Effect of Organic Inhibitors on Chloride Corrosion of Steel Rebars in Alkaline Pore Solution

Research ArticleEffect of Organic Inhibitors on Chloride Corrosion ofSteel Rebars in Alkaline Pore Solution

Marina Cabrini Francesca Fontana Sergio LorenziTommaso Pastore and Simone Pellegrini

Department of Engineering and Applied Sciences INSTM RU Bergamo and University of BergamoViale Marconi 5 24044 Dalmine Italy

Correspondence should be addressed to Marina Cabrini marinacabriniunibgit

Received 21 November 2014 Revised 21 January 2015 Accepted 22 January 2015

Academic Editor Sebastijan Peljhan

Copyright copy 2015 Marina Cabrini et alThis is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

The inhibition properties of aspartic and lactic acid salts are comparedwith nitrite ions with regard to their effect on critical chlorideconcentration The tests were carried out on carbon steel specimens in simulated pore solutions with initial pH in the range of126 to 138 The critical chloride concentrations were estimated through multiple specimen potentiostatic tests at potentials in theusual range for passive rebar in noncarbonated concrete structures During tests chloride ions were progressively added until allspecimens showed localized attack obtaining cumulative distribution curves reporting the fraction of corroded specimens as afunction of chloride concentration The presence of the organic inhibitors on the passivity film was detected by IR spectra Theresults confirm that 01M aspartate exhibits an inhibiting effect comparable with nitrite ions of the same concentration Calciumlactate does not increase critical chloride concentration however it appears to promote the formation of a massive scale reducingthe corrosion propagation

1 Introduction

The use of corrosion inhibitors as chemical admixturesduring concrete mixing would be a simple and cost-effectivesolution for increasing concrete structures durability How-ever so far the only inhibitor with demonstrated effectivenessin preventing chloride corrosion on real structures is calciumnitrite [1ndash4] Recently some literatureworks report the resultsof research on the use of salts of organic acids as an alternativesolution to nitrites In previous works [5 6] the effect ofchloridehydroxyl ions ratio on the inhibiting properties ofaspartate ions was evaluated by means of cyclic voltammetryFurthermore long-term tests in reinforced concrete pointedout the ability of lactate ions to retard corrosion damage onsteel bars [7]

Tests in simulated concrete pore solutions are widelyadopted for experimental study of chloride corrosion Thisapproach does not reproduce the metalhydrated cementpaste interface and its buffering capacity which is significantin pitting initiation as stressed by Page [8] However itallows cheap and rapid testing suitable for the screening of alarge number of substances in a well-controlled environment

Furthermore a significant amount of data can be collected tomatch the statistical nature of pitting Potentiostatic polarisa-tion tests utilizing a step-by-step increase in chloride concen-tration to define the critical chloride content were previouslysuccessfully adopted on commercial admixture inhibitor [3]

This paper reports on multiple specimen potentiostatictests comparing the inhibition properties of aspartate andlactate with nitrite ions IR spectra were also carried out inorder to highlight the presence of organic adsorbed specieson the passivity film of the specimens The effect of pH andchloride concentration on the pitting initiationwas evaluated

2 Experimental Details

21 Potentiostatic Tests The tests were carried out on ferritic-pearlitic carbon steel Disks of 5mm height were cut from10mm diameter bar The electrical junction was realizedthrough a steel wire welded on the backside of the speci-men placed in an insulating PTFE sheath Afterwards thelateral surface and electric connection were embedded bycasting with two component polyurethane resins Finally

Hindawi Publishing CorporationJournal of ChemistryVolume 2015 Article ID 521507 10 pageshttpdxdoiorg1011552015521507

2 Journal of Chemistry

the exposed surface was grinded with emery paper up to2400 grit

The tests were performed at room temperature in aeratedsaturated solution of calcium hydroxide The pH was main-tained between 126 and 135 by addition of sodiumhydroxideto limewater The inhibitors were directly added into thesolution at concentrations of 01molL for calcium lactate 01and 05molL for sodium aspartate and 01 and 1molL forsodium nitrite The concentrations were chosen on the basisof previous results [7]

The pH of test solutions was verified by potentiometrictitration by using a glass electrode

During test six specimens were immersed in a 2 Lpolypropylene cell and polarized at 0mV with respect tocalomel reference electrode (SCE) placed in the center of thecell A mixed metal oxide activated titanium wire counterelectrode on the cell bottom ensured the uniformdistributionof current The anodic current flowing through each speci-men was monitored as ohmic drop on shunt resistance

Initially the specimens were prepassivated in the alkalinesolution without chlorides After 70 or 90 hours NaCl wasadded to the solutions in an amount proportional to themolar content of hydroxyl ions that is 047 117 and 37 gLfor pH 126 13 and 135 respectively Further additions ofthe same chloride quantities were performed every 48 hoursuntil all specimens showed localized attacks The breakdownof passivity film was detected through the sudden increase ofthe ohmic drop on the shunt resistance After the initiationof corrosion the specimen was removed from the solutionand the test continued on the remaining passive specimens inorder to obtain the cumulative distribution curve of criticalchloride content that is the fraction of specimens showingpitting corrosion related to the chloride versus hydroxylratio The specimens were observed after the tests to confirmlocalized corrosion initiation

22 Fourier Transform Infrared Spectroscopy Fourier Trans-form Infrared Spectroscopy (FTIR) was performed on spec-imens polarized at 0mV versus SCE in saturated Ca(OH)

2

+ NaOH at pH 135 solutions in the absence of inhibitorsin the presence of 1M NaNO

2 01M calcium or sodium

lactate and 01M or 05M sodium aspartate The specimenswere passivated for 90 hours After exposure the specimenswere extracted from the solution and dried with warm airjust before the test Reflectance measurements were carriedout using a Bruker Tensor 27 FTIR spectrometer equippedwith ATR (attenuated total reflectance) device Spectra werecollected between 600 and 4000 cmminus1

3 Results and Discussion

31 Potentiostatic Tests in Absence of Inhibitors Figure 1shows cumulative distribution curves of corroded specimensas a function of chloride concentration In the absence ofinhibitor the critical chloride concentration which signifi-cantly promotes pitting increases with alkalinity At pH 126and pH 13 all the specimens showed localized corrosioninitiation even at chloride concentrations as low as 002 and006molL respectively

At pH 135 the critical chloride content rises up to07molL The distribution curve slightly shifts to higherchloride content for prolonged passivation time from 70 to90 hours

The appearance of specimens extracted from the testingcell after initiation of localized corrosion shows a largeamount of corrosion products (Figure 2(a)) The presenceof several pits on the surface was evidenced after picklingin diluted hydrochloric acid inhibited with 3 gL hexam-ethylenetetramine (HMTA) (Figure 2(b))

Hausmann [9] and Gouda [10] described the criticalcontent of chloride for localised corrosion in terms of chlo-ridehydroxyl ion molar ratio according to the general law

[Clminus][OHminus]119899

= 119896 (1)

