OPEN ACCESS
Eurasian Journal of Analytical Chemistry ISSN: 1306-3057
2017 12(3):275-294 DOI 10.12973/ejac.2017.00170a
© Authors. Terms and conditions of Creative Commons Attribution 4.0 International (CC BY 4.0) apply.
Correspondence: Karima Toumiat, Department of Materials Sciences & Physical Chemistry Laboratory Materials,
Laghouat University, Algeria.
Copper Corrosion Inhibition using BTAH Inhibitor in Sodium Chloride Medium: Experimental and Theoretical Studies
Karima Toumiat Laghouat University, ALGERIA
Abdenacer Guibadj Laghouat University, ALGERIA
Mohamed B. Taouti Laghouat University, ALGERIA
Received 8 June 2016 Revised 15 October 2016 Accepted 19 October 2016
ABSTRACT
The effect of 1H-benzotriazole (BTAH) with ppm (part per million) grade concentrations on
copper corrosion in aerated 0.5 M 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 0.5 M NaCl. The optimum inhibition efficiency is at 30
ppm of BTAH. The surface characterization performed using Scanning Electron Microscopy
(SEM) to confirm the adsorption of the inhibitor molecules after 21 days of immersion time
in aerated 0.5 M 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 (111) Surface.
Keywords: Copper, EIS, weight loss, theoretical study, 1H-benzotriazole
INTRODUCTION
From a wide range of metals used in industries, copper extensively used owing to its
remarkable thermal and electric properties. It is usually employed in heating and cooling
systems because of its excellent thermal conductivity [1- 7]. Copper also exclusively used for
piping and delivery of water in marine industry. These pipes 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 0.5 M NaCl in presence and absence of the inhibitor BTAH.
K. Toumiat et al.
276
In this context, several studies realized, BTAH 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 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.
EXPERIMENTAL
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 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 polished with same way. All
samples has cleaned successively with acetone, distilled water and deionized water.
Electrochemical measurements
The potentiodynamic polarization and EIS measurements had 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 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 100 MHz.
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). After polishing and weighing (m1), the samples
Eurasian J Anal Chem
277
introduced in 100 ml of 0.5 M 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 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 obtained for copper samples used in weight loss part. The
surface morphology of these copper samples investigated by using SEM analysis (VEGA 3,
TESCAN) at 5, 10 and 20.0 KV.
Theoretical study
Molecular simulation studies carried out 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 0.5 M 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, effect of 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 centres, dipole
moment and the energy of the gap, Equation (1).
𝑬 = 𝑬𝑳𝑼𝑴𝑶 − 𝑬𝑯𝑶𝑴𝑶 (1)
Interaction between BTAH molecules and Cu (111) surface carried out in a simulating
box (14.45 Å×10.22Å × 29.99 Å) with periodic boundary conditions. The Cu (111) surface firstly
built and relaxed by minimizing its energy using molecule mechanics then the surface of Cu
(111) increased by constructing a supercell, a vacuum slab of 30 Å thickness built on the Cu
(111) surface. The number of layers in the structure chosen so that the depth of surface is
greater than the non-bond cutoff used in the calculation; we choose six as a number of layers
which sufficient depth that the inhibitor molecules will only be involved in non-bond
interactions with Cu (111) surface. After minimizing Cu (111) surface and BTAH molecules,
the corrosion system will be built by layer builder to place the inhibitor molecule on Cu (111)
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].
