electrochemical, quantum chemical, and molecular dynamics studies on the interaction of...

Materials and Corrosion 2011, 62, No. 11 DOI: 10.1002/maco.201005938 1031

Electrochemical, quantum chemical, and molecular dynamicsstudies on the interaction of 4-amino-4H,3,5-di(methoxy)-

1,2,4-triazole (ATD), BATD, and DBATD on copper metal in1N H2SO4

S. John, J. Joy, M. Prajila and A. Joseph*

The interaction of 4-amino-4H,3,5-di(methoxy)-1,2,4-triazole (ATD),

(4-(benzylideneamino)-4H-1,2,4-triazole-3,5-diyl) dimethanol (BATD), and

(4-(4-(dimethylamino) benzylideneamino))-4H-1,2,4-triazole-3,5-diyl) dimethanol

(DBATD) on copper in 1N sulfuric acid was investigated by potentiodynamic

polarization (Tafel), ac impedance (EIS), molecular dynamic (MD) studies, and

quantum chemical calculations at 300K. Polarization studies clearly showed that

ATD, BATD, and DBATD act as mixed type inhibitors. As the electron density around

the inhibitor molecule increases due to substitution, the inhibition efficiency also

increases correspondingly. Quantum chemical approach was used to calculate

some electronic properties of thesemolecules to ascertain the correlation between

inhibitive effect and molecular structure. Both the experimental and theoretical

studies agree well in this regard and confirm that DBATD is having a better

interaction with the metal surface in 1N sulfuric acid than BATD and ATD. The

adsorption behaviors of these molecules on the copper surface have been

studied using MDs method and density functional theory.

1 Introduction

Due to excellent thermal conductivity and good mechanical

workability, copper is a metal of choice in heating and cooling

systems. Scale and corrosion products have negative effect on

heat transfer and decrease heating efficiency of the equipment

and require periodic de-scaling and acid pickling. The use of

corrosion inhibitors is necessary in such conditions. One of the

most important methods in the corrosion protection of copper is

the use of organic inhibitors. Nitrogen and sulfur containing

heterocyclic compounds may act as inhibitors for copper due to

the chelating action of heterocyclic molecules and/or the

formation of a physical blocking barrier on the copper surface

[1, 2]. This is explained by the presence of vacant ‘‘d’’ orbital in

copper ions that form co-ordinate bond with atoms that are able to

donate electrons. Interactions of metal ions with rings containing

conjugated p-electrons are also present [3].

It is known that themechanism of copper electro-deposition/

dissolution strongly depends on the medium of action. Extensive

research has been done on the mechanism of the anodic

dissolution of copper in the sulfate solution and a number of

S. John, J. Joy, M. Prajila, A. Joseph

Department of Chemistry, University of Calicut, Calicut University P O,

Calicut, Kerala, (India)

E-mail: [email protected]

www.matcorr.com wileyonlinelibrary.com

different dissolution mechanisms have been proposed. There is a

general agreement in the literature that the process of copper

dissolution/deposition through Cuþ ions, adsorbed Cu(I)

species, or intermediate Cuþ compounds is as follows [4–10].

Cu�e� ! Cuþsurf (1)

Cuþsurf�e� ! Cu2þsol (2)

It was concluded that the first step was much faster than the

second step in sulfate solutions. When a copper electrode is

immersed in a neutral aqueous solution, dissolution of the native

oxide species proceeds and aqueous complexes of copper are

formed. In a quiescent solution, soluble Cu(II) is probably not

fully reduced to Cu(0), even though reduction is thermodyna-

mically favored at very low oxygen levels [11, 12]. Alternatively,

Cu(I) can be oxidized by the remaining oxygen in the solution to

Cu(II) in a homogeneous reaction, or disproportionation of Cu(I)

to Cu(II) and Cu(0) can occur. The residual Cu(II) can act as

oxidant during corrosion of copper via its partial reduction to

Cu(I). This paper describes the interaction of 4-amino-4H,3,5-

di(methoxy)-1,2,4-triazole (ATD),(4-(benzylideneamino)-4H-

1,2,4-triazole-3,5-diyl) dimethanol (BATD), and (4-(4-(dimethyla-

mino) benzylideneamino))-4H-1, 2, 4-triazole-3, 5-diyl) dimetha-

nol (DBATD) on copper in 1N sulfuric acid at 300K.