The molar concentration ratio in equation reflects the com-petitive action between chloride and hydroxyl ions in theprocess of passive film rupture and reformation duringpitting initiation Hausmann reported 119896 values for simulatedalkaline pore solutions in the range 05ndash108 with 119899 = 1Gouda fixed the parameters at values respectively of 119899 = 08and 119896 = 03 Later work confirmed 119896 values between025 and 08 always assuming 119899 = 1 [11ndash17] The role ofcritical chloride-hydroxyl ratio was confirmed in previousexperimental works by means of cyclic voltammetry [5 6]which determined values 119899 = 1 and 119896 = 06

Figure 3 summarizes the results in terms of cumulativefrequency of corroded specimens as a function of chlorideto hydroxyl ions ratio Different populations are evidenced asa function of pH This fact can be ascribed to the featuresof the step-by-step potentiostatic tests At high pH thecritical chloride concentration increases so much so thatto initiate localised attack a longer testing time is requiredduringwhich passivation of the specimensrsquo surface continuesdetermining a further raise of critical chloride concentrationThus in order to evaluate the effect of inhibitors on chlorideconcentration a single critical chloride to hydroxyl ion ratiocannot be used for evaluating the results and the pH of thesolution must be also considered

From the experimental cumulative distributions of cor-roded specimens (Figure 3) the chloride content required toinitiate the pitting on 50 of specimens was derived (C

05)

Such chloride content is shown in Figure 4 as a function ofpH

32 Effect of Inhibitors Figure 5 reports the curves in solutionwith nitrite ion addition The chloride concentration valuewhere pitting initiation appears is strictly dependent upon theconcentration of nitrite ions A slight inhibition effect can benoticed for 01M sodium nitrite and 70-hour passivation butthe probability of pitting initiation is substantially in the samerange as in reference solution

However such nitrite concentration is below the rangereported in the literature [11 18ndash23] for the compositionof pore solutions in chloride-contaminated concrete withsignificant nitrite additions The inhibition effect is far moreevident at 1M concentration with 90 hours prepassivation

Journal of Chemistry 3

0

1

2

3

4

5

6

0001 001 01 1 10

Num

ber o

f cor

rode

d sp

ecim

ens

[Clminus] (molL)

pH126

pH13

pH135

pH138

(a)

0

1

2

3

4

5

6

0001 001 01 1 10

Num

ber o

f cor

rode

d sp

ecim

ens

pH13

pH135

[Clminus] (molL)

(b)

Figure 1 Number of corroded specimens as a function of chloride addition during potentiostatic test in lime solutions without inhibitor (a)70 h and (b) 90 h of passivation

3mm

(a)

500120583m

(b)

Figure 2 (a) Specimen extracted from the cell after pitting initiation during potentiostatic polarization test (b) details of the surface showingpits

The results in solutions with 01molL calcium lactateat pH 135 are shown in Figure 6 The chloride contentwhich promotes pitting initiation is almost comparable withthe reference solution without inhibitor The results of thetest in solution containing sodium aspartate are shown inFigure 7 Although the chloride concentration that promoteslocalized corrosion on all specimens does not change withrespect to the reference solution at pH 135 an effect canbe evidenced at 01M concentration and 70-hour passivationdespite the lower pH equal to 132 At 05M concentrationthe curve slightly shifts to the left compared to the curveat 01M The effect of inhibitors on the critical chloridecontent C

05 is summarized in Figure 8 as a function of pH

and passivation time A real strong increase of the chloridecritical concentration is evident only for nitrite ions in highconcentration where the pitting of 50 of the specimens wasnot reached even after addition of 2M of chlorides Aspartateions seem to slightly increase C

05 while on the contrary

lactate ions do not show any such effect

33 Mechanism of Inhibition The behaviour of the threesubstances considered in the experimental research can beanalysed on the basis of the pitting theory and the featuresof FTIR spectra

Figure 9 illustrates the typical activepassive anodicpolarization curve of carbon steel in alkaline media Inabsence of chlorides the steel maintains its passive state untilover a threshold potential the oxygen evolution takes placeowing to water decomposition In the presence of chlorideions over a critical concentration on the steel localised cor-rosion occurs at pitting potential Pitting potential decreasesas the chloride content rises

The polarization potential of potentiostatic tests is in thepassivity range This value was chosen because it approachesthe open circuit potential of passive rebar in aerated uncar-bonated concrete

Many authors evaluated the pitting potential for rebar inconcrete or pore solutions but as underlined by Castelloteet al [24] the obtained values are very different The reasons


0

20

40

60

80

100

0001 001 01 1 10

Cum

ulat

ive f

requ

ency

()

pH 126pH 13

pH 135pH 138

Tests withoutinhibitors

[Clminus][OHminus]

70h passivation

Figure 3 Cumulative frequency of corroded specimens at differentpH as a function of chloride-hydroxyl ratio

0001

001

01

1

10

124 126 128 13 132 134 136pH

70h90h

C05

(M)

Figure 4 Effect of pHon critical chloride content duringmultispec-imen potentiostatic tests

are due to the technique employed for the pitting potentialdetermination For instance it could be noticed that poten-tiostatic and galvanostatic tests give lower threshold valuesthan potentiodynamic tests

The adopted potentiostatic technique does not purporttherefore to determine precisely the pitting potential but onlyto comparewith amethodmultisample the effect of inhibitorsin solution on the resistance of the film to different levels ofchlorides

In the considered test conditions pitting initiationbecomes possible when the pitting potential falls below theimposed potentialThe current registered through each spec-imen during the potentiostatic test has the typical behaviour

0

1

2

3

4

5

6

0001 001 01 1 10

Num

ber o

f cor

rode

d sp

ecim

ens

Sodium nitrite

[Clminus] (molL)

01M pH 135 70h1M pH 135 90h

Reference pH 135 70hReference pH 135 90h

Figure 5 Number of corroded specimens as a function of chlorideaddition during potentiostatic test in solutions with sodium nitrite

0

1

2

3

4

5

6

0001 001 01 1 10

Num

ber o

f cor

rode

d sp

ecim

ens

Calcium lactate

[Clminus] (molL)

01M pH 135 70h01M pH 135 90h


Figure 6 Number of corroded specimens as a function of chlorideaddition during potentiostatic test in solutions with calcium lactate

shown in Figure 10 When the specimen is polarised thecurrent suddenly increases but then decreases rapidly toreach a very low value corresponding to the passivity currentThe mechanism commonly assumed for pitting initiationis the competitive chemisorption of chlorides and hydroxylions on passive film [25] the higher the chloride contentthe higher the probability for substitution of Clminus to OHminusions in the outer layer of passive film If chlorides substituteOHminus group in a sufficient number of adjacent sites therupture of the passive film can occur with formation ofembryo pit This pit is metastable and hydroxyl ions anddissolved oxygen can restore the protective film on the inner


0

1

2

3

4

5

6

Num

ber o

f cor

rode

d sp

ecim

ens

Sodium aspartate

0001 001 01 1 10[Clminus] (molL)

