecorrosion resistanceofcopperalloysduetotheircostsavingsandchanges

insituwithoutanyinterruptionofanoperationalprocess.Forthese reasons, many corrosion inhibitors have been investigated and developed[20–26].Coppercorrosioninhibitionhasbeenstudied fordecadesandisdoneextremelyeffectivelywithbenzotriazole (BTA),whichisnotparticularlytoxic.Therearenumerousstudies

ofBTAactiononcopperalloyinvariouscorrosionenvironments suchaschlorideions,acidicandneutralsolutions[27–32] Unfortu-nately,BTAactionisweakerinenvironmentcontainingaggressive ionsaswellasinhighlyacidicandalkalineenvironments Therecent conceptsrevealedbyvariousresearchersprovide guideforvariousnewapproachesintermsofdesigningsaferand http://dx.doi.org/10.1016/j.corsci.2016.08.005

0010-938X/© 2016 Elsevier Ltd All rights reserved.

Table 1

Copper pipe alloy compositions were checked by optical emission spectroscopy.

Chemical elements (wt.%

0.0369 0.0029 0.0039 0.0338 0.0066 0.0125 0.0041 0.0016 <0.0002 <0.0006 <0.0002 <0.0002 <0.0015 <0.0002 Bal.

environmentallyfriendlyinhibitors.Oneearlierapproachwasto

usepolyphosphateatrelativelyhighlevelswhichwasbasedon

undergoingaprocessofhydrolysis,resultingincalcium

orthophos-phatedeposition.Lateron,ortho-,poly-,andorganicphosphates

havebeencombinedtoimprovethelimitationofpolyphosphate

systems and provide the desired corrosion protection [33–36]

However,one ofconcern isassociated withcalcium phosphate

deposition,whichmakesthemproblematic.Otherapproachwas

todevelopsynergisticrareearthorganiccompoundsviasalvaging

a multifunctional inhibition containing inhibitive properties of

theircomponents[37–46]resultinginsuperiorinhibition when

comparedwitheitherofindividualcomponentsatthesame

con-centration.Inaddition, theuseof thi-andtriazolyl compounds

hasbeenrecommendedascorrosioninhibitorsforcopperalloys

due tothe generationof protective film onthe coppersurface

[47–49].Likewise,the potassium ethyl xanthate[50,51], indole

[52], 5-chloroindole [53], purine [54–56], adenine [55,56] (AD)

andothergroups[57–59]canalsofacilitatetheformationofthe

protectivefilmonthecoppersurfaceinaggressiveenviroments

Importantly,rareearth organiccompounds performedeffective

corrosion inhibitors for both steel and aluminum substrates

Thesecompoundsformbothcontinuousandheterogeneous

pro-tective surface film, leading to extremely improved corrosion

resistance[37,46].Therefore,theaimofthis presentworkisto

develop yttrium 3-(4-nitrophenyl)-2-propenoate compound, as

newinhibitoranddiscusstheireffectivenessinpreventing

corro-siononcopperpipealloy

2 Experimental procedures

2.1 Chemicalsandmaterials

Yttrium 3-(4-nitrophenyl)-2-propenoate (Y(4NO2Cin)3,

“4NO2Cin” is a derivative of 4-nitrocinnamic acid) was

syn-thesizedusingYCl3 and3-(4-nitrophenyl)-2-propenoicacidand

usedascorrosioninhibitor.Molecularstructureofyttrium

3-(4-nitrophenyl)-2-propenoate (Y(4NO2Cin)3) inhibitor is given in

Fig.1 The compounds includingYCl3 and

3-(4-nitrophenyl)-2-propenoicacidwerepurchasedfromSigmaAldrich.Y(4NO2Cin)3

wasadded to 0.1M NaClsolution to make final concentration

of 0.00, 0.02, 0.15, and 0.45mM using reagent grade sodium

chloride, distilled water, and 12h for stirring The working

electrodes used for the electrochemical tests and copper alloy

couponsweremachinedfromacopperalloywithdimensionof

10×10×1.5mm3.Thecopperalloyelectrodeswerecoatedwith

anepoxyresinandattachedtoaTeflonholder.Thecopperalloy

compositionswerecheckedbyopticalemissionspectroscopyand

giveninTable1.Thecopperalloyspecimensforcorrosiontests

werefinished by grindingwith 1200-grit silicon carbide paper

with10×10mm2ofexposedarea

2.2 Electrochemicalinvestigationmethods

Beforeelectrochemicaltest,thesampleswerekeptinthenatural

aeratedsolutionfor2htostabilizetheopen-circuitpotential(OCP)

