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Materials Chemistry and Physics 123 (2010) 218–224

Contents lists available at ScienceDirect

Materials Chemistry and Physics

journa l homepage: www.e lsev ier .com/ locate /matchemphys

lectrochemical and quantum chemical study of 4-[(E)-[(2,4-dihydroxy phenyl)ethylidine] amino]-6-methyl-3-sulphanylidine-2,3,4,5-tetra

ydro-1,2,4-triazin-5-one [DMSTT]

am John, Bincy Joseph, K.V. Balakrishnan, K.K. Aravindakshan, Abraham Joseph ∗

epartment of Chemistry, University of Calicut, Calicut University P.O, 673 635, India

r t i c l e i n f o

rticle history:eceived 20 September 2009eceived in revised form 14 March 2010

a b s t r a c t

The inhibition of mild steel in aerated 1 M hydrochloric acid solution was studied using conventionalweight loss method, potentiodynamic polarization studies (Tafel), linear polarization studies (LPR), elec-

ccepted 31 March 2010

eywords:orrosion inhibitorild steel

IS

trochemical impedance spectroscopy (EIS) and quantum chemical calculation in the presence and absenceof different concentrations of DMSTT. The inhibition efficiency increased markedly with increase in theadditive concentrations, but slightly decreased with increasing temperature. The presence of DMSTTdecreases the double layer capacitance and increases the charge-transfer resistance. The value of activa-tion energy (Ea) for mild steel corrosion and thermodynamic parameters such as adsorption equilibriumconstant (Kads), free energy of adsorption (�Gads) values were calculated and discussed. The inhibitormolecule first adsorbed on mild steel surface according to Langmuir adsorption isotherm.

uantum chemical calculation

. Introduction

The use of inhibitor is one of the most practical methods forrotecting metals against corrosion and it, in these days, becomes

ncreasingly popular. Organic and Inorganic compounds with func-ional groups containing hetero atoms (such as N, S, P, O, etc.),nsaturated bonds (such as double or triple bonds) and the pla-ar conjugated system including all kinds of aromatic cycles whichan offer active electrons or vacant orbitals to donate or acceptlectrons have been used as inhibitor [1–10]. The adsorption of therganic inhibitor at the metal solution interface is the first stepn the mechanism of the inhibitory action. Organic molecules maydsorb on the metal surface by

(a) Electrostatic interaction between a negatively charged surfaces,which is provided with specifically adsorbed anions (Cl−) onmetal and positive charge of the inhibitor.

b) Interaction of unshared electron pair in the inhibitor moleculewith metal.

(c) Interaction of � electron of the inhibitor molecule with themetal and/or

d) A combination of all the above processes.

∗ Corresponding author.E-mail address: drabrahamj@gmail.com (A. Joseph).

254-0584/$ – see front matter © 2010 Elsevier B.V. All rights reserved.oi:10.1016/j.matchemphys.2010.03.085

© 2010 Elsevier B.V. All rights reserved.

Adsorption of organic compounds on the metal surface can bedescribed by two types of interaction; physical adsorption andchemical adsorption. Physical adsorption requires the presence ofboth electrically charged surface in the metal and charged specieson the bulk of the solution. Chemisorptions involve charge-transferprocess.

Although chloride ions, hydroxyl ions and water molecules arealso present in the corrosion medium, inhibitor molecule (DMSTT)is more strongly adsorbed on the metal surface. This may beexplained with the position of various species/ligands in the spec-trochemical series. The order of magnitude of interaction betweenthe ligand and metal orbital depends on the nature of the � orbitalof the ligand. A strong coordinating ligand like DMSTT is an effi-cient � acceptor, favoring back bonding between the metal andligand. Cl−, OH−, and water molecules behave as poor � acceptorsand there is no back bonding interaction with metal is expected,indicating that DMSTT is a stronger adsorbent than other speciesin the medium.