01M pH 134 70h05M pH 132 90h


Figure 7 Number of corroded specimens as a function of chlorideaddition during potentiostatic test in solutions with sodium aspar-tate

surface of embryo pit which thus does not reach a stablepropagation On the contrary the pit propagates by occludedcell mechanism and consequently repassivation graduallybecomes less probable because of acidification and highconcentration of chlorides The formation and repassivationofmetastable pits are evident in the current versus time graphas spikes in the current that donot reach the threshold currentvalue corresponding to specimen failure Finally once thepitting starts to propagate by the occluded cell mechanismthe current increases

Corrosion inhibitors can act during one or more ofthe different stages of pitting initiation and propagationby stabilizing the passivity state and increasing the criticalchloride concentration to have embryo pitting initiation byincreasing the kinetic of repassivation of embryo pit or bydecreasing the propagation rate of the initiated pit

34 FTIR Spectra Fourier Transform Infrared Spectroscopy(FTIR) was performed in order to evidence the formation ofcompounds on the surface promoted by inhibitors Figure 11reports the FTIR spectrum of polished steel compared to thespectrumof steel passivated for 48 hours at 0V versus SCE atpH 135The two spectra are superimposable with the excep-tions of a broad band between 3500 and 3000 cmminus1 a smallband near 2600 cmminus1 and a group of peaks between 1586and 1552 cmminus1 only observed on the passivated specimen

The broad band is in the range of the stretching frequencyof the ndashOHgroups of the different allotropic forms of FeOOH(120572-goethite 120573-akaganeite 120574-lepidocrocite and 120575-feroxyhyte)[26]

The passivity film present on carbon steel in pore solutionwas studied in previous works using cyclic voltammetry [5ndash7] The peaks on the voltammogram indicated that filmformation proceeds by initial oxidation of Fe to Fe(II) inthe form of Fe(OH)

2 this reaction is partially reversible

The value of the peak current associated with this reactionremained constant with increasing of the number of voltam-metry cycles which indicates that the Fe(OH)

2film did not

increase The Fe(OH)2film is further oxidised to different

species depending on the environment and the potential scanrate [27 28] In the test conditions adopted in the consideredworks the most probable oxidation product is lepidocrocite120574-FeOOH Joiret et al [29] emphasized themagnetite (Fe

3O4)

formation Following Andrade et al [30] the external layeris constituted by magnetite Fe

3O4partially oxidised to

120574-FeOOH 120574-FeOOH can subsequently dehydrate to giveFe2O3 Electrochemical Impedance Spectroscopy confirmed

the double nature of the passivity film [23 31] Montemor etal using XPS analysis reported that the outermost layers ofpassive films were mostly composed of FeOOH (Montemoret al) [32]

FTIR spectra analysed only the external surface of thepassivity film It is reasonable to think that the peak in therange 3500 divide 3000 cmminus1 is due to a mixture of the polymor-phic forms of FeOOHpresent on the external side of the film

The other peaks are not typical of these hydroxidesSpectra with peaks in the range of 1650 and 1540 cmminus1 wereobserved on specimens covered by amorphous or crystallineFe(II) and Fe(III) hydroxides and carbonates with differentstoichiometric ratios called green rust [33]

The peaks at 1430 1785 and 2530 cmminus1 are character-istic of calcium carbonate which can form by reaction ofCa(OH)

2 incorporated in the passivity film [27 28] with

atmospheric CO2 Ghods et al determined by means of XPS

that microsize calcium hydroxide andor calcium carbonateparticles are present on the film surface and remainedalso after the specimens were removed from the calciumhydroxide solution and dried [34]

In Figure 12 the FTIR spectrum registered on the speci-men passivated at 0V versus SCE in alkaline solution addedwith 1M sodium nitrite is compared with that obtained insolution without inhibitor The absence of FeOOH signals inthe nitrite-containing sample is evident

The inhibitive action of nitrite ions depends on theirreaction with Fe2+ ions according to the following reactions

Fe2+ +OHminus +NO2

minus 997888rarr NO + 120574-FeOOH (2)

2Fe2+ + 2OHminus + 2NO2

minus 997888rarr 2NO + Fe2O3+H2O (3)

In the literature there is unanimous accord on the effect ofnitrite in accelerating the oxidation reaction of the Fe(II) toFe(III) but there are conflicting data about the compositionof the passivity film in the presence of nitrite AccordingGireiene the outer layer of the film consists of FeO AFManalysis demonstrated that the film formed in presence ofnitrite ions is less porous and more compact than thoseformed on Ca(OH)

2without inhibitor [35]

FTIR spectra seem to confirm the decrease of ndashOHgroups in the outermost layer of the film in the presence ofnitrite

Nitrite ions aid the formation of a stable passive layer evenin the presence of chloride ions because reactions (2) and (3)are faster than the transport of ferrous by means of a chloride


0001

001

01

1

10

124 126 128 13 132 134 136pH

Without inhibitor 70h passivationNitrite 01M

Aspartate 01MLactate 01M

C05

(M)

(a)

0001

001

01

1

10

124 126 128 13 132 134 136pH



C05

(M)

(b)

Figure 8 Effect of pH on critical chloride content during multispecimen potentiostatic tests (a) at 70 h of passivation and (b) at 90 h ofpassivation C

05was not reached in the case of nitrites

E

Epit

Eeq

ip

Epit for increasing [Clminus]

E polarization

log i

Figure 9 Example of polarization curves of carbon steel in alkalinesolution as a function of chloride concentration

Occluded cell

Pit embryo

i

ith

ip

t

[Clminus]1 [Clminus]2

Figure 10 Effect of time and chloride concentration on pittinginitiation

096

098

1

600160026003600

Tran

smitt

ance

FeOOHstretching

Polished surfaceSurface passivate at 0V versus SCE in alkaline solution

1120582 (cmminus1)

Fe Ca CO3 OH salts

Figure 11 FTIR spectra of a polished specimen and a specimenpassivated in solution at pH 135 and 0V versus SCE

ion complex formation [2 5 26] However full protectiondepends greatly on the concentration of chloride ion [5]and severe pitting may occur when insufficient quantity ofinhibitor is used compared to the level of chloride in theconcrete [3 11]

Nitrite ions cooperate with hydroxyl ions to rebuildthe protective film [5 6] one nitrite and one hydroxyl ionbeing involved to counteract the chlorides This effect is onlyoperating during the nucleation period before acidificationcaused by the occluded cell mechanism becomes too severeAfter initiation nitrite ions produce deep penetration of


096

098

1

600110016002100260031003600

Tran

smitt

ance

FeOOHstretching

1120582 (cmminus1)

Fe Ca CO3 OH salts

Surface passivated at 0V versus SCE in 01 M nitritesSurface passivated at 0V versus SCE in alkaline solution

Figure 12 FTIR spectra of specimens passivated in solution at pH135 and 0V versus SCE without and with 01M NaNO

2

092

094

096

098

1

600110016002100260031003600

Tran

smitt

ance

1120582 (cmminus1)

