electrochemical study and computational details of copper corrosion inhibition by 1h-benzotriazole...

Toumiat & al. / Mor. J. Chem. 3 N°4 (2015) 809-823

809

ELECTROCHEMICAL STUDY AND COMPUTATIONAL DETAILS OF

COPPER CORROSION INHIBITION BY 1H-BENZOTRIAZOLE IN 3

WT. % NACL MEDIUM

Karima TOUMIAT 1, 3,*

, Abdenacer GUIBADJ 1, 3

, Mohamed B. TAOUTI 2, 3

, Touhami

LANEZ 4

1 Department of Materials Sciences, Laghouat University, PO Box 37, 03000, Laghouat, Algeria

2 Department of Chemical Engineering, Laghouat University, PO Box 37, 03000, Laghouat, Algeria

3 physical chemistry laboratory materials, Laghouat University, PO Box 37, 03000, Laghouat, Algeria

4 VTRS Laboratory, El Oued University, PO Box 789, 39000, El Oued, Algeria

*Corresponding author. E-mail: [email protected]

Received 04 Aug 2015, Revised 17 Aug 2015, Accepted 15 Oct 2015

Abstract

The effect of 1H-benzotriazole (BTAH) with ppm (part per million) grade concentrations on copper

corrosion in aerated 3 wt. % NaCl solution is studied using chemical method (weight loss) and

electrochemical methods (Potentiodynamic Polarization and Electrochemical Impedance Spectroscopy

(EIS)). The present study confirm that the BTAH acts as a mixed-type inhibitor of copper corrosion in 3 wt.

% NaCl. The optimum inhibition efficiency is at 30 ppm of BTAH. The surface characterization is

performed using Scanning Electron Microscopy (SEM) to confirm the adsorption of the inhibitor molecules

after 21 days of immersion time in aerated 3 wt. % NaCl. The results obtained from different techniques

used in this research are in very good agreement and revealed that the BTAH is a very good inhibitor of

copper corrosion in sodium chloride medium. Computer Simulation techniques confirm that the BTAH

molecules adsorbed on the Cu (110) Surface.

Keywords: Copper, corrosion inhibition, potentiodynamic polarization, EIS, weight loss.

1. Introduction

From a wide range of metals used in industries, copper is extensively used owing to its remarkable thermal

andelectric properties. It’s usually employed in heating and cooling systems because of its excellent thermal

conductivity [1-7]. Copper is also exclusively used for piping and delivery of water in marine industry.

These pipes are used in a medium rich of Cl- [8]. It is known that the corrosion products caused by chloride

ions Cl-leads to a reduction in the efficiency of copper which causes huge economic loss [9, 10]. The

corrosion inhibition is one of several methods of protection against metals degradation in different aqueous

solutions [11-15]. To overcome this problem, an electrochemical monitoring was done by studying the

behaviour of copper in NaCl 3 wt. % in presence and absence of the inhibitor BTAH Fig.1.

mailto:[email protected]


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Figure1. Molecular structure of 1H-Benzotriazole (BTAH).

In this context several studies were done, BTAH has been known for six decades as a corrosion inhibitor for

copper.1. Cotton and al. [16] are the first contributors in the field of BTAH as copper corrosion inhibitor.

They demonstrated that the pre-treatment of the copper surface by BTAH induce a long lasting prevention of

staining, they elucidate the BTAH inhibitory action in the terms of physical barrier. Wall and Davies [17]

showed that, in the presence of BTAH dissolution of copper and pick up of copper ions from the solution is

reduced in closed circuit systems containing copper. They claimed that BTAH forms an insoluble and

invisible chelate on the copper surface. That is responsible for reducing corrosion attack.

Poling [18] confirmed the linear polymeric Cu (I) BTA structure proposed by Cotton [16] and stated more

decisively that the structure contains Cu(I) ions, the formation of Cu (I) BTA was not limited to a

monolayer, but could grow further to from films up to several thousand Å thick.

