The inhibition effect of hydroxyethylcellulose (HEC) on 1018 c-steel corrosion in 3.5% NaCl solution was investigated by using potentiodynamic polarization, electrochemical frequency modulation (EFM) and electrochemical impedance spectroscopy (EIS) techniques.
Trang 1jo u r n al h om ep a g e :w w w e l s e v i e r c o m / l o c a t e / c a r b p o l
Keywords:
Polarization
EIS
SEM
Theinhibitioneffectofhydroxyethylcellulose(HEC)on1018c-steelcorrosionin3.5%NaClsolution wasinvestigatedbyusingpotentiodynamicpolarization,electrochemicalfrequencymodulation(EFM) andelectrochemicalimpedancespectroscopy(EIS)techniques.Thepotentiodynamicpolarizationstudies suggestedthatHECactsasamixed-typeinhibitor.DataobtainedfromEISwereanalyzedtomodelthe corrosioninhibitionprocessthroughequivalentcircuit.ResultsobtainedfromEFMtechniquewereshown
tobeinagreementwithpotentiodynamicandEIStechniques.TheadsorptionbehaviorofHEConsteel surfacefollowstheLangmuiradsorptionisotherm.Thermodynamicparameter(G◦
ads)andactivation parameters(E∗,H*andS*)werecalculatedtoinvestigatemechanismofinhibition.Scanningelectron microscopy(SEM)andenergydispersiveX-ray(EDX)analysissystemwereperformedtocharacterize thefilmformedonthemetalsurface.DMol3quantumchemicalcalculationswereperformedtosupport theadsorptionmechanismwiththestructureofHECmolecule
©2014TheAuthors.PublishedbyElsevierLtd.ThisisanopenaccessarticleundertheCCBY-NC-ND
license(http://creativecommons.org/licenses/by-nc-nd/3.0/)
1 Introduction
Thecorrosioninhibitionof1018c-steelbecomesofsuch
inter-estbecauseitiswidelyusedasaconstructionalmaterialsinmany
industries,andthisisduetoitsexcellentmechanicalproperties
andlowcost.Topreventthebasemetalattackduringthese
pro-cesses,corrosion inhibitorsare widely used.It is reported that
organicmaterials suchas polymers or macromolecules,having
functionalgroups( OH, COOH, NH2,etc.),arefoundtobe
cor-rosioninhibitorsindifferentcorrosivemedia(Ashassi-Sorkhabi&
Ghalebsaz-Jeddi,2005;Baoa,Zhanga,&Wan,2011;Cheng,Chen,
Liu,Chang,&Yin,2007;Deng,Li,&Xie,2014;El-Haddad,2013;
El-Sayed,1996;Fekry&Mohamed,2010;Müller,Förster,&Kläger,
1997;Sathiyanarayanan,Balakrishnan,Dhawan,&Trivedi,1994;
Solomon&Umoren,2010;Umoren,Solomon,Udosoro,&Udoh,
2010;Waanders,Vorster,&Geldenhuys,2002).Largercorrosion
inhibitionefficiencies thatareobserved usingpolymersarenot
onlyduetothepresenceof-electronsbutitcanbealsoattributed
tothe largermolecularsize which ensures greatercoverage of
metallicsurface(Sathiyanarayananetal.,1994).HECiswater
sol-ublepolymerderivedfromcellulose,relativelycheap,non-toxic,
eco-friendlycorrosioninhibitor.It haswide spread applications
asabinder,thickener,stabilizer,suspensionandwaterretaining agentinfoodindustry,pharmaceutical,cosmetic,paperandother industrialareas(WHO,1998).HEChasbeenreportedtoinhibitthe corrosionofaluminumandmildsteelinHClsolution(Arukalam,
2012).Inthepresent workthecorrosioninhibiting behaviorof HECon1018c-steelcorrosion in3.5% NaClsolutionhave been investigatedusingpotentiodynamicpolarization,electrochemical frequencymodulation(EFM)andelectrochemicalimpedance spec-troscopy(EIS)techniques.Thesurfaceof1018c-steelwasanalyzed usingscanningelectronmicroscopy(SEM)andenergydispersive X-ray(EDX)analysissystemtoconfirmthecompositionsofthe corrosionproductsformedonthesurface.DMol3quantum chem-icalcalculationswerealsoemployedtodiscussthecorrelationof inhibitionefficiencyandmoleculestructureofHEC
2 Experimental
2.1 Materialsandsolutions Thechemicalcompositionof1018c-steelusedinthis investi-gationisthefollowing(mass%):C–0.20,Mn–0.35,Si–0.003,P– 0.024andrestFe.Thesteelsheetiscutintocouponsofdimension 1.0cm×1.0cm×0.8cm.Thecouponwasembeddedinepoxyresin