The bonding tendencies of the inhibitor towards the metal atom,Fe, can be discussed in terms of the HSAB (hard–soft–acid–base)and the frontier-controlled interaction concepts. General rule sug-gested by the principle of HSAB is that hard acid prefers tocoordinate to hard bases and soft acids prefer to coordinate to

soft bases. On the other hand, metal atoms known as soft acidsinteract with soft bases, which have small gap between HOMOand LUMO. Similar results can be reached from molecular orbitaltheory also. The inhibitor molecule (base) is the electron pairdonor and metal (acid) is the electron pair acceptor, the energy

S. John et al. / Materials Chemistry and Physics 123 (2010) 218–224 219

dmLbH[

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Table 1Corrosion rate of mild steel in 1N HCl solution.

Inhibitor conc. (ppm) Corrosion rate mm/yr with time in hours

24 48 72 96

Blank 2112 1456 1008 77710 946 569 428 356

Fig. 1. Structure of DMSTT.

ifference of the HOMO of the base and the LUMO of the metalust be considered. Theory suggests that the overlap between the

UMO (metal) and the HOMO (inhibitor) is the governing factor inonding: The lower the HOMO–LUMO energy difference, the higherOMO–LUMO overlap and stronger the base-acid bond formation

11].The adsorption of inhibitor molecules is influenced by their

lectronic structure, steric factors, aromaticity, electron den-ity at the donor atoms and � orbital character of donatinglectrons. The adsorption process is also affected by the pres-nce of hetero atoms, such N, O, P and S as well as multipleonds or aromatic rings in their molecular structure which aressumed to be active centers of adsorption [12,13]. The inhibitorolecule, DMSTT, is a triazine based Schiff base of 2,4-dihydroxy

enzaldehyde, which contains most of the active centers ofdsorption and hence decided to investigate the inhibition effectf 4-[(E)-[(2,4-dihydroxy phenyl) methylidine] amino]-6-methyl--sulphanylidine-2,3,4,5-tetra hydro-1,2,4-triazin-5-one [DMSTT]n the corrosion behavior of mild steel in 1 M HCl solution in bothhort and long immersion studies and clarifies its inhibition mech-nism.

. Experimental

.1. Inhibitor

The inhibitor, DMSTT is prepared by condensing 4-amino-3-mercapto--methyl-1,2,4-triazin-4H-one with 2,4-dihydroxy benzaldehyde. The formerompound is synthesized in the laboratory by reacting pyruvic acid with thio-arbohydrazide procured from E.merck. The purified and recrystallised sample isharacterized by physico-chemical methods. The compound is readily soluble in 1 MCl at room temperature and its various concentrations were tested in the present

tudy. The structure of the compound is given in Fig. 1.

.2. Medium

The medium for the study was prepared from reagent grade HCl from E.mercknd doubly distilled water. All the tests are performed in aerated medium at roomemperature (27 ◦C) and normal atmospheric pressure.

.3. Materials

The materials were of the following composition (wt); C (0.20%), Mn (1%), P0.03%), S (0.02%), and Fe (98.75%). The mild steel specimens used in the weight loss

easurements were cut in to 4.8 cm × 1.9 cm coupons. The same types of couponsere used for the electrochemical studies also. However, in electrochemical studies

nly 1 cm2 area is exposed. Before both the measurements, the samples were pol-shed using different grade emery papers followed by washing in ethanol, acetonend finally with distilled water.

