Electrochimica Acta 54 (2009) 21712179

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Electrochimica Acta

journa l homepage: www.e lsev ier .com

Effects ibprocess

R. Fuchs-Faculty of Chem loveni

a r t i c l

Article history:Received 21 JuReceived in reAccepted 10 OAvailable onlin

Keywords:Corrosion inhiMixturesCationic surfacZwitterionic suFloryHugginsSulphuric acid

cs rege/Palosionted usthe sue in agestm thsingle sho

1. Introduction

Surfactadomains, frthe part ofdrastically mtant for induindustries, dishing, as asubject of th

It is welseverity cansivemedia sthis goal. Seadsorbed othe surfacewords, theing the surfspecies to thThe organizface may beof a surfactato be respo

Fax: +386E-mail add

In order to be effective, the inhibitor molecule must displace waterfrom the metal surface, interact with anodic or cathodic reaction

0013-4686/$ doi:10.1016/j.ents are compounds that can be found in a multitude ofom industrial settings to research laboratories and areour daily lives. Due to their unique structure they canodify the interfacial properties. This effect is impor-

strial processes such asotation, the cosmetic and foodrugsdelivery, emulsication, chemicalmechanical pol-

lso for corrosion inhibition. The latter topic is also theis paper.

l known that corrosion never stops but its scope andbe lessened. The addition of surfactants into aggres-

uchas acid solutions is oneof themethods for achievingveral studies suggested that most organic inhibitors aren the metals surface, displacing water molecules fromand forming a compact lm as a barrier [1,2]. In otheradsorbed corrosion inhibitor may be sterically block-ace, thereby, either restricting the access of corrosione surface or transferring the corrosion product from it.ation and packing of the inhibitormolecules on the sur-important, as well as the coverage fraction. The abilitynt molecule to adsorb on the metal surface was found

nsible for the corrosion inhibition of the metal surface.

2 2527 774.ress: fuchs@uni-mb.si.

sites to retard oxidation and reduction corrosion reaction, and pre-vent the transport of water and other corrosion-active species tothe surface. Several studies have been presented regarding the cor-rosion of various types of steel and their inhibition by differenttypes of organic inhibitors in acid solution [39]. Both ionic andnon-ionic surfactants have been reported to inhibit the corrosionof metals such as copper, aluminium, and mild-steel [1014].

If a single surfactant molecule possesses both anionic andcationic functional groups, it is called amphoteric or zwitterionic.In most cases it is the pH that determines, which group dominates,thus favouring one ionisation or another. This can be anionic atalkaline pH and cationic at acid pH values, with an amphotericbehaviour at intermediate pH values [15,16]. Mixtures of surfac-tants have found many applications in technology. These mixturesoften show synergistic effects, which are evidence of non-idealbehaviour and are the reason for their extensive use in industry. Anobjective of the present work is to study the applicability of non-ionic surfactant mixtures and the zwitterionic type of surfactants,as corrosion inhibitors for stainless steel (SS), type X4Cr13 in aque-ous solutions of 2mol L1 H2SO4 (mol L1 =M). In the case of thenon-ionic surfactantmixture,we used the ethoxylated octyl phenylalcohol (under the tradenameTRITON-X series), knownas TRITON-X-405 with the chemical structure C8H17C6H4(OCH2CH2)40OHwith the addition of 1mM of KBr. Part of the present study isactually an extension of our previous work [17], in which we inves-

see front matter 2008 Elsevier Ltd. All rights reserved.lectacta.2008.10.014of surfactants and their mixtures on inhof ferritic stainless steel

Godec

istry and Chemical Engineering, University of Maribor, Smetanova 17, 2000 Maribor, S

e i n f o

ly 2008vised form 10 October 2008ctober 2008e 18 October 2008

bitor

tantrfactantisotherm

a b s t r a c t

The corrosion inhibition characteristi(Myristyltrimethylammonium bromid405 mixed with 1mM of KBr, as corrsolutions of 2M H2SO4 were investigaisation data showed that mixtures ofadsorbing on the stainless steel surfactensiometric results of this study sugonic/cationic surfactant mixtures. Fromixtures decreased with respect to awas stronger. The mixtures studied herX4Cr13 in 2M H2SO4 solution./ locate /e lec tac ta

ition of the corrosion

a

arding mixtures of cationic/zwitterionic types of surfactantmitylsulfo-betaineas), and non-ionic surfactant TRITON-X-inhibitors for stainless steel (SS) (type X4Cr13) in aqueousing potentiodynamic polarisation measurements. The polar-rfactants used in this study acted as mixed-type inhibitors,greement with the FloryHuggins adsorption isotherm. Thethe existence of a second state of aggregation for zwitteri-ese values of the free energy of adsorption, which in bothe surfactant, we concluded that the adsorption in mixtureswed good inhibition properties for ferritic stainless steel type

2008 Elsevier Ltd. All rights reserved.

2172 R. Fuchs-Godec / Electrochimica Acta 54 (2009) 21712179

tigated the inhibition abilities of two non-ionic surfactants fromthe TRITON-X series, namely TRITON-X-405 and TRITON-X-100.Conclusions obtained from these electrochemical measurements[17] indicatinhibitor mOne reasonthe numberbetween 9 athe inhibitiably morepresentingics of the aon the self-we studiedsulfonateZWITTER C1as the ionicdimethylpachosen sinctem. They rof the solutused class osofteners, h

