research article inhibiting effects of rabeprazole sulfide on...

Hindawi Publishing CorporationInternational Journal of ElectrochemistryVolume 2013 Article ID 714372 9 pageshttpdxdoiorg1011552013714372

Research ArticleInhibiting Effects of Rabeprazole Sulfide on the Corrosion ofMild Steel in Acidic Chloride Solution

M K Pavithra T V Venkatesha and M K Punith Kumar

Department of Chemistry School of Chemical Sciences Jnana Sahyadri Campus Kuvempu University ShankaraghattaKarnataka 577451 India

Correspondence should be addressed to T V Venkatesha drtvvenkateshayahoocouk

Received 18 February 2013 Revised 22 April 2013 Accepted 22 April 2013

Academic Editor Sheng S Zhang

Copyright copy 2013 M K Pavithra et al This 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 corrosion inhibition effect of Rabeprazole sulfide (RS) on mild steel in 1M hydrochloric acid (HCl) was investigated usingweight loss potentiodynamic polarization electrochemical impedance spectroscopy (EIS) and chronoamperometric measure-ments Protection efficiency of RS increases with the concentration and decreases with the rise in temperature Adsorption of RSonmild steel surface in 1MHCl follows Langmuir adsorption isothermThe kinetic and thermodynamic parameters governing theadsorption process were calculated and discussed The polarization results suggest that RS performed as an excellent mixed-typeinhibitor for mild steel corrosion in 1M HCl

1 Introduction

Mild steel is widely used in many industries due to its excelndashlent mechanical properties and low cost However it under-goes corrosion to a greater extent in acidic environmentAcids are employed in several industrial processes such asacid pickling cleaning acid descaling and oil well acidizingThe use of HCl in these processes is more economical effi-cient and trouble-free compared to other mineral acids [1]In order to avoid the base metal attack chemical inhibitorsare often used for these processes to control the metaldissolution The most well-known acid corrosion inhibitorsare the heterocyclic compounds containing nitrogen sulphurand oxygen atoms [2ndash5]

Generally inhibitors act through the process of surfaceadsorption and its adsorption depends on the nature andsurface charges on the metal the type of aggressive mediathe structure of inhibitor molecules and its interaction withthe metal surface [6] Previously large numbers of organiccompounds have been investigated as corrosion inhibitorsfor mild steel in HCl media [7ndash11] Even though thesecompounds show good anticorrosive action they are toxic innatureThis led investigations to focus on the development ofnontoxic corrosion inhibitors like drugs A few investigations

have been reported on the use of drugs such as cefazolin [1]Ampicillin [12] antifungal drugs [13] sulfa drugs [14] andrhodanine azosulpha drugs [15] as corrosion inhibitors Theinhibitory action of tramadol and tacrine onmild steel in 1MHCl has been reported by Prabhu et al [16] andNataraja et al[17]

Rabeprazole sulfide is the commercial name of (2-[[4-(3-Methoxypropoxy)-3-methylpyridine-2-yl]-methylthio]-1H-benzimidazole) It is ametabolite of an antiulcer drug Rabep-razole We have investigated the corrosion inhibition effectof this compound on mild steel in 05M H

2SO4media in a

previous article [18] However according to literature studythere is no report found on corrosion inhibition studies ofRabeprazole sulfide in HCl medium Hence the present workhas been carried out to examine the potential of Rabeprazolesulfide to control corrosion of mild steel in 1MHCl mediumThe aim of this study is to explore the use of Rabeprazolesulfide as an acid corrosion inhibitor for mild steel surface inHCl solution using weight loss potentiodynamic polariza-tion EIS and the chronoamperometric techniques Also thethermodynamic parameters for the adsorption process andactivation parameters for the mild steel dissolution reactionsare calculated and discussed

2 International Journal of Electrochemistry

2 Methods and Materials

The experiments were performed with mild steel specimenshaving the composition 004 C 035 Mn 0022 P and0036 S and the remainder being Fe which were used forweight loss as well as electrochemical studies The mild steelcoupons of dimension 4 cm times 2 cm times 01 cm were used forweight loss measurements and those of 1 cm2 area (exposed)with a 5 cm long stem isolated with araldite resin were usedfor electrochemical experiments Prior to each experimentthe mild steel samples were abraded with series of emerypapers of grade number 220 660 and 1200 followed bywashing in double distilled water and acetone and then dried

The aggressive solutions of 1M HCl were prepared usingAR grade chemicals and double distilled water The testinhibitor RSwas obtained fromRamdevChemicals India PvtLtd Mumbai and its structure is as shown in Figure 1 Thedesired concentrations of inhibitor solutions (005 01 05and 10mM) were prepared by dissolving specified amountof RS in 1M HCl solution

The weight loss of precleaned and dried mild steelspecimens were determined by weighing the metal samplesbefore and after immersing in 100 cm3 of 1M HCl in theabsence and presence of various concentration of RS at 303313 323 and 333K The experiments were performed intriplicate and the mean value is reported All experimentswere carried out in aerated and static conditions

The electrochemical measurements were conducted ina conventional glass cell using CHI 660C electrochemicalanalyzer (USA make) A mild steel specimen (of 1 cm2 area)a platinum electrode and a saturated calomel electrode wereused as working auxiliary and reference electrodes In caseof polarization and electrochemical impedance spectroscopicmeasurements (EIS) prior to each measurement a stabi-lization period of 30min was allowed to establish a steadystate open circuit potential (OCP) Each experiment wascarried out in triplicate and the average values of corrosionparameters are reported

The potentiodynamic polarization measurements werecarried out over a potential automatically from +200mV tominus200mV at OCP with a scan rate of 05mV sminus1 All thepotentials reported were with reference to SCE The corro-sion kinetic parameters such as corrosion potential (119864corr)corrosion current density (119868corr) and anodic (120573

119886)cathodic

(120573119888) Tafel slopes were generated from the software installed

in the instrument The EIS measurements were carried atOCP in the frequency range 1mHz to 100 kHz with 5mV sinewave as the excitation signal Impedance data were analyzedusing ZSimp-Win 321 software The chronoamperometricexperiments were performed by polarizing the workingelectrode anodically at minus041 V (SCE) for 600 s

3 Results and Discussion

31 Weight Loss Measurements Weight loss method is usedfor monitoring corrosion rate because of its simple applica-tion and reliability Weight loss of mild steel surface in 1MHClwas determined at 301ndash333K in the absence and presence

NH

N

S N

O OCH3

CH3

Figure 1 The chemical structure of RS

of different concentration of RS The obtained corrosionparameters are tabulated in Table 1 The corrosion rate (120592corr)of mild steel was determined using the relation

120592corr =Δ119898

119878119905

(1)

whereΔ119898 is the corrosionweight loss ofmild steel (g) 119878 is thesurface area of mild steel specimen (cm2) and 119905 is the time ofexposure

The percentage inhibition efficiency 120578119908()was calculated

using the relationship

120578119908() =

120592119900

corr minus 120592corr

120592119900

corrtimes 100 (2)

where 120592119900corr and 120592corr are the corrosion rates of mild steel inthe absence and presence of RS respectively

It can be seen from Table 1 that the 120592corr decreases andthe inhibition efficiency increases with the concentration ofthe inhibitor This is due to an increase in the amount ofadsorption and coverage of inhibitor onmild steel surface [1]It is also apparent from the table that the 120592corr increases andinhibition efficiency decreases with increasing the tempera-tureThis suggests the physisorption of the inhibitor onmetalsurface [19]The increase in 120592corr ismore pronounced at lowerconcentration of RS (005 and 01mM) However at higherconcentration (05 and 10mM) the temperature has very littleeffect on the 120592corr which can be attributed to slight change inthe nature of mode of adsorption where the chemisorptionaccompanied by physisorption may occur

311 Thermodynamic Parameters of the Adsorption IsothermBasic information on the interaction between the inhibitorand the mild steel surface can be provided by the adsorptionisotherm Hence in order to know the mode of adsorption ofRS on mild steel surface in 1M HCl at 303ndash333K attemptswere made to fit experimental data with several adsorp-tion isotherms like Langmuir Temkin Bockris-SwinkelsFreundlich and Flory-Huggins isotherms The best fit wasobtained with Langmuir isotherm given by the equation [20]