.4. Weight loss measurements

The weight loss experiments were carried out under total immersion conditionsn test solution maintained at 300 K. Mild steel specimens of required dimension isrst rubbed with different grade of emery papers to remove rust particles and thenubjected to the action of a buffing machine attached with a cotton wheel and a

50 636 551 425 344100 442 252 186 154200 204 163 139 123400 157 122 102 91

fiber wheel having buffing soap to ensure mirror bright finish. All specimens werecleaned according ASTM standard G-1-72 procedure [14–20]. The experiments werecarried out in 250-ml beaker containing the solution. After the exposure periodthe specimens were removed, washed initially under running tap water, to removethe loosely adhering corrosion products and finally cleaned with a mixture of 20%NaOH and 200 g/L zinc dust for 5 min followed by acetone. Similar experimentswere performed at the same temperature with different inhibitor concentrations tofind out the most suitable inhibitor concentration that shows maximum inhibitiveefficiency. From the weight loss in each experiment the corrosion rate was calculatedin millimeter per year (mm/yr). In each case duplicate experiments were conductedand showed that the second results were within ± 1% of the first. Whenever thevariations were very large, the data were confirmed by a third test. The inhibitionefficiency was taken to represent the surface coverage (�). The percentage inhibitiveefficiency was calculated using the relation:

IE% = W0 − W

W0× 100 (1)

In which both W0 and W are the weight losses in the uninhibited and inhibitedsolutions respectively.

2.5. Electrochemical measurements

Electrochemical tests were carried out in a conventional three-electrode con-figuration with platinum sheet (1 cm2 surface area) as auxiliary electrode andsaturated calomel electrode (SCE) as the reference electrode. The working electrodewas first immersed in the test solution and after establishing a steady state OCP,the electrochemical measurements were carried out in a Gill A C computer con-trolled electrochemical workstation (ACM, U.K, model No: 1475). Electrochemicalimpedance spectroscopy (EIS) measurements were carried out in frequency rangeof 10 KHz to 10 Hz with amplitude of 10 mV (RMS) using a.c. signals at open circuitpotential. The potentiodynamic polarization curves obtained in the potential rangeare −250 mV to +250 mV with a sweep rate of 1000 mV/min.

2.6. Quantum chemical calculation

Quantum chemical calculation was performed based on ab initio method and6-31G* basis set. The Mullicken charge distribution on DMSTT molecule as well asthe highest occupied molecular orbital (HOMO) and lowest unoccupied molecularorbital (LUMO) were calculated. All calculations, including geometry optimizationsof the structure were performed with the B3LYP exchange correlation correctedfunctional with the 6-31G (d) basis set using the Gaussian 03W package.

3. Results and discussion

3.1. Weight loss measurements

Weight loss of mild steel was performed at various timeintervals in the absence and presence of different concentrations(10 ppm–400 ppm) of DMSTT. The corrosion rate obtained in thepresence of different concentration of inhibitor falls significantlybelow that of free acid, these values are tabulated in Table 1,and the corrosion inhibition efficiency with different concentra-tions of inhibitor in millimeter/year (mm/yr) is given in Table 2.The increase in the inhibitor concentration was accompanied bya decrease in weight loss and increase in percentage of IE. Theseresults lead to the conclusion that DMSTT acts as inhibitor for mildsteel dissolution in 1 M HCl solution.

3.2. Potentiodynamic polarization studies

Anodic and cathodic polarization were carried out potentiody-namically in unstirred 1 M HCl solution in the absence and presence

220 S. John et al. / Materials Chemistry and Physics 123 (2010) 218–224

Table 2Percentage inhibition efficiency of mild steel in 1N HCl solution.

Inhibitor conc. (ppm) % of inhibition efficiency with time in hours24 48 72 96

Blank – – – –10 55.18 60.92 57.49 54.8650 69.85 62.17 57.85 55.72100 79.23 82.69 81.47 80.19200 90.31 88.76 86.22 84.16400 92.52 91.62 89.82 88.23

Fp

opsmTt(eiu

�

TE

TE

ig. 2. Linear polarization curves (Tafel) for mild steel in 1 M HCl in the absence andresence of different concentrations of DMSTT at 303 K.