K. Toumiat et al.
278
RESULTS AND DISCUSSION
Potentiodynamic Polarization Results
Figure 1 represent the behavior of pure copper electrodes in aerated 0.5 M NaCl solution
at room temperature, in the absence and in the presence of different concentrations from 0.5
×10-4 M to 3.5 ×10-4 M 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
𝑶𝟐 + 𝟐𝑯𝟐𝟎 + 𝟒𝒆− → 𝟒𝑶𝑯− (2)
usually, the dissolution of copper (anodic corrosion reactions) is:
𝑪𝒖 → 𝑪𝒖+ + 𝟏𝒆− (3)
moreover, Cu+ ions can undergo disproportionation according to Equation (4) [21-24]
𝟐𝑪𝒖+ 𝑪𝒖𝟐+ + 𝑪𝒖 (4)
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
𝐶𝑢𝐶𝑙2− as indicated by following anodic reactions:
𝑪𝒖𝑪𝒍𝒂𝒅𝒔 + 𝑪𝒍− 𝑪𝒖𝑪𝒍𝟐− (5)
𝑪𝒖 + 𝑪𝒍− 𝑪𝒖𝑪𝒍𝒂𝒅𝒔 + 𝟏𝒆− (6)
Compared with the solution without inhibitor the corrosion potential (Ecorr) shifted to
the more positive values and both the anodic and cathodic currents (icorr) decreased. This
-400 -200 0 200 400
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
log
i (A
/cm
²)
Potential (mV/ECS)
Blank
0.5 ×10-4 M BTAH
1.5 ×10-4 M BTAH
2.5 ×10-4 M BTAH
3.5 ×10-4 M BTAH
Figure 1. Polarisation curves of copper electrode in the absence and in the presence of various
concentrations of BTAH in aerated 0.5 M NaCl solution
Eurasian J Anal Chem
279
indicates that the BTAH inhibitor acts as a mixed-type corrosion inhibitor. The cathodic and
the anodic currents progressively diminish with an increment in BTAH concentration that is
clearer in anodic current. The electrochemical parameters shown in Table 1 extracted from
polarization curves shown in Figure 1 obtained after an electrochemical follow of the behavior
of pure copper in 0.5 M NaCl medium in absence and presence of different concentrations of
BTAH at room temperature. The results obtained using Tafel extrapolation method. Figure 1
shows clearly that the cathodic polarisation curves does not display an extensive Tafel region
which confirm a limiting diffusion current return to the reduction of dissolved oxygen, 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]. The Butler –Volmer equation given by Equation
(7).
𝒊 = 𝒊𝒄𝒐𝒓𝒓 − [𝒆𝜶𝒏𝑭(𝑬−𝑬𝒄𝒐𝒓𝒓)/𝑹𝑻 − 𝒆−(𝟏−𝜶)𝒏𝑭(𝑬−𝑬𝒄𝒐𝒓𝒓/𝑹𝑻)] (7)
Where icorr 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:
𝑬 = 𝒂 + 𝒃𝒍𝒐𝒈𝒊 (8)
where a and b constants. In Equation (8), when E=Ecorr and when i=icorr 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:
𝜼𝒊(%) =𝒊𝒄𝒐𝒓𝒓
𝟎 − 𝒊𝒄𝒐𝒓𝒓
𝒊𝒄𝒐𝒓𝒓𝟎
× 𝟏𝟎𝟎 (9)
Where 𝑖𝑐𝑜𝑟𝑟0 and 𝑖𝑐𝑜𝑟𝑟 are the corrosion current densities for Cu electrode in aerated 0.5 M NaCl
in absence and presence of different concentrations of BTAH.
Table 1. Corrosion inhibition parameters of copper in aerated 0.5 M NaCl solution in the absence and
presence of various concentrations of BTAH using Tafel method
C
(×10-4 M)
Ecorr
(mV/SCE)
ba
(mV/dec)
bc
(mV/dec)
icorr
(µA/cm²)
ηi
(%)
Blank -232.4 65.3 205.2 7.865 --
0.5 -153.6 66.7 149.9 0.241 96.93
1.5 -153.1 111.6 144.0 0.208 97.35
2.5 -103.9 88.8 141.6 0.043 99.45
3.5 -190.9 92.9 136.2 0.088 98.88
K. Toumiat et al.
280
The inhibition effect of BTAH on the polarization behaviors of copper in chloride
medium, it known that the corrosion current density of copper usually calculated by the use
of the Stern-Geary equation as:
𝑰𝒄𝒐𝒓𝒓 =𝑩
𝑹𝑷
(10)
where Rp is the polarization resistance and B in a constant, which varies with the expression
with the expression that:
𝑩 =𝒃𝒂𝒃𝒄
𝟐. 𝟑(𝒃𝒂 + 𝒃𝒄)
(11)
where 𝑏𝑎, 𝑏𝑐 are the anodic and the cathodic Tafel slopes obtained from anodic and cathodic
polarization curves of copper [26].
Generally, the calculation of the determination of Rp and rarely gives attention on the
value of B [27]. The value of B commonly considered being between 10 and 30 mV for almost
metals. Table 2 shows the calculated parameters obtained using Stern-Geary method.