Surface passivated at 0V versus SCE in 01M calcium lactateSurface passivated at 0V versus SCE in alkaline solutionSurface passivated at 0V versus SCE in 01M sodium lactate

FeOOH + COOminus stretching

Ca(OH)2 2CaCOand lactate

Figure 13 FTIR spectra of a specimen passivated in solution withand without calcium lactate 01M or sodium lactate 01M at pH 135and 0V versus SCE

localised attack owing to their oxidizing character contrib-uting to the anodic process Insufficient nitrite content withrespect to chloride can therefore produce deeper penetrationof localised corrosion hence the well-known necessity tomaintain a high concentration of nitrite ions in solutionto preserve the steel from localised corrosion Adverseeffects due to insufficient concentration represent the mainproblem in the use of this inhibitor in concrete Figures 5and 8 show that inhibition by nitrite ions becomes evidentwhen their concentration is comparable with hydroxyl ionsconcentration

Figure 13 compares the spectrum obtained on a specimenpassivated in solution with calcium lactate at pH 135 with the

Surface passivated at 0 V versus SCE in 01 M sodium aspartateSurface passivated at 0 V versus SCE in alkaline solution

096

098

1

600110016002100260031003600

Tran

smitt

ance

FeOOHstretching

1120582 (cmminus1)

Fe Ca CO3 OH salts

Figure 14 FTIR spectra of a specimen passivated in solution withand without sodium aspartate 01M at pH 134 and 0V versus SCE

spectrum obtained in absence of inhibitor After passivationa clearly visible white scale covers the surface of the specimenBoth spectra show the presence of a broad peak at 3272 cmminus1and several well-defined peaks at 1576 1454 1417 13661315 1122 1042 855 and 638 cmminus1 These latter peaks arecharacteristic of lactate while the first one is characteristicof the stretching of the ndashOH groups of both the iron oxideand the OH group of the organic acid Such peaks overlapgiving a broad band The spectrum confirms the presenceon the surface of the specimen passivated in alkaline calciumlactate solution of a mixed composition film containinglactate ions On the other hand the presence of signalsattributable to lactate ions is not evident in the spectrumwhen the samples are treated with sodium lactate instead ofcalcium lactate the spectrum obtained in these conditions isessentially superimposable to the one recorded in the absenceof inhibitor This confirms that as soluble calcium lactate isadded Ca2+ ions become supersaturated in the alkaline solu-tion andprecipitate in the formof a calciumhydroxide gel Nomacroscopic adsorption effect is therefore evidenced for thisinhibitor Actually infrared spectroscopy is not in itself anextremely sensitive detection technique so that the presenceof very small quantities of analyte would not be observed

The above results demonstrate that lactate ions have noeffect on pitting initiation confirming previous works [5 6]On the contrary long time tests carried out on concretespecimens [7] evidenced the possibility of lactate ions to slowdown the pit propagation Lactate ions do not contribute tothe protectivity of the passive film but their steric hindrancecould reduce the contribution of the cathodic process andslow down the pit propagation This effect is not visible inthe electrochemical tests but becomes evident in long timeexposure tests at the corrosion potential

Figure 14 presents the FTIR spectra of specimens passi-vated in alkaline solution at 0V versus SCE with and withoutsodium aspartate Like the spectrum obtained in solution of


H

O OC

H O C

minus

CH3

Fe2O3 surface

(a)

OO

O

minusNH2

minusO

Fe2O3 surface

(b)

O

OH

HO O

Fe2O3 surface

OminusOminus

(c)

Figure 15 From left to right lactate aspartate and ascorbate ions adsorbing on the iron oxide surface

sodium nitrite the IR spectrum in the presence of sodiumaspartate did not show the peaks characteristic of Fe(III)oxide However contrary to nitrites aspartate ions are notoxidizing

The behaviour of aspartate ions can be interpreted byconsidering their chelating properties Ormellese et al [36]stated that organic acid salts act as inhibitors in pore solutionby adsorption of carboxylic groups on the metal surface bythe delocalised charge on the two oxygen atoms (Figure 15)Electron-donating groups namely hydroxyl in the caseof lactic acid and amine for aspartic acid favour thiseffect However steric hindrance penalizes their competitionagainst chloride adsorption Aspartic however is a weakbicarboxylic acid that can adsorb on the iron oxide byassuming an annular configuration and counteract chlorideadsorption by negative charge repulsion (Figure 15)

In fact Kalota and Silverman [37] demonstrated thatfor the inhibiting properties of aspartic acid on iron thefully ionised form is required in solutions above pH 10 Theyperformed tests at pH values below the range of concretepore solutions and showed that in less alkaline solutionsaspartic acid stimulates corrosion by complex formation withiron ions Thus high pH is necessary to counteract theacidification taking place on the film surface in the presenceof chloride ions during the first stage of pitting initiationin fact acidification moves the dissociation equilibrium ofaspartic acid towards the undissociated form which is unableto adsorb on the film

Valek et al [38] found a similar complex behaviour inevaluating the inhibition effect of ascorbic acid in alkalinemedia the inhibition efficiency decreases with increasingacid concentration The anion of this acid is known to formchelates through the hydroxyl groups of the lactone ringhence it can be adsorbed onto the metal surface throughformation of stable chelates with coordinatively unsaturatedsurface Fe ions (Figure 15) These authors discuss literaturedata and outline that an increase in the concentration of thecomplexing agent shifts its effect from inhibitive to stimu-lative one towards iron dissolution Solubility of a complexis mainly determined by metalligand ratio since for higherratios sparingly soluble mono- or polynuclear complexescould be formed while for lower ratios soluble complexescould be formed They concluded that the increase in ligandconcentration and the resulting decrease of the metalligandratio in the near electrode layer create favourable conditionsfor soluble complexes formation while at low concentration

insoluble chelates are formed [38] Moreover these authorshypothesized that the chelating action could stabilize theFe(II) ions of the passive film giving a much less solublecomplex than the one formed by Fe(III) ions Thereforethe chelating agent addition promotes thinner passive filmwhereas the adsorption of molecules on the surface tends toblock the adsorption of chlorides extending the pitting initia-tion time Similar behaviour has been assumed for the passivelayer of steel in presence of EDTA [38] It was suggested thatEDTA supported dissolution of the barrier layer andhinderedformation of the outer barrier because of its ability to chelateFe(II) cations ejected from the oxide layer On the otherhand EDTA adsorbs strongly on the oxygen vacancies at thebarrier layersolution interface thereby effectively blockingthe adsorption of Clminus at the surface of the passive filmHowever previous tests demonstrated that 028molL ofEDTA enhanced generalised dissolution of steel [39]

The hypothesis that aspartate creates a similar chelatingcomplex adsorbed on Fe(II) oxide and a soluble complexwith Fe(III) ions is in agreement with FTIR spectra Thepotentiostatic results evidenced that this substance showsan inhibition effect in concentration 01M but its beneficialeffect decreases by increasing its concentration to 05M