2. Experim

2.1. Materia

The zwithe cationicstudy wereThe non-iowas a Flukaout purica

All the sMillipore Suwithin the rand in mixtrange being

Table 1The composition of ferritic stainless steel type X4Cr13 in wt%.

tterioher

.01d MT

ricallss sten in

rface

surfmy-pC. Th

watlutionn of kthe

ectro

trocal t

red a

r electrode was made from Pt. In all experiments, elec-mical polarisation was started 30min after the workingde was immersed in solution, to allow the stabilization oftionary potential. Before eachmeasurement, the samplewasically polarized at 1.0V (SCE) for 10min (electrochemical-ed the difculties in organization, and the packing ofolecules of type TRITON-X-405 on the metal surface.for these difculties is probably the surfactant size,of polar ethylene oxide groups of TRITON-X-100 beingnd 10, and for TRITON-X-405 around 40. Consequently,ng lm formed during cathodic polarisation was prob-porous and of lower grade, as was in the case whenTRITON-X-100 in the solution. Therefore the dynam-nodic process could have a more destructive effectassembling layer. For zwitterionic surfactant mixtures,

the system 3-N-dimethylpalmitylammoniopropaneor palmitylsulfo-betaineas (zwitterionic surfactant,6), and Myristyltrimethylammonium bromide (MTABr)component in solutions of sulphuric acid. The (3-N-

lmitylammoniopropane sulfonate) sulfobetaines weree these surfactants are insensitive to the pH of the sys-emain as real zwitterionic surfactant for all pH valuesion. This is the reason why they are the most commonlyf amphoteric surfactants; they can be found in textileair rinse formulas and as corrosion inhibition additives.

ental

ls

tterionic (SigmaAldrich, CAS Number 2281-11-0) andsurfactant (Fluka, CAS Number 1119-97-7) used in thisof pure quality (>97%) and used without purication.

nic surfactant TRITON-X-405 (with activity of 70wt%)product (CAS Number 9002-93-2) and also used with-tion. The surfactants had the following structures:

olutions were prepared using water obtained from aper-Q system. The experimental concentrations wereange 7.0107 to 3.5104 mol L1 for TRITON-X-405,ures where 1mM of KBr was added, the concentrationbetween 7.0107 and 7.0104 mol L1. In the case

CSiSCrNiCu

of zwitems, wat c=1of addeCylindstainleis show

2.2. Su

TheWilhelat 25

ing theThe sosolutiotion iname.

2.3. El

Elecventionmeasu

countetrocheelectrothe stacathodwt%

0.040.4710.02

13.200.3070.213

nic/cationic surfactant mixtures we studied two sys-e the concentration of zwitterionic surfactant was xed05 and at 1.0104 mol L1, while the concentrationABr was changing from 1.0105 to 1.0103 mol L1y shaped specimens were made from a rod of ferriticel of type X4Cr13. The composition of used steel in wt%Table 1

tension measurements

ace tension () in 2mol L1 H2SO4 was measured by thelate method, using a Krss-K12 processor tensiometere temperature was kept constant (0.1 C) by circulat-er through a jacketed vessel containing the solution.s concentration was varied by adding aliquots of stocknown concentration, to the known volume of the solu-vessel. The plate was cleaned over a methanbutan

chemical measurements

hemical experiments were performed with a con-hree-electrode conguration. All the potentials weregainst a saturated calomel electrode (SCE) and the

R. Fuchs-Godec / Electrochimica Acta 54 (2009) 21712179 2173

Fig. 1. Variatio TRITOH2SO4 at 25 C

cathodic clemechanicalment) andwhich wasrent potentelectrode pof 2mVs1

SOLATRONcontrol theinterpretedoped by Scrstainless stePTFE holdeelectrolytesuccessively1200. Next,to obtain aing electroddistilled wa

3. Results

3.1. Determsurfactants

The resuthe surfactaconcentratiresulting cudecade logaFig. 1ac forof KBr. Fig. 2

catioect, tns in surface tension regarding concentrations for (a) TRITON-X-405 in water, (b).

aningbyH2 evolution. In thisway thehydrogenbubblesly remove the remainders of the hand polishing treat-

rionic/the effthen allowed to reach a stable open-circuit potential,attained after about 30min. The potentiodynamic cur-ial curves were recorded by automatically changing theotential from 0.7V to 0.9V (SCE) at a scanning rate. All the experiments were performed at 25 C1 C. A1287 Electrochemical Interface was used to apply andpotential. The data were collected using CorrWare andusing the CorrView software. This software was devel-ibner Associates, Inc. Theworking electrodewas ferriticel of type X4Cr13. The test specimens were xed in a

r, and the geometric area of the electrode exposed towas 0.785 cm2. The metal surface was hand polishedwith emery papers of grades 400, 600, 800, 1000 andthe specimen was ne polished with diamond pastemirror-like shined surface. After polishing, the work-e was washed with ethanol, rinsed several times withter, and nally dried using hot air.

and discussions

ination of the critical micelle concentration ofand mixtures in 2M H2SO4

lts for surface tension were plotted as a function ofnt concentrations logarithm and the critical micelleon (cmc) was estimated from the break-point in therve. Representative plots of surface tension vs. therithm of surfactant concentration log10 C are shown inTRITON-X-405 with and without the addition of 1mMad represents the same relationship valid for zwitte-

shown. At leach systemcurves.