Theelectrochemicalimpedancespectroscopy(EIS)testswere

per-formedatEOCPandconductedeverytwohouroveraperiodof20h

TheEIStestswereconductedusingaVSPsystem(BioLogicScientific

Fig 1.Molecular structure of yttrium 3-(4-nitrophenyl)-2-propenoate corrosion inhibitor.

Instruments)withacommercialsoftwareprogramforAC measure-ments.Thepeak-to-peakamplitudeofthesinusoidalperturbation was10mV.Thefrequencyrangedfrom100kHzto10mHz Poten-tiodynamicpolarizationtestswerecarriedoutafterEIS.Atitanium counterelectrodewasusedwithasilver/silverchloride(Ag/AgCl) electrodeasthereferenceelectrode.Thepotentialoftheelectrodes wassweptatarateof0.166mV/srangingfromaninitialpotential

of−250mVvs.EOCPto500mVAg/AgCl.Potentiostatictestwas per-formedtofurtherexaminetheeffectofY(4NO2Cin)3onthestability

ofprotectivefilmformedonthealloysurface.Thepotentiostatic testswereperformedataconstantpotentialof0mVAg/AgClusing BiologicVSPmultichannelpotentiostatafterimmersionfor20hin thesolution.Toensurereproducibility,threemeasurementswere runforelectrochemicalandimmersiontests

2.3 Thewirebeamelectrode Wirebeamelectrode(WBE)wasusedtostudythetendencyof localizedcorrosionofcopperalloyinthetestsolutions.TheWBE wasmadefromonehundredidenticalcopperalloywires embed-dedinepoxyresin,insulatedfromeachotherwithathinepoxy layer.Eachwirehadadiameterof0.19cmandactedbothasa sen-sorand asacorrosionsubstrate.Theworkingareawasgrinded using1200-gritsiliconcarbidepaper,rinsedwithdeionisedwater andethanolbeforebeingexposedtothreelitersof0.1MNaCl solu-tionatroomtemperature.After30minsofinitialcorrosiontesting, inhibitorwereinjectedintothetestingcellwithregularaddition

atevery20h.Corrosionprocesses weremonitoredbymapping galvaniccurrentsbetweenachosenwireandalltheotherwires shortedtogetherusingapre-programmedAutoswitchdeviceand

anACMAutoZRA.Galvaniccurrentdatawereobtainedand ana-lyzed.The measurements weretaken regularlyto examinethe changestakingplacewiththeintroductionoftheinhibitors

Table 2

Summary of corrosion parameters as obtained from potentiodynamic polarization measurements, showing average and standard deviations.

(mM) (mV Ag/AgCl ) (×10 8 A/cm 2 ) (mV/decade) (mV/decade) (R p  cm 2 )

2.4 Surfacecharacterization

To investigatethe relationship between theelectrochemical

behaviourandsurfacemorphology,thespecimenswereexamined

byscanningelectronmicroscopy(SEM) usingSEMSupra55 VP

afterimmersionfor20hin0.1MNaClsolutioncontainingdifferent

Y(4NO2Cin)3concentrationsatroomtemperature.Inaddition,the

protectivefilmwasalsoevaluatedbyattenuatedtotalreflectance

Fouriertransforminfraredspectroscopy(Alpha-FTIR

spectrome-ter)after2and30min,1and20hattheopen-circuitpotential

3 Results and discussion

Fig.2(a)presentsthepotentiodynamicpolarizationcurvesof

copperalloywithoutandwithY(4NO2Cin)3additionin0.1MNaCl

solutionatroomtemperature(approximately25◦C).In

uninhib-itedsystem,theanodicpolarizationcurveshowedthreeregions:

(i)fromcorrosionpotential,thecopperwasdissolutedduetoa

continuousincreaseof theanodiccurrentdensity with

increas-ingofpotential;(ii)filmformationduetoadecreaseoftheanodic

currentdensitywiththeincreasingofpotential;and(iii)the

disso-lutionofthefilmduetoanincreaseoftheanodiccurrentdensity

withtheincreasingpotential.Incontrast,thepresenceofinhibitors

performedthesignificantdecreasein anodiccurrent densityto

lowervaluescomparedtothoseintheuninhibitedsystem

Fur-thermore,theincreaseofY(4NO2Cin)3concentrationleadstolower

corrosioncurrentdensities.Theresultsalsoindicatedbothanodic

andcathodicinhibition.However,asignificanteffectontheanodic

reactionswasobservedduetotheshifttohigherpotentialswhen

theconcentrationofinhibitorwasincreased,resultinginananodic

inhibition Therefore, anincrease of theinhibitorconcentration

shouldresultinashifttomorepositivepotentialsandanoverall

decreaseincorrosioncurrentdensity.Inaddition,theY(4NO2Cin)3

incrementsignificantlyreducedtheanodiccurrentdensityandit

didnotshowrapidincreaseuntil400mVAg/AgClasshownin

polar-ization curveof thespecimen immersedin solutioncontaining

0.45mMinhibitorinFig.2(a).Thiscouldbeduetothefactthatthe

protectivefilmformedonthealloysurface,whichobstructs

diffu-sionofionsinelectrolyteinvolvedintheanodicprocessoccurring

ontheelectrodesurface,suchaschlorideions.Thefilmformation

isensuredbyothertechniquesinnextsections.Table2showsthe

corrosionparametersofthespecimensdeterminedfromthe

poten-tiodynamicpolarizationtest.Thecorrosionparametersaccording

topotentiodynamicpolarizationofthefirst,second,andthirdtests

arelistedas1st,2ndand3rdandcomparedinTable2.Theinhibition

Fig 2.(a) Potentiodynamic polarization curves after 20-h immersion in solutions and (b) inhibition performance measured from potentiodynamic polarization. efficiencyinFig.2(b)wasdeterminedfromthepolarizationcurves usingthefollowingequations:

=iocorr−icorr

io

where (%)istheinhibitionperformance,icorr andio

corrare thecorrosioncurrentdensityinthepresenceandabsenceofthe

Fig 3.Current density as a function of time under a constant applied anodic

poten-tial of 0 mV Ag/AgCl after 20-h immersion in solutions.

Y(4NO2Cin)3 inhibitor, respectively.It is noted thatthe current

density (icorr) values were calculated using Tafel extrapolation

methods.Thecomparisonoftheinhibitionperformancerevealed

thattheadditionof Y(4NO2Cin)3 inhibitor ledtoa high

inhibi-tionperformance.Thevalueincreasedwithincreasinginhibitor

concentration,indicatinganimprovedinhibitionperformance

Toensurethefilmformationinpotentiodynamicpolarization

resultsandtocheckthestabilityoftheprotectivefilm,

potentio-statictestswereperformedusinganappliedpotentialthatwas

determinedbaseduponthedatafromthepotentiodynamic

polar-izationcurvesinFig.2(a),correspondingtotheenrichmentofthe

protectivefilm.Fig.3showstheresultsofthepotentiostatictest

performedataconstantpotentialof0mVAg/AgClfor1h.The

cur-rentdensitiesofthecopperalloyin0.1MNaClsolutioncontaining

Y(4NO2Cin)3remainedatalowvalueascomparedwiththatofthe

copperalloyinsolutionwithoutY(4NO2Cin)3.Thissuggeststhat

theY(4NO2Cin)3 additionresultedinthelowanodicdissolution

ofthecopperalloy.Theresultsuggeststheformationofprotective filmmayhavehinderedtheoutwarddiffusionofcorrosionproduct ionssuchasCu+,Cu2+andtheinwardpenetrationofCl−ions.The decreaseincurrentdensitywithincreasingY(4NO2Cin)3 concen-trationcouldbeduetotheincreasedcoverageofthemoleculeson thealloysurface,resultinginprotectivefilmformationtopromote highinhibitionperformancewhichhasbeenshownwithEISand surfaceanalysisresults