� 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

1032 John, Joy, Prajila, and Joseph Materials and Corrosion 2011, 62, No. 11

N

NN NH2

HO

HO

(a)

N

NN N

HO

HO

C

H

(b)

N

NN N

HO

HO

C

H

N

CH3

CH3

(c)

Figure 1. Molecular structure of (a) ATD, (b) BATD; (c) DBATD

Figure 2. Energy dispersive X-ray spectrum of copper metal

2 Experimental method

2.1 Inhibitor

The method adopted for the preparation of 1,2,4-triazole

precursor, 4-amino-4H-1,2,4-triazole-3,5-dimethanol (ATD) is

the condensation of glycolic acid with hydrazine hydrate.

Hydrazine monohydrate (E. Merck) (3.75 g, 0.75mol) was added

drop wise at 0 8C to 70% aqueous glycolic acid (E. Merck) (54.3 g,

0.50 mol). The resulting solution was heated at 120 8C for 6 h.

Then the reflux condenser was replaced with a downward

condenser and the reaction mixture was heated at 160 8C for a

further 18 h allowing excess hydrazine and water to distil off. After

cooling, the resulting yellowish crystalline solid was recrystallized

from water to give analytically pure ATD [13, 14]. BATD was

prepared by the condensation of ATD with benzaldehyde (E.

Merck) (1:1 molar ratio) using alcohol as the solvent. DBATD was

prepared by the condensation of ATD with dimethylaminoben-

zaldehyde (E. Merck) (1:1 molar ratio) using alcohol as the solvent.

The structure of the inhibitor molecules are shown in Fig. 1a–c.

2.2 Medium

The medium for the study was made from reagent grade H2SO4

(E. Merck) and doubly distilled water. All tests were performed in

aerated medium under room temperature and atmospheric

pressure.

2.3 Materials

The working electrode, copper metal, was of 100% purity

(determined by EDX spectrum Fig. 2). The copper specimens

used in weight loss measurements are cut in 4.8� 1.9 cm2

coupons and polished as recommended by the ASTM (0–4 Grit of

1200mesh). For electrochemical studies, same type of coupons

was used but only 1 cm2 area is exposed during each

measurement. Before the measurements the samples were

polished using different grade of emery papers followed by

washing with water and acetone.

2.4 Weight loss measurements

The weight loss experiments were carried out under total

immersion conditions in test solution maintained at 300K.

Copper specimens of required dimension are first rubbed with

different grade of emery papers to remove oxide layer and then

subjected to the action of a buffing machine attached with a cotton

wheel and a fiber wheel having buffing soap to ensure mirror

bright finish. All specimens were cleaned according ASTM

standard G-1-72 procedure [15–20]. The experiments were carried

out in a beaker containing 250ml solution. After the exposure

period the specimens were removed, washed initially under

running tap water, to remove the loosely adhering corrosion

products and finally cleaned with 15–20% HCl for 5min followed

by acetone. Similar experiments were performed at the same

temperature with different inhibitor concentrations to get the

optimum inhibitor concentration that shows maximum inhibitive

efficiency. From the weight loss in each experiment, the corrosion


rate was calculated in millimeter/year (mm/yr). In each case

duplicate experiments were conducted and showed that the second

results were within�1% of the first. Whenever the variations were

very large, the data were confirmed by a third test. The inhibition

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Materials and Corrosion 2011, 62, No. 11 Electrochemical, quantum chemical, and molecular dynamics studies 1033

efficiency was taken to represent the surface coverage (u). The

percentage inhibitive efficiency was calculated using the relation:

%IE ¼ W0�W

W0� 100 (3)

where W0 and W are the weight losses in the uninhibited and

inhibited solutions, respectively.

2.5 Electrochemical measurements

Electrochemical tests were carried out in a conventional three-

electrode corrosion cell with platinum sheet (1 cm2 surface area)

as auxiliary electrode and saturated calomel electrode (SCE) as the

reference electrode. The working electrode was first immersed in

the test solution and after establishing a steady state open circuit

potential (OCP), the electrochemical measurements were carried

out in a Gill AC computer controlled electrochemical workstation

(ACM, UK, model no: 1475). Electrochemical impedance spectro-

scopy (EIS) measurements were carried out with amplitude of

10mV (RMS) AC sine wave with the frequency range of 10KHz–

1Hz. The polarization curves are obtained in the potential range

from �250 to þ250mV with a sweep rate of 1000mV/min.