The addtypes of surtants aqueoaggregationeffect on adtives, the inimprovedoHofmeisterdegree. Thepotency fro

SO42, HPSCN, ClO4

Ions on tare called saThe opposiare knownions. This eamphiphilesalt, compeamount oftion. Thus, mconcentratibecause thelar interactihydration oN-X-405 in 2.0M H2SO4 and (c) TRITON-X-405+1mM KBr in 2.0M

nic surfactant mixtures and, for a better illustration ofhe corresponding plots for single surfactants are also

east three independent measurements were done for, to check for the reproducibility of the surface tension

ition of electrolytes, organic compounds or differentfactants, is known to modify the properties of surfac-us solutions; this includes their solubility, the cmc andnumbers. Therefore the additives may equally have ansorption at the solid/liquid interface. Using the addi-hibition properties of non-ionic surfactants could be

rworsened. These phenomena are related to the famousseries, which is an empirical measure of ions hydrationHofmeister series orders ionswith increased salting-in

m left to right, and is as follows:

O42, OH, F, HCOO, CH3COO, Cl, Br, NO3, I,

he left of Cl represent in some way a borderline. Theylting-out ions (structure-makers) or cosmotropic ions.

te holds true for the ions on the right of Cl, whichas salting-in ions (structure-breakers) or chaotropicffect usually leads to an increase in the solubility ofs [1823]. The salting-out effect is produced when thetingwith the surfactant for hydrationwater, reduces thewater available in the micelles for polar chain hydra-icelle formation will be produced at lower surfactant

on. The salting-in effect (micelle hydration) is producedsalt ions break the water structure (intermolecu-

ons), making the water molecules more accessible forf the surfactant molecules [24].

2174 R. Fuchs-Godec / Electrochimica Acta 54 (2009) 21712179

Fig. 2. Variati WITTEZWITTER C16 c

Since thsurfactantsof non-ioniof inorganicinuence oadded in hpoints andsalting-out

In the cinduced bysalt-induceunits hydrmedia. NotTRITON-X-4tric elds aandcompetphenomenohydrophilicthe non-ionmicelles.

The opp(TRITON-X-icebergs oconcentratihydrogen bfactant. Thuthe hydrophone of the cthe additionmentionedons in surface tension regarding concentrations for (a) palmitylsulfo-betaineas (Z

=1.0104 M+MTABr all in 2.0M H2SO4 at 25 C.

e interaction between the ionic species and non-ionicis weak, the effect of inorganic salts on the propertiesc surfactants is usually small. However, a large amountsaltwouldaffect the solutions properties through theirn the water properties. It is well known that the salts,igh concentration, either depress or elevate the cloudcmcs of the non-ionic surfactants, depending on theor salting-in nature of the salt species [20].ase of TRITON-X-405 in 2M H2SO4, the salt effectan addition of KBr has been interpreted in terms of

d reduction or the enhancement of the ethylene oxideation regarding the surfactant molecules in aqueousice that the number of these units is around 40 for05. Cosmotropic anions as SO42, producing high elec-t short distances, bind their water molecules stronglyeefciently forwaterwith theethyleneoxideunits. Thisn leads to the dehydration of the surfactant moleculespart, an effect which depresses the cmc value ofic and increases attractive interactions between these

osite effect can be achieved with chaotropic ions Br

405+1mM KBr in 2.0M H2SO4), which disrupt thef water molecules in bulk solution and increase the

on of free water molecules, which in turn may formonds with the ethylene oxide units of the non-ionic sur-s, the chaotropic ions act to promote the hydration ofilic part of the TRITON-X-405, which possibly becomesontributions to the elevation of cmc value, caused byof the 1mM KBr. Fig. 1 clearly shows the phenomenon

above. For TRITON-X-405 in 2M H2SO4 mixtures, up to

one order owith respec

The nexing zwitterithe zwitterconcentratithe cmc ofone order omixture. Onin additionthe curve. Tbefore [25

Velazquof the catioand that anyzwitterionition [28] thinteractionsbetween antants can be[31]. In zwitmicelle corthe negativtive chargeof oppositeof the catiomaking this

The tensgest the exsurfactant sRC16), (b) MTABr, (c) ZWITTER C16 c=1.0105 M+MTABr and (d)f magnitude higher values for the cmc were observed,t to the KBr salt free solution (Fig. 1b and c).t subject of our investigation was the system contain-onic/cationic surfactant mixture. The concentration ofionic surfactant was kept constant while we varied theon of cationic surfactant. It can be noticed in Fig. 2, thata surfactant when alone is signicantly lower (at leastf magnitude) compared to the situation when it is in athe other hand, it is evident from Fig. 2c and d that,

to a normal break-point, another break appeared inwo different stages of aggregation have been observed29].ez and co-workers [30] reported that aqueous solutionsnic DTAB and the zwitterionic surfactants, mix ideallyinteraction is reduced as the hydrocarbon length of the

c surfactant increases. They emphasized their observa-at, in addition to electrostatic attraction, ion-speciccan also be important. The differences in interaction

ionic surfactants with zwitterionic and cationic surfac-interpreted on the basis location of the charged groupsterionic sulfobetaines, the positive charge is close to thee, therefore, in an anionic/zwitterionic mixed micelle,e charge of the anionic surfactant is close to the posi-of the dipole. In orders to achieve the closest proximitycharges in the cationic/zwitterionic micelles, the tailsnic surfactants would have to protrude from the core,way the micellization process less favourable.iometric results discussed in this study seem to sug-istence of a second aggregation state in the mixedystems. The cmcs of mixtures composed from zwit-