Tofurtherstudyinterfacialchangesatthecopperalloysurface withandwithoutinhibitoraddition,electrochemicalimpedance measurementshavebeencarriedout.Fig.4showstheimpedance spectraintheformoftheNyquistplots ofthealloyspecimens immersedin 0.1MNaClsolutions containingdifferentinhibitor concentrationsrangedfrom0.00to0.45mMfor20h.The semi-circular depression in the Nyquist diagram was attributed to theheterogeneityofthesurface,thesurfaceroughnessandthe existenceoftwodifferentprocesseshavingpracticallythesame relaxation time In this study, the heterogeneityof the surface wasincreasedforthespecimensimmersedin0.1MNaClsolutions withoutandwithlowinhibitorconcentrationsduetothepitting, consistingwithahighcorrosionrate.Theincreaseinthediameter

ofthearcindicatedthatthereistheimprovementofamore capac-itivesurfacefilm,promotingtheformationoftheprotectivelayer Fig.5presentstheBodeplots(phaseanglevs.frequency)obtained fromthecopperalloywithdifferentY(4NO2Cin)3 contentsin a 0.1MNaClsolutionfor20h.Thephaseanglediagramsobtained fromcopperalloyelectrodeintheY(4NO2Cin)3-containing solu-tions showed more complicated than that from copper alloy electrode in solution withoutY(4NO2Cin)3 addition, suggesting thattheadditionofY(4NO2Cin)3promotestheformationofa pro-tectivefilmonthealloysurface[60,61].Theapertureofthephase anglesincreasedwithincreasingY(4NO2Cin)3concentrationwhich

Fig 4.Nyquist plots of copper specimens in 0.1 M NaCl solution containing: (a) 0.00, (b) 0.02, (c) 0.15 and (d) 0.45 mM Y(4NO 2 Cin) 3

Fig 5.Bode plots (phase angle vs frequency) of copper specimens in 0.1 M NaCl solution containing: (a) 0.00, (b) 0.02, (c) 0.15 and (d) 0.45 mM Y(4NO 2 Cin) 3

couldbea resultof animprovedsurface coverageleading toa

morecapacitivesurfacefilmwhichisconsistentwiththe

potentio-dynamicpolarizationandpotentiostaticresultsdescribedabove

Furtherinformationaboutelectrochemicalprocessesoccurringat

thesolution-electrodeinterfaceis obtainedby detailedanalysis

ofimpedancespectrausingsuitablydesignedequivalentcircuits

Fig.6(a)showsthecircuitforanuninhibitedcopperalloysurface

(Rproisreplacedbycorrosionproductresistanceforthespecimen

immersedinsolutionwithoutinhibitoraddition)atlowinhibitor

concentrationandFig.6(b)shows morecomplicated equivalent

circuitdesigned tosimulate theprotective film formed onthe

copperalloysurfaceimmersedin0.1MNaClsolutionswithhigh

Y(4NO2Cin)3concentrations.Inthecircuit,Rsrepresentsthe

solu-tionresistance, CPEtheconstantphaseelement,CPE1andCPE2

theconstantphaseelementofthefirstandthesecondprotective

films,Rpro1 and Rpro2 thefirstand secondprotectivefilm

resis-tances,CPEdltheconstantphaseelementofthedoublelayer,Rctthe

chargetransferresistance.Inthiscase,thecapacitorwasreplaced

withaCPEtoimprovethefittingquality,wheretheCPEcontains

adouble-layercapacitance(C)andphenomenologicalcoefficient

(n).Thevalueofnseemstobeassociatedwiththenon-uniform

distributionofcurrentasaresultofroughnessandsurfacedefects

ThenvalueofaCPEindicates:n=1,acapacitance;n=0.5,a

War-burgimpedance;n=0,aresistanceandn=−1,aninductance.Inthe

presentstudy,nwasconsistentlymaintainednear0.75,asaresult

ofthedeviationfromidealdielectricbehavior[60,61]