119862

120579

=

1

119870ads+ 119862 (3)

where 119862 is the molar concentration of inhibitor 119870ads is theequilibrium constant of adsorption process and 120579 is thedegree of surface coverage defined as 120578

119908()100 The plots

of 119862120579 against 119862 for the inhibitor were straight lines and aregiven in Figure 2 It is found that all the regression coefficients

International Journal of Electrochemistry 3

Table 1 Effect of temperature on the corrosion rate of mild steel in 1M HCl at different concentrations of RS

C (mM)

Temperature303K 313 K 323K 333K

120592corr(mg cmminus2 hminus1) 120578

119908() 120592corr

(mg cmminus2 hminus1) 120578119908() 120592corr


(mg cmminus2 hminus1) 120578119908()

Blank 085 248 808 1695005 033 6062 144 4212 611 2437 1473 130801 027 6835 121 5132 487 3967 1332 214105 014 8347 043 8248 153 8103 337 801210 007 9142 023 9076 082 8983 186 8902

Table 2 Thermodynamic parameters for the adsorption of RS in1M HCl on the mild steel at different temperatures

Temperature (K) Slope 1198772

119870ads (Mminus1) Δ119866ads (kJmolminus1)

303K 1065 0998 25000 minus3563

313K 1025 0999 12195 minus3494

323K 0953 0999 6536 minus3438

333K 0764 0981 3058 minus3333

0

02

04

06

08

1

12

0 02 04 06 08 1 12

(a) 119910 = 1065119909 + 0040

1198772 = 0998(b) 119910 = 1024119909 + 0082

1198772 = 0999(c) 119910 = 0953119909 + 0153

1198772 = 0999(d) 119910 = 0764119909 + 0327

1198772 = 0981

(a) 303K(b) 313K(c) 323K(d) 333K

119862120579

(mM

)

119862 (mM)

Figure 2 Langmuir adsorption isotherm for adsorption of RS onthe mild steel surface in 1M HCl

are very close to one which indicates that the adsorption ofRS on the mild steel surface in 1M HCl follows Langmuiradsorption isotherm

The 119870ads can be calculated from the intercepts of thestraight lines on the 119862120579 axis and it is related to the standardfree energy of adsorption (Δ119866119900ads) by the relation [21]

119870ads =1

555

exp(minusΔ119866119900

ads119877119879

) (4)

The obtained thermodynamic parameters are given inTable 2 The negative values of Δ119866119900ads indicate the sponta-neous adsorption of RS on mild steel surface [22] Also thehigh values of 119870ads suggest the strong adsorption ability ofRS on mild steel surface

It is generally accepted that the values of Δ119866119900

ads upto minus20 kJmolminus1 are consistent with physisorption and thevalues around minus40 kJmolminus1 or smaller are associated withchemisorption resulting from the sharing or transfer ofelectrons from organic molecule to the metal surface to forma coordinate bond [23] However the calculated Δ119866119900ads valuesare betweenminus20 kJmolminus1 andminus40 kJmolminus1This signifies thatthe adsorption of RS on mild steel in 1M HCl involves com-prehensive adsorption where physisorption accompanied bychemisorption will take place

Further the dependence of Δ119866119900ads on temperature can beexplained by two cases as follows [24]

(a) Δ119866119900ads may increase (become less negative) with theincrease in temperature which indicates the occur-rence of exothermic process

(b) Δ119866119900ads may decrease (become more negative) withincreasing the temperature indicating the occurrenceof endothermic process

It is clear from Table 2 that with the increase in the tem-perature Δ119866119900ads also increases and it specifies the corrosioninhibition of mild steel by RS is an exothermic process Herethe adsorption of RS on metal surface becomes unfavorablewith increasing the reaction temperature due to the desorp-tion of inhibitor from themild steel surface [25]The enthalpyof adsorption (Δ119867119900ads) and entropy of adsorption can beevaluated by the integrated version of the Vanrsquot Hoff equationexpressed as follows [26]

ln119870ads =minusΔ119867119900

ads119877119879

+

Δ119878119900

ads119877

+ ln 1

555

(5)

The variation of ln119870ads versus 1119879 gives a straight line(Figure 3) with the slope of (minusΔ119867119900ads119877) and intercept of(Δ119878119900ads119877 + ln 1555) The calculated values of Δ119867119900ads andminusΔ119878119900

ads are minus5876 kJmolminus1 and 76103 Jmolminus1 Kminus1 respec-tively


6

65

7

75

8

85

9

95

10

105

295 3 305 31 315 32 325 33 335

119910 = 7065119909 minus 1317

1198772 = 09963

ln119870

ads

(Mminus1)

1000119879 (Kminus1)

Figure 3 The relationship between ln119870ads and 1119879

300 305 310 315 320 325 330 335

119910 = 00764119909 minus 5887

1198772 = 09812

minus36

minus355

minus35

minus345

minus34

minus335

minus33

(kJ m

olminus1)

119879 (K)

ΔGo ad

s

Figure 4 The relationship Δ119866119900

ads of RS and temperature (119879)

On the other hand the enthalpy and entropy for theadsorption of RS on mild steel were also calculated using thethermodynamic equation [27]

Δ119866119900

ads = Δ119867119900

ads minus 119879Δ119878119900

ads (6)

A plot of Δ119866119900

ads against 119879 was linear (Figure 4) withthe slope equal to minusΔ119878

119900

ads and intercept of Δ119867119900

ads Theobtained values of Δ119867119900ads and minusΔ119878

119900

ads are minus5887 kJmolminus1 and76 Jmolminus1Kminus1 respectively

The negative values of Δ119867119900

ads reflect the exothermicbehavior of the adsorption of inhibitor on mild steel Gener-ally an exothermic adsorption process signifies either physis-orption or chemisorption while endothermic process isattributable to chemisorption [28] In an exothermic processboth physisorption and chemisorption can be distinguishedby considering the absolute value ofΔ119867119900ads For physisorptionprocess Δ119867119900ads is lower that is 40 kJmolminus1 while that forchemisorption approaches 100 kJmolminus1 [29] In the presentcase Δ119867119900ads is 5887 kJmolminus1 which is an intermediate caseclearly specifies the existence of both physical and chemi-cal adsorption Thus Δ119866119900ads and Δ119867

119900

ads values complement

Table 3 Activation parameters of dissolution reaction of mild steelin 1M HCl with RS at different concentrations

119862 (mM) 119860

(g cmminus2 hminus1)119864119886

lowast

(kJmolminus1)Δ119867lowast


(Jmolminus1 Kminus1)Blank 427 times 10

118522 8255 minus3134

005 1338 times 1015

10775 10509 3592

01 2512 times 1015

10983 10717 4090

05 2615 times 1015

11274 10999 4115

10 2695 times 1015

11448 11182 4149

295 3 305 31 315 32 325 33 335

minus10

minus9

minus8

minus7

minus6

minus5

minus4

minus3ln c

orr

(g cm

minus2

hminus1)

(a) Blank(b) 005mM(c) 01mM

(d) 05mM(e) 10mM

1000119879 (Kminus1)

Figure 5 Arrhenius plot for mild steel in 1M HCl solution with RSat different concentrations

each other As expected the values of Δ119878119900ads are negativebecause the exothermic adsorption process is associated withthe decrease of entropy Before adsorption the inhibitormolecules move freely in bulk solution and as the adsorp-tion progresses the adsorption of inhibitor molecules ontothe mild steel surface becomes more orderly resulting ina decrease in entropy [29] Moreover the values ofΔ119867119900ads andminusΔ119878119900

ads obtained by the two methods are in good agreement

312 Effect of Temperature To assess the effect of tempera-ture on corrosion and corrosion inhibition process weightloss experiments were carried out for mild steel in 1M HClat 303 313 323 and 333K in the absence and presence ofdifferent concentrations of RS Usually corrosion reactionsare regarded as Arrhenius processes and the 120592corr can beexpressed by the relation

ln 120592corr = ln119860 minus

119864lowast

119886

119877119879

(7)

where 120592corr is the corrosion rate 119864lowast

119886is the apparent activation

energy 119877 is the Universal gas constant (8314 J Kminus1molminus1) 119879is the absolute temperature and 119860 is the frequency factorThe Arrhenius plot is shown in Figure 5 and the plot ofln 120592corr against 1119879 gives straight lines with slope minus119864lowast