2.6 Computational study

Complete geometrical optimization of the investigated metals are

performed using density functional theory (DFT) with Beck’s three

parameter exchange functional alongwith Lee–Yang–Parr non-local

correlation functional (B3 LYP) with 6-31G� basis set is

implemented in Gaussian 03 program package [21–24]. Frontier

molecular orbitals (HOMO and LUMO) may be used to interpret

the adsorption of the inhibitor molecules on the metal surface. For

the simplest transfer of electrons, adsorption should occur at the

part of the molecule where softness ‘‘s’’ which is a local property,

Table 1. Inhibition efficiency obtained from weight loss measurements

for copper in 1N H2SO4 solutions in the absence and presence of

different concentrations of inhibitors at room temperature

Inhibitor Conc.(ppm)

% of corrosion inhibition efficiency atdifferent hours

24 48 72 96 120

Blank – – – – – –

10 9.49 8.88 8.23 7.69 6.94

50 13.92 13.62 12.46 11.96 11.23

ATD 100 17.72 17.43 16.97 16.59 16.15

150 28.80 28.47 27.11 26.85 24.39

200 29.34 28.86 27.62 27.05 23.36

BATD 10 15.37 14.84 13.36 12.94 12.24

50 21.42 20.84 20.05 18.65 18.32

100 28.13 27.96 27.47 27.12 26.84

150 3.29 32.07 31.84 31.84 30.86

200 34.38 34.03 33.79 33.45 32.98

DBATD 10 17.15 16.20 15.12 14.52 13.29

50 23.80 23.05 22.48 21.81 20.15

100 31.98 31.86 31.00 30.48 29.47

150 35.23 34.94 34.21 33.38 32.27

200 40.95 40.33 39.81 39.27 38.16

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has the highest value. Themolecular dynamic (MD) simulation was

performed using Material Studio 4.3 software from Accelrys Inc.

2.7 Scanning electron microscopy

The study of the surface morphology of the metal specimens in

both the absence and presence of inhibitor was carried out by

using a Digital Microscope Imaging Scanning Electron Micro-

scope model SU6600 (Serial No: HI-2102-0003) with an

accelerating voltage of 20.0 kV. Samples were attached on the

top of an aluminum stopper by means of carbon conductive

Figure 3. Anodic and cathodic Tafel lines for copper in uninhibited

1N H2SO4 and with different concentration of inhibitors: (a) ATD,

(b) BATD, and (c) DBATD



adhesive tape. All micrographs of the specimen were taken at

the magnification of 500X.

3 Results and discussion

3.1 Weight loss measurements

Weight loss studies were performed at various time intervals in

the absence and presence of different concentrations (10–

200 ppm) of ATD, BATD, and DBATD. The increase in the

concentration of these molecules was accompanied by a

decrease in weight loss and corrosion rate and increase in

percentage inhibition efficiency. A very thin surface inhibitor film

on the metal surface provides considerable protection to copper

against corrosion. This film reduces the active surface area

exposed to the corrosive medium and delays the hydrogen

evolution and copper dissolution. Formation of the surface film is

confirmed by scanning electron microscopy (SEM). The results

are summarized in Table 1. These results show that ATD, BATD,

andDBATD interacting with themetal surface in 1N sulfuric acid

decrease the corrosion rate 1N H2SO4 solution.

3.2 Potentiodynamic polarization studies

Polarization measurements have been carried out to gather

knowledge concerning the kinetics of anodic and cathodic

reactions. The polarization curves for copper in 1N H2SO4

solution in the absence and presence of various concentrations of

the inhibitors are shown in Fig. 3. The values of electrochemical

kinetic parameter, corrosion potential (Ecorr), corrosion current

density (icorr), and Tafel slopes (ba and bc) determined from

these experiments by extrapolation method are listed in Table 2.