f various concentrations of the inhibitors at 303 and 313 K over aotential range of −250 mV to +250 mV and these results are repre-ented in Figs. 2 and 3. It is clear from the figure that both the anodicetal dissolution and cathodic hydrogen evolution would exhibit

afel type behavior. Electrochemical corrosion kinetics parametershat is corrosion potential (Ecorr), cathodic and anodic Tafel slopesˇc and ˇa) and corrosion current density (Icorr) obtained from Tafelxtrapolation of the polarization curve at 303 and 313 K were given

n Tables 3 and 4. The corrosion inhibition efficiency was calculatedsing the relation

= ICorr∗ − Icorr

ICorr∗× 100 (2)

able 3lectrochemical parameters for mild steel obtained from polarization curves in 1 M HCl a

Conc. (ppm) Ecorr (mV) Rp (� cm−2) ˇa (mV dec−1) ˇc (

Blank −497 12 156 21310 −512 15 140 19350 −521 29 84 116100 −502 28 73 89200 −496 46 62 78400 −498 46 55 61

able 4lectrochemical parameters for mild steel obtained from polarization curves in 1 M HCl a

Conc. (ppm) Ecorr (mV) Rp (� cm−2) ˇa (mV dec−1) ˇc (

Blank −455 13 153 20210 −508 13 128 19550 −513 19 113 162100 −509 27 106 157200 −511 25 79 119400 −490 28 47 75

Fig. 3. Linear polarization curves (LPR) for mild steel in 1 M HCl in the absence andpresence of different concentrations of DMSTT at 303 K.

where ICorr∗ and Icorr are uninhibited and inhibited corrosion cur-rent density respectively. These results suggest that DMSTT actsas a mixed type inhibitor. The inhibitor molecule first adsorbs onthe mild steel surface and blocking the available reaction sites [21].The surface coverage increases with the inhibitor concentration.The presence of defects on the metal surface permits free accessto H+ ions [22] and a significant dissolution of metal takes place,followed by desorption of inhibition film from the metal surface[23]. The formation of surface inhibitor film on the mild steel sur-face provides considerably proper protection to mild steel againstcorrosion. This film reduces the active surface area exposed to thecorrosive medium and delays the hydrogen evolution and iron dis-solution.

3.3. Electrochemical impedance spectroscopy

The performance of the organic coatings on the metal surfacecan be evaluated from the EIS studies and this has been widely usedfor investigating the protective properties of organic inhibitors onmetals. It does not disturb the double layer at the metal/solution

interface [24, 25]. Therefore, results that are more reliable can beobtained through this technique. The Nyquist plots and the Bodediagrams for the MS in uninhibited 1 M HCl and those containingvarious inhibitor concentrations after 1 h of immersion are givenin Figs. 4 and 5. It is clear from the figures that in uninhibited

t 303 K.

mV dec−1) Icorr (�A cm2) Corrosion rate (mm yr−1) � (%)

3.1889 15.52 –2.3285 10.65 26.980.7240 7.30 77.300.6164 0.82 80.070.2389 0.57 92.500.2272 0.24 92.88

t 313 K.

mV dec−1) Icorr (�A cm2) Corrosion rate (mm yr−1) � (%)

2.9246 18.43 –2.6448 14.72 9.571.5296 10.08 47.701.0177 5.35 65.200.8299 3.87 71.620.7160 2.16 86.54

S. John et al. / Materials Chemistry and Physics 123 (2010) 218–224 221

Fc

sosapqTtcitmiatdt

Ft

ig. 4. Nyquist plots for MS in 1 M HCl in the absence and presence of differentoncentrations of DMSTT at 303 K

olution, Nyquist plot yields a slightly depressed semi circles andnly one time constant in Bode format. This indicates the corro-ion of the MS in the absence of inhibitor and mainly controlled bycharge-transfer process [24, 26, 27]. In the evaluation of Nyquistlots, the difference in real impedance at lower and higher fre-uencies is commonly considered as a charge-transfer resistance.he charge-transfer resistance must be corresponding to the resis-ance between the metal and OHP (Outer Helmholtz Plane). Theontribution of all resistances corresponds to the metal/solutionnterface, i.e., charge-transfer resistance (Rct), diffuse layer resis-ance (Rd), accumulation resistance (Ra), film resistance (Rf), etc.