It can be conclude 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 0.5 ×10-4 M of BTAH
to the electrolyte can reduces to great importance of inhibition efficiency. The optimal
inhibition efficiency of 99.45% was obtains for 2.5 ×10-4 M of BTAH. The parameters calculated
using linear polarization method or Stern-Geary method confirmed the results from Tafel
method.
EIS results
In this experimental part of electrochemical measurements the Electrochemical
Impedance Spectroscopy (EIS) used to confirm results of the potentiodynamic polarization
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 done using copper electrode in different
electrolytes in the absence and in the presence of four different concentrations of the inhibitor
Table 2. Corrosion inhibition parameters of copper in aerated 0.5 M NaCl solution in the absence and
presence of various concentrations of BTAH using Stern-Geary method
C
(×10-4 M)
Rp
(KΩ/cm²)
Ecorr*
(mV/SCE)
icorr*
(µA/cm²)
B Constant
(mV)
ηi*
(%)
Blank 3.26 -236.48 7.975 21.84 --
0.5 94.55 -155.67 0.274 20.06 96.56
1.5 147.58 -152.5 0.176 21.64 97.79
2.5 597.45 -103.79 0.043 22.79 99.46
3.5 240.97 -190.29 0.107 23.84 98.65
Eurasian J Anal Chem
281
(BTAH) in aerated 0.5 M NaCl medium at room temperature. The results obtained at an open
circuit potential immersed for 30 min represented as typical Nyquist and Bode plots, shown
in (Figures 2, 3 and 4).
In the presence of BTAH the impedance spectra for the Nyquist plots Figure 2 shows a
depressed semicircle in the high frequency region. This high frequency semicircle attributed
to the charge transfer and double layer capacitance [28].
The lowest frequency area generally known as Warburg impedance related to the
diffusion of soluble copper species from electrode surface to bulk solution [28]. The diameter
of semicircles in extent with the increasing of the inhibitor concentrations. The Bode plots
Figure 3 show that the impedance values over the whole frequency range increased with
increasing the BTAH concentration.
0 1000 2000 3000 4000 5000 6000-200
0
200
400
600
800
1000
1200
1400
1600
Blank
0.5 ×10-4 M BTAH
1.5 ×10-4 M BTAH
2.5 ×10-4 M BTAH
3.5 ×10-4 M BTAH
-Zi
(oh
m.c
m²)
Zr (ohm.cm²)
Figure 2. Nyquist plots of copper electrode at an open-circuit potential after 30 min in aerated 0.5 M
NaCl solution without and with various concentrations of BTAH
K. Toumiat et al.
282
It can be obtains from Bode phase plots Figure 4 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. We can also observe 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.
The equivalent circuit model used to construe impedance characteristics is shown in this
circuit was reported in several studies for copper/solution interface [28, 30].
-1 0 1 2 3 4 5
0.5
1.0
1.5
2.0
2.5
3.0
3.5 Blank
0.5 ×10-4 M BTAH
1.5 ×10-4 M BTAH
2.5 ×10-4 M BTAH
3.5 ×10-4 M BTAH
log
|Z|(
ohm
.cm
²)
log f (Hz)
Figure 3. Bode plot for copper electrode in aerated 0.5 M NaCl solution without and with different
concentrations of BTAH
-1 0 1 2 3 4 5-80
-70
-60
-50
-40
-30
-20
-10
0
10
Blank
0.5 ×10-4 M BTAH
1.5 ×10-4 M BTAH
2.5 ×10-4 M BTAH
3.5 ×10-4 M BTAH
Ph
ase
(deg
ree)
log f (Hz) Figure 4. Phase angle plot for copper electrode in aerated 0.5M NaCl solution without and with different
concentrations of BTAH
Eurasian J Anal Chem
283
The parameters obtained by fitting the equivalent circuit and the inhibition efficiency
represented in Table 3.
Here Rs represented the solution resistance. 𝑄 represents 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:
𝑸 = 𝒀𝒐(𝒋𝝎 )𝒏 (12)
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 centres below the real axis. This phenomenon known as the dispersing effect [31].
The inhibition efficiency (ηi) is calculated using charge transfer resistance as follow:
𝜼𝒊 = (𝟏 −𝑹𝒕𝒐
𝑹𝒕) × 𝟏𝟎𝟎
(13)
Weight loss and SEM analyses results
In this part the variation of the weight loss of copper at different immersion times in
aerated 0.5 M NaCl solution, at room temperature 25°C for (2, 4, 7, 10, 14 and 21) days, without
inhibitor and with 2.5 10-4 M of BTAH results shown in Figure 6.