TheZsimpwinprogramwasusedtofittheEISdatato

deter-minetheoptimizedvaluesforthesolution,protectivelayers,charge

transfer,total resistanceparameters(Rs,Rpro,RctandRtotal)and

capacitances,whicharepresentedinFigs.7and8.Thevariationof

thesolutionresistance(Rs)withtheimmersiontimeforall

spec-imensisprovidedinFig.7(a).Itcanbeobservedthatthesolution

resistancesarestableduringthe20hofimmersiontimeforall

spec-imens.Inaddition,thesolutionresistanceincreasedwithincrease

Fig 6.Proposed equivalent circuits used to fit EIS data for copper immersed in 0.1 M NaCl solution with inhibitor additions: (a) two constant phase element (R pro

is replaced by corrosion product resistance for solution without inhibitor addition) and (b) three constant phase element.

inhibitorconcentration,indicatingeffectofinhibitoronthe con-ductivityofsolutions.Fig.7(b–d)showstheprotectiveresistances

ofallspecimens.Solutionswithoutandwith0.02mMinhibitor

per-Fig 7. Effect of Y(4NO 2 Cin) 3 inhibitor concentrations on: (a) solution resistance, (b) first protective film, (c) second protective film, (d) total protective film, (e) charge transfer and (f) total resistances as a function of immersion time.

formedsinglelayer,whileamorecomplicatedprotectivelayerwas

performedatconcentrations of0.15and0.45mMinhibitor.The

fittedresultsareinagreementwithBodeplotsinFig.5(candd)

andsurfaceanalysisresults.Itcanbeobservedthattheprotective

layerresistanceincreasessteadilyastheimmersiontimeincreases

during20hofimmersiontimeandstronglyincreaseswith

increas-inginhibitorconcentration.Thisresultindicatesthattheincreasing

inhibitorcontentincreasesnotonlytheprotectivelayerresistance

butalsoitsstability.Thiscouldbeattributedtothefactthatthe

protectivelayersareformedonthesurfaceofthecopperalloyand

thesebarrierlayersarefurtherimprovedbyincreaseininhibitor

additiontothesolutionasnotedabovefromthepotentiodynamic

andpotentiostaticpolarizationmeasurements.Fig.7(eandf)show

thechargetransfer(Rct)andtotalresistances(Rtotal=Rs+Rpro+Rct),

whichalsoincreaseastheimmersiontimeincreasesand asthe

inhibitoradditionincreases.Thisisveryimportantbecausehigher

RctandRtotalvaluesindicatebetterinhibitionperformance

The important capacitance values reflect aggressive

compo-nents in solution such as water and electrolyte ingress in the

protectivelayers.TheCproandCdlareplottedandshowninFig.8 Fig.8(a–c)showsthecapacitanceoftheprotectivelayers.It indi-catesthattheCprovaluesaredecreasedwithexposuretimeand withincreasinginhibitorconcentration,meaningthattheingress

ofaggressivecomponentsinsolutionishinderedbythe protec-tivefilmformedonthecopperalloysurfaces.Thisprotectivefilm becomesmorestabileandcompactwheninhibitoradditiontothe solutionincreases.CdlvaluesinFig.8(d)werealsodeterminedby fittingtheimpedancespectrawiththesuggestedelectricalmodel describingtheelectrochemicalreactionsoccurringattheexposed metalsurfaceinFig.6.Higherdoublelayercapacitancevaluesare observedforsolutionswithoutandwith0.02Minhibitorexplained

bythepooradhesionofcorrosionproductandlowcoverof protec-tivefilmformedonthesurfaces.Forsolutionwithhigherinhibitor concentrations,thesevalues decreasedduring20h.Accordingly, thetendencyobservedforCdlvaluesofthesespecimensfullyagrees withincreaseofcoveredsurfaceareabyprotectivefilm.Theresults indicatedthatCdlvaluesdecreasedwithincreasinginhibitor con-centration.Thiscanbeaccountedforthelowerdensityofpores