R. Fuchs-Godec / Electrochimica Acta 54 (2009) 21712179 2175

Fig. 3. ut the

terionic suM+MTABradded MTcmc2 =4.6where theorder of mof the micmc2 =1.6

An interlows. In bonitrogen atothe driving-mixtures ispart and than attractivmixed mice

When tmixed micetion predomformed. Thboth cases,centrationssolution (i.eobserved atants was awhere thec=1.010higher concto overcomduring the atures of thadsorptionco-adsorptithe formerl

A studypublishedpolyelectroand coworfound withand free owhen apprI might lomixture wic=1.010composedtherefore, tin [32]. Atmide count

itterarrano-adtothi

s soase,10

imatemenstatiwerant bFor

idera1.6ionicionicr aggthanzwittre, waterionic

ectro

effe) onation2SO4ant dtly, tPotentiodynamic polarisation curves (2mVs1) for TRITON-X-405 with and witho

rfactant C16 of xed concentration; c=1.0105were determined to be at a concentration of

ABr equal to: cmc1 =2.00.2104 mol L1 and0.2104 mol L1 of added MTABr. In the case

concentration of zwitterionic surfactant C16 was oneagnitude higher c=1.0104 M+MTABr, the cmcs

xture were be cmc1 =1.20.02104 mol L1 and0.02104 mol L1 of added MTABr.

pretation of the micellization process is possible as fol-th surfactants the hydrophilic head is a quaternizedmhaving, a positive charge.We assume, therefore, thatforce for the micellization in the zwitterionic/cationiccompetition between the repulsion of the hydrophilice hydrophobic (via water) interaction of alkyl chains ase interaction between the constituent surfactants in thelle.he concentration of alkyl chains located inside thelle is sufciently high, attractive hydrophobic interac-inated and normal spherical mixed micelles were

is was conrmed by the fact that cmc1 had, inapproximately the same values for the total con-of both surfactants (zwitterionic + cationic) in the. 2.12.2104 mol L1). A noticeable difference wast cmc2, where the total concentration of surfac-pproximately twice as high, in contrast to the casexed concentration of zwitterionic surfactant was at4 mol L1. This phenomenon could be interpreted asentrations for ionic surfactants being needed, in ordere electrostatic repulsion between ionic head groupsggregation process. Further,more highly ordered struc-e adsorbed aggregates could be achieved by furtherfrom the solution (the step from cmc1 to cmc2), as areon structural transformations, or rearrangement, inside

the zwThis retion (cleadingformedperhapother cc=1.0approxarrangElectrowas losurfactaction.a cons(cmc2 =zwitterthe catmicellahigherin thetherefomore wzwitter

3.2. El

Theof KBrpolaris2M Hsignicsequeny existing micelles.of some relevance for our work has recently been

[32]. In their molecular dynamics study of a shortlyte with quaternized ammonium ion (ionene) Vlachykers [32], divided the counter ions to adsorbed ifin certain arbitrary distance from the nitrogen atom,therwise. The results of this analysis indicated that,oaching an ionene counterions such as Cl, Br andose one or two water molecules. In our case, when ath a xed concentration of zwitterionic surfactant of5 mol L1 was used, the micelles at cmc1 were mostlyof the cationic surfactant MTABr. We can speculate,hat something similar can happen, as documenteda sufciently high concentration of MTABr, the bro-erion can approach the quaternized nitrogen atom of

reduced, evphenomenosubstantialat this lowmention thtwo orderseffect on inwas observe

It is nectant, the prThe at porregard to thabsence ofciency is exat minimumaddition of 1mM of KBr on SS type X4Cr13 in 2.0M H2SO4.

ionic surfactant close enough to release some water.gement may yield further adsorption from the solu-sorption), which is eventually concluded at cmc2,more-ordered structures. The shapes of the micelless way cannot be completely spherical anymore; butmewhere between spherical and cylindrical. In thewhen the concentration of zwitterionic surfactant was4 mol L1, the amount for both surfactants at cmc1 wasely 1:1. In the micelle core, therefore, an alternativet of surfactants A and B is expected (pattern ABAB. . .).c repulsion between the ionic head groups of MTABrbecause of a higher concentration of the zwitterioniceing present, which thus reduced ionic charge inter-this reason, the cmc2 of such a mixture is attained atbly lower concentration of added cationic surfactant104 mol L1 of added MTABr). The alky chain of thesurfactant was slightly longer than the alky chain ofsurfactant. Thus, it could be suggested that the mixedregates formed in this system,havehydrodynamic radiithose formed in the rst mixture. The SO3H group

erionic surfactant is believed to be strongly hydrated,e assumed that the bromide counter-ion would loosethan in the rst case, when the xed concentration ofsurfactant was equal to c=1.0105 mol L1.

chemical results

ct of TRITON-X-405 (in presence and absence of 1mMthe currentpotential characteristics displayed by thecurves of the ferritic stainless steel type X4Cr13 in

, is presented in Fig. 3. Voltammogram exhibited aecrease in anodic current peaks in 2.0M H2SO4. Con-

he charge under the oxidation curves was progressively

en at very low concentrations of added surfactant. Thisn was observed at c=3.5106 mol L1. Moreover, adecrease in the cathodic current density was observedconcentration of added surfactant. It is necessary toat further increase in surfactant concentrations (up toof magnitude higher than the initial value) had littlehibition. Further, decreasing of anodic current peaksd with the addition of KBr in a concentration of 1mM.essary to mention that with addition of the surfac-oles on voltammogram (Fig. 3) obtain at proles.tion extends to about 100mV in both directions, withe corrosion potential of the 2M H2SO4 solution in theinhibitors (0.461V vs. SCE). The best inhibition ef-pected within the potential region where the current is. The at portion was additionally extended by about