119886119877 and

the intercept of ln119860 The obtained values of 119864lowast119886and 119860 are

presented in Table 3


295 3 305 31 315 32 325 33 335

minus16

minus15

minus14

minus13

minus12

minus11

minus10

minus9


(d) 05mM(e) 10mM

119879(g

cmminus2

hminus1

Kminus1)

1000119879 (Kminus1)

ln120592

corr

Figure 6 Transition state plot for mild steel in 1M HCl solutionwith RS at different concentrations

The change in enthalpy (Δ119867lowast) and entropy (Δ119878

lowast) of

activation was calculated by the transition state equationgiven below

ln120592corr119879

= [ln 119877

119873ℎ

+

Δ119878lowast

119877

] minus

Δ119867lowast

119877119879

(8)

where ℎ is the Planckrsquos constant and 119873 is the Avogadrorsquosnumber The plot of ln 120592corr119879 against 1119879 for mild steelcorrosion in 1M HCl without and with RS is shown inFigure 6 Straight lines were obtained with slope of minusΔ119867lowast119877and intercept of [ln119877119873ℎ+Δ119878

lowast119877) from which the values of

Δ119867lowast and Δ119878

lowast were calculated and tabulated in Table 3It is evident from the table that both the119864lowast

119886and frequency

factor values with increasing concentration of RS and the119864lowast

119886in the inhibited solution are higher than those in the

uninhibited solution The higher value of 119864lowast119886in presence

of RS can be attributed to an increase in the thickness ofdouble layer which increases the 119864

lowast

119886for corrosion process

[17]The119864lowast119886for the corrosion process both in the absence and

presence of inhibitor is greater than 20 kJmolminus1 and hencethe entire process is controlled by surface reaction [30]Theseresults disclose that the corrosion reaction of mild steel isinhibited by RS

Based on the temperature effects the relationshipsbetween the temperature dependence of 120578

119908() of an inhibitor

and the 119864lowast119886can be classified into three groups [31]

(1) 120578119908() decreases with the increase in temperature 119864lowast

119886

(inhibited solution) gt 119864lowast

119886(uninhibited solution)

(2) 120578119908() increases with the increase in temperature 119864lowast

119886

(inhibited solution) lt 119864lowast


(3) 120578119908() does not change with temperature 119864lowast

119886(inhib-

ited solution) = 119864lowast


In the present case 120578119908() decreases with the increase

in temperature and hence 119864lowast

119886(inhibited solution) gt 119864

lowast

119886

minus07 minus06 minus05 minus04 minus03 minus02

minus7

minus6

minus5

minus4

minus3

minus2

minus1

119864 versus SCE (V)

log119894

(A cm

minus2)

Blank005mM01mM

05mM10mM

Figure 7 Polarisation curves for mild steel in 1M HCl in thepresence of various concentrations of RS

(uninhibited solution) This suggests the physisorption Butin some cases the chemical adsorption is accepted as themostprobable type of adsorption although inhibition efficiencydecreases with rising the temperature and 119864

lowast

119886is higher

than that in the absence of inhibitor [32] The activationparameters (Δ119867lowast and Δ119878lowast) of mild steel dissolution reactionin 1M HCl in the presence of RS are higher than those in theabsence of inhibitor The positive values of enthalpy reflectthe endothermic nature of mild steel dissolution processTheaverage difference value of the 119864

lowast

119886minus Δ119867

lowast is 266 kJmolminus1which is approximately equal to the average value of 119877119879(2685 kJmolminus1) at 323K This infers that the corrosionprocess is an unimolecular reaction which is characterized bythe following equation [25]

119864lowast

119886minus Δ119867

lowast= 119877119879 (9)

The positive values of Δ119878lowast in the presence of inhibitorimply that the rate determining step for the activated complexis dissociation step rather than an association meaning thatthe adsorption process is accompanied by an increase inentropy which is the driving force for the adsorption ofinhibitor molecules on the mild steel surface [33]

32 Electrochemical Measurements

321 Polarisation Measurements The influence of RS on thecathodic and anodic potentiodynamic polarization curves ofmild steel in 1MHCl at 303K is shown in Figure 7The corro-sion kinetic parameters such as corrosion potential (119864corr)corrosion current density (119868corr) and anodic (120573

119886)cathodic

(120573119888) Tafel slopes are presented in Table 4 The percentage


Table 4 Polarization parameters ofmild steel in 1MHCl containingdifferent concentrations of RS

119862

(mM)minus119864corr(mV)

120573119888

(mV decminus1)120573119886

(mV decminus1)119868corr

(120583A cmminus2)120578119879

()Blank 494 14050 7751 1656

005 490 11630 5648 6548 6051

01 486 14916 7638 5992 6381

05 475 13106 6740 3258 8033

10 462 12637 6344 1654 9001

inhibition efficiency 120578119879() was computed from (119868corr) values

using the following expression

120578119879() =

119868119900


119868119900

corrtimes 100 (10)

where 119868119900

corr and 119868corr are the corrosion current densitieswithout and with RS respectively

As it can be seen from the polarization result the 119868119900

corrdecreases and 120578

119879() increases with increasing inhibitor

concentration This confirms the corrosion inhibition actionof RS Moreover the cathodic and anodic Tafel slope valueschanged with the inhibitor concentration indicating thatRS controlled both the cathodic hydrogen evolution andanodic mild steel dissolution reactions It can be seen thatthe addition of RS to 1M HCl shifted the 119864corr values tomore positive direction and also the anodic and cathodicbranches of polarization curves of pure acid solution towardslower current densities An inhibitor can be classified as ananodic or cathodic type when the change in 119864corr value islarger than 85mV [34] But the largest displacement exhibitedby RS was 32mV versus SCE and hence it acts as a mixed-type inhibitor So it can be concluded that RS behaves as amixed-type inhibitor by inhibiting both anodic and cathodicreactions

322 Electrochemical Impedance SpectroscopicMeasurementsEIS has beenwidely used in investigating corrosion inhibitionprocess since it provides more information on both theresistive and capacitive behavior at metalsolution interfaceThe corrosion behavior of mild steel in 1M HCl with andwithout RS at 303K was investigated using this techniqueand the obtained impedance data represented as Nyquist andBode plots in Figures 8 and 9 respectively Both these figuresendorse that the impedance response of mild steel increasesby the addition of RS

The impedance spectra (Figure 8) exhibit single semicir-cle which can be attributed to the charge transfer that takesplace at electrodesolution interface and this process controlsthe corrosion of mild steel The presence of RS does notchange the mechanism of mild steel dissolution [35] Dueto frequency dispersion the Nyquist plots are not perfectsemicircle which is attributed to surface inhomogeneity androughness [36]

The EIS results are simulated using the electrochemi-cal equivalent circuit shown by the inset of Figure 8 The

0 200 400 600 800 1000

0

200

400

600

800

1000

119885real (Ω cm2)

minus119885

img

(Ωcm

2) 119877ct

Rs

Blank005mM01mM

05mM10mM

119876

Figure 8 Nyquist plot (solid line shows fitted results) of mild steelin 1MHCl solution without and with different concentrations of RS

00

05

10

15

20

25

30

0 1 2 3 4

0

Phas

e ang

le (d

eg)

5minus2 minus1

minus20

minus40

minus60

minus80

log frequency (Hz)

log

IZI (Ω

cm2)

Blank005mM01mM

05mM10mM

Figure 9 Bode plots of mild steel in 1M HCl solution without andwith different concentrations of RS

equivalent circuit composed of the solution resistance (119877119904)

the charge transfer resistance (119877ct) and the constant phaseelement (CPE) which describes the interfacial double layerThe impedance of CPE can be represented as follows

119885CPE = 119876minus1(119895120596)minus119899

(11)

where 119876 is the CPE constant 120596 is the angular frequency1198952= minus1 is the imaginary number and 119899 represents phase


Table 5 Electrochemical impedance parameters of mild steel in 1MHCl containing different concentrations of RS