Fig 8.Effect of Y(4NO 2 Cin) 3 inhibitor concentrations on: (a) first protective, (b) second protective, (c) total protective and (d) double layer capacitances as a function of immersion time.

reachingthemetal leadingto a total lower valueof theactive

metallicsurfacearea.Higherinhibitorconcentrationconsequently

resultsinhigherinhibitionofthecorrosionprocessandconsequent

improvementsof compactibility, adhesive capacity, and surface

coverageoftheprotectivefilmformedonthesubstratesurface

A WBE was used to consider the localized corrosion

phe-nomenonofcopperalloyina0.1MNaClsolution.Galvaniccurrent

as a local electrochemical parameter has been measuredfrom

local areas of a WBE surface, determining the localized

corro-sion processes The galvanic current distribution mapsshowed

instantaneousgalvanic current distributionover a WBE surface

aregiveninFig.9(a–d),thesearecharacterizedbyalarge

num-berofminoranodesrandomlydistributedovertheWBEsurface

Thelocalizedcorrosiondissolutioncanbedescribedbythe

max-imumanodiccurrentdensityofthemostactiveanode,whereas

overallcorrosionofthespecimenisdescribedbythetotalanodic

currentdensity.Inaddition,theresultsalsoshowthatthe

loca-tionsofmostanodeskeptchanging ina randommanner.After

the addition of Y(4NO2Cin)3, almost all locations behaved as

anodes, cathodes and the values of current density decreased

with increasing Y(4NO2Cin)3 addition Furthermore, the

maxi-mumanodicdissolutionandcathodiccurrentdensitiesdropped

to2.88×10−6 and−1.76×10−6A/cm2respectively,after20hof

0.45mMY(4NO2Cin)3contentin0.1MNaClsolution,suggesting

thataddingY(4NO2Cin)3 to0.1MNaClsolutionactedasamixed

typeinhibitor,predominantly anodicinhibitor,thatprefers

uni-formcorrosionratherthanlocalizedcorrosion.Theanodic,cathodic

andtotalcurrentdensitiesinFig.9(e)alsodecreasedsignificantly,

indicatingreductioninbothoverallanodicdissolutionandcathodic

currentandtheinhibitionofgeneralcorrosion.Thisisalso

con-sistentwithboth anodicandcathodicinhibitionwithdominant

anodicinhibitionas showninthepotentiodynamicpolarization

results

Surfaceanalysiswascarriedouttofurtherunderstandthe sur-face morphology and properties and their effects oncorrosion behavior.Fig.10showsSEMimagesofthecopperalloysurfaces after 20h immersion in 0.1M NaCl solution withoutand with Y(4NO2Cin)3addition.Theresultsindicatethesignificantinfluence

ofthecorrosioninhibitoronthecopperalloysurface.Fig.10(aand b)correspondstothemorphologyofcopperalloysurfaceexposed

to0.1MNaClsolution withoutand with0.02mMY(4NO2Cin)3

addition,whichshowagreaterlevelofcorrosionforcopperalloy withoutinhibitor,resultingintheinwardpenetrationofions,such

asCl−.Whilealessattackofcorrosionhasbeenobservedonthe surfaceofcopperalloyexposedto0.1MNaClsolutioncontaining 0.15mMY(4NO2Cin)3 asshowninFig.10(c).Fig.10(d)doesnot showanycorrosionattack,suggestingtheadditionofY(4NO2Cin)3

compoundleadstoamoreinhibitedcorrosion

Fig 11 presents the attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) results Fig 11(a) demonstrates ATR-FTIR result of raw Y(4-NO2Cin)3 powder, this showed ␯(C C)propenyl bands in the infrared spectra of the yttrium 4-nitrocinnamate complexes located at 1643 and