2176 R. Fuchs-Godec / Electrochimica Acta 54 (2009) 21712179

50mV, but only in regard to the anodic direction, with the addi-tion of bromide ions (KBr) to TRITON-X-405 in 2M H2SO4 solution.As mentioned previously, the TRITON-X-405 has difculty whenorganizingprobably). Iof the protstarted soospecies, whor micelles,corrosion player forme

Thereforachieved, wsolution. Wthe corrosiocharged sureffect betwwater moleTRITON-X-4

An increcomposed oH2SO4 soluterionic surillustrates tat various ceffect occurextension oonly the zwThis phenomof added bIt could bepositive synThe electroccorrosion ppolarisationin Table 2. Tisation withExtrapolatiorosion currsimultaneo

It is cleashifted towing the anoblank curvetype inhibitnoble valuecurrent denof magnituinhibitor-fr

3.3. Adsorp

The surfRp, and thethe kineticthe followin

= 1 icoricor

IE (%) =[1

= 1 RpRp

otentiodynamic polarisation curves (2mVs1) for palmitylsulfo-betaineasRC16) with and without the addition of x M MTABr on SS type X4Cr13 inSO4.

uence of added TRITON-X-405 with and without the addition of 1mM ofhe cathodic and anodic behaviour of stainless steel type X4Cr13 in 2.0Mand packing on the metal surface (because of its size,n our previous study it was conrmed, that desorptionective layer formed in the presence of TRITON-X-405ner, as in the case of TRITON-X-100 [17]. The freeich appeared on the metal surface between monomersalso, represent those active points which initialised therocess with a destructive effect on the self-assemblingd during cathodic polarisation.e the improvement in inhibition efciency (IE) wasith the addition of bromide ions (KBr) in the chosene can assume that the bromide ions additionally inhibitn by getting adsorbed electrostatically on the positivelyface in the anodic region, or with the help of synergisticeen KBr and TRITON-X-405 (with displacement of morecules from the metal surface than in the case, when05 was individually presented in the solution).ase in IE was also obtained in the cases of mixturesf zwitterionic surfactant and cationic surfactant in 2Mtions in comparison with the example where zwit-factants was alone in sulphuric acid solutions. Fig. 4hose of inhibitions properties on corrosion parametersoncentrations of both surfactants inmixtures. The samered in the case of TRITON-X-405+1mMKBrmixture i.e.f the at portion in the anodic direction but only, whenitterionic surfactant was present in the acid solution.enon was observed at exactly the same concentration

romide ions (cMTABr = 1.0103 M, cKBr = 1.0103 M).speculated that bromide ions are responsible for theergism and for improvement of inhibition efciency.hemical parameters obtained frompolarisation curves,otential (Ecorr), corrosion current density (icorr), theresistance (Rp) and the inhibition efciency, are shown

he polarisation resistance was obtained by linear polar-in the potential range of 10mV with respect to Ecorr.n of the Tafel line allowed for calculation of the cor-

ent density (icorr). These parameters were determinedusly (CorrView software).r, from the obtained corrosion data, that Tafel linesards more negative and more positive potentials dur-dic and cathodic processes, respectively, relative to the. Thismeans that the selected compound acts asmixed-or. Next, a shift of Ecorr was observed towards a more, and to an order of magnitude for lower corrosionsity icorr was attained. Moreover, to an order and halfde lower icorr for chosen mixtures with respect to theee solution was observed (Figs. 5 and 6).

tion isotherms

ace coverage, , as well as, the polarisation resistancecorrosion current density icorr, were calculated from

parameters measured in corrosion processes by usingg equations:

r

r(1)

icorricorr

] 100 (2)

(3)

Fig. 4. P(ZWITTE2.0M H2

Fig. 5. InKBr on tH2SO4.

R. Fuchs-Godec / Electrochimica Acta 54 (2009) 21712179 2177

Table 2Kinetic parameters for corrosion of stainless steel type X4Cr13 obtained frompotentiodynamic polarisation curves in 2.0M H2SO4 for TRITON-X-405, TRITON-X-405+1mM ofat 25 C.

2.0M H2SO4 +

x M TRITON-X07.01073.51067.01063.51057.0105

x M TRITON-X07.01073.51067.01063.51057.01053.51047.0104

x M ZWITTER01.01063.01061.01052.51055.01051.01045.0104

105 M ZWITT01.01053.01051.01042.01044.51045.01041.0103

104 M ZWITT01.01053.01051.01041.21041.61045.01041.0103

IE (%) =[1

The notatioadded surfawhen the su

The adsoH2SO4 wasthe form:

log

[

cinh

]=

The same btant mixturare for bothmodel, plot(x) and inteused non-ioindicate thaKBr and aroKBr, for palmitylsulfo-betaineas with and without added x M MTABr

icorr (A cm2) Ecorr (V vs. SCE) Rp ( cm2) icorr Rp

-4059.96104 0.461 15.601.55104 0.438 97.10 0.844 0.8391.36104 0.429 115.09 0.863 0.8641.29104 0.430 118.10 0.870 0.8681.10104 0.428 141.32 0.889 0.8901.02104 0.420 143.61 0.897 0.891