Figure 5. Equivalent circuit used to fit experimental EIS data in Figure 2, symbols in the circuit indicated
in the text
Table 3. Impedance parameters for copper electrode in 0.5 M 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.sa-1) a
Blank 11.43 66.27 0.920 797.6 784.9 --
0.5 ×10-4 M 8.414 54.97 0.736 2 047 674.2 61.03
1.5 ×10-4 M 10.25 40.34 0.775 2 832 439.0 71.83
2.5 ×10-4 M 6.814 47.24 0.727 5 241 148.8 84.78
3.5 ×10-4 M 8.467 43.68 0.736 2 761 26.58 71.11
K. Toumiat et al.
284
The concentration of inhibitor used in this part has 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 [32, 33] :
𝚫𝒎 =𝒎𝟏 − 𝒎𝟐
𝑨 (14)
𝑹𝒄𝒐𝒓𝒓 =𝚫𝒎
𝑨𝒕
(15)
𝜼𝒘% =𝑹𝒄𝒐𝒓𝒓
𝒖𝒏 − 𝑹𝒄𝒐𝒓𝒓𝒊𝒏
𝑹𝒄𝒐𝒓𝒓𝒖𝒏
(16)
Here, 𝐴 is the total area exposed to the solution, 𝑡 is the time of immersion, 𝑹𝒄𝒐𝒓𝒓𝒖𝒏 is the
corrosion rate without inhibitor and 𝑹𝒄𝒐𝒓𝒓𝒊𝒏 is the corrosion rate with inhibitor.
We found that the inhibition efficiency of BTAH on copper immersed in aerated solution
of 0.5 M NaCl, varied from 50% after two days of immersion time to 84.84 % after 21 days
immersion time Figure 7, 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.
-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
gh
t lo
ss (
mg.c
m-²
)
t (day)
Blank
2.5 ×10-4 M BTAH
Figure 6. Variation of the weight loss as function of time for copper coupons in in aerated solution of
0.5 M NaCl without and with 2.5 ×10-4 M of BTAH
Eurasian J Anal Chem
285
The SEM micrograph for the copper samples immersed in aerated 0.5 M NaCl in absence
and presence of BTAH with concentration equals to 2.5 ×10-4 M for 21 days shown in Figure
8 and 9 . It is obvious that the BTAH molecules partially distributed on the copper surface. The
surface coverages obtained from:
𝜽 =𝒎 − 𝒎𝒊𝒏𝒉
𝒎 (17)
where 𝑚, 𝑚𝑖𝑛ℎ are weight loss obtained from previous measurements. The corrosion rates
obtained from equation (15).
The inhibition efficiency, coverages and corrosion rates tabulate in Table 4.
The Figure 8 represents the copper sample before immersion, the Figure 9(a) shows the
surface morphology of the copper sample immersed in solution without inhibitor, it is clear
that the surface strongly corroded by the Sodium Chloride solution.
0 2 4 6 8 10 12 14 16 18 20 22 240
20
40
60
80
100
57.14
84.84
78.94
66.66
50
81.81
inh
ibit
ion
eff
icie
ncy
%
t (day)
2.5 ×10-4
M BTAH
50
Figure 7. Variation of the inhibition efficiency as function of time for copper coupons in aerated solution
of 0.5 M NaCl containing 2.5 ×10-4 M of BTAH
Table 4. The inhibition efficiency (𝜂w %), changes of the degree of copper surface coverages (𝜃) and
corrosion rates (𝑅𝑐𝑜𝑟𝑟𝑖𝑛 : with 2.5 ×10-4 M of BTAH and 𝑅𝑐𝑜𝑟𝑟
𝑢𝑛 solution without inhibitor) obtained from
weight loss data in aerated 0.5 M NaCl solutions
2.5 ×10-4 M BTAH Time (day)
2 4 7 10 14 16 21
𝜂 w (%) 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
𝑹𝒄𝒐𝒓𝒓𝒖𝒏 (10-5 cm/d) 3.23 3.23 3.23 3.87 4.38 4.44 5.07
𝑹𝒄𝒐𝒓𝒓𝒊𝒏 (10-5 cm/d) 1.61 1.61 1.38 1.29 0.92 0.80 0.79
K. Toumiat et al.
286
The Figure 9(b) shows the morphology of the copper sample, immersed in the presence
of 2.5 ×10-4 M of BTAH. Protection layers formed on the copper surface, which indicate that
the BTAH adsorbed on the copper surface.