ust be taken into account. Therefore, in this study, the differencen real impedance at lower and higher frequencies is considered

s the polarization resistance (Rp) [24–27]. The addition of DMSTTo the aggressive solution leads to a change of the impedanceiagrams in both shape and size, with a depressed semicircle athe high frequency part of the spectrum. As seen from Fig. 4, the

ig. 5. Bode curves for Mild steel in 1 M HCl in the presence of different concentra-ions of DMSTT at 303 K.

Fig. 6. Langmuir adsorption isotherm for Mild steel in 1 M HCl at 303 K and 313 Kin the presence of DMSTT.

Rp values increased with the DMSTT concentration, which can beattributed to the formation of a protective layer at the metal surfaceand this layer acts as a barrier for the mass and the charge transfers.The values of polarization resistance and percentage inhibition effi-ciency were determined from the EIS measurements are given inTable 4. The inhibition efficiency was calculated using the equation:

� = Rct∗ − Rct

Rct∗× 100 (3)

where Rct∗ and Rct are values of the charge-transfer resistanceobserved in the absence and presence of DMSTT. In this case, theMS corrosion takes place only on the free surface of the metaland/or within the pores due to the diffusion of dissolved oxygenor chlorine through the pores of the protective layer. The values ofboth polarization resistance and corrosion inhibition efficiency (�)correspond to the EIS at 303 K and 313 K are given in Tables 5 and 6.

3.4. Adsorption studies

In order to understand the mechanism of corrosion inhibition,the adsorption behavior of the organic compound must be known.The surface coverage, � for different inhibitor concentration hasbeen evaluated from potentiodynamic polarization measurements.On plotting log (�/1 − �) Vs. log C may give a straight line, suggestingthat the adsorption of the compound on mild steel surface followsLangmuir adsorption isotherm model [25], where � = U0 − Ui/U0,where U0 is the uninhibited corrosion rate and Ui is the inhibitedcorrosion rate and C is the molar concentration of the inhibitor. Theadsorption isotherm for DMSTT on mild steel at two temperatures;303 K (R2 = 0.9778) and 313 K (R2 = 0.9750) in 1 M HCl is shown inFig. 6.

3.5. Activation energy (Ea)

Activation energy is calculated using the relation

lnr2

r1= Ea

T2 − T1

RT1T2

where r1 and r2 are the corrosion rate at temperature T1 and T2,

respectively. The activation energies obtained are given in Table 7.Activation energy Ea increases with the increase of inhibitor con-centration and that indicates strong absorption of the inhibitormolecule on mild steel surface [28,29].

222 S. John et al. / Materials Chemistry and Physics 123 (2010) 218–224

Table 5A C impedance data of mild steel with DMSTT at 303 K in 1 M HCl solution.

Conc. (ppm) Rct (� cm2) Cdl (�F cm−2) Icorr (�A cm2) Corrosion rate (mm yr−1) � (%)

Blank 50.3 116 1.2980 9.93 –10 50.4 112 0.7580 3.41 42.5050 180.1 46 0.1591 1.66 72.08100 187.4 58 0.1071 1.26 73.16200 398.3 51 0.0826 0.75 87.38400 597.9 46 0.0531 0.50 91.58

Table 6A C impedance data of mild steel with DMSTT at 313 K in 1 M HCl solution.