119862

(mM)119877ct

(Ω cm2)119876

(120583Ωminus1 S119899 cmminus2) 119899119862dl

(120583F cmminus2) 120578119911()

Blank 85 11520 0863 5527

005 2093 9214 0870 5097 5933

01 2548 8909 0864 4912 6667

05 4982 7324 0856 4198 8293

10 8296 3162 0877 1896 8976

0 100 200 300 400 500 6000000

0002

0004

0006

0008

0010

Time (s)

Curr

ent (

A)

(e)

(d)

(c) (b)

(a)


(d) 05mM(e) 10mM

Figure 10 Chronoamperometric curves of mild steel in 1M HClwithout and with different concentrations of RS

shift which gives details about the degree of surface inhomo-geneity resulting from surface roughness inhibitor adsorp-tion porous layer formation and so forth [37]

Further the double layer capacitance (119862dl) can be calcu-lated by the relation

(119862dl) = (1198761198771minus119899

ct )

1119899

(12)

The values of impedance parameters derived fromNyquist plots for corrosion of mild steel in 1M HCl inthe absence and presence of RS are tabulated in Table 5The inhibition efficiency 120578

119885() was evaluated from charge

transfer resistance (119877ct) values using the following equation

120578119885() =

119877ct minus 119877119900

ct119877ct

times 100 (13)

where 119877119900ct and 119877ct are the charge transfer resistances withoutand with RS respectively

It is clear from Table 5 that by increasing the concen-tration of inhibitor 119876 and 119862dl decrease and 119877ct increasesThe decrease in 119862dl and 119876 values can be attributed to a

decrease in local dielectric constant andor an increase in thethickness of electrical double layer Meanwhile the increasein 119877ct indicates the increase in the extent of adsorption ofinhibitormolecules and also the adsorbed RSmolecules forma protective film on the mild steel surface which becomesa barrier to hinder the mass and charge transfer processes[6] In Figure 9 only one time constant was observed andthe phase angle increases with increasing concentration ofRS This signifies the decrease in surface inhomogeneity[38] As a result the protection efficiency increases byincreasing the concentration of RS The obtained valuesof inhibition efficiency are in good agreement with thoseobtained from weight loss and potentiodynamic polarizationmeasurements

323 Chronoamperometric Measurements The ability of RSto inhibit anodic processes of mild steel was investigatedby the chronoamperometricmeasurementsThe experimentswere carried out by polarizing anodically the electrodepotential at minus041 V (versus SCE) for 600 s The currentdensity values obtained during the electrooxidation of mildsteel were recorded in 1MHCl in the absence and presence ofdifferent concentrations of RS and the chronoamperometriccurves are depicted in Figure 10 By the addition of RS thecurrent density get reduced and the reduction in the current ismore pronounced in 1mM solution compared to uninhibitedsolution This confirms that the rate of mild steel dissolutiondecreases in the presence of RS in 1M HCl

33 Mechanism of Inhibition Based on the experimentalresults obtained we could propose a probable mechanism forcorrosion inhibition behavior of RS in 1M HCl The pola-rization data suggested the mixed inhibition mechanism ofRS

In acidic media RS might be protonated as follows

RS + 119899H+ 997888rarr [RSH119899]119899+

(14)

The cationic forms of RS may be adsorbed directly at thecathodic sites and hinder the hydrogen evolution reactionIn acid solutions mild steel possesses positive charge atthe corrosion potential The chloride ions present in thesolution get adsorbed on metal surface by creating an excessnegative charge towards solution and it favors the adsorptionof protonated inhibitor molecules on metal surface throughelectrostatic attraction [39 40] Therefore the protonated RSmolecules get adsorbed on mild steel surface by means ofelectrostatic interaction between chloride ions and inhibitorcations Simultaneously RS may also adsorb at anodic sitesof metal surface via chemisorption mechanism by sharingelectrons of S N and O atoms and also by donor acceptorinteractions between 120587-electrons of methyl pyridine ringbenzimidazole ring and vacant d orbital of iron [3 41] Byfollowing the above mechanism RS shows mixed inhibitionbehavior by inhibiting cathodic hydrogen evolution andanodic mild steel dissolution reactions

Oguzie et al reported that sulphur containing substancesprefers chemisorption on metal surface in acidic mediawhereas nitrogen containing compounds tends to favor


physisorption [42] However RS molecule is composed ofboth N and S atoms and hence it prefers physisorptionaccompanied by chemisorption which is also supported bythermodynamic calculations

Even though RS shows mixed inhibition behavior viacomprehensive adsorption in bothH

2SO4andHCl solutions

the performance of inhibitor is not of equal importance in1M HCl compared to 05M H

2SO4 In the previous work it

has been reported that RS shows 98 inhibition efficiency at1mM concentration in 05M H

2SO4but in the present work

it shows nearly 90 efficiency in 1MHClThis may be due tothe availability of more sites on the metal surface in sulphuricacid solution because of lesser adsorption of sulfate ions onthe mild steel surface [43] but RS is an effective inhibitor in1MHCl alsoThe effectiveness of RS is due to the presence ofelectron donating S two O and three N atoms as well as the120587-electrons of methyl pyridine and benzimidazole rings

4 Conclusion

The results reveal that RS is an efficient acid corrosion inhibi-tor for mild steel in 1M HCl It acts as a mixed-type inhibi-tor by inhibiting both anodic and cathodic reactionsThe cor-rosion rate decreases with inhibitor concentration andincreases with the temperature The adsorption of RS followsthe Langmuir adsorption isothermmodel and the adsorptionis spontaneous and exothermic process The kinetic andthermodynamic parameters of corrosion and adsorptionprocesses are determined The results obtained from weightloss measurements are comparable with those obtained fromelectrochemical measurements

Acknowledgments

The authors are grateful to the authorities of the Departmentof Chemistry Kuvempu University Karnataka India forproviding lab facilities They also thank the Department ofScience and Technology New Delhi Government of India(DST Project Sanction no 100IFD19242008-2009 datedJuly 2 2008) for providing instrumental facilities

References

[1] A K Singh and M A Quraishi ldquoEffect of Cefazolin on thecorrosion of mild steel in HCl solutionrdquo Corrosion Science vol52 no 1 pp 152ndash160 2010

[2] A Doner R Solmaz M Ozcan and G Kardas ldquoExperimentaland theoretical studies of thiazoles as corrosion inhibitors formild steel in sulphuric acid solutionrdquo Corrosion Science vol 53no 9 pp 2902ndash2913 2011

[3] Z Tao S Zhang W Li and B Hou ldquoAdsorption and inhi-bitory mechanism of 1H-1 2 4-triazol-l-yl-methyl-2-(4-chlorophenoxy) acetate on corrosion of mild steel in acidicsolutionrdquo Industrial and Engineering Chemistry Research vol50 no 10 pp 6082ndash6088 2011

[4] M Lebrini F Robert H Vezin and C Roos ldquoElectrochemicaland quantum chemical studies of some indole derivatives ascorrosion inhibitors for C38 steel in molar hydrochloric acidrdquoCorrosion Science vol 52 no 10 pp 3367ndash3376 2010

[5] F Bentiss M Lebrini M Traisnel and M Lagrenee ldquoSyn-ergistic effect of iodide ions on inhibitive performance of25-bis(4-methoxyphenyl)-134-thiadiazole during corrosionof mild steel in 05 M sulfuric acid solutionrdquo Journal of AppliedElectrochemistry vol 39 no 8 pp 1399ndash1407 2009

[6] W Chen H Q Luo and N B Li ldquoInhibition effects of 2 5-dimercapto-1 3 4-thiadiazole on the corrosion of mild steel insulphuric acid solutionrdquo Corrosion Science vol 53 no 10 pp3356ndash3365 2011

[7] K M Govindaraju D Gopi and L Kavitha ldquoInhibiting effectsof 4-amino-antipyrine based schiff base derivatives on thecorrosion of mild steel in hydrochloric acidrdquo Journal of AppliedElectrochemistry vol 39 no 12 pp 2345ndash2352 2009

[8] XWangH Yang and FWang ldquoAn investigation of benzimida-zole derivative as corrosion inhibitor for mild steel in differentconcentration HCl solutionsrdquo Corrosion Science vol 53 no 1pp 113ndash121 2011