2. Experimental

2.1. Chemicals and preparation of the simples

BTAH (self-prepared 97%), NaCl electrolyte prepared with deionized water. A three-electrode

electrochemical cell was used which contain counter electrode of Platinum (Pt. 1 cm ²) and saturated

calomel electrode (SCE) as reference electrode. The working electrodes were made using pure copper 99.99

% cylinder. The samples were mechanically cut into cylinders (D1= 1.1 cm &D2= 0.8 cm) x 1cm

dimensions. The samples used for the electrochemical study were welded with electric cables for easier use,

then coated with epoxy resin and finally polished with abrasive papers (1200,1500,2000 and 2500) followed

by a finishing polishing (Felt) with Diamond Polishing Paste (0.1 µm). The samples used for weight loss

experiment were polished with same way. All samples were cleaned successively with acetone, distilled

water and deionized water.

2.2. Electrochemical measurements

The potentiodynamic polarization and EIS measurements were performed using an Auto lab (PGZ-402)

electrochemical workstation and an electrochemical cell (100 ml) with three electrodes, the solution was not

stirred or deaerated. Before the potentiodynamic polarization measurements, an open circuit measurement

for 30 min was performed to stabilize the potential. The potential was scanned from – 400 to 400 mV at a

scan rate of 1mV.min-1

. The EIS measurements were performed at open circuit potential for 30 min, in a

frequency range from 100 KHz to 100mHz.

2.3. Weight loss and SEM analyses

Samples used for weight loss measurement were prepared by the same method mentioned previously

(Paragraph 2.1.). In a cylindrical shape (d = 0.8 cm & h = 0.3 cm) with an exposed total area (A=1.76 cm²).


811

After polishing and weighing (m1) the samples introduced in 100 ml of 3 wt. % of NaCl solution with and

without inhibitor used for (2-21) days. Subsequently, the tested samples were removed, cleaned and weighed

(m2). In order to see if the BTAH molecules are effectively adsorbed on the copper surface executed the

SEM analysis, SEM is widely used to detect the morphological features of metal surface.The SEM

micrograph were obtained for copper samples used in weight loss part. The surface morphology of these

copper samples were investigated by using SEM analysis (VEGA 3, TESCAN) at 5, 10 and 20.0 KV.

2.4. Computational details

Molecular simulation studies were carried using Materials Studio 7 software from accelrys Inc. to find the

correlation between theoretically calculated properties and experimentally determined inhibition efficiency

for copper corrosion in 3 wt. % NaCl solution by BTAH organic inhibitor.

The DFT+ semi-empirical tight binding method was used for building and to optimize BTAH

molecule,determine the electronic properties of BTAH, effectof the frontier molecular orbital energies The

energy of the highest occupied molecular orbital (EHOMO), the energy of the unoccupied molecular orbital

(ELUMO), electronic charges on reactive centers, dipole moment and the energy of the gap, Equation (1).

LUMO HOMOE E E

(1)

Interaction between BTAH molecules and Cu (110) surface was carried out in a simulating box (14.45

Å×10.22Å× 29.99 Å) with periodic boundary conditions. The Cu (110) surface was first built and relaxed by

minimizing its energy using molecule mechanics then the surface of Cu (110) was increased by constructing

a supercell, a vacuum slab of 30 Å thickness was built on the Cu (110) surface. The number of layers in the

structure was chosen so that the depth of surface is greater than the non-bond cutoff used in the calculation,

we choose 6 as a number of layers which sufficient depth that the inhibitor molecules will only be involved

in non-bond interactions with Cu (110) surface. After minimizing Cu (110) surface and BTAH molecules,

the corrosion system will be built by layer builder to place the inhibitor molecule on Cu (110) surface using

a forcefield COMPASS (Condensed phase Optimized Molecular Potentials for Atomistic Simulation

Studies). The adsorption locator module in Materials Studio 7 software from accelrys Inc. [19] allows

selecting thermodynamic ensemble and associated parameters, temperature and pressuring and initiating a

dynamic calculation. The dynamic simulations procedures have been described elsewhere [20].