Conc. (ppm) Rct (� cm2) Cdl (�F cm−2) Icorr (�A cm2) Corrosion rate (mm yr−1) � (%)

Blank 19.5 151 1.3330 15.24 –10 29.4 142 0.8876 10.15 33.1450 119.9 64 0.2176 2.48 83.67100 218.7 66 0.1193 1.36 91.05

3

�

wnamam

ao

3

sttopnmrco(at

TT

200 262.9 61400 287.1 53

.6. Free energy of adsorption (�Gads)

The free energy of adsorption �G is calculated using the relation

Gads = −RT ln55.5�

C(1 − �)

here ‘C’ is the concentration of the inhibitor in mol dm−3. Theegative value of �Gads suggests that DMSTT is spontaneouslydsorbed on the mild steel surface [30]. The addition of inhibitorolecule transforms the metal–solution interface from a state of

ctive dissolution to the passive state due to adsorption on to theetal surface.The value of �Gads obtained in this case is less than 40 kJ/mol

nd is a clear indication of physical adsorption with the formationf an adsorptive film with an electrostatic interaction.

.7. Quantum chemical calculations

Classical theory suggests that, all chemical reactions are electro-tatic or orbital interactions. Electrical charges in the molecule arehe driving force of electrostatic interactions. In order to investigatehe charge distribution as well as the nature of molecular orbitalsn DMSTT molecule ab initio quantum chemical calculations wereerformed using density functional theory (DFT). The effective-ess of an inhibitor can be related with its electronic and spatialolecular structure. The charge distribution on DMSTT molecule

anges from −0.633 to 0.633. Some quantum chemical values were

omputed using DFT and energies of highest occupied molecularrbital (EHOMO = −1.8231 eV), lowest unoccupied molecular orbitalELUMO = −5.7555 eV) and total energy (Etotal = 795676.40 Kcal/mol)re also calculated. The dipole moment of the molecule is calculatedo be 4.0852 D. The inhibition efficiency of a molecule is related

able 7he value of activation parameters for mild steel in1 M HCl in the absence and the presen

Inhibitor conc. (ppm) Ea (kJ mol−1) Kadsorption

303 K

Blank 6.66 –10 25.53 0.531650 32.88 0.9799100 148.59 0.6005200 151.46 0.8873400 172.87 0.4692

0.0992 1.13 92.560.0832 0.98 93.44

to the metal–orbital interactions. Good inhibitor molecules offerelectrons to the unoccupied orbital of metal but also accept freeelectrons from metal. That is a charge-transfer phenomenon, whichmay take place. From quantum chemical calculation it is clear thathigher the HOMO energy of the inhibitor greater is the trend ofdonating electrons to the unoccupied ‘d’ orbital of the metal, andhigher the corrosion inhibition efficiency. The lower the LUMOenergy level makes easy acceptance of electrons from the metal sur-face [31,32]. The magnitude of �E value (�E = ELUMO − EHOMO) alsohelps us predict probable roots of the inhibitory action. Structureof the optimized geometry and molecular orbital plots of DMSTTare given in Fig. 7.

3.8. Local selectivity

The local reactivity of DMSTT can be analyzed by means of thecondensed Fukui function. The condensed Fukui functions and con-densed local softness indices allow us to distinguish each part ofthe molecule on the basis of its distinct chemical behavior due tothe different substituent functional groups [33]. Thus, the site fornucleophilic attack will be the place where the value of

∫+ is the

maximum. In turn, the sight for electrophilic attack is controlledby the value of

∫ −, for nucleophilic attack the most reactive siteof DMSTT is on the N (5) and C (4) atoms. For electrophilic attackthe most reactive site of DMSTT is on the S (25) atom. These resultsare shown in Table 8. The condensed local softness indices Sk− andSk+ are related to the condensed Fukui functions. The local softness

follows the same trend of Fukui functions.

Molecular modeling studies give clear indication of strongmolecular attraction between the metal and DMSTT molecule.In Monte Carlo simulation, DMSTT molecule is placed on theFe2O3 (1 1 1) surface and performed molecular dynamics stud-

ce of different concentrations of DMSTT.