inaglasstube.Acopperwirewassolderedtotherearsideofthe couponasanelectricalconnection.Theexposedsurfaceareaofthe electrode(0.5cm2)wasabradedwithaseriesofemerypapersup http://dx.doi.org/10.1016/j.carbpol.2014.06.032
Trang 2O O
HO
O O
HO
O
CH2CH2OH
n
to1200grade.Theelectrodewasthenrinsedwithdistilledwater
andethanoltoremovepossibleresidueofpolishingandairdried
Thiswasusedastheworkingelectrodeduringthe
electrochem-icalmethods.Testingelectrolytewas3.5%NaClsolutiondiluted
indistilledwater, usedasblanksolution.Theinhibitor
hydrox-yethylcellulose(HEC)waspurchasedfromSigma–AldrichCo.,and
chemicalstructureof therepeatunitis presentedinFig.1.The
concentrationrangeofHECusedinthisworkwas0.1–0.5mM
2.2 Electrochemicalexperiments
Theelectrochemicalmeasurementswereperformedinatypical
three-compartmentglasscellconsistedofthe1018c-steel
speci-menasworkingelectrode (WE),platinum electrodeasauxiliary
electrode(AE),andasaturatedcalomelelectrode(SCE)asthe
ref-erenceelectrode(RE).Theexperimentswerepreformedusinga
GamryinstrumentPotentiostat/Galvanostat/ZRA(PCI4G750)
con-nectedwithapersonalcomputer;theseincludeGamryframework
systembasedontheESA400.Variouselectrochemicalparameters
weresimultaneouslydeterminedusingdc105corrosionsoftware,
EFM140softwareand EIS300 impedancesoftware Echem
Ana-lyst5.5softwarewasusedforcollecting,fittingandplottingthe
data.Eachrunwascarriedoutinaeratedsolutionsattherequired
temperature,usingawaterthermostat.Allgivenpotentialswere
referredtoSCE.Theworkingelectrodewasimmersedinthetest
solutionfor30minuntiltheopenpotentialcircuitpotential(EOC)
reached.Thepotentiodynamiccurrent–potentialcurveswere
car-riedoutatascanrate1.0mVs−1,andthepotentialwasstarted
from(−1200mV upto +200mV) versusopen circuitpotential
EFMcarriedoutusingtwofrequencies 2.0and 5.0Hz.Thebase
frequencywas1.0Hz Weusea perturbationsignalwith
ampli-tudeof10mVforbothperturbationfrequenciesof2.0and5.0Hz
(Bosch,Hubrecht,Bogaerts,&Syrett,2001;Khaled,2008).EIS
mea-surementswerecarriedoutusingACsignalsofamplitude10mV
peaktopeakattheopen-circuitpotentialinthefrequencyrange
100–50kHz
2.3 Quantumchemicalcalculations
ThemoleculesketchofHECwasdrawnbyChemBioDrawUltra
12.0 Thenthe quantum chemical calculations were performed
usingDMOL3methodinMaterialsStudiopackage(MaterialsStudio,
2009).DMOL3isdesignedfortherealizationoflargescaledensity
functionaltheory(DFT)calculations DFTsemi-corepseudopods
calculations (dspp) were performed with the double
numeri-cal basis sets plus polarization functional (DNP) to obtain the
optimized geometry Then the molecule’s frontier orbital was
expressedasrelativedensitydistributionfigure
2.4 SEMandEDXexamination
Specimensof1018c-steelwereimmersedin3.5%NaClsolution
withoutandwithHEC(0.5Mm)for2daysat25◦C.Afterthat,the
surfaceoftestcouponsexaminedusingascanningelectron
micro-scope(SEM,JOEL, JSM-T20, Japan) and an X-raydiffractometer
0.0 -0.1 -0.2 -0.3 -0.4 -0.5 -0.6 -0.7 -0.8 -0.9 -1.0 -1.1 -6.0 -5.5 -5.0 -4.5 -4.0 -3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5
3.5% NaCl 0.1mM 0.3mM 0.5mM
E, mV vs SCE
Philips(pw-1390)withCu-tube (CuK␣1, l=1.54051 ˚A)analysis system
3 Results and discussion
3.1 Electrochemicalmeasurements 3.1.1 Potentiodynamicpolarization Potentiodynamicpolarizationcurvesfor 1018c-steelin3.5% NaClinabsenceandpresenceofdifferentconcentrationsofHEC
at25◦CareshowninFig.2.Tafelslopes(ˇa,ˇc)andcorrosion cur-rentdensity(Icorr),obtainedbyextrapolationoftheTafellines.The percentageinhibitionefficiency(εp%)andthedegreeofsurface cov-erage(),werecalculatedfromthefollowingequation(Sahin,Gece, Karc,&Bilgic,2008):