The corrosion inhibition efficiency was calculated using the

relation

%IE ¼ ICorr��ICorrICorr�

� 100 (4)

Table 2. Polarization parameter and inhibition efficiency for the corrosion o

concentrations of inhibitors at room temperature

Inhibitor Conc. (ppm) Ecorr (mV) ba (mV/dec)

Blank – �144 64.32

10 �131 57.00

50 �136 50.00

ATD 100 �122 43.00

150 �101 41.00

200 �107 40.00

10 �92 55.50

50 �104 49.00

BATD 100 �115 40.33

150 �103 39.33

200 �104 35.41

10 �137 60.43

50 �139 52.42

DBATD 100 �92 48.80

150 �90 45.31

200 �88 40.62


where ICorr� and ICorr are uninhibited and inhibited corrosion

current density, respectively, determined by extrapolation of

Tafel lines at the corrosion potential. The inhibitor molecule first

adsorb on the copper surface and blocking the available reaction

sites [25]. The surface coverage increases with the inhibitor

concentration. The presence of defects on the metal surface

permits free access to Hþ ions [26] and a significant dissolution

of metal takes place [27]. The formation of a surface film due

the interaction of these molecules on the metal electrode

provides considerable protection to copper against corrosion.

This film reduces the active surface area exposed to the corrosive

medium and delays the hydrogen evolution and copper

dissolution.

3.3 Electrochemical impedance spectroscopy

All impedance measurements were carried out under potentio-

static conditions after 1 h of immersion. Nyquist plots of

uninhibited and inhibited solution containing different concen-

tration of triazole derivatives are performed over a frequency

range from 10KHz to 1Hz and are shown in Fig. 4. These

diagrams have similar shape; the shape is maintained throughout

all tested concentration, indicating that almost no change in

the corrosion mechanism occurs due to inhibitor addition. The

Nyquist diagrams show one capacitive loop at high frequencies

with one capacitive time constant in Bode phase plot and

one inductive loop at low frequency values (LF) (Fig. 5). The

first capacitive loop at high frequencies (HF) represents

the phenomenon associated with electrical double layer. The

presence of the inductive loop at LF may be attributed to the

relaxation process obtained by adsorption species like Hþads, on

the electrode surface [28–31]. It may also be attributed to the

adsorption of inhibitor molecules on the electrode surface or to

the re-dissociation of the passivated surface at low frequencies.

The capacitive loop corresponds to the charge transfer reaction,

which depends on either direct electron transfer at the metal

surface or the electron conduction through the film surface. The

above impedance diagrams (Nyquist) contain depressed semi-

f copper in 1NH2SO4 solutions in the absence and presence of different

bc (mV/dec) icorr (mA/cm2) CR (mm/yr) h (%)

80.00 0.00215 0.0251 –

78.80 0.00214 0.0249 0.46

72.00 0.00210 0.0246 2.33

65.81 0.00207 0.0232 3.72

52.96 0.00199 0.0215 7.44

46.50 0.00192 0.0204 10.69

77.88 0.00212 0.0250 1.40

72.00 0.00201 0.0241 6.51

64.21 0.00192 0.0223 10.70

49.26 0.00149 0.0174 30.69

42.50 0.00139 0.0166 35.34

75.23 0.00209 0.0244 2.79

43.21 0.00199 0.0232 7.44

35.06 0.00148 0.0173 31.16

33.20 0.00142 0.0166 33.95

31.47 0.00136 0.0158 36.74

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Figure 4. Nyquist diagrams for copper in 1N H2SO4 containing

different concentrations of (a) ATD, (b) BATD, and (c) DBATD

Figure 5. Bode diagrams for copper in 1N H2SO4 containing different

concentrations of (a) ATD, (b) BATD, and (c) DBATD

circles with the center under the real axis. Such behavior is

characteristic of solid electrodes and often referred to frequency

dispersion could be attributed to different physical phenomenon

such as roughness, inhomoginities of the solid surfaces,

impurities, grain boundaries, and distribution of surface active

sites. In this case, the constant phase element CPE is introduced

in the circuit instead of a pure double layer capacitor to give a

more accurate fit [32–34]. The impedance function of a CPE has

the following equation.

ZCPE ¼ ½Y0ðjvÞn��1 (5)

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where Y0 is the magnitude of the CPE, n the CPE exponent (phase

shift), v the angular frequency (v¼ 2pf, where f is the AC

frequency), and j is the imaginary unit. When the value of n is 1,

the CPE behaves like an ideal double-layer capacitance (Cdl) [35,

36]. As compared to a parallel combination of resistor and

capacitor, the CPE is able to provide a much better fit to most

impedance data. The CPE can achieve this fit using only three

parameters, that is one parameter more than a typical Rp couple.