In addition, we conclude that the BTAH has a good inhibiting effect on copper corrosion
which confirmed in weight loss part, at 2.5 ×10-4 M of BTAH an after 21 days the inhibition
efficiency attain 84.84 %.
Theoretical Calculation methods results
DFT simulation 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 Figure 10. We find
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
Figure 8. SEM image for polished copper electrode
(a) (b)
Figure 9. SEM images for copper electrodes after 21 days immersion in aerated 0.5 M NaCl solution without inhibitor (a) and with 2.5 ×10-4 M of BTAH (b).
Eurasian J Anal Chem
287
located within the region around the Nitrogen (azole function) atoms belonging to the benzene
ring [34].
According to DFT-Koopmans’ theorem [35], the ionization potential I written as follow:
𝑰 = −𝑬𝑯𝑶𝑴𝑶 (18)
Then the negative of the energy of the LUMO represent the electron affinity A Equation
(17):
𝑨 = −𝑬𝑳𝑼𝑴𝑶 (19)
Other quantum chemical parameters has been correlated recently using DFT modules
[36], these calculated parameters such as dipole moment µ which given as follow:
𝝁 = 𝒒𝑹 (20)
Where 𝑞 represents the charge and 𝑅 is the distance.
The value of the electronegativity and the chemical potential [37] given by Equation
(19):
𝑿 = (𝑰 + 𝑨)/𝟐 (21)
Figure 9. Molecular structure, Charge distribution, Electron density and frontier molecular orbitals for
the optimized BTAH by DFT+ module
K. Toumiat et al.
288
Other parameters [38, 39] calculated such as the global hardness and the global softness
where the global hardness given by Equation (20):
𝜼 = (𝑰 − 𝑨)/𝟐 (22)
The global softness S or the absolute hardness defined by the inverse of the global
hardness where:
𝑺 = 𝟏 / 𝟐𝜼 (23)
The propensity of chemical species to accept electrons defined as the global
electrophilicity 𝝎 it given by Par et Al. [40] as follow:
𝝎 = 𝝁𝟐 / 𝟒𝜼 (24)
The Equation (22) becomes as follow:
𝝎 =(𝑰 + 𝑨)𝟐
𝟖(𝑰 + 𝑨)
(25)
Finally and according to Person [41] the fraction of electrons transferred from the
inhibitor molecule to the metallic surface gives by:
𝚫𝑵 = 𝑿𝑴 − 𝑿𝒊𝒏𝒉 / 𝟐(𝜼𝑴 + 𝜼𝒊𝒏𝒉) (26)
where 𝑋𝑀 and 𝑋𝑖𝑛ℎ denote the absolute electronegativity of metal and inhibitor molecule,
𝜂𝑀and 𝜂𝑖𝑛ℎ 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 shows in Table 5.
Table 5. 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 4.210
EHOMO, eV -5.743
ELUMO, eV -1.816
∆E, eV 3.927
Ionization potential (I) 5.743
Electron affinity (A) 1.816
Chemical potential ( ) 3.779
Global hardness (𝜂) 1.96
Global softness (S) 0.25
Global electrophilicity (𝛚) 0.944
(∆N) 0.479
Eurasian J Anal Chem
289
According to Lukovits [42], if ΔN < 3.6 (our case Δ𝑁 = 0.479) the inhibition efficiency
of organic inhibitor increase with increasing electron donating ability at the metal surface. We
concluded the BTAH could adsorbed on the copper surface by donating the unshared pair of
electrons from the N atoms to the vacant d orbitals of copper.
The high value of 𝐸𝐻𝑂𝑀𝑂 (-5.743 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 𝐸𝐿𝑈𝑀𝑂 (-1.816 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).
Molecular dynamics simulation
Forcite tools, adsorption locator, molecular dynamics in Materials Studio 7 software
from accelrys Inc. [20] performed on a system comprising BTAH molecule and Cu (111)
surface.