εp%=×100=
1−Iinh
Ib
whereIbandIinharethecorrosioncurrentdensitiesintheabsence and thepresence of theinhibitor, respectively Asshown from Fig.2,anodicandcathodiccurrentdensity(Icorr)decreasedwith theincreaseininhibitorconcentration,soinhibitionefficiency(εp) increased.Thisduetothat,theadditionofinhibitorreducesanodic dissolutionofmetalandalsoretardsevolutionofhydrogen reac-tion.Thiseffectisduototheadsorptionofinhibitorontheactive centersof steelsurface(Singh&Quraishi, 2010).Thecorrosion parameters,evaluatedfromTafelpolarizationcurvesarelistedin Table1 It wasfoundthat(Table1 theslopes ofthecathodic andanodicTafellinesareapproximatelyconstantand indepen-dentontheinhibitorconcentration.Thisbehaviorsuggeststhatthe inhibitormoleculeshavenoeffectonthemetaldissolution mech-anism.Inaddition,thevaluesof(Ecorr)donotchangesignificantly
inthepresenceofinhibitor.So,HECactsasamixedtypeinhibitor (El-Haddad&Elattar,2012)
3.1.2 Electrochemicalfrequencymodulation(EFM) TheEFMtechniqueisusedtocalculatetheanodicandcathodic Tafelslopesaswellascorrosioncurrentdensitieswithoutprior knowledgeofTafelconstants.EFMisanon-destructivetechnique andisarapidtest.Fig.3aandbshowsrepresentativeexamplesfor EFMintermodulationspectraof1018c-steelin3.5%NaClsolutions devoidofandcontaining0.5mMHECat25◦C.Similarresultswere recordedfortheotherconcentrations.Eachspectrumisacurrent
Trang 3Table 1
Fig 3. Intermodulation spectra of 1018 c-steel in 3.5% NaCl solution (a), and intermodulation spectra of 1018 c- steel in 3.5% NaCl solution in presence of 0.5 mM HEC (b) at
25 ◦ C.
valuesdecrease,whilethoseof(εEFM%)increasewithincreasein
theinhibitorconcentration,indicatingthatHMCinhibitsthe
cor-rosionofmetalthroughadsorption.Thevaluesofcausalityfactors
(CF2,CF3)areapproximatelyequalthetheoreticalvalues(2)and
(3)according totheEFM theory,indicatingthat, thevalidityof
Tafelslopesandcorrosioncurrentdensities(AbdelRehim,Hazzazi,
Amin,&Khaled,2008;Amin,AbdElRehim,&Abdel-Fatah,2009)
3.1.3 Electrochemicalimpedancespectroscopy(EIS) EISmeasurementswerecarriedoutattherespectivecorrosion potentialsafter30minofimmersionof1018c-steelin uninhib-ited and inhibitedsolutions of 3.5% NaCl.Fig.4 shows Nyquist plots (a)and Bodeplots (b) of 1018c-steel inuninhibited and inhibited 3.5%NaClsolutions containing variousconcentrations
ofHECat25◦C.TheNyquistplots showssinglecapacitiveloop, bothinuninhibitedandinhibitedsolutionsandthediameterofthe capacitiveloopincreasesonincreasingtheinhibitorconcentration indicatingthat,thecorrosioninhibitionofsteel.It isfoundthat theobtainedNyquistplotsarenotyieldperfectsemicirclesdue
tothefrequencydispersion,aswellaselectrodesurface hetero-geneityresultingfromsurfaceroughness,impurities,adsorption
ofinhibitorsandformationofporouslayers(Growcock&Jasinski, 1989; Machnikoval, Pazderova, Bazzaoui, & Hackerman, 2008; Paskossy,1994).ANyquistplotsdoesnotshowanyfrequencyvalue althoughsomedefinitefrequencywasusedtogettheimpedance
ateachdatapoint.Toovercomethisshortcoming,aBodeplotwas developed toindicateexactly whatfrequency wasused to cre-ateadatapoint.Theexperimentaldatafittedusingtheelectrical
1200 1100 1000 900 800 700 600 500 400 300 200 100
0
0
-100
-200
-300
-400
0.1 mM 0.3 mM 0.5 mM
Z real , Ohm.Cm 2
(a)
5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 -0.5 0.4 0.8 1.2 1.6 2.0 2.4 2.8
3.5% NaCl 0.1mM 0.3mM 0.5mM
log Freq., Hz
0 -20 -40 -60 -80
-100
(b)
◦
Trang 4Table 2
Fig 5. Electrical equivalent circuit (R s , solution resistance; R ct , charge transfer
resis-tance; C dl , double layer capacitance) used in fitting the experimental impedance
data.
