Inhibitive effect of imidazopyridine derivative towards corrosion of C38 steel in hydrochloric acid solution

Article abstract of DOI:10.1007/s11164-012-0763-y

The effect of adding 2-phenylimidazo[1,2-a]pyridine-3-carbaldehyde derivative named (P2), newly synthesized on the electrochemical behavior of C38 steel in molar hydrochloric acid was investigated by using the weight-loss method, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) measurements. EIS results show that the transfer resistance increases with the increase of concentration of P2 and it also had an inhibiting effect on C38 steel corrosion in HCl solutions. Weight-loss essays confirm that the corrosion rate decreases as the P2 concentration increases. The inhibition efficiency for this compound studied increased with the increase in the inhibitor concentrations to attain 91.7 % at the 10^-3 M of P2. The potentiodynamic polarization curves indicated that P2 acted as a mixed-type inhibitor in hydrochloric acid.

Full text of DOI:10.1007/s11164-012-0763-y

Res Chem Intermed (2013) 39:2369–2377
DOI 10.1007/s11164-012-0763-y
Inhibitive effect of imidazopyridine derivative
towards corrosion of C38 steel in hydrochloric
acid solution
•
A. Ghazoui R. Saddik B. Hammouti A. Zarrouk
•
•
•
•
N. Benchat M. Guenbour S. S. Al-Deyab I. Warad
•
•
Received: 3 July 2012 / Accepted: 6 August 2012 / Published online: 25 August 2012
ꢀ Springer Science+Business Media B.V. 2012
Abstract The effect of adding 2-phenylimidazo[1,2-a]pyridine-3-carbaldehyde
derivative named (P2), newly synthesized on the electrochemical behavior of C38
steel in molar hydrochloric acid was investigated by using the weight-loss method,
potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS)
measurements. EIS results show that the transfer resistance increases with the
increase of concentration of P2 and it also had an inhibiting effect on C38 steel
corrosion in HCl solutions. Weight-loss essays confirm that the corrosion rate
decreases as the P2 concentration increases. The inhibition efficiency for this
compound studied increased with the increase in the inhibitor concentrations to
attain 91.7 % at the 10-3 M of P2. The potentiodynamic polarization curves indi-
cated that P2 acted as a mixed-type inhibitor in hydrochloric acid.
Keywords Imidazopyridine derivative ꢀ Corrosion ꢀ C38 steel ꢀ HCl ꢀ
Polarization curves ꢀ EIS
A. Ghazoui ꢀ R. Saddik ꢀ B. Hammouti ꢀ A. Zarrouk (&) ꢀ N. Benchat
´ ´
LCAE-URAC18, Faculte des Sciences, Universite Mohammed Premier, B.P. 717,
60000 Oujda, Morocco
e-mail: azarrouk@gmail.com
M. Guenbour
Laboratoire d’Electrochimie, Corrosion et Environnement, Faculte des Sciences, Universite
Mohammed V, Rabat, Morocco
´
´
S. S. Al-Deyab ꢀ I. Warad
Petrochemical Research Chair, Chemistry Department, College of Science, King Saud University,
PO Box 2455, Riyadh 11451, Saudi Arabia
123

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A. Ghazoui et al.
Introduction
Acid solutions find more and more applications in industry, the most important of
which are acid pickling, industrial acid cleaning, acid descaling, and oil well
acidizing. The commonly used acids are hydrochloric acid, sulphuric acid, and nitric
acid, etc. Since acids are used for cleaning of oxides and corrosion products from
surfaces, not to attack the metal, the addition of inhibitors is still recommended.
Among the metals most used, mild steel is widely used in many chemical industries
due to its low cost and easy availability for fabrication of reaction vessels, tanks,
and pipes. Then, inhibitors are added to aggressive acid solutions. Organic inhibitors
(OI) are widely added in a lot of industrial processes and have been investigated by
several workers [1–5]. OIs act by adsorption, which is facilitated by nitrogen,
sulphur, and oxygen atoms as well as cyclic rings or double bonds [6–8] of donating
electrons and electronic structure of the molecules leading to physical adsorption
and/or chemisorptions [9–11]. Inhibitors behave as a protective barrier against the
attack of the corrosive environment and can provide protection for the metal and so
they reduce corrosion rate of the metal.
Some organic compounds have also been used as inhibitors of steel corrosion in
1.0 M HCl solution, such as pyrazoles [12–15], triazoles [16–19], tetrazoles
[20–23], imidazole derivatives [24–28], and pyridine [29–31].
In the present paper, an imidazopyridine derivative newly synthesized was tested
as corrosion inhibitor for C38 steel in 1.0 M HCl using potentiodynamic
polarization methods and electrochemical impedance spectroscopy (EIS) measure-
ments and gravimetric method.
Experimental
The aggressive solution (1.0 M HCl) was prepared by dilution of analytical-grade
35.4 % HCl with bidistilled water. Prior to all measurements, the C38 steel samples
were polished with different emery paper up to 1,200 grade and washed thoroughly
with bidistilled water and dried with acetone. The chemical structures of the studied
imidazopyridine derivatives are given in Fig. 1. The chemical synthesis procedure
is: 10 mol of the precursor imidazo[1,2-a]pyridine is added portions-wise to de
N,N-dimethylformamide (DMF) 26 mols (1.9 g) cooled at 0 ꢁC and containing
phosphoryl chloride (POCl3) (4 g, 26 mmol). The mixture is then heated at 100 ꢁC
for 1 h and neutralized at 0 ꢁC with Na2CO3. The products are extracted with
dichloromethane. The organic layer is dried over sodium sulphate and the
Fig. 1 Chemical structure of
the imidazopyridine derivative
(P2)
N
N
CHO
123