[9] P LowmunkhongDUngthararak and P Sutthivaiyakit ldquoTryp-tamine as a corrosion inhibitor ofmild steel in hydrochloric acidsolutionrdquo Corrosion Science vol 52 no 1 pp 30ndash36 2010

[10] A Singh E E Ebenso and M A Quraishi ldquoCorrosion inhi-bition of carbon steel in HCl solution by some plant extractsrdquoInternational Journal of Corrosion vol 2012 Article ID 89743020 pages 2012

[11] D Ben Hmamou R Salghi A Zarrouk et al ldquoCorrosion inhi-bition of steel in 1M hydrochloric acid medium by chamomileessential oilsrdquo International Journal of Electrochemical Sciencevol 7 pp 2361ndash2373 2012

[12] NO Eddy E E Ebenso andU J Ibok ldquoAdsorption synergisticinhibitive effect and quantum chemical studies of ampicillin(AMP) and halides for the corrosion of mild steel in H 2SO4rdquoJournal of Applied Electrochemistry vol 40 no 2 pp 445ndash4562010

[13] I B Obot N O Obi-Egbedi and S A Umoren ldquoAntifungaldrugs as corrosion inhibitors for aluminium in 01 M HClrdquoCorrosion Science vol 51 no 8 pp 1868ndash1875 2009

[14] M M El-Naggar ldquoCorrosion inhibition of mild steel in acidicmedium by some sulfa drugs compoundsrdquo Corrosion Sciencevol 49 no 5 pp 2226ndash2236 2007

[15] M Abdallah ldquoRhodanine azosulpha drugs as corrosion inhibi-tors for corrosion of 304 stainless steel in hydrochloric acidsolutionrdquo Corrosion Science vol 44 no 4 pp 717ndash728 2002

[16] R A Prabhu A V Shanbhag and T V Venkatesha ldquoInfluenceof tramadol [2-[(dimethylamino)methyl]-1-(3-methoxyphenyl)cyclohexanol hydrate] on corrosion inhibition of mild steel inacidic mediardquo Journal of Applied Electrochemistry vol 37 no 4pp 491ndash497 2007

[17] S E Nataraja T V Venkatesha and H C Tandon ldquoCom-putational and experimental evaluation of the acid corrosioninhibition of steel by tacrinerdquoCorrosion Science vol 60 pp 214ndash223 2012

[18] M K Pavithra T V Venkatesha M K Punith Kumar and HC Tandon ldquoInhibition of mild steel corrosion by Rabeprazolesulfiderdquo Corrosion Science vol 60 pp 104ndash111 2012

[19] A Popova E Sokolova S Raicheca and M Christov ldquoAC andDC study of the temperature effect on mild steel corrosionin acid media in the presence of benzimidazole derivativesrdquoCorrosion Science vol 45 no 1 pp 33ndash58 2003

[20] M Liang H Zhou Q Huang S Hu and W Li ldquoSynergisticeffect of polyethylene glycol 600 and polysorbate 20 on corro-sion inhibition of zinc anode in alkaline batteriesrdquo Journal ofApplied Electrochemistry vol 41 no 8 pp 991ndash997 2011


[21] M A Quraishi M Z A Rafiquee S Khan and N SaxenaldquoCorrosion inhibition of aluminium in acid solutions by someimidazoline derivativesrdquo Journal of Applied Electrochemistryvol 37 no 10 pp 1153ndash1162 2007

[22] D Gopi K M Govindaraju and L Kavitha ldquoInvestigation oftriazole derived Schiff bases as corrosion inhibitors for mildsteel in hydrochloric acid mediumrdquo Journal of Applied Electro-chemistry vol 40 no 7 pp 1349ndash1356 2010

[23] R Laamari J Benzakour F Berrekhis A Abouelfida ADerja and D Villemin ldquoCorrosion inhibition of carbon steelin hydrochloric acid 05M by hexa methylene diamine tetra-methyl-phosphonic acidrdquo Arabian Journal of Chemistry vol 4no 3 pp 271ndash277 2011

[24] E A Noor ldquoTemperature effects on the corrosion inhibition ofmild steel in acidic Solutions by aqueos extract of Fenugreekleavesrdquo International Journal of Electrochemical Science vol 2pp 996ndash1017 2007

[25] A Ostovari S M Hoseinieh M Peikari S R Shadizadehand S J Hashemi ldquoCorrosion inhibition of mild steel in 1M HCl solution by henna extract a comparative study of theinhibition by henna and its constituents (Lawsone Gallic acid120572-d-Glucose and Tannic acid)rdquo Corrosion Science vol 51 no 9pp 1935ndash1949 2009

[26] E A Noor ldquoPotential of aqueous extract of Hibiscus sabdariffaleaves for inhibiting the corrosion of aluminum in alkalinesolutionsrdquo Journal of Applied Electrochemistry vol 39 no 9 pp1465ndash1475 2009

[27] A M Badiea and K N Mohana ldquoEffect of temperatureand fluid velocity on corrosion mechanism of low carbonsteel in presence of 2-hydrazino-47-dimethylbenzothiazole inindustrial water mediumrdquo Corrosion Science vol 51 no 9 pp2231ndash2241 2009

[28] M G Hosseini H Khalilpur S Ershad and L SaghatforoushldquoProtection of mild steel corrosion with new thia-derivativeSalens in 0 5 M H

2SO4rdquo Journal of Applied Electrochemistry

vol 40 pp 215ndash223 2009[29] G Mu X Li and G Liu ldquoSynergistic inhibition between tween

60 and NaCl on the corrosion of cold rolled steel in 0 5 Msulfuric acidrdquo Corrosion Science vol 47 no 8 pp 1932ndash19522005

[30] A S Fouda F E Heakal and M S Radwan ldquoRole of somethiadiazole derivatives as inhibitors for the corrosion of C-steelin 1 M H

2SO4rdquo Journal of Applied Electrochemistry vol 39 no

3 pp 391ndash402 2009[31] A R S Priya V S Muralidharam and A Subramania ldquoDevel-

opment of novel acidizing inhibitors for carbon steel corrosionin 15 boiling hydrochloric acidrdquo Corrosion vol 64 no 6 pp541ndash552 2008

[32] A Y Musa A A Amir H Kadhum et al ldquoOn the inhibition ofmild steel corrosion by 4-amino-5-phenyl-4H-1 2 4-trizole-3-thiolrdquo Corrosion Science vol 52 no 2 pp 526ndash533 2010

[33] NOObi-Egbedi and I BObot ldquoInhibitive properties thermo-dynamic and quantum chemical studies of alloxazine on mildsteel corrosion in H

2SO4rdquo Corrosion Science vol 53 no 1 pp

263ndash275 2011[34] W Li Q He S Zhang C Pei and B Hou ldquoSome new tria-

zole derivatives as inhibitors for mild steel corrosion in acidicmediumrdquo Journal of Applied Electrochemistry vol 38 no 3 pp289ndash295 2008

[35] X Li S Deng H Fui and G Mu ldquoSynergistic inhibition effectof rare earth cerium(IV) ion and sodiumoleate on the corrosion

of cold rolled steel in phosphoric acid solutionrdquo CorrosionScience vol 52 no 4 pp 1167ndash1178 2010

[36] M Lebrini F Robert and C Roos ldquoAlkaloids extract fromPalicourea guianensis plant as corrosion inhibitor for C38 steelin 1 M hydrochloric acid mediumrdquo International Journal ofElectrochemical Science vol 6 no 3 pp 847ndash859 2011

[37] Z Wu Z Fang L Qiu et al ldquoSynergistic inhibition betweenthe gemini surfactant and bromide ion for steel corrosion insulphuric acidrdquo Journal of Applied Electrochemistry vol 39 no6 pp 779ndash784 2009

[38] S S A Rehim O A Hazzazi M A Amin and K F KhaledldquoOn the corrosion inhibition of low carbon steel in concentratedsulphuric acid solutions Part I chemical and electrochemical(AC and DC) studiesrdquo Corrosion Science vol 50 no 8 pp2258ndash2271 2008