3. Results and discussion

3.1. Potentiodynamic Polarization results

Fig. 2 represent the behavior of pure copper electrodes in aerated 3% wt. NaCl solution at room temperature,

in the absence and in the presence of different concentrations from 10 to 40 ppm grade of BTAH after an

immersion time of 30 min. as an open circuit potential measurement.

The cathodic corrosion reaction of copper in NaCl solution is the reaction of oxygen [21-24]:

2 22 4 4O H O e OH

(2)

Usually, the dissolution of copper (anodic corrosion reactions) is:

1Cu Cu e

(3)

Moreover, Cu+

ions can undergo disproportionation according to Equation (4) [21-24]

22Cu Cu Cu (4)


812

When we use an aerated corrosive aqueous medium in near neutral pH, which contained complexing agents

such as Cl- , we have to consider the formation of copper complex such as

2CuCl ; as indicated by following

anodic reactions:

2adsCuCl Cl CuCl (5)

1 adsCu Cl CuCl e (6)

Compared with the solution without inhibitor the corrosion potential (Ecorr) is shifted to the more positive

values and both the anodic and cathodiccurrents (icorr) were decreased. This indicates that the BTAH

inhibitor acts as a mixed-type corrosion inhibitor.

-400 -200 0 200 400

-10

-9

-8

-7

-6

-5

-4

-3

-2

-1

log i (

A/cm

²)

Potential (mV/ECS)

Blank

10 ppm BTAH

20 ppm BTAH

30 ppm BTAH

40 ppm BTAH

Figure 2. Polarisation curves of copper electrodein the absence and in the presence of various

concentrations of BTAH in aerated 3% wt. NaCl solution.

The cathodic and the anodic currents progressively diminish with an increment in BTAH concentration,

that’s clearer in anodic current.The electrochemical parameters shown in Table 1extracted from polarization

curvesshown in Fig. 2 were obtained after an electrochemical follow of the behavior of pure copper in 3%

wt. NaCl medium in absence and presence of different concentrations of BTAH at room temperature. The

results were obtained using Tafel extrapolation method. Fig. 2 showsclearly that the cathodic polarisation

curves does not display an extensive Tafel region which confirm a limiting diffusion current return to the

reduction of dissolvedoxygen, the Tafel extrapolation method was used for both anodic and cathodic Tafel

region using Voltamaster 4.0 program.

The kinetics of electron transfer at the metal-solution interface can be shown using Butler-Volmer equation

[25]. For the present study the Butler –Volmer equation is given by Equation (7).

corr corr

αnF (E-E )/RT -(1-α) nF (E-E /RT) e corri i e

(7)

whereicorr is the corrosion current density at the corrosion potential Ecorr, α is the transfer coefficient (α =

0.5), and n the number of electrons transferred. When the rate of the back reaction is negligible Equation (7)

gives:

logE a b i (8)

where𝑎 and 𝑏 constants. In Equation (8), when corrE E and when

corri i this is the basis of Tafel

exploitation.The inhibition efficiency (ηi (%)) shown in table 1 was calculated from values of (icorr) using the

following equation:

0

0

% 1 00corr corr

corr

i ii

i

(9)


813

here0

corri and corri

are the corrosion current densities for Cu electrode in aerated 3% wt. NaCl in absence and

presence of different concentrations of BTAH.

Table 1. Corrosion inhibition parameters of copper in aerated 3% wt. NaCl solution in the absence and

presence of various concentrations of BTAH.

C

(ppm)

Ecorr

(mV/SCE)

bc

(mV.dec-1

)

icorr

(µA.cm-²)

ηi

(%)

Blank -232.4 217.8 7.865 --

10 -153.6 149.9 0.241 96.93

20 -153.1 144.0 0.208 97.35

30 -103.9 141.6 0.043 99.45

40 -190.9 136.2 0.088 98.88

It can be concluded that the corrosion current density decreased and the inhibition efficiency increased with

the increase of BTAH concentration, The BTAH adsorbed on copper surface acted as a barrier layer to block

corrosion process. The addition of 10 ppm of BTAH to the electrolyte can reduces to great importance of

inhibition efficiency. The optimal inhibition efficiency of 99.45% was obtained for 30 ppm of BTAH.The

obtained result was also confirmed by weight loss method.