&Zhang,2014).Inthiscircuit,RsandRctrepresentthesolution
resistancebetweenthesteelelectrodeandthereferenceelectrode
andthecharge-transferresistancecorrespondingwiththe
corro-sionreactionat metalsubstrate/solution interface,respectively
ThedoublelayercapacitanceCdlisplacedinparalleltothecharge
transferresistanceRct due tothecharge transfer reaction(Wu,
Ma,&Chen,1999).Thedoublelayercapacitancevalues(Cdl)at
differentinhibitor concentrations,iscalculated accordingtothe
following equation (Benchikh, Aitout, Makhloufi, Benhaddad, &
Saidani,2009):
Cdl= 1
ωRct = 1
2
maxRct
(3) where(ω)istheangularfrequencyand
maxisthefrequencyatthe apexofthefirstcapacitiveloop.Thesemicirclesathighfrequencies
inFig.4areassociatedwiththeelectricaldoublelayercapacitors
(Cdl)andthediametersofthehighfrequencysemicirclescanbe
consideredasthecharge-transferresistance(Rct)(Maetal.,2002)
So,theinhibitionefficiency,(εEIS%)andthedegreeofsurface
cover-age()ofHECcanbecalculatedfromthecharge-transferresistance
asthefollowingequation(El-Haddad,2013):
εEIS%=×100=
1−R∗ct
Rct
whereR∗
ctandRctarethecharge-transferresistancesfor
uninhib-itedandinhibitedsolutions,respectively.Thevariousparameters
derived from EIS measurements and inhibition efficiencies are
giveninTable3
AsseenfromTable3,theRs valuesareverysmallcompared
totheRctvalues.TheRctvaluestendtoincreasewiththeincrease
ofinhibitorconcentration,sothattheεEFM%increased.This
indi-catesthattheinhibitormoleculeshavethecapabilityofforming
uniformcompactadsorbedlayerovermetalelectrode(Benchikh
etal.,2009).Ontheotherhand,thevaluesof Cdl aredecreased
withincreaseininhibitorconcentration,areduetoareductionin
Inhibitor Conc (mM) R ct ( cm 2 ) C dl (F cm−2) ε EIS (%)
&Rawat,2001)
3.2 Adsorptionisothermandthermodynamicparameters
Inordertogainmoreinformationabouttheadsorptionmodeof HEConthemetalsurface,theexperimentaldatahavebeentested withseveraladsorption isotherms includingLangmuir,Temkin, FrumkinandFlory–Huggins.Inordertoobtaintheisotherm,the valuesofsurfacecoverage()werecalculatedfromthefromEFM dataasthefollowingequation(Chenetal.,2012):
=εEFM%
The best correlation between the experimental results and isotherm functions was obtained using Langmuir adsorption isotherm.Accordingtothisisotherm,isrelatedtoinhibitor con-centration(Cinh)bythefollowingequation(Li,Deng,&Fu,2009):
Cinh
1
whereKadsistheadsorptionequilibriumconstant.Theplotsof(C/)
vs.(Cinh)yieldstraightlinewithnearlyunitslopeandthelinear correlationcoefficient(R2)isalmostequalto1(R2=0.998), sug-gestingthattheadsorptionofHEConthemetalobeystheLangmuir adsorptionisothermaspresentedinFig.6.Theinterceptpermits thecalculationoftheequilibriumconstant(Kads)whichisequals 56.08525M−1.ThehighvalueofKadsimpliesmoreadsorptionthan desorptionandconsequentlybetterinhibitionefficiency(Refaey, Taha,&AbdEl-Malak,2004).Kadsisrelatedtothestandardfree
0.5 0.4
0.3 0.2
0.1 0.1 0.2 0.3 0.4 0.5 0.6 R 2 = 0.9998
θθ,,mM
Cinh, mM
◦
Trang 5Table 4
(Ansari,Quraishi,&Singh,2014):
Kads= 551.5exp
−G◦ads RT
(7)
where isthe valueof 55.5beingtheconcentrationof water in
solutionexpressedinmole,RistheuniversalgasconstantandT
istheabsolutetemperature.Thestandardfreeenergyof