0 10 20 30 40 50 60 7060
80
100
120
140
160
180
200
Ene
rgy/
Kca
l.mol
-1
Optimization step
BTAH
Figure 10. DFT+ geometry optimization and energy step of BTAH
The BTAH molecule placed on the surface of copper, optimized then quench molecular
dynamics run. Figure 11 shows the optimization energy step for BTAH molecule, before
putting it on the Cu (111) surface.
Total energy, average energy, Van der Waals energy, electrostatic energy and
intermolecular energy in interaction of BTH/Cu (111) surface figured in Figure 12. The
adsorption locator process tries to get to the lowest energy for the system in comprising
BTAH/Cu (111).
K. Toumiat et al.
290
The possibility of BTAH adsorption on Cu (111) surface simulated in Figure 13(a). We
can see that BTAH molecule moves near to the copper surface, indicating that the BTAH
adsorbed at copper surface [43].
Figure 13(a) shows that the adsorption occurred through the Nitrogen atoms. The
adsorption density of BTAH on Cu (111) surface shown in Figure 13(b). Therefore, the studied
molecules are likely to the copper surface to form a stable adsorption layer and protect copper
from corrosion.
The parameters tabulated in Table 6 include total energy of the BTAH-Cu (111)
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 (111) surface) taken as zero. Then adsorption energy reports
energy required when the relaxed adsorbate BTAH adsorbed on the substrate surface Cu (111).
The adsorption energy defined as the sum of rigid adsorption energy and the deformation
energy for BTAH molecule.
0.0 5.0x104
1.0x105
1.5x105
2.0x105
2.5x105
-40
-20
0
20
40
60
80
100
120
Total energy
Avearge total energy
Van der Waals energy
Electrostatic energy
Intermolecular energy
En
ergy
/ K
cal.m
ol-1
Step Figure 11. Total energy distribution for BTAH/Copper system during energy optimization process
Eurasian J Anal Chem
291
The rigid adsorption energy released when the unrelaxed BTAH molecule (before
geometry optimization step) adsorbed on Cu (111) surface. The deformation energy required
when the BTAH molecule is relaxed on the Cu (111) surface. The report (dEads/ dNi) of
BTAH-Cu (111) configurations where one of the BTAH molecule removed is also shows in
Table 6.
CONCLUSIONS
The BTAH known as a very good inhibitor for copper corrosion in aerated 0.5 M NaCl
solution. The inhibition mechanism is attributable to the adsorption of the inhibitor on the
copper surface and blocking its active sites. All results obtained from electrochemical
measurements and chemical measurement 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 0.5
M NaCl solution. The molecular modelling as well as quantum chemical simulation precisely
(a) (b)
Figure 12. (a) Most suitable configuration for adsorption of BTAH on the Cu (111) surface obtained by
Adsorption locator module; (b) Adsorption density of BTAH on the Cu (111) substrate
Table 6. Outputs and descriptors calculated with adsorption locator for BTAH on Cu (111) surface
Inhibitor BTAH
Total energy (Kcl.mol-1) 39.59
Adsorption energy (Kcl.mol-1) -50.51
Rigid adsorption energy (Kcl.mol-1) -36.32
Deformation energy (Kcl.mol-1) -14.18
dEads/ dNi (Kcl.mol-1) -50.51
K. Toumiat et al.
292
the calculation of the both energies EHOMO 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 Nitrogen atoms, which confirm that the BTAH molecule adsorb
on the Cu (111) surface.
REFERENCES
1. Jafari, A. H., Hosseini, S. M., & Jamalizadeh, E. (2010). Investigation of Smart Nanocapsules Containing Inhibitors for Corrosion Protection of Copper. Electrochimica Acta, 55, 9004-9009.
2. Hong, S., Chen, W., Luo, H. Q., & Li, N. B. (2010). Inhibition Effect of 4-amino-antipyrine on the Corrosion of Copper in 3wt. % NaCl Solution. Corrosion Sci., 57, 270-278.
3. Annibaldi, V., Rooney, A. D., & Breslin, B. C. (2012). Corrosion Protection of Copper using Polypyrrole Electrosynthesised from a Salicylate Solution. Corrosion Sci., 59, 179-185.
4. Nüñez, L., Reguera, E., Corvo, F., Gonzãlez, R., & Vazquez, C. (2005). Corrosion of Copper in Seawater and its Aerosols in a Topical Island. Corrosion Sci., 47, 464-481.