4 Conclusions

This paper studies the effect of the addition of lactic andaspartic acid salts on localized corrosion of passive rebars inalkaline simulated pore solution initiated by chloride ionsPotentiostatic multiple specimen tests were used to evaluatethe time required for pitting initiation as a function ofchloride content and pH while FTIR spectroscopy allowedgaining further insight into the nature of the species consti-tuting the passive film

The effectiveness of these organic substances was com-pared with the well-known inhibiting properties of nitriteions and hypotheses have been put forward on the possibleinhibition mechanisms

Under test conditions considered in the research theinhibition effect of 1M nitrite concentration is evident whileat 01M concentration there is only a slight effect FTIRspectra confirm the effect of nitrite ions on the stability ofthe Fe(II) film and their inhibition mechanisms both onthe initiation stage and on the kinetic of repassivation ofmetastable pits


In the case of calcium lactate FTIR spectra evidenced thepresence of a massive scale constituted by calcium hydroxidegel incorporating lactate ions shielding the specimen surfaceand slowing down the pit propagation though without effecton the critical chloride concentration

Aspartate ions on the opposite appear to adsorb onFe(II) oxide surface due to their chelating properties andexert their inhibiting properties through a negative chargerepulsion by their nonadsorbed carboxylate group effectivelyincreasing the critical chloride content This inhibitor iseffective in concentration 01M but its beneficial actiondecreases by increasing its concentration to 05M

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This research project has been made possible thanks to fund-ing from Italy Project by University of Bergamo Specialthanks are due to Matteo Cortinovis and Alessandro Milesifor their contribution to the experimental section

References

[1] B Elsener Corrosion Inhibitors for Steel in Concrete State of theArt Report vol 35 EFC Publications 2001

[2] T A Soylev and M G Richardson ldquoCorrosion inhibitorsfor steel in concrete state-of-the-art reportrdquo Construction andBuilding Materials vol 22 no 4 pp 609ndash622 2008

[3] M Ormellese M Berra F Bolzoni and T Pastore ldquoCorrosioninhibitors for chlorides induced corrosion in reinforced con-crete structuresrdquo Cement and Concrete Research vol 36 no 3pp 536ndash547 2006

[4] M Collepardi R Fratesi G Moriconi V Corradetti and LCoppola ldquoUse of nitrite salt as corrosion inhibitor admixturesin reinforced concrete structures immersed in sea-waterrdquo inProceedings of the International RILEM Symposium on Admix-tures for Concrete E Vazquez Ed pp 279ndash288 Chapman ampHall Barcelona Spain 1990

[5] M Cabrini S Lorenzi and T Pastore ldquoCyclic voltammetryevaluation of inhibitors for localised corrosion in alkalinesolutionsrdquo Electrochimica Acta vol 124 pp 156ndash164 2014

[6] M Cabrini S Lorenzi and T Pastore ldquoStudio della corrosionelocalizzata degli acciai per armature in soluzioni alcaline inib-iterdquo La Metallurgia Italiana vol 105 no 7-8 pp 21ndash31 2013

[7] T Pastore M Cabrini L Coppola S Lorenzi P Marcassoliand A Buoso ldquoEvaluation of the corrosion inhibition of salts oforganic acids in alkaline solutions and chloride contaminatedconcreterdquo Materials and Corrosion vol 62 no 2 pp 187ndash1952011

[8] C L Page ldquoMechanism of corrosion protection in reinforcedconcrete marine structuresrdquo Nature vol 258 no 5535 pp 514ndash515 1975

[9] D A Hausmann ldquoSteel corrosion in concretemdashhow does itoccurrdquoMaterial Protection vol 6 no 11 pp 19ndash23 1967

[10] V K Gouda ldquoCorrosion and corrosion inhibition of reinforcingsteel I Immersed in alkaline solutionsrdquo British CorrosionJournal vol 5 no 5 pp 198ndash203 1970

[11] G K Glass and N R Buenfeld ldquoThe presentation of thechloride threshold level for corrosion of steel in concreterdquoCorrosion Science vol 39 no 5 pp 1001ndash1013 1997

[12] M C Alonso and M Sanchez ldquoAnalysis of the variabilityof chloride threshold values in the literaturerdquo Materials andCorrosion vol 60 no 8 pp 631ndash637 2009

[13] S Goni and C Andrade ldquoSynthetic concrete pore solutionchemistry and rebar corrosion rate in the presence of chloridesrdquoCement and Concrete Research vol 20 no 4 pp 525ndash539 1990

[14] S Diamond ldquoChloride concentrations in concrete pore solu-tions resulting from calcium and sodium chloride admixturesrdquoCement Concrete and Aggregates vol 8 no 2 pp 97ndash102 1986

[15] T Yonezawa V Ashworth and R P M Procter ldquoPore solutioncomposition and chloride effects on the corrosion of steel inconcreterdquo Corrosion vol 44 no 7 pp 489ndash499 1988

[16] U Angst and Oslash Vennesland ldquoCritical chloride content inreinforced concreterdquo in Concrete Repair Rehabilitation andRetrofitting II M G Alexander H D Beushausen F Dehn andPMoyo Eds pp 311ndash317 Taylor amp Francis Group London UK2009

[17] U Angst B Elsener C K Larsen and Oslash Vennesland ldquoCriticalchloride content in reinforced concretemdasha reviewrdquo Cement andConcrete Research vol 39 no 12 pp 1122ndash1138 2009

[18] J Tritthart and P F G Banfill ldquoNitrite binding in cementrdquoCement andConcrete Research vol 31 no 7 pp 1093ndash1100 2001

[19] N S Berke M C Hicks and R J Hoopes ldquoCondition assess-ment of field structures with calcium nitriterdquo in ConcreteBridges inAggressive Environments PhilipDCady InternationalSymposium SP-151 ACI Publication pp 43ndash72 AmericanConcrete Institute Detroit Mich USA 1994

[20] N S Berke and M C Hicks ldquoPredicting long-term durabilityof steel reinforced concrete with calcium nitrite corrosioninhibitorrdquo Cement and Concrete Composites vol 26 no 3 pp191ndash198 2004

[21] N S Berke andA Rosenberg ldquoCalciumnitrite inhibitor in con-creterdquo in Proceedings of the International RILEM SymposiumAdmixture for Concrete Improvment of Properties E VazquezEd pp 297ndash315 Chapman amp Hall London UK 1990

[22] N S Berke F Gianetti P G Tourney and Z GMatta ldquoThe useof calcium nitrite corrosion inhibitor to improve the durabilityof reinforced concrete in the Arabian Gulfrdquo in Deteriorationand Repair of Reinforced Concrete in the Arabian Gulf G LMacMillan Ed vol II pp 873ndash885 BSE Manama Bahrain1993

[23] M Sanchez J Gregori M C Alonso J J Garcıa-Jareno and FVicente ldquoAnodic growth of passive layers on steel rebars in analkaline medium simulating the concrete poresrdquo ElectrochimicaActa vol 52 no 1 pp 47ndash53 2006

[24] M Castellote C Andrade and C Alonso ldquoChloride thresholddependence of pitting potential of reinforcementsrdquoElectrochim-ica Acta vol 47 no 21 pp 3469ndash3481 2002