adsorp-tion(G◦ads),whichcancharacterizetheinteractionofadsorption
molecules withmetalsurface, wascalculated by Eq (7) and is
equal to−19.9kJmol−1.The negativevalueof G◦ads indicates
thespontaneous adsorption of HEC molecules from NaCl
solu-tion to themetal surface It is well known that, thevalues of
G◦adsaround−20kJmol−1orlowerareassociatedwithan
elec-trostaticinteractionbetweenchargedmoleculesandchargedmetal
surface(physisorption);thoseof −40kJmol−1 orhigherinvolve
charge sharing or transfer from theinhibitor molecules tothe
metalsurfacetoformacoordinatecovalentbond(chemisorption)
(Ehteshamzadeh,Shahrabi,&Hosseini,2006).ThevalueofG◦
ads
inourexperimentislessthan−40kJmol−1,indicatedthatphysical
adsorption.Inadditiontoelectrostaticinteraction,theremaybe
molecularinteraction(Obot,Obi-Egbedi,&Umoren,2009)
3.3 Effectoftemperatureandkineticparameters
Theeffectof temperatureontheinhibition effectof HECon
1018c-steelcorrosionwasstudiedbypolarizationmethod.Inthis
study,differentconcentrationsoftheinhibitorwereusedat
differ-enttemperaturesaregiveninTable4.Itwasfoundthat(Table4
the(Icorr)increasedwithincreasingtemperatureintheabsence
andpresenceofvariousconcentrationsofinhibitorin3.5%NaCl
solutions,butthe(εp%),decreasedwithincreasingtemperature
ThisbehaviorcanberelatedtotheweaknessofHECadsorptionon
themetalsurfaceathighertemperaturesandsuggestsaphysical
adsorptionofinhibitoronthemetalsurface(Ashassi-Sorkhabi&
Ghalebsaz-Jeddi,2005).Theactivationparameterswerecalculated
fromArrheniusequationandtransitionstateequation(delCampo,
Perez-Saez,Gonzalez-Fernandez,&Tello,2009;Karakus,Sahin,&
Bilgic¸,2005):
Icorr= RT
Nhe((S
Inhibitor Conc (mM) E ∗
a (kJ mol−1) H * (kJ mol−1) −S * (J mol−1k−1)
ofE∗obtainedfromtheslopeof thelinesarelistedinTable5. Fig.7 showedtheplotoflogIcorr/Tvs.1/T.Straightlines were obtained with a slope of (−H*/2.303R) and an intercept of,
have beencalculatedand listedin Table5.It is foundthat, the valuesofE∗determinedinsolutioncontaininginhibitor concen-trationsarehigherthanthatofinabsenceofinhibitorisattributed
tothephysical adsorptionof inhibitoronthemetalsurface.On theotherhand,thehighervaluesofE∗inthepresenceofinhibitor comparedtothatinitsabsenceandthedecreaseofthe(ε%)with temperatureincreasecanbeinterpretedasanindicationof physi-caladsorption(Umoren,2008).ThepositivevaluesofH*indicated thatthecorrosionprocessisendothermicone(Bentissetal.,2007)
Ontheotherhand,theentropyofactivation(S*)isnegativein bothinabsenceandpresenceofinhibitor,implyingthatthe acti-vatedcomplexrepresentedtheratedeterminingstepwithrespect
totheassociationratherthanthedissociationstep.Itmeansthata decreaseindisorderoccurredwhenproceedingfromreactantsto theactivatedcomplex(AbdEl-Rehim,Hassan,&Amin,2001) 3.4 SurfacemorphologybySEM/EDX
Fig.8a–cshowstheresultsofSEMimagesfor1018c-steelin3.5% NaClintheabsence(blank)andpresenceof0.5mMHECinhibitor afterimmersionfor2daysat25◦C,respectively.Themorphology
ofspecimensurfaceintheabsenceofHEC(Fig.8a)showsthat,a veryroughsurfacewasobservedduetorapidcorrosionattackof themetalinthecorrosivesolution.Onthecontrary,inthe pres-enceoftheinhibitor(Fig.8c),theroughsurfaceissuppressed,due
totheformationofanadsorbedprotectivefilmoftheinhibitoron themetalsurface(Badiea&Mohana,2008;Okafor,Liu,&Zheng,