-405+103 M KBr9.96104 0.461 15.608.59105 0.429 152.24 0.913 0.8977.81105 0.424 173.77 0.922 0.9107.45105 0.421 183.13 0.925 0.9156.71105 0.416 198.66 0.932 0.9216.34105 0.405 208.02 0.936 0.9255.67105 0.408 233.15 0.943 0.9335.00105 0.405 264.73 0.949 0.941

C169.96104 0.4618.66104 0.459 17.531 0.140 0.110

7.53104 0.457 19.832 0.223 0.2135.11104 0.455 29.800 0.487 0.4773.59104 0.452 39.800 0.630 0.6082.35104 0.445 63.600 0.764 0.7551.41104 0.444 104.860 0.858 0.8518.49105 0.436 175.051 0.915 0.911

ER C16 + x M MTABr9.96104 0.4615.33104 0.451 31.99 0.464 0.5123.70104 0.450 39.80 0.628 0.6082.15104 0.443 83.35 0.784 0.8121.48104 0.440 103.31 0.852 0.8499.28105 0.433 184.05 0.907 0.9158.75105 0.431 219.25 0.912 0.9285.83105 0.419 253.93 0.941 0.938

ER C16 + x M MTABr9.961042.12104 0.447 77.74 0.786 0.7991.65104 0.446 113.86 0.834 0.8631.17104 0.440 135.42 0.883 0.8851.06104 0.440 140.54 0.893 0.8909.71105 0.441 155.14 0.902 0.9006.60105 0.427 230.04 0.930 0.9325.15105 0.417 304.23 0.949 0.949

RpRp

] 100 (4)

n icorr, and Rp was used for measurements withoutctant, while the primed quantities icorr and Rp appliedrfactant was added to the solution of 2.0M H2SO4.rption of TRITON-X-405 mixed with 1mM KBr in 2Min good agreement with the FloryHuggins isotherm in

log(xK) + x log[1 ] (5)

ehaviour was shown for cationiczwitterionic surfac-e. The adsorption isotherms plotted in Figs. 7 and 8,investigated systems. According to the FloryHuggins

s of log[/C] vs. log[1 ] produce straight lines of slopercept log (xK), as shown in Fig. 7, which is valid for thenic surfactant mixture (TRITON-X-405, KBr). The datat the values of x were approximately 10 without addedund 13 when KBr was in the mixture. This suggests

Fig. 6. Inuenthe addition otype X4Cr13 in

that one moreplaces 10synergistic

At a lowthe additionreplaced wawas approxpresent in torder ofmamolecules i

The samated from tequilibriumadsorption

K = 1csolventce of added palmitylsulfo-betaineas (ZWITTER C16) with and withoutf x M MTABr on the cathodic and anodic behaviour of stainless steel2.0M H2SO4.

lecule of TRITON-X-405 adsorbed on the metal surfacewater molecules, and increases to 13 with the help of aeffect between KBr and TRITON-X-405.concentration of Palmityl sulfobetaine, c=1.0105 M,of MTABr had no noticeable effect on the number of

ter molecules by one mole of Palmityl sulfobetaine. Itimately the same as in the case where MTABr was nothe mixture. When the concentration increased by angnitude (c=1.0104 M), thenumber of replacedwaterncreased from 1.6 to around 3.0.e behaviourwasobtained in the casewhere wasevalu-he polarisation resistance. K is the modied adsorptionconstant, which can be related to the free energy of

Gads given by Eq. (6):

exp(Gads

RT

)(6)

2178 R. Fuchs-Godec / Electrochimica Acta 54 (2009) 21712179

Fig. 7. FloryHuggins adsorption isotherm for TRITON-X-405 with and without the addition of 1mM of KBr on SS type X4Cr13 in 2.0M H2SO4 obtained from the corrosioncurrent densit

Fig. 8. FloryH ithouthe corrosion

Here csolventhe case ofFigs. 7 andthe spontan

Values20kJmolstatic intera(physical adinvolve chato themetation). The cdecreased w87.5 kJmocase when 1so chemisowith unpairable to adsoon O atomsture (MTABaddition of

Table 3Calculated vawhere waspalmitylsulfo-1.0104 M Z

Surfactant

TRITON-X-405TRITON-X-405palmitylsulfo-1.0105 M Z1.0104 M Z

taineded ty (icorr).

uggins adsorption isotherm for palmitylsulfo-betaineas (ZWITTERC16) with and wcurrent density (icorr).

t is the molar concentration of the solvent, which, inwater, is 55.5mol L1. G values calculated from

the obconcluads

8 are negative in accordance with Eq. (6), suggestingeity of the adsorption process (Table 3).for the free energy of adsorption Gads, up to1 are generally consistent with the strength of electro-ction between charged molecules and charged metalsorption),while thosemorenegative than40kJmol1rge sharing or its transfer from the inhibitor moleculesl surface to form a co-ordinate type of bond (chemisorp-alculated values of Gads for all investigated mixturesith respect to a single surfactant. It was reduced from

l1 to around 115.66kJmol1 for TRITON-X-405, inmM of KBr was added in to the solution of 2M H2SO4,

rption is assumed. Triton has a large number of oxygened electrons. It is for this reason that TRITON-X-100 isrb on the metal surface through lone pairs of electrons. In the instance of cationic/zwitterionic surfactant mix-r/Palmityl sulfobetaine) thesevaluesdecreasedwith theMTABr from38.15 to 46.77kJmol1. On the basis of

lues of Gads (from the FloryHuggins adsorption isotherm,obtained from icorr) for TRITON-X-405, TRITON-X-405+1mM KBr,betaineas (ZWITTERC16), 1.0105 M ZWITTER C16 +xM MTABr andWITTER C16 + x M MTABr all in 2.0M H2SO4 at 25 C.