[39] M K Pavithra T V Venkatesha M K Punith Kumar and BS Shylesha ldquoAcalypha torta leaf extract as green corrosion inhi-bitor formild steel in hydrochloric acid solutionrdquo Industrial andEngineeringChemistry Research vol 52 no 2 pp 722ndash728 2013

[40] M K Pavithra T V Venkatesha K Vathsala and K O NayanaldquoSynergistic effect of halide ions on improving corrosion inhi-bition behaviour of benzisothiozole-3-piperizine hydrochlorideon mild steel in 05M H

2SO4mediumrdquo Corrosion Science vol

52 no 11 pp 3811ndash3819 2010[41] X Li S Deng H Fui and G Mu ldquoInhibition effect of 6-benzy-

laminopurine on the corrosion of cold rolled steel in H2SO4

solutionrdquo Corrosion Science vol 51 no 3 pp 620ndash634 2009[42] E E Oguzie Y Li and F H Wang ldquoCorrosion inhibition and

adsorption behavior of methionine on mild steel in sulfuricacid and synergistic effect of iodide ionrdquo Journal of Colloid andInterface Science vol 310 no 1 pp 90ndash98 2007

[43] I Ahamad and M A Quraishi ldquoBis (benzimidazol-2-yl) disul-phide an efficient water soluble inhibitor for corrosion of mildsteel in acid mediardquo Corrosion Science vol 51 no 9 pp 2006ndash2013 2009

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


2 Methods and Materials

The experiments were performed with mild steel specimenshaving the composition 004 C 035 Mn 0022 P and0036 S and the remainder being Fe which were used forweight loss as well as electrochemical studies The mild steelcoupons of dimension 4 cm times 2 cm times 01 cm were used forweight loss measurements and those of 1 cm2 area (exposed)with a 5 cm long stem isolated with araldite resin were usedfor electrochemical experiments Prior to each experimentthe mild steel samples were abraded with series of emerypapers of grade number 220 660 and 1200 followed bywashing in double distilled water and acetone and then dried

The aggressive solutions of 1M HCl were prepared usingAR grade chemicals and double distilled water The testinhibitor RSwas obtained fromRamdevChemicals India PvtLtd Mumbai and its structure is as shown in Figure 1 Thedesired concentrations of inhibitor solutions (005 01 05and 10mM) were prepared by dissolving specified amountof RS in 1M HCl solution

The weight loss of precleaned and dried mild steelspecimens were determined by weighing the metal samplesbefore and after immersing in 100 cm3 of 1M HCl in theabsence and presence of various concentration of RS at 303313 323 and 333K The experiments were performed intriplicate and the mean value is reported All experimentswere carried out in aerated and static conditions

The electrochemical measurements were conducted ina conventional glass cell using CHI 660C electrochemicalanalyzer (USA make) A mild steel specimen (of 1 cm2 area)a platinum electrode and a saturated calomel electrode wereused as working auxiliary and reference electrodes In caseof polarization and electrochemical impedance spectroscopicmeasurements (EIS) prior to each measurement a stabi-lization period of 30min was allowed to establish a steadystate open circuit potential (OCP) Each experiment wascarried out in triplicate and the average values of corrosionparameters are reported

The potentiodynamic polarization measurements werecarried out over a potential automatically from +200mV tominus200mV at OCP with a scan rate of 05mV sminus1 All thepotentials reported were with reference to SCE The corro-sion kinetic parameters such as corrosion potential (119864corr)corrosion current density (119868corr) and anodic (120573

119886)cathodic

(120573119888) Tafel slopes were generated from the software installed

in the instrument The EIS measurements were carried atOCP in the frequency range 1mHz to 100 kHz with 5mV sinewave as the excitation signal Impedance data were analyzedusing ZSimp-Win 321 software The chronoamperometricexperiments were performed by polarizing the workingelectrode anodically at minus041 V (SCE) for 600 s

3 Results and Discussion

31 Weight Loss Measurements Weight loss method is usedfor monitoring corrosion rate because of its simple applica-tion and reliability Weight loss of mild steel surface in 1MHClwas determined at 301ndash333K in the absence and presence

NH

N

S N

O OCH3

CH3

Figure 1 The chemical structure of RS

of different concentration of RS The obtained corrosionparameters are tabulated in Table 1 The corrosion rate (120592corr)of mild steel was determined using the relation

120592corr =Δ119898

119878119905

(1)

whereΔ119898 is the corrosionweight loss ofmild steel (g) 119878 is thesurface area of mild steel specimen (cm2) and 119905 is the time ofexposure

The percentage inhibition efficiency 120578119908()was calculated

using the relationship

120578119908() =

120592119900


120592119900

corrtimes 100 (2)

where 120592119900corr and 120592corr are the corrosion rates of mild steel inthe absence and presence of RS respectively

It can be seen from Table 1 that the 120592corr decreases andthe inhibition efficiency increases with the concentration ofthe inhibitor This is due to an increase in the amount ofadsorption and coverage of inhibitor onmild steel surface [1]It is also apparent from the table that the 120592corr increases andinhibition efficiency decreases with increasing the tempera-tureThis suggests the physisorption of the inhibitor onmetalsurface [19]The increase in 120592corr ismore pronounced at lowerconcentration of RS (005 and 01mM) However at higherconcentration (05 and 10mM) the temperature has very littleeffect on the 120592corr which can be attributed to slight change inthe nature of mode of adsorption where the chemisorptionaccompanied by physisorption may occur

311 Thermodynamic Parameters of the Adsorption IsothermBasic information on the interaction between the inhibitorand the mild steel surface can be provided by the adsorptionisotherm Hence in order to know the mode of adsorption ofRS on mild steel surface in 1M HCl at 303ndash333K attemptswere made to fit experimental data with several adsorp-tion isotherms like Langmuir Temkin Bockris-SwinkelsFreundlich and Flory-Huggins isotherms The best fit wasobtained with Langmuir isotherm given by the equation [20]

119862

120579

=

1

119870ads+ 119862 (3)

where 119862 is the molar concentration of inhibitor 119870ads is theequilibrium constant of adsorption process and 120579 is thedegree of surface coverage defined as 120578

119908()100 The plots

of 119862120579 against 119862 for the inhibitor were straight lines and aregiven in Figure 2 It is found that all the regression coefficients



C (mM)



119908() 120592corr




Blank 085 248 808 1695005 033 6062 144 4212 611 2437 1473 130801 027 6835 121 5132 487 3967 1332 214105 014 8347 043 8248 153 8103 337 801210 007 9142 023 9076 082 8983 186 8902




303K 1065 0998 25000 minus3563

313K 1025 0999 12195 minus3494

323K 0953 0999 6536 minus3438

333K 0764 0981 3058 minus3333

0

02

04

06

08

1

12

0 02 04 06 08 1 12

(a) 119910 = 1065119909 + 0040

1198772 = 0998(b) 119910 = 1024119909 + 0082

1198772 = 0999(c) 119910 = 0953119909 + 0153

1198772 = 0999(d) 119910 = 0764119909 + 0327

1198772 = 0981

(a) 303K(b) 313K(c) 323K(d) 333K

119862120579

(mM

)

119862 (mM)




119870ads =1

555


ads119877119879

) (4)








ln119870ads =minusΔ119867119900

ads119877119879

+

Δ119878119900

ads119877

+ ln 1

555

(5)




6

65

7

75

8

85

9

95

10

105

295 3 305 31 315 32 325 33 335

119910 = 7065119909 minus 1317

1198772 = 09963

ln119870

ads

(Mminus1)

1000119879 (Kminus1)


300 305 310 315 320 325 330 335

119910 = 00764119909 minus 5887

1198772 = 09812

minus36

minus355

minus35

minus345

minus34

minus335

minus33

(kJ m

olminus1)

119879 (K)

ΔGo ad

s




Δ119866119900

ads = Δ119867119900

ads minus 119879Δ119878119900

ads (6)

A plot of Δ119866119900


119900



119900




119900



119862 (mM) 119860


lowast




118522 8255 minus3134

005 1338 times 1015

10775 10509 3592

01 2512 times 1015

10983 10717 4090

05 2615 times 1015

11274 10999 4115

10 2695 times 1015

11448 11182 4149

295 3 305 31 315 32 325 33 335

minus10

minus9

minus8

minus7

minus6

minus5

minus4

minus3ln c

orr

(g cm

minus2

hminus1)