2009).Fig.8b–dpresentstheEDXspectrafor1018c-steelin3.5% NaClsolutionintheabsence(blank)andpresenceof0.5mMHEC inhibitorafterimmersionfor2daysat25◦C,respectively.TheEDX spectraofsteelinabsenceofHECin3.5%NaClsolution(Fig.8b) showsthecharacteristicspeaksoftheelementsconstitutingthe
1018c-steelsample.InpresenceofHEC(Fig.8d),theintensitiesof
CandOsignalsareenhanced.ThisenhancementinCandO sig-nalsisduetothecarbonandoxygenatomsoftheadsorbedHEC Also,thesamespectrashowthattheironpeaksobservedinthe presenceofinhibitorareconsiderablysuppressedrelativetothose observedinblanksolution(Fig.8b),andthissuppressionofthe ironpeaks,occursbecauseoftheoverlyinginhibitorfilm(Amara, Braisaz,Villemin,&Moreau,2008)
3.5 Molecularstructureandinhibitionmechanism TheoptimizedgeometryofHECmoleculeisshowninFig.9a TheadsorptionofHEConthesteelsurfacein3.5%NaClsolution
Trang 63.0x10 -3 3.1x10 -3 3.2x10 -3 3.3x10 -3 3.4x10 -3
0.0
0.3
0.6
0.9
1.2
1.5
I corr
1/T, K
(a)
-2.6 -2.4 -2.2 -2.0 -1.8 -1.6 -1.4 -1.2
-2 , K
1/T, K
maybeachievedbytheinteractionbetweentheunshared
elec-tronpairsinoxygenwithd-orbitalsofironatoms.Theelectron
configurationof iron was[Ar] 4s23d6, it is clear that, 3dorbit
was not fully filled with electron This unfilled orbital of iron
couldbondwiththehighestoccupiedmolecularorbital(HOMO)
ofHECwhilethefilled4sorbitalcouldinteractwiththelowest
unoccupiedmolecularorbital(LUMO)of theinhibitor(Li,Zhao,
Liang,&Hou,2005).Theelectronicorbitaldensity distributions
ofHOMOandLUMOforHECmoleculeareexpressedinFig.9b–c
ItcanbeobservedthatcycleAfor theHOMO(seeFig.9b),has larger electronic density and was more feasible to bind with 3dorbitalof Fe;while fortheLUMO(see Fig.9c), cycleB, and
C had larger orbitaldensity and could takepriorityof interac-tionwith4sorbitalof iron.Fromthegeometryoptimizationof HEC,itcanshowthattheoxygenatomsof inhibitorhave Mul-likenatomicchargeswithhighernegativeelectrondensities.This suggested that the oxygenatoms donatethe unshared pair of electronstothevacantd-orbitalsofiron(Bereket,Gretir,&Yurt,
◦
Trang 7Fig 9. Optimization geometry of HEC; (a), the molecule orbital of HEC that corresponds to bonding with iron atoms: (b) HOMO orbital density; (c) LUMO orbital density.
2001;Mulliken, 1955).Sothat, theactivesites (oxygenatoms)
facilitatedtheadsorptionofinhibitormoleculeonthesurfaceof
metal
4 Conclusion
Thecorrosioninhibitionof1018c-steelin3.5%NaClsolutionby
hydroxyethylcellulose(HEC)asaneco-friendlyinhibitorhasbeen
studiedusingelectrochemicaltechniques,SEMandEDXanalysis
Theprincipleconclusionsare:
• Resultsobtainedfrompotentiodynamicpolarization indicated
thattheHECismixed-typeinhibitor
• Resultsobtainedfromallelectrochemicaltechniquesareingood
agreement
• AdsorptionofHEConthesteelsurfaceisspontaneousandobeys
theLangmuir’sisotherm
• Corrosioninhibitiondecreaseswhenthetemperatureincreases
• SEMandEDXanalysisofthesteelsurfaceshowedthatafilmof
inhibitorisformedonthesteelsurface.Thisfilminhibitedmetal
dissolutionin3.5%NaClsolution
• DMol3quantumchemicalcalculationswereperformedtosupport
theadsorptionmechanismwiththestructureofHECmolecule
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