[25] M B Valcarce and M Vazquez ldquoCarbon steel passivity exam-ined in alkaline solutions the effect of chloride and nitrite ionsrdquoElectrochimica Acta vol 53 no 15 pp 5007ndash5015 2008

[26] BWeckler and H D Lutz ldquoLattice vibration spectra Part XCVInfrared spectroscopic studies on the iron oxide hydroxidesgoethite (120572) akaganeite (120573) lepidocrocite (120574) and feroxyhite(120575)rdquo European Journal of Solid State and Inorganic Chemistryvol 35 no 8-9 pp 531ndash544 1998

[27] O A Albani J O Zerbino J R Vilche and A J Arvia ldquoAcomparative electrochemical and ellipsometric study of the


iron electrodes in different alkaline electrolytesrdquo ElectrochimicaActa vol 31 no 11 pp 1403ndash1411 1986

[28] L Freire X R Novoa M F Montemor and M J CarmezimldquoStudy of passive films formed onmild steel in alkalinemedia bythe application of anodic potentialsrdquo Materials Chemistry andPhysics vol 114 no 2-3 pp 962ndash972 2009

[29] S Joiret M Keddam X R Novoa M C Perez C Rangeland H Takenouti ldquoUse of EIS ring-disk electrode EQCM andRaman spectroscopy to study the film of oxides formed on ironin 1 M NaOHrdquo Cement and Concrete Composites vol 24 no 1pp 7ndash15 2002

[30] C Andrade M Keddam X R Novoa M C Perez C MRangel and H Takenouti ldquoElectrochemical behaviour of steelrebars in concrete influence of environmental factors andcement chemistryrdquo Electrochimica Acta vol 46 no 24-25 pp3905ndash3912 2001

[31] M Sanchez J Gregori C Alonso J J Garcıa-Jareno HTakenouti and F Vicente ldquoElectrochemical impedance spec-troscopy for studying passive layers on steel rebars immersedin alkaline solutions simulating concrete poresrdquo ElectrochimicaActa vol 52 no 27 pp 7634ndash7641 2007

[32] M F Montemor A M P Simoes and M G S FerreiraldquoAnalytical characterization of the passive film formed on steelin solutions simulating the concrete interstitial electrolyterdquoCorrosion vol 54 no 5 pp 347ndash353 1998

[33] S Savoye L Legrand G Sagon et al ldquoExperimental in-vestigations on iron corrosion products formed in bicarbon-atecarbonate-containing solutions at 90∘Crdquo Corrosion Sciencevol 43 no 11 pp 2049ndash2064 2001

[34] P Ghods O B Isgor J R Brown F Bensebaa and D KingstonldquoXPS depth profiling study on the passive oxide film of carbonsteel in saturated calcium hydroxide solution and the effect ofchloride on the film propertiesrdquo Applied Surface Science vol257 no 10 pp 4669ndash4677 2011

[35] O Gireiene R Ramanauskas L Gudavieiute and A Martusi-ene ldquoInhibition effect of sodium nitrite and silicate on carbonsteel corrosion in chloride-contaminated alkaline solutionsrdquoCorrosion vol 67 no 12 pp 125001-1ndash125001-12 2011

[36] M Ormellese L Lazzari S Goidanich G Fumagalli andA Brenna ldquoA study of organic substances as inhibitors forchloride-induced corrosion in concreterdquo Corrosion Science vol51 no 12 pp 2959ndash2968 2009

[37] D J Kalota and D C Silverman ldquoBehavior of aspartic acid as acorrosion inhibitor for steelrdquo Corrosion vol 50 no 2 pp 138ndash145 1994

[38] L Valek S Martinez D Mikulic and I Brnardic ldquoTheinhibition activity of ascorbic acid towards corrosion of steel inalkalinemedia containing chloride ionsrdquoCorrosion Science vol50 no 9 pp 2705ndash2709 2008

[39] M Cabrini and T Pastore ldquoEffect of chemical substanceson localized corrosion of steel in alkaline environments andconcreterdquo in Frontiers in Corrosion Science and TechnologyProceedings of 15th International Corrosion Congress GranadaSeptember 22ndash27 2002 pp 2481ndash2488 Curran Associated RedHook NY USA 2002

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy


Carbohydrate Chemistry

International Journal of


Journal of

Chemistry


Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of


Chromatography Research International


Applied ChemistryJournal of



Theoretical ChemistryJournal of


Journal of

Spectroscopy

Analytical ChemistryInternational Journal of


Journal of


Quantum Chemistry


Organic Chemistry International

ElectrochemistryInternational Journal of



CatalystsJournal of


the exposed surface was grinded with emery paper up to2400 grit

The tests were performed at room temperature in aeratedsaturated solution of calcium hydroxide The pH was main-tained between 126 and 135 by addition of sodiumhydroxideto limewater The inhibitors were directly added into thesolution at concentrations of 01molL for calcium lactate 01and 05molL for sodium aspartate and 01 and 1molL forsodium nitrite The concentrations were chosen on the basisof previous results [7]

The pH of test solutions was verified by potentiometrictitration by using a glass electrode

During test six specimens were immersed in a 2 Lpolypropylene cell and polarized at 0mV with respect tocalomel reference electrode (SCE) placed in the center of thecell A mixed metal oxide activated titanium wire counterelectrode on the cell bottom ensured the uniformdistributionof current The anodic current flowing through each speci-men was monitored as ohmic drop on shunt resistance

Initially the specimens were prepassivated in the alkalinesolution without chlorides After 70 or 90 hours NaCl wasadded to the solutions in an amount proportional to themolar content of hydroxyl ions that is 047 117 and 37 gLfor pH 126 13 and 135 respectively Further additions ofthe same chloride quantities were performed every 48 hoursuntil all specimens showed localized attacks The breakdownof passivity film was detected through the sudden increase ofthe ohmic drop on the shunt resistance After the initiationof corrosion the specimen was removed from the solutionand the test continued on the remaining passive specimens inorder to obtain the cumulative distribution curve of criticalchloride content that is the fraction of specimens showingpitting corrosion related to the chloride versus hydroxylratio The specimens were observed after the tests to confirmlocalized corrosion initiation

22 Fourier Transform Infrared Spectroscopy Fourier Trans-form Infrared Spectroscopy (FTIR) was performed on spec-imens polarized at 0mV versus SCE in saturated Ca(OH)

2

+ NaOH at pH 135 solutions in the absence of inhibitorsin the presence of 1M NaNO

2 01M calcium or sodium

lactate and 01M or 05M sodium aspartate The specimenswere passivated for 90 hours After exposure the specimenswere extracted from the solution and dried with warm airjust before the test Reflectance measurements were carriedout using a Bruker Tensor 27 FTIR spectrometer equippedwith ATR (attenuated total reflectance) device Spectra werecollected between 600 and 4000 cmminus1