(d) 05mM(e) 10mM

1000119879 (Kminus1)






119864lowast

119886

119877119879

(7)




119886119877 and




295 3 305 31 315 32 325 33 335

minus16

minus15

minus14

minus13

minus12

minus11

minus10

minus9


(d) 05mM(e) 10mM

119879(g

cmminus2

hminus1

Kminus1)

1000119879 (Kminus1)

ln120592

corr



lowast) of


ln120592corr119879

= [ln 119877

119873ℎ

+

Δ119878lowast

119877

] minus

Δ119867lowast

119877119879

(8)





119886and frequency





lowast








119886




119886




119886(inhib-






lowast

119886


minus7

minus6

minus5

minus4

minus3

minus2

minus1


log119894

(A cm

minus2)

Blank005mM01mM

05mM10mM



lowast

119886is higher


lowast

119886minus Δ119867


119864lowast

119886minus Δ119867

lowast= 119877119879 (9)




119886)cathodic




119862


120573119888

(mV decminus1)120573119886


(120583A cmminus2)120578119879

()Blank 494 14050 7751 1656

005 490 11630 5648 6548 6051

01 486 14916 7638 5992 6381

05 475 13106 6740 3258 8033

10 462 12637 6344 1654 9001



120578119879() =

119868119900


119868119900

corrtimes 100 (10)

where 119868119900









0 200 400 600 800 1000

0

200

400

600

800

1000

119885real (Ω cm2)

minus119885

img

(Ωcm

2) 119877ct

Rs

Blank005mM01mM

05mM10mM

119876


00

05

10

15

20

25

30

0 1 2 3 4

0

Phas

e ang

le (d

eg)

5minus2 minus1

minus20

minus40

minus60

minus80

log frequency (Hz)

log

IZI (Ω

cm2)

Blank005mM01mM

05mM10mM




119885CPE = 119876minus1(119895120596)minus119899

(11)




119862

(mM)119877ct

(Ω cm2)119876


(120583F cmminus2) 120578119911()

Blank 85 11520 0863 5527

005 2093 9214 0870 5097 5933

01 2548 8909 0864 4912 6667

05 4982 7324 0856 4198 8293

10 8296 3162 0877 1896 8976

0 100 200 300 400 500 6000000

0002

0004

0006

0008

0010

Time (s)

Curr

ent (

A)

(e)

(d)

(c) (b)

(a)


(d) 05mM(e) 10mM




(119862dl) = (1198761198771minus119899

ct )

1119899

(12)




120578119885() =

119877ct minus 119877119900

ct119877ct

times 100 (13)







RS + 119899H+ 997888rarr [RSH119899]119899+

(14)












4 Conclusion


Acknowledgments


References
































































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



C (mM)



119908() 120592corr




Blank 085 248 808 1695005 033 6062 144 4212 611 2437 1473 130801 027 6835 121 5132 487 3967 1332 214105 014 8347 043 8248 153 8103 337 801210 007 9142 023 9076 082 8983 186 8902




303K 1065 0998 25000 minus3563

313K 1025 0999 12195 minus3494

323K 0953 0999 6536 minus3438

333K 0764 0981 3058 minus3333

0

02

04

06

08

1

12

0 02 04 06 08 1 12

(a) 119910 = 1065119909 + 0040

1198772 = 0998(b) 119910 = 1024119909 + 0082

1198772 = 0999(c) 119910 = 0953119909 + 0153

1198772 = 0999(d) 119910 = 0764119909 + 0327

1198772 = 0981

(a) 303K(b) 313K(c) 323K(d) 333K

119862120579

(mM

)

119862 (mM)




119870ads =1

555


ads119877119879

) (4)








ln119870ads =minusΔ119867119900

ads119877119879

+

Δ119878119900

ads119877

+ ln 1

555

(5)




6

65

7

75

8

85

9

95

10

105

295 3 305 31 315 32 325 33 335

119910 = 7065119909 minus 1317

1198772 = 09963

ln119870

ads

(Mminus1)

1000119879 (Kminus1)


300 305 310 315 320 325 330 335

119910 = 00764119909 minus 5887

1198772 = 09812

minus36

minus355

minus35

minus345

minus34

minus335

minus33

(kJ m

olminus1)

119879 (K)

ΔGo ad

s




Δ119866119900

ads = Δ119867119900

ads minus 119879Δ119878119900

ads (6)

A plot of Δ119866119900


119900



119900




119900



119862 (mM) 119860


lowast




118522 8255 minus3134

005 1338 times 1015

10775 10509 3592

01 2512 times 1015

10983 10717 4090

05 2615 times 1015

11274 10999 4115

10 2695 times 1015

11448 11182 4149

295 3 305 31 315 32 325 33 335

minus10

minus9

minus8

minus7

minus6

minus5

minus4

minus3ln c

orr

(g cm

minus2

hminus1)


(d) 05mM(e) 10mM

1000119879 (Kminus1)






119864lowast

119886

119877119879

(7)




119886119877 and




295 3 305 31 315 32 325 33 335

minus16

minus15

minus14

minus13

minus12

minus11

minus10

minus9


(d) 05mM(e) 10mM

119879(g

cmminus2

hminus1

Kminus1)

1000119879 (Kminus1)

ln120592

corr



lowast) of


ln120592corr119879

= [ln 119877

119873ℎ

+

Δ119878lowast

119877

] minus

Δ119867lowast

119877119879

(8)





119886and frequency





lowast








119886




119886




119886(inhib-






lowast

119886


minus7

minus6

minus5

minus4

minus3

minus2

minus1


log119894

(A cm

minus2)

Blank005mM01mM

05mM10mM



lowast

119886is higher


lowast

119886minus Δ119867


119864lowast

119886minus Δ119867

lowast= 119877119879 (9)




119886)cathodic




119862


120573119888

(mV decminus1)120573119886


(120583A cmminus2)120578119879

()Blank 494 14050 7751 1656

005 490 11630 5648 6548 6051

01 486 14916 7638 5992 6381

05 475 13106 6740 3258 8033

10 462 12637 6344 1654 9001



120578119879() =

119868119900


119868119900

corrtimes 100 (10)

where 119868119900









0 200 400 600 800 1000

0

200

400

600

800

1000

119885real (Ω cm2)

minus119885

img

(Ωcm

2) 119877ct

Rs

Blank005mM01mM

05mM10mM

119876


00

05

10

15

20

25

30

0 1 2 3 4

0

Phas

e ang

le (d

eg)

5minus2 minus1

minus20

minus40

minus60

minus80

log frequency (Hz)

log

IZI (Ω

cm2)

Blank005mM01mM

05mM10mM




119885CPE = 119876minus1(119895120596)minus119899

(11)




119862

(mM)119877ct

(Ω cm2)119876


(120583F cmminus2) 120578119911()

Blank 85 11520 0863 5527

005 2093 9214 0870 5097 5933

01 2548 8909 0864 4912 6667

05 4982 7324 0856 4198 8293

10 8296 3162 0877 1896 8976

0 100 200 300 400 500 6000000

0002

0004

0006

0008

0010

Time (s)

Curr

ent (

A)

(e)

(d)

(c) (b)

(a)


(d) 05mM(e) 10mM




(119862dl) = (1198761198771minus119899

ct )

1119899

(12)




120578119885() =

119877ct minus 119877119900

ct119877ct

times 100 (13)







RS + 119899H+ 997888rarr [RSH119899]119899+

(14)












4 Conclusion


Acknowledgments


References
































































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


6

65

7

75

8

85

9

95

10

105

295 3 305 31 315 32 325 33 335

119910 = 7065119909 minus 1317

1198772 = 09963

ln119870

ads

(Mminus1)

1000119879 (Kminus1)


300 305 310 315 320 325 330 335

119910 = 00764119909 minus 5887

1198772 = 09812

minus36

minus355

minus35

minus345

minus34

minus335

minus33

(kJ m

olminus1)

119879 (K)

ΔGo ad

s




Δ119866119900

ads = Δ119867119900

ads minus 119879Δ119878119900

ads (6)