1651cm−1,respectively.Theas(CO2)ands(CO2)absorptionsfor theY(III)complexesoccurat1420and1553cm−1,respectively Furthermore, the as(NO2)and s(NO2) absorptions of yttrium 4-nitrocinnamatewereassignedat1346and1512cm−1, respec-tively[62].TostudytheeffectofY(4-NO2Cin)3concentrationson thecopperalloysurface, alloysurfacesafter20himmersion in 0.1MNaClsolutionscontainingvariousY(4-NO2Cin)3 concentra-tionswerealsomeasuredbyATR-FTIR.Fig.11(b)presentsATR-FTIR spectra results of copperalloy surfaces exposed to 0.1M NaCl solution containing 0.02, 0.15, and 0.45mM Y(4-NO2Cin)3.The mainC Cstretchingofpropenylgrouphasbeenobservedaround

1611and1657cm−1bands.Theinformationpeaksaround1413 and1551cm−1areattributedtotheas(CO2)ands(CO2)

absorp-Fig 9. Galvanic current distribution maps measured over a WBE surface in 0.1 M NaCl solution: (a) without Y(4NO 2 Cin) 3 addition, and with (b) 0.02 mM, (c) 0.15 mM, (d) 0.45 mM Y(4NO 2 Cin) 3 addition, and (e) changes of current densities obtained from WBE results.

tions,respectively.Othermainpeaksassignedtotheas(NO2)and

s(NO2)absorptionswereobservedaround1452and1571cm−1,

respectively.Theinformativepeaksaround1200and2150cm−1

are assigned to the C C bands The results indicated that the

absorptionpeakintensitiesoftheC C,(CO2),and(NO2)

absorp-tionsonthecoppersurfacewereincreasedwithanincrease of

Y(4-NO2Cin)3concentration,suggestinganincreaseofthe

forma-tionofamixedmetal4-nitrocinnamatespeciesdepositiononthe

coppersurfaces.Furthermore, tostudy theprocess of film

for-mationonthecoppersurfaces,coppersurfaceswereevaluated

usingATR-FTIRafterimmersionin0.1MNaClsolutioncontaining

0.45mMY(4-NO2Cin)3 after2and 30min,1and20h.Fig.11(c)

presentsATRspectraresultsofcoppersurfacesexposedtoa0.1M

aqueousNaClsolutioncontaining0.45mMY(4-NO2Cin)3 after2

and30min,1and20himmersiontimes.After2minof

immer-sion,ATR-FTIRwasconductedandshowedstrongabsorptionbands

around497,603,and660cm−1,respectively.Thesebandsmaybe

attributedtotheCu-Ostretchingandvibration[63,64]attributed

tothepresenceofthehydratedcopperoxide/hydroxideinsurface

films.Whenimmersiontimeincreased,theintensitiesof

absorp-tion peaks for C C, (CO2), and (NO2) absorptions increased,

indicatingthattheprotectivefilmwasenrichedwithimmersion

time.Thisisconsistentwithelectrochemicalresults,particularly

EISresults.Inaddition,hydratedcopperoxide/hydroxidewasstill present,indicatingthatthehydratedcopperoxide/hydroxidewas initiallyformedonthesurfaces.Thesesituationsleadtopromotea compactandadhesiveprotectivelayerformationonthespecimen surface,resultinginhinderingoftheattackofaggressiveionsin solutions

Theresultsoftheelectrochemicaldataandsurface characteri-sationsuggestedthatinhibitionmechanismcouldberelatedtothe filmformationonthealloysurface.Itshowedevidenceofa domi-nantanodicinhibitionmechanismandalsocharacteristicofanodic protection,butsomeinfluencesonthecathodicreactionprocesses arealsoevident.Thepotentiodynamicpolarizationresultsshowed mixedinhibitionbehaviorwithdominantanodicinhibitioninthe presenceofY(4-NO2Cin)3compoundandtheEISdatadisplayedthe developmentofaprotectivesurfacefilmbytheincreaseof pro-tectiveandchargetransferresistances,aswellasthedecreaseof protectiveanddoublelayercapacitances.Thesurfaceanalysisdata alsoprovidetheevidenceofthefilmformationonalloysurface