The double layer between charged metal surface and the solution

is considered as an electrical double capacitor. The adsorption of

triazole derivatives on the copper metal decreases its electrical



Table 3. Impedance parameter and inhibition efficiency for the corrosion of copper in 1N H2SO4 solutions in the absence and presence of different

concentrations of inhibitors at room temperature

Inhibitor Conc. (ppm) Rct (mF/cm2) Cdl (mA cm2) icorr (mA/cm2) CR (mm/yr) n IE (%)

Blank – 1685 992.7 0.0154 0.1801 0.75 –

10 1691 987.1 0.0152 0.1799 0.74 0.35

50 1780 860.1 0.0150 0.1761 0.70 5.33

ATD 100 1821 195.0 0.0147 0.1658 0.69 7.47

150 1856 167.1 0.0139 0.1588 0.69 9.21

200 1999 154.1 0.0122 0.1502 0.70 15.70

BATD 10 1781 145.6 0.0149 0.1761 0.71 4.82

50 1850 145.1 0.0146 0.1701 0.68 8.37

100 1913 138.6 0.0141 0.1643 0.69 11.39

150 2101 133.3 0.0136 0.1470 0.70 19.32

200 2843 122.4 0.0103 0.1181 0.71 40.37

DBATD 10 1782 131.6 0.0146 0.1703 0.72 4.88

50 1859 153.3 0.0140 0.1632 0.72 8.82

100 1982 125.6 0.0132 0.1531 0.69 14.48

150 3271 104.3 0.0079 0.0927 0.67 48.18

200 3413 101.2 0.0075 0.0797 0.69 50.34

capacity because they displace the water molecule and other ions

originally adsorbed on the metal surface. The decrease in this

capacity with increase in concentration of the inhibitors may be

attributed to the formation of a protective film on the electrode

surface [37]. The thickness of this protective layer also increases

with increase in inhibitor concentration as more inhibitors

electrostatically adsorbed on the electrode surface, resulting in a

noticeable decrease in Cdl. This trend is in accordance with the

Helmholtz model given by the equation

Cdl ¼SS0A

d(6)

where d is the thickness of the protective layer, S the dielectric

constant of the medium, S0 the vacuum permittivity, and A is the

surface area of the electrode. The percentage inhibitive efficiency

was calculated using the relation:

%IE ¼ Rct��Rct

Rct�(7)

Where Rct� and Rct are values of the charge transfer

resistance observed in the presence and absence of inhibitor

molecules. The values of both polarization resistance and

corrosion inhibition efficiency (IE%) corresponding to the EIS

at 300K are given in Table 3.

3.4 Quantum chemical calculations

The optimized structure of the compounds ATD, BATD, and

DBATD in their ground state are shown in Fig. 6. The

MD simulation was performed using Material Studio 4.3

software from Accelrys Inc. Cu(110) plane was chosen for

the simulation study. The interaction energy Einteractionbetween the copper surface and the inhibitor molecule was

calculated as:

Einteraction ¼ Etotal�ðEsurface þ EinhibitorÞ (8)


Where Etotal is the total energy of copper and inhibitor

molecule. Esurface and Einhibitor are the energy of copper and

inhibitor molecules, respectively. The binding energy of the

inhibitor molecule is the negative value of the interaction energy

Ebonding ¼ �Einteraction (9)

3.5 Global reactivity

The frontier orbitals (highest occupied molecular orbital HOMO

and lowest unoccupied molecular orbital LUMO) of a chemical

species are very important in defining its reactivity. Fukui et al.[38] first recognized this. A good correlation has been found

between the speed of corrosion and EHOMO that is often

associated with the electron-donating ability of the molecule. The

literature shows that the adsorption of the inhibitor on the metal

surface can occur on the basis of donor–acceptor interactions

between the p-electrons of the heterocyclic compound and the

vacant d-orbital of the metal surface atoms [39]. High values of

EHOMO have a tendency of the molecule to donate electrons to

appropriate acceptor molecules with low energy, empty molecular

orbital. Increasing values of EHOMO facilitate adsorption and

therefore enhance the inhibition efficiency, by influencing

the transport process through the adsorbed layer. Similar

relations were found between the rates of corrosion and

DE¼ ELUMO� EHOMO [40–42]. The energy of the lowest

unoccupied molecular orbital indicates the ability of the molecule

to accept electrons. The lower the value of ELUMO, the more

probable the molecule would accept electrons. Consequently,

concerning the value of the energy of the gap DE, larger values ofthe energy difference will provide low reactivity to a chemical

species. Lower values of the energy difference will render good

inhibition efficiency, because the energy to remove an electron

from the highest occupied orbital will be low [43, 44]. In Table 4,

certain quantum-chemical parameters related to the molecular

electronic structure such as EHOMO, ELUMO, and DE are

presented. The pictorial representation of the HOMO and

LUMO of ATD, BATD, andDBATD are presented in Figs. 7 and 8.