3.2. EIS results

In this experimental part of electrochemical measurements the Electrochemical Impedance Spectroscopy

(EIS) was used to confirm results of the potentiodynamicpolarization step and to get further information of

the inhibition process with the same concept with potentiodynamic measurement, The EIS is an excellent

tool to investigate the corrosion and the adsorption phenomena. [25]Several experiences were done using

copper electrode in different electrolytes in the absence and in the presence offour different concentrations

of the inhibitor (BTAH) in aerated 3wt. % NaCl medium at room temperature. The results obtained at an

open circuit potential immersed for 30 min are represented as typical Nyquist and Bode plots, are shown in

(Fig. 3-4.1-4.2)

0 1000 2000 3000 4000 5000 6000-200

0

200

400

600

800

1000

1200

1400

1600

-Zi (

ohm

.cm²)

Zr (ohm.cm²)

Blank

10 ppm BTAH

20 ppm BTAH

30 ppm BTAH

40 ppm BTAH

Figure3. Nyquist plotsof copper electrode at an open-circuit potential after 30 min in aerated 3% wt. NaCl

solution without and with various concentrations of BTAH.


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In the presence of BTAH the impedance spectra for the Nyquist plots Fig. 3 shows a depressed semicircle in

the high frequency region. This high frequency semicircle is attributed to the charge transfer and double

layer capacitance [26]. The lowest frequency area is generally known as Warburg impedance related to the

diffusion of soluble copper species from electrode surface to bulk solution [26]. The diameter of semicircles

in extent with the increasing of the inhibitor concentrations.

-1 0 1 2 3 4 5

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.1

log

|Z|(o

hm.c

m²)

log f (Hz)

Blank

10 ppm BTAH

20 ppm BTAH

30 ppm BTAH

40 ppm BTAH

Figure 4.1. Bode plot for copper electrode in aerated 3 wt. NaCl solution without and with different

concentrations of BTAH.

The Bode plots Fig. 4.1 show that the impedance values over the whole frequency range increased with

increasing the BTAH concentration. It can be obtained from Bode phase plots Fig. 4.2 that the corrosion

process taking place at the electrode surface has one relaxation time constant related to the relaxation of the

electrical double layer capacitor.

It is also observed that the increasing of BTAH concentrations results an increase in the maximum phase

angle which confirm the inhibiting action of BTAH on copper in the study medium.

-1 0 1 2 3 4 5-80

-70

-60

-50

-40

-30

-20

-10

0

10

Phas

e (d

egre

e)

log f (Hz)

Blank

10 ppm BTAH

20 ppm BTAH

30 ppm BTAH

40 ppm BTAH

Figure 4.2. Phase angle plot for copper electrode in aerated 3 wt. NaCl solution without and with different

concentrations of BTAH.


815

The equivalent circuit model used to construe impedance characteristics is shown in this circuit was reported

in several studies for copper/solution interface [26, 27].

Figure 5. Equivalent circuit used to fit experimental EIS data in Fig. 3, symbols in the circuit were indicated

in the text.

The parameters were obtained by fitting the equivalent circuit and the inhibition efficiency are represented

in Table 2. Here Rs represented the solution resistance. Q represented the constant phase element (CPE), Rt

represent the charge transfer resistances and W is the Warburg impedance.

The impedance of CPE represented by the following equation:

0

nQ Y j (10)

Where 𝑌0 is the modulus, j is the imaginary root, 𝛚 is the angular frequency and n is the phase.