aswellasthehydratedcopperwhich isinitiallyformedonthe surfaces.Therefore,Y(4-NO2Cin)3 moleculesmostlikelyhavean uprighttiltedposition,withtheOandNatomspointingtoward thehydratedcopperoncoppersubstrate.Itcouldbeappropriate

toconsiderthefollowinginhibitionmechanismforcopperalloy

Fig 10. SEM images of copper surfaces after immersion in 0.1 M NaCl solution containing: (a) 0.00, (b) 0.02, (c) 0.15 and (d) 0.45 mM Y(4NO 2 Cin) 3

Fig 11. ATR-FTIR spectra of (a) Y(4NO 2 Cin) 3 powder as raw material, (b) the copper surface after 20-h immersion in Y(4NO 2 Cin) 3 -containing solutions, and (c) the copper surface after 2-min, 30-min, 1 and 20-h immersion in solution containing 0.45 mM Y(4NO 2 Cin) 3

Fig 12.Schematic figure of (a) corrosion process of copper alloy in 0.1 M NaCl

solu-tion without inhibitor, (b) and (c) Y(4NO 2 Cin) 3 inhibition processes of copper alloy

in 0.1 M NaCl solution with inhibitor addition.

in0.1MNaClsolutions.Electrochemicalcorrosioninitiatesatthe

imperfectplaceswhichshouldbesignificantlymorereactivethan

thealloymatrix,makinga changeoflocalizedpH.Thisleadsto

formaninitialhydratedcopperlayeronthesurfacesassimulatedin

Fig.12(a)andthendepositionofprotectiveinhibitivelayers(either

optioninFig.12(b)oroption2inFig.12(c)),thusslowingdown

theelectrochemistryintheseactivelocationsonthecopper

sur-face,whichmostlikelyaccountsfortheinducedanodicinhibition

Inaddition,athin surfacefilmcouldbedepositedontheentire

alloysubstrateduetothecathodicreductionreactions.Itleadsto

formanuniformprotectivefilmonthesubstratesurface,which

correspondsforthehighdegreeofcorrosioninhibition,whichis

alsoconsistentwiththeinfluenceofinhibitorconcentration.When

differentinhibitor concentrationswereaddedtosolutions,they

resultinanimprovedperformanceduetoincreasingamountof

inhibitorcoverage.Thegoodcorrelation,betweenelectrochemical

techniquesandsurfaceanalysisfortheprotectivefilmformation

onthealloysurface,suggeststhatthehighestinhibition

perfor-manceaswellasthefilmformationonthealloysurfacedependon

inhibitorconcentrations

4 Conclusions

Yttrium 3-(4-nitrophenyl)-2-propenoate compound −

Y(4NO2Cin)3 − is abletoinhibit corrosionof copperpipealloy

in0.1Msodiumchloridesolution.Inhibitionefficiencycouldbe

increasedwithanincrease ofinhibitor concentration

Potentio-dynamicpolarizationresultssuggestthat Y(4NO2Cin)3 provided

mixedtype inhibitorwithdominantanodicinhibition ofcopper

alloy in 0.1M sodium chloride solution Y(4NO2Cin)3 inhibitor producedareductioninicorrfrom816nA/cm2to32nA/cm2,high protective inhibiting deposit (Rpro), charge transfer resistances (Rct),and randomdistributionofminoranodes, indicatinggood inhibitionperformance in0.1Msodiumchloridesolutions.SEM andATR-FTIRanalysesofcopperalloysurfaces,afterexposureto Y(4NO2Cin)3-containingsolutions,revealedprogressive,formable depositionofprotectiveinhibitivelayerthathindersthecorrosion reactionsonthecopperalloysurface,therebysignificantly improv-ingthecorrosionresistanceofthecopperalloyunderinvestigated conditions

Acknowledgment

Thisworkisfunded byPetroVietnamUniversityundergrant codeGV1601

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