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Figure 6. Optimized molecular structure of the inhibitor molecules:

(a) ATD, (b) BATD, and (c) DBATD

Figure 7. The highest occupied molecular orbital (HOMO) of the

inhibitors: (a) ATD, (b) BATD, and (c) DBATD

The higher value of EHOMO and lower value of the gap energy DEshow that DBATD acts as a better inhibitor than BATD and ATD.

The results for the calculations of the ionization potential (I) andthe electron affinity (A) by application of the Koopmans’ theorem

are shown in Table 4. According to the Hartree–Fock theorem, a

relationship exists between the energies of the HOMO, LUMO,

ionization potential (I), and the electron affinity as �EHOMO¼ I;�ELUMO¼A. Although no formal proof of this theorem exists

within DFT, its validity is generally accepted. For electronegativity

Table 4. The calculated quantum chemical properties for the triazole de

Molecule Total energy (eV) HOMO (eV) LUMO (eV) DE

ATD �14330 �0.1382 �6.9805 6

BATD �21653 �2.4035 �6.9190 4

DBATD �25299 �1.7910 �5.9402 4

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(x) and hardness (h), their operational and approximate

definitions are �m¼ (IþA)/2¼x, h¼ (I�A)/2. Two systems,

Cu and inhibitor, are brought together, electrons will flow from

lower x (inhibitor) to higher x (Cu), until the chemical potentials

become equal. As a first approximation, the fraction of electrons

transferred (DN) [45] will be given by

DN ¼ xCu�xinhi

2ðxCu þ xinhiÞ(10)

where Cu is the Lewis acid according to the HSAB concept [45].

The difference in electronegativity drives the electron transfer,

and the sum of the hardness parameters acts as a resistance [46].

In order to calculate the fraction of electrons transferred, a

theoretical value for the electronegativity of bulk copper was used

xCu� 4.48 eV, and a global hardness of hCu� 0, by assuming that

for a metallic bulk I¼A [47–51] because they are softer than the

neutral metallic atoms. From Table 4, it is possible to observe that

rivatives ATD, BATD, and DBATD

(eV) m I A x h DN

.8423 4.9367 0.1382 6.9805 3.5500 3.4212 0.1812

.5155 7.1341 2.4035 6.9190 4.6612 �2.2577 0.0305

.1491 9.5912 1.7910 5.9402 3.8656 �2.0745 0.2246



Figure 8. The lowest unoccupied molecular orbital (LUMO) of the

inhibitors: (a) ATD, (b) BATD, and (c) DBATDFigure 9.Mode of adsorption of (a) ATD, (b) BATD, and (c) DBATD on Cu

(110) surface

the fraction of electrons transferred DN, will be high for DBATD

and hence it shows higher inhibition efficiency.

3.6 Molecular simulation study

To understand the performance mechanism of interaction of

these molecules with copper metal in 1N sulfuric acid, molecular

modeling studies have been carried out which indicate a strong

molecular attraction to the metal surface by the indicator

molecules. The modeling studies were designed to examine this

relationship by predicting the inhibitor–metal surface interaction

that lead to optimal molecular binding on the copper metal

surface [52–54].

Table 5. The outputs and descriptors calculated by Monte Carlo simulati

Inhibitor Totalenergy(kJ/mol)

Adsorptionenergy(kJ/mol)

Rigid adsorptienergy(kJ/mol)

ATD 11231.54 �181024.7 5913.457

BATD 39156.88 �223221.6 23051.8

DBATD 141992.9 �166525.5 101302.2


In Monte Carlo simulation, MDs were performed on a

system comprising triazole derivatives, solvent molecules, and

copper surface. Each triazole derivative is placed on the Cu (110)

surface, optimized, and then MDs simulations were performed.