In the practical electrode system, the impedance spectra are offer depressed semicircles with their centers

below the real axis. This phenomena is known as the dispersing effect [28].The inhibition efficiency (ηi) is

calculated using charge transfer resistance as follow:

01 100

Rti

Rt

(11)

Table 2. Impedance parameters for copper electrode in 3 wt. % NaCl solution in the absence and presence

of various concentrations of BTAH inhibitor at room temperature

Solution

Parameters

Rs(Ω) Q

Rt (Ω) W(Ω.s-1/2

) ηi(%) Y

0(µF.s

a-1) a

Blank 11.43 66.27 0.920 797.6 784.9 --

10 8.414 54.97 0.736 2 047 674.2 61.03

20 10.25 40.34 0.775 2 832 439.0 71.83

30 6.814 47.24 0.727 5 241 148.8 84.78

40 8.467 43.68 0.736 2 761 26.58 71.11

3.3. Weight loss and SEM analyses results

In this part the variation of the weight loss of copper at different immersion times in aerated 3 wt. % NaCl

solution, at room temperature 25°C for (2, 4, 7, 10, 14 and 21) days, without inhibitor and with 30 ppm of

BTAH results shown in Fig. 6. The concentration of inhibitor used in this part was chosen as the optimal

concentration confirmed in the electrochemical study part. The loss of weight mentioned (∆m: mg.cm-²).

The corrosion rate (Rcorr: mg.cm-1

.day-1

) and the inhibition efficiency (ηw %) were calculated as follow

[29,30]:


816

1 2 m m

mA

(12)

corr

mR

At

(13)

%

un in

corr corr

w un

corr

R R

R

(14)

Here, A is the total area exposed to the solution, t is the time of immersion, corr

unR is the corrosion rate

without inhibitor and corr

inRis the corrosion rate with inhibitor.

-2 0 2 4 6 8 10 12 14 16 18 20 22 24

0.0000

0.0004

0.0008

0.0012

0.0016

0.0020

wei

ght

loss

(m

g.cm

-²)

t (day)

Blank

30 ppm BTAH

Figure 6. Variation of the weight loss as function of timefor copper coupons in in aerated solution of 3 wt.

% NaCl without and with 30 ppm of BTAH.

0 2 4 6 8 10 12 14 16 18 20 22 240

20

40

60

80

inhi

bitio

n ef

ficie

ncy

%

t (day)

30 ppm BTAH

Figure 7.Variation of the inhibition efficiencyas function of time for copper coupons in in aerated solution

of 3 wt. % NaCl containing 30 ppm of BTAH.

It can be seen that the inhibition efficiency of BTAH on copper immersed in aerated solution of 3 wt. %

NaCl varied from 50 % after two days of immersion time to84.84 % after 21 days immersion time Fig. 7.


817

It’s clear that the BTAH has a very good effect against copper corrosion in the study solution, also it stays

effective after 21 days of immersion without forget the low concentration of inhibitor used in this part.

The SEM micrograph for the copper samples immersed in aerated 3 wt. % NaCl in absence and presence of

BTAH with concentration 30 ppm for 21 days is shown in Fig. 8-9. It is obvious that the BTAH molecules

are partially distributed on the copper surface. The surface coverages were obtained from:

inhm m

m

(15)

m , inhm

are weight loss obtained from previous measurements. The corrosion rates were obtained from

equation (15). The inhibition efficiency, coverages and corrosion rates are tabulated as follow:

Table 3. The inhibition efficiency (𝜂w %), changes of the degree of copper surface coverages (𝜃) and

corrosion rates (corr

unR : solution without inhibitor andcorr

inR : with 30 ppm of BTAH) obtained from weight

loss data in aerated 3 wt. % NaCl solutions

30 ppm

BTAH

Time (day)

2 4 7 10 14 16 21

𝜂w(%) 50 50 57.14 66.66 78.94 81.81 84.84

𝜃 (10-4

) 0.203 0.406 0.601 0.881 1.442 1.559 2.441

corr

unR (10-5

cm/d) 3.23 3.23 3.23 3.87 4.38 4.44 5.07

corr

inR (10-5

cm/d) 1.61 1.61 1.38 1.29 0.92 0.80 0.79

Figure 8. SEM image for polished copper electrode

(a) (b)

Figure 9. SEM images for copper electrodes after 21 days immersion in aerated 3 wt. % NaCl solution

without inhibitor (a) and with 30 ppm of BTAH (b).