5. Sherif, E. M., Erasmus, R. M., & Comins, J. D. (2007). Corrosion of Copper in Aerated Synthetic Seawater Solutions and its Inhibition by 3-amino-1,2,4-triazole. J. Colloid Interface Sci., 309, 470-477.
6. Hammouti, B., Dafali, A., Touzani, R., & Bouachrine, M. (2012). Inhibition of Copper Corrosion by Bipyrazole Compound in Aerated 3%NaCl. J. Saudi Chemical Soc., 16, 413-418.
7. Zhang, D. Q., Wu, H., & Gao, L. X. (2012). Synergistic Inhibition Effect of L-Phenylalanine and Rare Earth Ce(IV) Ion on the Corrosion of Copper in Hydrochloric Acid Solution. Materials Chemistry and Physics, 133, 981-986.
8. Hack, H. P., & Pickering, H. W. (1991). AC Impedance study of Cu and Cu-Ni Alloys in Aerated Salt Water I. Pd Coating and Corrosion Product Stripping. J. Electrochem. Soc., 138, 690-695.
9. Benedetti, A. V., Sumodjo, P. T. A., Nobe, K., Cabot, P. L., & Proud, W. G. (1995). Electrochemical Studies of Copper, Copper-aluminium and Copper-aluminium-silver Alloys: Impedance Results in 0.5 M NaCl. Electrochimica Acta, 40, 2657.
10. Zhou, G., Shao, H., & Loo, B. H. (1997). A study of the copper electrode behavior in borax buffer solutions containing chloride ions and Benzotriazole-type inhibitors by voltammetry and the photocurrent response method. J. Electroanal. Chem, 421, 129.
11. Walker, R. (1973). Benzotriazole as a Corrosion Inhibitor for Immersed Copper. Corrosion, 29, 290-296.
12. Brusic, V., Frisch, M. A., Eldridge, B. N., Novak, F. P., Kaufman, F. B., Rush, B. M., & Frankel, G. S. (1991). Copper Corrosion with and without Inhibitors. J. Electrochem. Soc., 138, 3483.
13. Tromans, D., & Sun, R. (1991). Anodic Polarization Behavior of Copper in Aqueous Chloride/Benzotriazole Solutions. J. Electrochem. Soc., 138, 3235.
14. Antonijevic, M. M., & Petrovic, M. B. (2008). Copper Corrosion Inhibition. A review. Int. J. Electrochem. Sci., 3, 1.
15. Tuck, C. D. S., Powell, C. A., & Nuttall, J. (2010). Corrosion of Copper and its Alloys. Shereir’s Corrosion, 3, 1937-1973.
16. Cotton, & Scholes, I. R. (1967). Benzotriazole and Related Compounds as Corrosion Inhibitors for CopperBrit. Corros. J., 2, 1-5.
17. Wall, K. H., & Davies, I. (1965). Corrosion Control in Water Cooled Stator. J. Appl. Chem., 15, 389-392.
18. Wall, K. H., & Davies, I. (2007). Corrosion Control in a water Cooled Stator. J. Appl. Chem., 15, 389-392.
19. Poling, G. W. (1970). Reflection Infra-red Studies of films formed by Benzotriazole on Cu. Corrosion Sci., 10, 359-370.
Eurasian J Anal Chem
293
20. Bariga, J., Coto, B., & Fernandez, B. (2007). Molecular Dynamics Study of Optimal Packing Structure of OTS Self-assembled Monolayers on SiO2 Surface. Tribol. Int., 40, 960-966.
21. Khaled, K. F. (2009). Monte Carlo simulations of corrosion inhibition of mild steel in 0.5 M sulfuric acid by some green corrosion inhibitors. J. Solid Stat. Electrochem, 13, 1743.
22. Strehblow, H. H., & Titze, B. (1980). The investigation of the passive behaviour of copper in weeklyacid and alkaline solutions and the examination of the passive film by ESCA and ISS. Electrochimca Acta, 25, 839-850.
23. Hashemi, T., & Hogarth, C. A. (1988). The mechanism of corrosion inhibition of copper in NaCl solution by benzotriazole studied by electron spectroscopy. Electrochimca Acta, 33, 1123-1127.