−�Gadsorption (kJ mol−1)

313 K 303 K 313 K

– – –0.1523 8.53 5.550.2623 10.06 6.970.2695 8.83 7.040.1816 9.82 6.010.1084 8.21 4.67

S. John et al. / Materials Chemistry an

Fhp

ir(ckoro

TF

ig. 7. (A). The optimized molecular structure of the inhibitor molecule. (B). Theighest occupied molecular orbital (HOMO) of the inhibitor. (C) The lowest unoccu-ied molecular orbital (LUMO) of the inhibitor.

es. The adsorption energy (−32.067 Kcal/mol); the sum of theigid adsorption energy (−10.64 Kcal/mol) and deformation energy−32.057 Kcal/mol) for the adsorbate components have been cal-

ulated. The rigid adsorption energy reports the energy released incal mol−1, when the unrelaxed adsorbate components adsorbedn the substrate. The deformation energy reports the energyeleased when the adsorbed adsorbate components are relaxedn the substrate surface. The total energy (19.3998 Kcal/mol) and

able 8ukui functions and local softness values for DMSTT.

Atom f(−) f(+) Sk(+) Sk(−)

1 C 0.0419 0.0393 0.0590 0.06292 N 0.0082 0.0788 0.1184 0.01323 C 0.0020 0.1086 0.1632 0.00304 C 0.0008 0.2114 0.3177 0.00125 N 0.0110 0.2401 0.3609 0.01656 O 0.0058 0.0730 0.1097 0.00877 C 0.0009 0.0019 0.0028 0.001411 N 0.0086 0.0253 0.0380 0.012913 N 0.0240 0.0446 0.0670 0.036014 C 0.0064 0.0529 0.0795 0.009616 C 0.0119 0.0075 0.0112 0.017817 C 0.0020 0.0202 0.0304 0.003018 C 0.0047 0.0126 0.0189 0.007119 C 0.0077 0.0006 0.0009 0.011621 C 0.0003 0.0025 0.0037 0.000422 C 0.0062 0.0237 0.0035 0.009325 S 0.8429 0.0325 0.0488 1.267026 O 0.0046 0.0051 0.0076 0.006928 O 0.0036 0.0031 0.0046 0.0054

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d Physics 123 (2010) 218–224 223

dEad/dNi (−32.067 Kcal/mol) were also calculated. The bond lengthanalysis also agrees well with the Fukui results of DMSTT.

4. Conclusion

Chemical and electrochemical measurements were used tostudy the corrosion inhibition characteristics of DMSTT on mildsteel in aerated 1 M HCl solutions at 303 and 313 K. The principleassumptions are given below:

1. Addition of DMSTT derivative effectively reduces the corrosionof mild steel in 1 M HCl.

2. The inhibition efficiency of this compound increases with theincrease in their concentration due to the formation of a surfacefilm on the mild steel surface.

3. The DMSTT inhibits the corrosion of mild steel in acid mediumby physisorption, and the adsorption of the compound on themetal surface obeyed Langmuir adsorption isotherm.

4. DMSTT behaves as mixed type inhibitor.5. Even at higher temperature DMSTT possess effective corrosion

inhibition.6. Molecular dynamic simulations are performed to investigate the

adsorption behavior of DMSTT on mild steel surface.7. The relationship between inhibition efficiency of mild steel in

1 M HCl and8. EHOMO, ELUMO and ELUMO − EHOMO of the inhibitor, DMSTT were

calculated by DFT method.

Acknowledgement

The authors are grateful to Kerala State Council for Science Tech-nology and Environment (KSCSTE) for financial assistance in theform of a major research project 018/SRSPS/2006/CSTE.

References

[1] P. Zhao, Q. Liang, Y. Li, Appl. Surf. Sci. 252 (2005) 1956.[2] W.H. Li, Q. He, C.L. Pei, B.R. Hou, Electrochim. Acta 52 (2007) 6386.[3] M.A. Quraishi, H.K. Sharma, Mater. Chem. Phys. 78 (2002) 18.[4] A.M.S. Abdennbi, A.I. Abdulhabi, S. Abu-Orabi, Anti-Corros. Methods Mater. 45

(1998) 103.[5] N. Pebere, M. Duprat, F. Dabosi, A. Lattes, A. de Savinagic, J. Appl. Electrochem.