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The Fig. 9.a represent the copper sample before immersion, the Fig. 9.bshown the sample, the surface

morphologyof copper sample immersed in solution without inhibitor, it is clear that surface strongly

corroded by the Sodium Chloride solution. The last figure shows the morphology of the copper sample

immersed in the solution contains 30 ppm of BTAH, protection layers were formed on the copper surface, it

can be concluded that the BTAH has a good inhibiting effect on copper corrosion which confirmed in

weight loss part, at 30 ppm of BTAH an after 21 days the inhibition efficiency attain 84.84 %.

3.4. Calculation method results

3.4.1. DFTsimulation results

The present part focus on the geometry optimization step of the BTAH molecule using DFT+ module, this

optimization step aim to calculate the Mullikan charge distributions of BTAH as well as HOMO and LUMO

were calculated and represented in Fig.10.It’s found that the HOMO is located on the Benzene ring which

indicate that the preferred active sites for an electronic attack and the favourite sites for interactions with the

metal surface are located within the region around the Nitrogen (azole function) atoms belonging to the

benzene ring [31].

Figure 10. Molecular structure, Charge distribution and frontier molecular orbitals for the optimized BTAH

by DFT+ module.

According to DFT-Koopmans’ theorem [32], the ionization potential I can be written as follow:

HOMOI E

(16)

Then the negative of the energy of the LUMO represent the electron affinity A Equation (17):

LUMOA E

(17)

Other quantum chemical parameters has been correlated recently using DFT modules [33], these calculated

parameters such as dipole moment µ which given as follow:

R ｑ (18)

HOM

O LUM

O

BTA

H


819

whereｑ represents the charge and R is the distance.

Thevalue of the electronegativity and the chemical potential [34] is given by Equation (19):

( ) / 2µ I A (19)

Other parameters [35, 36] can be calculated such as the global hardness and the global softness where the

global hardness given by Equation (20):

/ 2I A (20)

The global softness S or the absolute hardness is defined by the inverse of the global hardness where:

1 / 2S (21)

The propensity of chemical species to accept electronsis defined as the global electrophilicity it was

given by Par et Al. [37] as follow:

² / 4 (22)

The Equation(22) can be written as follow:

2

8

I A

I A

(23)

Finally and according to Person [38] the fraction of electrons transferred from the inhibitor molecule to the

metallic surfaceis given by:

/ 2( )

M inh M inhN

(24)

M and inhare denote the absolute electronegativity of metal and inhibitor molecule, M and inh

are the

absolute hardness of the metal and the inhibitor.

Obtained results for BTAH molecule and interaction of BTAH molecule with copper surface calculated with

DFT+ module are shown in table 4.

Table 4. Quantum chemical and molecular dynamics parameters for BTAH molecule calculated with DFT+

module in aqueous phase

Propriety Value

ET, KJ.mol-1

-51679.558

µ, D 5.775

EHOMO, eV -6.732

ELUMO, eV -2.771

∆E, eV 3.961

Ionization potential (I) 6.732

Electron affinity (A) 2.771

Chemical potential( ) -4.751

Global hardness (𝜂) 1.98

Global softness(S) 0.27

Global electrophilicity (𝛚) 1.187

(∆N) 0.595

According to Lukovits [39], if 3.6N (our case 0.595N ) the inhibition efficiency of organic inhibitor

increase with increasing electron donating ability at the metal surface. We concluded the BTAH can

adsorbed on the copper surface by donating the unshared pair of electrons from the N atoms to the vacant d


820

orbitals of copper. The high value of HOMOE (-6.73 eV) indicate the tendency of BTAH molecule to donate

electrons to the appropriate acceptor molecule with the low energy and the empty molecular orbital.

Whereas the value of LUMOE (-2.77 eV) indicate the ability of BTAH molecule to accept electrons.

Observing the value of the energy of the gap ∆E which indicate the stability of the formed complex (Cu-

BTAH).