24. Gardiner, D. J., Gorvin, A. C., Gutteridge, C., Jackson, A. R. W., & Raper, E. S. (1985). In Situ Characterization of Corrosion Inhibition Complexes on Copper Surfaces using Raman Microscopy. Corrosion Sci., 25, 1019-1027.
25. Scendo, M. (2005). Potassium Ethyl Xanthate as Corrosion Inhibitor for Copper in Acidic Chloride Solutions. Corrosion Sci., 47, 1738-1749.
26. Stern, M., & Geary, A. L. (1957). Electrochemical Polarization. J. of Electrochemical Soceity. 27. Keenan, A. G., Webb, C. A., & Karmen, D. A. (1976). Polarisation Resistance Study of the Effect
of Alpha-amino Acids on Copper Corrosion Kinetics. Anodic Oxide of Vanadium, 123, N 02. 28. Schlesinger, M. (2009). Mathematical Modeling in Electrochemistry, Modern Aspect of
Electrochemistry No. 43. Modeling and Numerical Simulations. 29. Amin, M. M. (2006). Weight loss, Polarization, Electrochemical Impedance Spectroscopy, SEM
and EDX Studies of the Corrosion Inhibition of Copper in Aerated NaCl Solutions. J. Appl. Electrochem., 36, 215-216.
30. Rao, A., Iqbal, Y., & Sreedhar, B. (2010). Electrochemical and Surface Analytical Studies of the Self-assembled Monolayer of 5-methoxy-2-(octadecalthio) benzamidazole in Corrosion Protection of Copper. Electrochim. Acta, 55, 620-631.
31. Wu, X., Ma, H., Chem, S., Xu, Z., & Sui, A. (1999). General Equivalent Circuits for Faradic Electrode Processes under Electrochemical Reaction Control. Electrochem. Soc., 146, 1847-1853.
32. Sherif, E. M., & Park, S. M. (2006). Inhibition of Copper Corrosion in Acidic Picking solutions by N-phenyl-1, 4-phenylenediamine. Electrochimica Acta, 51, 4655-4673.
33. Sherif, E. M., & Almajid, A. A. (2010). Surface Protection of Copper in Aerated 3.5 % Sodium Chloride Solutions by 3-amino-5-mercapto-1, 2, 4-triazole as a Copper Corrosion Inhibitor. J. Appl. Electrochem., 40, 1555-1562.
34. Liao, Q. Q., Yue, Z. W., Wang, Z. H., Li, Z. H., Ge, H. H., & Li,Y. J. (2011). Inhibition of copper corrosion in sodium chloride solution by the self-assembled monolayer of sodium diethyldithiocarbamate. Corrosion Science, 53, 1999-2005.
35. Koopmans, T. (1934). Über Die Zuordnug von Wellenfunktionen und Eigenwerten zu den Einzelnen Elektronen Eines Atoms. Physica, 1, 104-113.
36. Atkins, P., & De Paula, J. (2006). ATKINS’ Physical Chemistry. 37. Chermette, H. (1999). Chemical Reactivity Indexes in Density Functional Theory. J. Comp. Chem.,
20, 129-154. 38. Parr, R. G., & Pearson, R. G. (1991). Principle of Maximum Hardness. J. Am. Chem. Soc., 105,
7512-7516. 39. Yang, W., & Parr, R. G. (1985). Proc. Natl, Hardness, Softness and the Fukui Function in the
Electronic Theory of Metals and Catalysis. Acad. Sci., 82, 6723-6726. 40. Parr, R. G., Sventpaly, L., & Liu, S. (1999). Electrophilicity Index. J. Am. Chem. Soc., 121, 1922-
1824. 41. Pearson, R. G. (1963). Hard and Soft Acids and Bases. J. Am. Chem. Soc., 85, 3533-3539. 42. Lukovits, I., Kálmán, E., & Zucchi, F. (2001). Corrosion Inhibitors-Correlation between
Electronic Structure and Efficiency. Corrosion, 57, 3-8.
K. Toumiat et al.
294
43. Al-Mubarak, N. A., Khaled, K. F., Hamed, M. N. H., Abdel-Azim, K. M., & Abdelshafi, N. S. (2010). Corrosion inhibition of copper in chloride media by 2-mercapto-4-(p-methoxyphenyl)-6-oxo-1,6-dihydropyrimidine-5-carbonitrile: Electrochemical and theoretical study. Arab. J. Chem., 3, 233-242.
http://iserjournals.com/journals/ejac