Gads/kJmol1

87.77+1mM KBr 115.66betaineas (ZWITTER C16) 38.16WITTER C16 + x M MTABr 37.57WITTER C16 + x M MTABr 46.77

bromide iosurfactant Tionic surfacimproved thsion inhibitsolution.

Fig. 9 sonic/cation(the concen

Fig. 9. The in1.0105 M Zall in 2.0MH2SC16).t added x M MTABr on SS type X4Cr13 in 2.0M H2SO4 obtained from

d values for the free energy of adsorption, it could behat adsorption increased. It can be speculated that the

n, (which is added as KBr and mixed with non-ionicRITON-X-405 or it is presented as counterion in thetant MTABr and mixed with zwitterionic surfactant),e inhibition properties of the used mixtures, as corro-

ors, for ferritic stainless steel type X4Cr13 in 2M H2SO4

hows the inhibitors efciency for both zwitteri-ic surfactantmixtures as a function of the concentrationtration of the zwitterionic surfactant was at a xed

hibition efciency as a function of concentration regarding addedWITTER C16 +xM MTABr and 1.0104 M ZWITTER C16 +xM MTABrO4 at 25 C ( obtained from icorr)(palmitylsulfo-betaineasZWITTER

R. Fuchs-Godec / Electrochimica Acta 54 (2009) 21712179 2179

value,while the concentration of the cationic surfactantMTABr var-ied. A curve with three slopes, was found in both cases. The slopechanges at a certain concentration of added cationic surfactant,namely at the same values obtained regarding the surface tensionmeasurements.

The rst slope was below the rst cmc (cmc1); another trendwith somethe rst ancmc2, i.e. cfor the mixFor the miM MTABrcmc2 =1.6of good agrchemical mthe existentural changanother geo

Furthercationic anaggregatesformed byforming (camide forms(zwitterionfonate, a heranging fromobvious chamole fractiotify becauseof the surfaobtain the cthose forcesmetal surfagroups andbonds (or laMore experabout the aOn the basirosion procsame amou(i.e. 2.1 to 2value for th(IE =85, 90%results, it cthe solutiontant, are pro(due to theons), and dumore strongGads value

4. Conclus

From theshifted tothe anodiblank curtures acts

The tensioof a seconfactant m

Adsorption of the used surfactants and theirs mixtures agreedwith FloryHuggins adsorption isotherm.

In the case of TRITON-X-405, about 10 to 11 molecules of waterseem to be replaced by one molecule of surfactant. By adding the1mM of KBr, the value of replaced molecules of water increasedto 13.

e casplaceentrar thaGad

el, s5 an5+1eencatiorostalles)polarsione loitor-indtype

nces

hang,tkin,.. Migaentissagren

(2001)Popov3.Hosseuemin.entissuchsuchsranzoKeeraEvan

k, 199Tadro5.aria, Kuchs-iyagi

. Sharmeontidchot,u, P.Aribar,. Nev(1998. Mu,opez-06) 85Gonz01) 12. SharmF. Tay

opez.hiloacDruch.. Duclinearity and a reduced slope was found betweend the second cmc (cmc2); and the third above themc1 =2.0104 mol L1 and cmc2 =4.6104 mol L1ture of the 1.0105 M ZWITTER C16 + x M MTABr.xture composed from 1.0104 M ZWITTER C16 + xthe cmcs values were cmc1 =1.2104 mol L1 and104 mol L1 all in 2.0M H2SO4 at 25 C. On the basiseement between the surface tension and the electro-easurements, it can be assumed, that either (i) then isce of a second aggregation state, and/or (ii) the struc-es of the original micelles, that is transformation intometry.to this point, Ducker et al. [33] showed thatd zwitterionic surfactant mixtures form surface-with a structure intermediate between the structureseach of the pure surfactants. A mixture of cylinder-tionic surfactanttetradecyltrimethylammonium bro-cylinders on mica) and sphere-forming surfactants

ic surfactantdodecyldimethylammoniopropane sul-misphere-forming surfactant onmica) produces shapes

cylinders to truncated cylinders or spheres. The mostnge is the length of the aggregates, depending on then of the two surfactants. This one is difcult to quan-it is non-linear with the mole fraction. Only about 20%ctant molecules in bulk need be cylinder-forming toylindrical aggregates Finally, it is important to includewhich concentrate one surfactant over another at the

ce (electrostatic interactions between surfactant head-the charges at the solid substrate, and the hydrogenck of) between the solvent and the solid substrate) [33].imental data are needed to obtain fuller informationccurate sizes and shapes of the formed mixed micelles.s of those kinetic parameters measured during the cor-esses, it was found that both chosen mixtures had thents of surfactants total concentrations in the solution.2104 mol L1) at the cmc1, but a slightly differente achieved inhibition efciency at that concentration). In regard to this, and from the adsorption isotherm

ould be speculated that the mixed micelles formed inwith a higher concentration of the zwitterionic surfac-bably larger (due to longer alky chain), highly chargedloss of more water molecules of the bromide counteri-e to the stronger electrostatic attraction, they are alsoly adsorbedon themetal surface: notice that calculateds decrease from 37.57to 46.77kJmol1.

ion

obtained corrosion data, it is clear that the Tafel lineswards more negative and more positive potentials forc and cathodic processes, respectively relative to theve. This means that the selected compound in the mix-as a mixed-type inhibitor.metric results in this study could suggest the existenced state of aggregation for the zwitterionic/cationic sur-ixtures.