3 Results and Discussion

31 Potentiostatic Tests in Absence of Inhibitors Figure 1shows cumulative distribution curves of corroded specimensas a function of chloride concentration In the absence ofinhibitor the critical chloride concentration which signifi-cantly promotes pitting increases with alkalinity At pH 126and pH 13 all the specimens showed localized corrosioninitiation even at chloride concentrations as low as 002 and006molL respectively

At pH 135 the critical chloride content rises up to07molL The distribution curve slightly shifts to higherchloride content for prolonged passivation time from 70 to90 hours

The appearance of specimens extracted from the testingcell after initiation of localized corrosion shows a largeamount of corrosion products (Figure 2(a)) The presenceof several pits on the surface was evidenced after picklingin diluted hydrochloric acid inhibited with 3 gL hexam-ethylenetetramine (HMTA) (Figure 2(b))

Hausmann [9] and Gouda [10] described the criticalcontent of chloride for localised corrosion in terms of chlo-ridehydroxyl ion molar ratio according to the general law

[Clminus][OHminus]119899

= 119896 (1)

The molar concentration ratio in equation reflects the com-petitive action between chloride and hydroxyl ions in theprocess of passive film rupture and reformation duringpitting initiation Hausmann reported 119896 values for simulatedalkaline pore solutions in the range 05ndash108 with 119899 = 1Gouda fixed the parameters at values respectively of 119899 = 08and 119896 = 03 Later work confirmed 119896 values between025 and 08 always assuming 119899 = 1 [11ndash17] The role ofcritical chloride-hydroxyl ratio was confirmed in previousexperimental works by means of cyclic voltammetry [5 6]which determined values 119899 = 1 and 119896 = 06

Figure 3 summarizes the results in terms of cumulativefrequency of corroded specimens as a function of chlorideto hydroxyl ions ratio Different populations are evidenced asa function of pH This fact can be ascribed to the featuresof the step-by-step potentiostatic tests At high pH thecritical chloride concentration increases so much so thatto initiate localised attack a longer testing time is requiredduringwhich passivation of the specimensrsquo surface continuesdetermining a further raise of critical chloride concentrationThus in order to evaluate the effect of inhibitors on chlorideconcentration a single critical chloride to hydroxyl ion ratiocannot be used for evaluating the results and the pH of thesolution must be also considered

From the experimental cumulative distributions of cor-roded specimens (Figure 3) the chloride content required toinitiate the pitting on 50 of specimens was derived (C

05)

Such chloride content is shown in Figure 4 as a function ofpH

32 Effect of Inhibitors Figure 5 reports the curves in solutionwith nitrite ion addition The chloride concentration valuewhere pitting initiation appears is strictly dependent upon theconcentration of nitrite ions A slight inhibition effect can benoticed for 01M sodium nitrite and 70-hour passivation butthe probability of pitting initiation is substantially in the samerange as in reference solution

However such nitrite concentration is below the rangereported in the literature [11 18ndash23] for the compositionof pore solutions in chloride-contaminated concrete withsignificant nitrite additions The inhibition effect is far moreevident at 1M concentration with 90 hours prepassivation


0

1

2

3

4

5

6

0001 001 01 1 10

Num

ber o

f cor

rode

d sp

ecim

ens

[Clminus] (molL)

pH126

pH13

pH135

pH138

(a)

0

1

2

3

4

5

6

0001 001 01 1 10

Num

ber o

f cor

rode

d sp

ecim

ens

pH13

pH135

[Clminus] (molL)

(b)


3mm

(a)

500120583m

(b)












0

20

40

60

80

100

0001 001 01 1 10

Cum

ulat

ive f

requ

ency

()

pH 126pH 13

pH 135pH 138


[Clminus][OHminus]

70h passivation


0001

001

01

1

10

124 126 128 13 132 134 136pH

70h90h

C05

(M)





0

1

2

3

4

5

6

0001 001 01 1 10

Num

ber o

f cor

rode

d sp

ecim

ens

Sodium nitrite

[Clminus] (molL)

01M pH 135 70h1M pH 135 90h



0

1

2

3

4

5

6

0001 001 01 1 10

Num

ber o

f cor

rode

d sp

ecim

ens

Calcium lactate

[Clminus] (molL)

01M pH 135 70h01M pH 135 90h





0

1

2

3

4

5

6

Num

ber o

f cor

rode

d sp

ecim

ens

Sodium aspartate

0001 001 01 1 10[Clminus] (molL)

01M pH 134 70h05M pH 132 90h










2film did not



3O4)













Fe2+ +OHminus +NO2









0001

001

01

1

10

124 126 128 13 132 134 136pH



C05

(M)

(a)

0001

001

01

1

10

124 126 128 13 132 134 136pH



C05

(M)

(b)



E

Epit

Eeq

ip


E polarization

log i


Occluded cell

Pit embryo

i

ith

ip

t



096

098

1

600160026003600

Tran

smitt

ance

FeOOHstretching


1120582 (cmminus1)

Fe Ca CO3 OH salts





096

098

1

600110016002100260031003600

Tran

smitt

ance

FeOOHstretching

1120582 (cmminus1)

Fe Ca CO3 OH salts



2

092

094

096

098

1

600110016002100260031003600

Tran

smitt

ance

1120582 (cmminus1)








096

098

1

600110016002100260031003600

Tran

smitt

ance

FeOOHstretching

1120582 (cmminus1)

Fe Ca CO3 OH salts






H

O OC

H O C

minus

CH3

Fe2O3 surface

(a)

OO

O

minusNH2

minusO

Fe2O3 surface

(b)

O

OH

HO O

Fe2O3 surface

OminusOminus

(c)








4 Conclusions









Acknowledgments


References



















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


0

1

2

3

4

5

6

0001 001 01 1 10

Num

ber o

f cor

rode

d sp

ecim

ens

[Clminus] (molL)

pH126

pH13

pH135

pH138

(a)

0

1

2

3

4

5

6

0001 001 01 1 10

Num

ber o

f cor

rode

d sp

ecim

ens

pH13

pH135

[Clminus] (molL)

(b)


3mm

(a)

500120583m

(b)












0

20

40

60

80

100

0001 001 01 1 10

Cum

ulat

ive f

requ

ency

()

pH 126pH 13

pH 135pH 138


[Clminus][OHminus]

70h passivation


0001

001

01

1

10

124 126 128 13 132 134 136pH

70h90h

C05

(M)





0

1

2

3

4

5

6

0001 001 01 1 10

Num

ber o

f cor

rode

d sp

ecim

ens

Sodium nitrite

[Clminus] (molL)

01M pH 135 70h1M pH 135 90h



0

1

2

3

4

5

6

0001 001 01 1 10

Num

ber o

f cor

rode

d sp

ecim

ens

Calcium lactate

[Clminus] (molL)

01M pH 135 70h01M pH 135 90h





0

1

2

3

4

5

6

Num

ber o

f cor

rode

d sp

ecim

ens

Sodium aspartate

0001 001 01 1 10[Clminus] (molL)

01M pH 134 70h05M pH 132 90h










2film did not



3O4)













Fe2+ +OHminus +NO2









0001

001

01

1

10

124 126 128 13 132 134 136pH



C05

(M)