A plot of Δ119866119900


119900



119900




119900



119862 (mM) 119860


lowast




118522 8255 minus3134

005 1338 times 1015

10775 10509 3592

01 2512 times 1015

10983 10717 4090

05 2615 times 1015

11274 10999 4115

10 2695 times 1015

11448 11182 4149

295 3 305 31 315 32 325 33 335

minus10

minus9

minus8

minus7

minus6

minus5

minus4

minus3ln c

orr

(g cm

minus2

hminus1)


(d) 05mM(e) 10mM

1000119879 (Kminus1)






119864lowast

119886

119877119879

(7)




119886119877 and




295 3 305 31 315 32 325 33 335

minus16

minus15

minus14

minus13

minus12

minus11

minus10

minus9


(d) 05mM(e) 10mM

119879(g

cmminus2

hminus1

Kminus1)

1000119879 (Kminus1)

ln120592

corr



lowast) of


ln120592corr119879

= [ln 119877

119873ℎ

+

Δ119878lowast

119877

] minus

Δ119867lowast

119877119879

(8)





119886and frequency





lowast








119886




119886




119886(inhib-






lowast

119886


minus7

minus6

minus5

minus4

minus3

minus2

minus1


log119894

(A cm

minus2)

Blank005mM01mM

05mM10mM



lowast

119886is higher


lowast

119886minus Δ119867


119864lowast

119886minus Δ119867

lowast= 119877119879 (9)




119886)cathodic




119862


120573119888

(mV decminus1)120573119886


(120583A cmminus2)120578119879

()Blank 494 14050 7751 1656

005 490 11630 5648 6548 6051

01 486 14916 7638 5992 6381

05 475 13106 6740 3258 8033

10 462 12637 6344 1654 9001



120578119879() =

119868119900


119868119900

corrtimes 100 (10)

where 119868119900









0 200 400 600 800 1000

0

200

400

600

800

1000

119885real (Ω cm2)

minus119885

img

(Ωcm

2) 119877ct

Rs

Blank005mM01mM

05mM10mM

119876


00

05

10

15

20

25

30

0 1 2 3 4

0

Phas

e ang

le (d

eg)

5minus2 minus1

minus20

minus40

minus60

minus80

log frequency (Hz)

log

IZI (Ω

cm2)

Blank005mM01mM

05mM10mM




119885CPE = 119876minus1(119895120596)minus119899

(11)




119862

(mM)119877ct

(Ω cm2)119876


(120583F cmminus2) 120578119911()

Blank 85 11520 0863 5527

005 2093 9214 0870 5097 5933

01 2548 8909 0864 4912 6667

05 4982 7324 0856 4198 8293

10 8296 3162 0877 1896 8976

0 100 200 300 400 500 6000000

0002

0004

0006

0008

0010

Time (s)

Curr

ent (

A)

(e)

(d)

(c) (b)

(a)


(d) 05mM(e) 10mM




(119862dl) = (1198761198771minus119899

ct )

1119899

(12)




120578119885() =

119877ct minus 119877119900

ct119877ct

times 100 (13)







RS + 119899H+ 997888rarr [RSH119899]119899+

(14)












4 Conclusion


Acknowledgments


References
































































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


295 3 305 31 315 32 325 33 335

minus16

minus15

minus14

minus13

minus12

minus11

minus10

minus9


(d) 05mM(e) 10mM

119879(g

cmminus2

hminus1

Kminus1)

1000119879 (Kminus1)

ln120592

corr



lowast) of


ln120592corr119879

= [ln 119877

119873ℎ

+

Δ119878lowast

119877

] minus

Δ119867lowast

119877119879

(8)





119886and frequency





lowast








119886




119886




119886(inhib-






lowast

119886


minus7

minus6

minus5

minus4

minus3

minus2

minus1


log119894

(A cm

minus2)

Blank005mM01mM

05mM10mM



lowast

119886is higher


lowast

119886minus Δ119867


119864lowast

119886minus Δ119867

lowast= 119877119879 (9)




119886)cathodic




119862


120573119888

(mV decminus1)120573119886


(120583A cmminus2)120578119879

()Blank 494 14050 7751 1656

005 490 11630 5648 6548 6051

01 486 14916 7638 5992 6381

05 475 13106 6740 3258 8033

10 462 12637 6344 1654 9001



120578119879() =

119868119900


119868119900

corrtimes 100 (10)

where 119868119900









0 200 400 600 800 1000

0

200

400

600

800

1000

119885real (Ω cm2)

minus119885

img

(Ωcm

2) 119877ct

Rs

Blank005mM01mM

05mM10mM

119876


00

05

10

15

20

25

30

0 1 2 3 4

0

Phas

e ang

le (d

eg)

5minus2 minus1

minus20

minus40

minus60

minus80

log frequency (Hz)

log

IZI (Ω

cm2)

Blank005mM01mM

05mM10mM




119885CPE = 119876minus1(119895120596)minus119899

(11)




119862

(mM)119877ct

(Ω cm2)119876


(120583F cmminus2) 120578119911()

Blank 85 11520 0863 5527

005 2093 9214 0870 5097 5933

01 2548 8909 0864 4912 6667

05 4982 7324 0856 4198 8293

10 8296 3162 0877 1896 8976

0 100 200 300 400 500 6000000

0002

0004

0006

0008

0010

Time (s)

Curr

ent (

A)

(e)

(d)

(c) (b)

(a)


(d) 05mM(e) 10mM




(119862dl) = (1198761198771minus119899

ct )

1119899

(12)




120578119885() =

119877ct minus 119877119900

ct119877ct

times 100 (13)







RS + 119899H+ 997888rarr [RSH119899]119899+

(14)












4 Conclusion


Acknowledgments


References
































































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



119862


120573119888

(mV decminus1)120573119886


(120583A cmminus2)120578119879

()Blank 494 14050 7751 1656

005 490 11630 5648 6548 6051

01 486 14916 7638 5992 6381

05 475 13106 6740 3258 8033

10 462 12637 6344 1654 9001



120578119879() =

119868119900


119868119900

corrtimes 100 (10)

where 119868119900









0 200 400 600 800 1000

0

200

400

600

800

1000

119885real (Ω cm2)

minus119885

img

(Ωcm

2) 119877ct

Rs

Blank005mM01mM

05mM10mM

119876


00

05

10

15

20

25

30

0 1 2 3 4

0

Phas

e ang

le (d

eg)

5minus2 minus1

minus20

minus40

minus60

minus80

log frequency (Hz)

log

IZI (Ω

cm2)

Blank005mM01mM

05mM10mM




119885CPE = 119876minus1(119895120596)minus119899

(11)




119862

(mM)119877ct

(Ω cm2)119876


(120583F cmminus2) 120578119911()

Blank 85 11520 0863 5527

005 2093 9214 0870 5097 5933

01 2548 8909 0864 4912 6667

05 4982 7324 0856 4198 8293

10 8296 3162 0877 1896 8976

0 100 200 300 400 500 6000000

0002

0004

0006

0008

0010

Time (s)

Curr

ent (

A)

(e)

(d)

(c) (b)

(a)


(d) 05mM(e) 10mM




(119862dl) = (1198761198771minus119899

ct )

1119899

(12)




120578119885() =

119877ct minus 119877119900

ct119877ct

times 100 (13)







RS + 119899H+ 997888rarr [RSH119899]119899+

(14)












4 Conclusion


Acknowledgments


References
































































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



119862

(mM)119877ct

(Ω cm2)119876


(120583F cmminus2) 120578119911()

Blank 85 11520 0863 5527

005 2093 9214 0870 5097 5933

01 2548 8909 0864 4912 6667

05 4982 7324 0856 4198 8293

10 8296 3162 0877 1896 8976

0 100 200 300 400 500 6000000

0002

0004

0006

0008

0010

Time (s)

Curr

ent (

A)

(e)

(d)

(c) (b)

(a)


(d) 05mM(e) 10mM




(119862dl) = (1198761198771minus119899

ct )

1119899

(12)




120578119885() =

119877ct minus 119877119900

ct119877ct

times 100 (13)







RS + 119899H+ 997888rarr [RSH119899]119899+

(14)












4 Conclusion


Acknowledgments


References
































































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of










4 Conclusion


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

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