In thof reconclowe

ThemodX-40X-40betwonic/electmice

Thecorronitudinhibturessteel

Refere

[1] R. Z[2] R. A

236[3] M.A[4] F. B[5] M. L

43[6] A.

133[7] M.[8] L. X

308[9] F. B

[10] R. F[11] R. F[12] V. B[13] S.T.[14] D.F.

Yor[15] T.F.

200[16] S. P[17] R. F[18] S. M[19] K.S[20] E. L[21] H. S[22] T. G[23] B. H[24] D.M

205[25] J.-H[26] D. L

(20[27] P.A.

(20[28] K.S[29] D.J.

69.[30] D. L

153[31] A. S[32] M.

281[33] W.Ae of ZWITTER C16 palmitylsulfo-betaineas, the numberd water molecules increased from 1.6 to 3, when thetion of the ZWITTER C16 in the chosen mixture was notn 1.0104 M.svalues, calculatedusing the FloryHuggins adsorptionuggest the chemisorption mechanism for TRITON-d also the same for the mixture of the TRITON-mM of KBr. The calculated values of Gads were37.57kJmol1 and 46.77kJmol1, for the zwitteri-nic surfactant mixtures. This indicates a very strongtic attraction between the solvent (monomers orand the solid substrate (metal surface).isation curves show an order of magnitude lower forcurrent density icorr and to an order and a half of mag-wer icorr for the chosen mixtures with respect to thefree solution. From this reason, all of the selected mix-icated good inhibition properties for ferritic stainlessX4Cr13 in 2M H2SO4 solution.

P. Somasundaran, Adv. Colloid Interface Sci. 213 (2006) 123.V.S.J. Craig, E.J. Walness, S. Biggs, J. Colloid Interface Sci. 266 (2003)

hed, Mater. Chem Phys. 93 (2005) 48., M. Traisnel, M. Lagrene, Corros. Sci. 42 (2000) 127.e, B. Mernaru, N. Chaibi, M. Traisnel, H. Vezin, F. Bentiss, Corros. Sci.951.

a, M. Christov, S. Raicheva, E. Sokolova, Corros. Sci. 46 (2004)

ini, F.L. Mertens, M.R. Arshadi, Corros. Sci. 45 (2003) 1473.g, T. Libin, L. Lin, M. Guannan, L. Guangheng, Corros. Sci. 48 (2006)

, M. Lebrini, M. Lagrene, Corros. Sci. 47 (2005 2915).Godec, Colloids Surf. A 280 (2006) 130.Godec, V. Dolecek, Colloids Surf. A 244 (2004) 73.i, F. Golgovici, F. Branzoi, Mater. Chem. Phys. 78 (2002) 122., M.A. Deyab, Colloids Surf. A 266 (2005) 129.s, H. Wennerstrm, The Colloidal Domain, 2nd ed., WileyVCH, New9.s,AppliedSurfactants,WileyVCHVerlag,GmbH&CoKgaA,Winheim,

.C. Khilar, Adv. Colloid Interface Sci. 110 (2004) 75.Godec, Electrochim. Acta 52 (2007) 4974.shi, K. Okada, T. Asakawa, J. Colloid Interface Sci. 238 (2001) 91.a, S.R. Patil, A.K. Rakshit, Colloids Surf. A 219 (2006) 67.is, Curr. Opin. Colloid Interface Sci. 7 (2002) 81.J. Colloid Interface Sci. 189 (1997) 117..G. Gomez, Colloids Surf. A 147 (1999) 365.N.T. Southall, V. Vlachy, K.A. Dill, J. Am. Chem. Soc. 124 (2002) 12302.skaia, A. Guerrero-Ruz, J.D. LpezGonzlez, J. Colloid Interface Sci.) 97.

G.-Z. Li, W.-C. Zhang, Z.-W. Wang, Colloids Surf. A 194 (2001) 1.Diaz, I. Garcia-Mateos, M.M. Velazquez, J. Colloid Interface Sci. 2998.alez, J.L. Czapkiewicz, J.L.D. Castilo, J.R. Rodriguez, Colloids Surf. A 1939.a, S.R. Patil, A.K. Rakshit, et al., J. Phys. Chem. B 108 (2004) 355.

lor, R.K. Thomas, J. Penfold, Adv. Colloid Interface Sci. 132 (2007)

Diaz, I. GarciaMateos, M.M. Velazquez, Colloids Surf. A 270 (2005)

h, D. Blankschtein, Langmuir 13 (1997) 3968.ok, B. Hribar-Lee, H. Krienke, V. Vlachy, Chem. Phys. Lett. 450 (2008)

ker, E.J. Wanless, Langmuir 12 (1996) 5915.

Effects of surfactants and their mixtures on inhibition of the corrosionpenalty -@M process of ferritic stainless steelIntroductionExperimentalMaterialsSurface tension measurementsElectrochemical measurements

Results and discussionsDetermination of the critical micelle concentration of surfactants and mixtures in 2M H2SO4Electrochemical resultsAdsorption isotherms

ConclusionReferences