The Monte Carlo simulation process tries to find out the lowest

energy of the whole system. The output and descriptors calculated

by Monte Carlo simulation are presented in Table 5. The

parameters presented in Table 5 include total energy of the

substrate–adsorbate configuration. The total energy is defined as

the sum of the energies of the adsorbate components, rigid

adsorption energy, and deformation energy. In this study, the

substrate energy is taken as zero. The adsorption energy is

defined as the sum of the rigid adsorption energy and

on for adsorption of ATD, BATD, and DBATD on Cu(110) surface

on Deformationenergy(kJ/mol)

Atomistic:dEad/dNi

Calculatedbinding energy

(kJ/mol)

�186938.2 �181024.7 28159.27

�246273.5 �223221.6 175362.4

�267827.7 �166523.7 585143.5

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deformation energy for the adsorbate components. The rigid

adsorption energy reports the energy, in kcal/mol, released (or

required) when the unrelaxed adsorbate components are

adsorbed on the substrate. The deformation energy reports the

energy released when the adsorbed adsorbate components

are relaxed on the substrate surface dEad/dNi which defines

the energy of substrate–adsorbate configurations where one of

the adsorbate components has been removed. As can be seen

from Table 5, DBATD has maximum total energy and rigid

adsorption energy and it confirms the experimental results. The

close contact between the triazole derivatives and Cu (110) surface

Figure 10. SEM images of (a) copper metal, (b) in 1MH2SO4 without inhibit

200ppm of BATD after 24 h, and (e) in the presence of 200 ppm of DBAT

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as well as the best adsorption configuration for the studied

compounds are shown in Fig. 9.

3.7 Scanning electron microscopy

Surface examination using SEM was carried out to investigate the

effect of these three inhibitors on the surface morphology of

copper. Figure 10a shows the surface of a polished copper sample.

Figure 10b shows a SEM image of the surface of the copper

specimen after immersion in 1.0N H2SO4 solution with no

additives for 24 h. This micrograph reveals that the surface was

or, (c) in the presence of 200ppm of ATD after 24 h, (d) in the presence of

D after 24 h weight loss measurements



strongly damaged in the absence of inhibitors. Figure 10c–e

shows SEM images of the surface of the copper specimens

immersed for the same time interval in 1N H2SO4 solution

containing 200 ppm of ATD, BATD, and DBATD. After the

addition of the inhibitors the surface damage is drastically

reduced and the faceting observed in Fig. 10b has gone and the

surface is smooth. So it can be concluded that copper corrosion

does not occur or the rate of corrosion was inhibited strongly in

the presence of ATD, BATD, andDBATD in themedium. It is also

clear from Fig. 10c–e that more polished surfaces are formed in

the presence of inhibitors compared to uninhibited samples

proving its higher inhibition efficiency [55–58].

4 Conclusions

1. T

�

he ATD, BATD, and DBATD molecules act as inhibitors for

copper in aerated 1N H2SO4 only at high concentrations.

However the inhibition efficiency is not very high as evident

from the experimental and theoretical studies.

2. T
he percentage inhibition efficiency increases with increase in
concentration of ATD, BATD, and DBATD and decreases with

longer exposure periods at 300K.

3. H
igher surface coverage on the metal surface was obtained in
1N H2SO4 solution with higher inhibitor concentrations.

4. R
esults of polarization studies suggest that the inhibitors,
ATD, BATD, and DBATD act as mixed type inhibitors.

5. T
he inhibitor molecules adsorb on the metal surface and
blocking the reaction sites.

6. T
he surface area available for the attack of the corrosive species
decreases with increasing inhibitor concentrations.

7. M
olecular dynamics simulations studies confirm the adsorp-
tion behavior of ATD, BATD, and DBATD on the copper

surface.

8. T
he relationship between efficiency of inhibition of copper
corrosion in 1N H2SO4 by ATD, BATD, and DBATD and the

EHOMO, ELUMO, ELUMO–EHOMO and DN were calculated by

DFT method.

9. T
he results of quantum chemical calculations and the
electroanalytical results are in conformity with each other

and the extent of interaction of DBATD molecules on copper

metal in 1N sulfuric acid is greater than BATD and ATD.

Acknowledgements: The authors are grateful to Kerala State

Council for Science Technology and Environment (KSCSTE)

for financial support in the form of a major research project

018/SRSPS/2006/CSTE. One of the authors (PM) is also grateful

to CSIR New Delhi for providing research fellowship.

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(Received: September 15, 2010)

(Accepted: January 7, 2011)

W5938


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