(a)

0001

001

01

1

10

124 126 128 13 132 134 136pH



C05

(M)

(b)



E

Epit

Eeq

ip


E polarization

log i


Occluded cell

Pit embryo

i

ith

ip

t



096

098

1

600160026003600

Tran

smitt

ance

FeOOHstretching


1120582 (cmminus1)

Fe Ca CO3 OH salts





096

098

1

600110016002100260031003600

Tran

smitt

ance

FeOOHstretching

1120582 (cmminus1)

Fe Ca CO3 OH salts



2

092

094

096

098

1

600110016002100260031003600

Tran

smitt

ance

1120582 (cmminus1)








096

098

1

600110016002100260031003600

Tran

smitt

ance

FeOOHstretching

1120582 (cmminus1)

Fe Ca CO3 OH salts






H

O OC

H O C

minus

CH3

Fe2O3 surface

(a)

OO

O

minusNH2

minusO

Fe2O3 surface

(b)

O

OH

HO O

Fe2O3 surface

OminusOminus

(c)








4 Conclusions









Acknowledgments


References



















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


0

20

40

60

80

100

0001 001 01 1 10

Cum

ulat

ive f

requ

ency

()

pH 126pH 13

pH 135pH 138


[Clminus][OHminus]

70h passivation


0001

001

01

1

10

124 126 128 13 132 134 136pH

70h90h

C05

(M)





0

1

2

3

4

5

6

0001 001 01 1 10

Num

ber o

f cor

rode

d sp

ecim

ens

Sodium nitrite

[Clminus] (molL)

01M pH 135 70h1M pH 135 90h



0

1

2

3

4

5

6

0001 001 01 1 10

Num

ber o

f cor

rode

d sp

ecim

ens

Calcium lactate

[Clminus] (molL)

01M pH 135 70h01M pH 135 90h





0

1

2

3

4

5

6

Num

ber o

f cor

rode

d sp

ecim

ens

Sodium aspartate

0001 001 01 1 10[Clminus] (molL)

01M pH 134 70h05M pH 132 90h










2film did not



3O4)













Fe2+ +OHminus +NO2









0001

001

01

1

10

124 126 128 13 132 134 136pH



C05

(M)

(a)

0001

001

01

1

10

124 126 128 13 132 134 136pH



C05

(M)

(b)



E

Epit

Eeq

ip


E polarization

log i


Occluded cell

Pit embryo

i

ith

ip

t



096

098

1

600160026003600

Tran

smitt

ance

FeOOHstretching


1120582 (cmminus1)

Fe Ca CO3 OH salts





096

098

1

600110016002100260031003600

Tran

smitt

ance

FeOOHstretching

1120582 (cmminus1)

Fe Ca CO3 OH salts



2

092

094

096

098

1

600110016002100260031003600

Tran

smitt

ance

1120582 (cmminus1)








096

098

1

600110016002100260031003600

Tran

smitt

ance

FeOOHstretching

1120582 (cmminus1)

Fe Ca CO3 OH salts






H

O OC

H O C

minus

CH3

Fe2O3 surface

(a)

OO

O

minusNH2

minusO

Fe2O3 surface

(b)

O

OH

HO O

Fe2O3 surface

OminusOminus

(c)








4 Conclusions









Acknowledgments


References



















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


0

1

2

3

4

5

6

Num

ber o

f cor

rode

d sp

ecim

ens

Sodium aspartate

0001 001 01 1 10[Clminus] (molL)

01M pH 134 70h05M pH 132 90h










2film did not



3O4)













Fe2+ +OHminus +NO2









0001

001

01

1

10

124 126 128 13 132 134 136pH



C05

(M)

(a)

0001

001

01

1

10

124 126 128 13 132 134 136pH



C05

(M)

(b)



E

Epit

Eeq

ip


E polarization

log i


Occluded cell

Pit embryo

i

ith

ip

t



096

098

1

600160026003600

Tran

smitt

ance

FeOOHstretching


1120582 (cmminus1)

Fe Ca CO3 OH salts





096

098

1

600110016002100260031003600

Tran

smitt

ance

FeOOHstretching

1120582 (cmminus1)

Fe Ca CO3 OH salts



2

092

094

096

098

1

600110016002100260031003600

Tran

smitt

ance

1120582 (cmminus1)








096

098

1

600110016002100260031003600

Tran

smitt

ance

FeOOHstretching

1120582 (cmminus1)

Fe Ca CO3 OH salts






H

O OC

H O C

minus

CH3

Fe2O3 surface

(a)

OO

O

minusNH2

minusO

Fe2O3 surface

(b)

O

OH

HO O

Fe2O3 surface

OminusOminus

(c)








4 Conclusions









Acknowledgments


References



















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


0001

001

01

1

10

124 126 128 13 132 134 136pH



C05

(M)

(a)

0001

001

01

1

10

124 126 128 13 132 134 136pH



C05

(M)

(b)



E

Epit

Eeq

ip


E polarization

log i


Occluded cell

Pit embryo

i

ith

ip

t



096

098

1

600160026003600

Tran

smitt

ance

FeOOHstretching


1120582 (cmminus1)

Fe Ca CO3 OH salts





096

098

1

600110016002100260031003600

Tran

smitt

ance

FeOOHstretching

1120582 (cmminus1)

Fe Ca CO3 OH salts



2

092

094

096

098

1

600110016002100260031003600

Tran

smitt

ance

1120582 (cmminus1)








096

098

1

600110016002100260031003600

Tran

smitt

ance

FeOOHstretching

1120582 (cmminus1)

Fe Ca CO3 OH salts






H

O OC

H O C

minus

CH3

Fe2O3 surface

(a)

OO

O

minusNH2

minusO

Fe2O3 surface

(b)

O

OH

HO O

Fe2O3 surface

OminusOminus

(c)








4 Conclusions









Acknowledgments


References



















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


096

098

1

600110016002100260031003600

Tran

smitt

ance

FeOOHstretching

1120582 (cmminus1)

Fe Ca CO3 OH salts



2

092

094

096

098

1

600110016002100260031003600

Tran

smitt

ance

1120582 (cmminus1)








096

098

1

600110016002100260031003600

Tran

smitt

ance

FeOOHstretching

1120582 (cmminus1)

Fe Ca CO3 OH salts






H

O OC

H O C

minus

CH3

Fe2O3 surface

(a)

OO

O

minusNH2

minusO

Fe2O3 surface

(b)

O

OH

HO O

Fe2O3 surface

OminusOminus

(c)








4 Conclusions









Acknowledgments


References



















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


H

O OC

H O C

minus

CH3

Fe2O3 surface

(a)

OO

O

minusNH2

minusO

Fe2O3 surface

(b)

O

OH

HO O

Fe2O3 surface

OminusOminus

(c)








4 Conclusions









Acknowledgments


References



















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of






Acknowledgments


References



















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of
























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of










Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

Documents

Effect of Organic Inhibitors on Chloride Corrosion of Steel Rebars in Alkaline Pore Solution