3.4.2. Molecular dynamics simulation

Forcite tools, adsorption locator, molecular dynamicsin Materials Studio 7 software from accelrys Inc. [20]

were performed on a system comprising BTAH molecule and Cu (110) surface. The BTAH molecule is

placed on the surface of copper, optimized then quench molecular dynamics is run. Fig. 11 shows the

optimization energy step for BTAH molecule, before putting it on the Cu (110) surface.

0 20 40 60 80 100 120

74

76

78

80

82

84

86

88

90

Ene

rgy/

Kca

l.mol

-1

Optimization step

BTAH

Figure11. DFT+ geometry optimization energy step of BTAH

Total energy, average energy, Van der Waals energy, electrostatic energy and intermolecular energy in

interaction of BTH/Cu (110) surface are figured in Fig. 12. The adsorption locator process tries to get to the

lowest energy for the system in comprising BTAH/Cu (110).

0.0 5.0x104

1.0x105

1.5x105

2.0x105

2.5x105

-40

-20

0

20

40

60

80

Ene

rgy

/ Kca

l.mol

-1

Step

Total energy

Avearge total energy

Van der Waals energy

Electrostatic energy

Intermolecular energy

Figure 12.Total energy distribution for BTAH/Copper system during energy optimization process


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The possibility of BTAH adsorption on Cu (110) surface was simulated in Fig. 13(a). It could be seen that

BTAH molecule moves near to the copper surface, indicating that the BTAH adsorbed at copper surface

[40]. Fig. 13(a) shows that the adsorption occurred through the Nitrogen atoms. The adsorption density of

BTAH on Cu (110) surface shown in Fig.13 (b). Therefore the studied molecules are likely to the copper

surface to form a stable adsorption layer and protect copper from corrosion.

Figure 13. (a)Most suitable configuration for adsorption of BTAH on the Cu (110) surface obtained by

Adsorption locator module; (b) Adsorption density of BTAH on the Cu (110) substrate.

The parameters tabulated in Table 5 include total energy of the BTAH-Cu (110) configuration. The total

energy is defined is the sum of the energies of the adsorbate components, the rigid adsorption energy and the

deformation energy. In the present study the energy of the substrate (Cu (110) surface) is taken as zero. Then

adsorption energy reports energy required when the relaxed adsorbate BTAH is adsorbed on the substrate

surface Cu (110). The adsorption energy is defined as the sum of rigid adsorption energy and the

deformation energy for BTAH molecule.

The rigid adsorption energy released when the unrelaxed BTAH molecule (before geometry optimization

step) is adsorbed on Cu (110) surface. The deformation energy required when the BTAH molecule is relaxed

on the Cu (110) surface. The report (dEads/ dNi) of BTAH-Cu (110) configurations where one of the BTAH

molecule has been removed, is also shown in Table 5.

Table 5. Outputs and descriptors calculated with adsorption locator for BTAH on Cu (110) surface

Inhibitor Total

energy

(Kcl.mol-

1)

Adsorption energy

(Kcl.mol-1

)

Rigid

adsorption

energy

(Kcl.mol-1

)

Deformation energy

(Kcl.mol-1

)

dEads/

dNi(Kcl.mol-1

)

BTAH 48.47 -27.29 -27.51 0.222 -27.29

(a) (b)


822

4. Conclusions

The BTAH is known as a very good inhibitor for copper corrosion in aerated 3 wt. % NaCl solution. The

inhibition mechanism is attributable to the adsorption of the inhibitor on the copper surface and blocking its

active sites. Results obtained from electrochemical measurements Potentiodynamic polarization and EIS

techniques and from chemical measurement weight loss method are reasonably in good accord.

To go so far and follow the stability of the inhibition efficiency, BTAH stays stable and it has a very good

inhibition efficiency 84.84 % after 21 days of immersion time in aerated 3 wt. % NaCl solution. The

molecular modelling as well as quantum chemical simulation precisely the calculation of the both

energiesEHOMO and ELUMO indicate that the preferred active sites for an electronic attack and the

favourite sites for interaction with the copper surface are located within the region around the

Nitrogenatoms, which confirm that the BTAH molecule adsorb on the Cu (110) surface.

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