18 (1988) 225.[6] F. Bentiss, M. Lagrenee, M. Traisnel, J.C. Hornez, Corros. Sci. 41 (1999) 789.[7] K.F. Khaled, Electrochim. Acta 48 (2003) 2493.[8] H. Shokry, M. Yuasa, I. Sekine, R.M. Issa, H.Y. El-Baradie, G.K. Gomma, Corros.

Sci. 40 (1998) 2173.[9] K. Emergul, O. Atakol, Mater. Chem. Phys. 82 (2003) 188.10] Y. Li, P. Zhao, Q. Liang, B.R. Hou, Appl. Surf. Sci. 252 (2005) 1245.11] K.F. Khaled, M.A. Amin, J. Appl. Electrochem. 39 (2009) 12.12] R. Hasanov, M. Sadikoglu, S. Bilgic, Appl. Surf. Sci. 253 (2007) 3913.13] F. Bentiss, M. Lagrenee, M. Traisnel, B. Mernari, H. El Attari, J. Hetrocycl. Chem.

36 (1999) 149.14] E. McCafferty, V. Pravadic, A.C. Zettlemoyer, Trans. Faraday Soc. 66 (1999) 237.15] S.K. Bag, S.B. Chakra borty, S.R. Chaudhari, J. Indian Chem. Soc. 70 (1993) 24.16] W.H. Ailor, Hand Book of Corrosion Testing and Evaluation, John Wiley and

Sons, New York, 1971.17] J.D. Talati, R.M. Modi, Br. Corros. J. 10 (1975) 103.18] J.D. Talati, G.A. Patel, Br. Corros. J. 11 (1976) 47.19] F.A. Champion, Corrosion Testing Procedure, 2nd ed., Chapman and Hall, Lon-

don, 1964.20] M.G. Fontana, N.D. Greene, Corrosion Engineering, McGraw Hill, 1984.21] R. Fuchs-Godec, Colloids Surf. A: Physicochem. Eng. Aspects 280 (2006) 130.22] A. Chetouani, B. Hammouti, T. Benhadda, M. Daoudi, App. Surf. Sci. 249 (2005)

375.23] B. El Mehdi, B. Mernari, M. Traisnel, F. Bentiss, M. Lagrenee, Mater. Chem. Phys.

77 (2002) 489.24] M. El Achouri, S. Kertit, H.M. Gouttaya, B. Nciri, Y. Bensouda, L. Perez, M.R.

Infante, K. Elkacemi, Prog. Org. Coat. 43 (2001) 267.25] W.J. Lorenz, F. Mansfeld, Corros. Sci. 31 (1986) 467.26] M. Erbil, Chim. Acta Turcica 1 (1988) 59.27] I. Dehri, H. Sözü saglam, M. Erbil, Prog. Org. Coat. 48 (2003) 118.28] M.M. Osman, R.A. El-Ghazawy, A.M. Al-Sabagh, Mater. Chem. Phys. 80 (2003)

55.

2

[

[

24 S. John et al. / Materials Chemistry an

29] D. Gapi, N. Bhuvaneswaran, S. Rajeswarai, K. Ramadan, Anti-Corros. MethodsMater. 47 (2000) 332.

30] M.A. Ameer, E. Khamis, G. Al-Senani, J. Appl. Electrochem. 32 (2002)149.

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d Physics 123 (2010) 218–224

31] N. Khalil, Electrochim. Acta 48 (2003) 2635.32] I. Lukovits, K. Pálfi, I. Bakó, E. Kálmán, Corrosion 53 (1997) 915.33] K. Fukui, T. Yonezawa, H. Shingu, J Chem. Phys. 20 (1952) 722.