Inhibitive effect of imidazopyridine derivative
2371
dichloromethane is removed under reduced pressure. The crude product gel is
purified on a silica column and a colorless solid is obtained with 70 % yield.
M:p: ¼ 145 ꢁ 147 ꢂC:
RMN1H ð300:134MHz; CDCl3Þ d ðppmÞ : 10:13ðs; 1H; CHOÞ;
9:70 ðdd; 1H; H5; JH5ꢁH6 ¼ 6:7HzÞ; 7:82ðm; 3HÞ; 7:55ðm; 4HÞ; 7:06ðpst; H6Þ
RMN13C ð100MHz; CDCl3Þ d ðppmÞ : 179:26ðCHOÞ; 157:90 ðC2=C8aÞ;
147:51ðC8a=C2Þ; 132:32ðCphÞ; 130:18ðC5Þ; 129:45ð3CphÞ; 128:92ð2CphÞ;
128:36ðC7Þ; 120:62ðC3Þ; 117:22ðC8Þ; 115:10 ðC6Þ:
Gravimetric measurements were carried out in a double-walled glass cell
equipped with a thermostat cooling condenser. The solution volume was 50 mL.
The steel specimens used had a rectangular form (1 9 1 9 0.05 cm2). The
immersion time for the weight loss was 6 h at 308 K. Electrochemical experiments
were conducted using impedance equipment (Tacussel-Radiometer PGZ 301) and
controlled with Tacussel corrosion analysis software model Voltamaster 4.
A three-electrode electrochemical cell was used. The working electrode was C38
steel with the different surfaces area. Before each experiment, the electrode was
polished using emery paper until 1,200 grade. After this, the electrode was cleaned
ultrasonically with distillate water.
All potentials were given with reference to the saturated calomel electrode
(SCE). The counter electrode was platinum. The aggressive medium used here was
1.0 M HCl solution. The organic compound tested was imidazopyridine derivative.
Its molecule formula is shown in Fig. 1. The concentration range of this compound
was 10-6–10-3 M.
The working electrode was immersed in test solution for 30 min until a steady-
state open-circuit potential (Eocp) was obtained. The polarization curve was
recorded by polarization from -800 to 500 mV under potentiodynamic conditions
corresponding to 1 mV/s (sweep rate) and under air atmosphere.
The EIS measurements were carried out using a transfer function analyzer
(Analytical Radiometer PGZ 301), with a small amplitude AC signal (10 mV rms),
over a frequency domain from 100 kHz to 100 MHz at 308 K and an air
atmosphere. The polarization resistance, Rp, is obtained from the diameter of the
semicircle in Nyquist representation.
Results and discussion
Electrochemical impedance spectroscopic studies
The corrosion behavior of C38 steel, in acidic solution containing different
concentration of imidazopyridine compound, was investigated by the EIS at 308 K
after 30 min of immersion. The obtained results are presented in Fig. 2. The
impedance parameters calculated are given in Table 1. The diagrams are composed
of one capacitive loop. The charge-transfer resistance values (Rct) were calculated
123

2372
A. Ghazoui et al.
P2
1M HCl
10-3
10-4
10-5
10-6
M
M
M
M
100
50
0
0
50
100
Z re (Ω cm2)
150
200
Fig. 2 Nyquist diagrams C38 steel in 1.0 M HCl without and with different concentrations of inhibitor
from the difference in real impedance at lower and higher frequencies as suggested
by Tsuru et al. [32]. To obtain the double-layer capacitance (Cdl), the frequency at
which the imaginary component of the impedance is maximum (-Zmax) is found
and Cdl values were obtained from the Eq. (1):
1
f ðꢁZmaxÞ ¼
ð1Þ
2pCdl Rct
In this case, the inhibition efficiency is calculated using charge-transfer resistance
from Eq. (2):
ꢁ1
ꢁ1
ꢁ
R
RctðinhÞ
ct
ER % ¼
ꢃ 100
ð2Þ
ꢁ1
R
ct
where Rct(inh) and Rct are the charge-transfer resistance in the presence and absence
of different products, respectively.
Results obtained show that Rct increases and Cdl tends to decrease with increasing
of inhibitor concentration.
A decrease in the Cdl values, which can result from a decrease in the local
dielectric constant and/or an increase in the thickness of the electrical double layer,
suggests that the inhibitor acted by adsorption at the metal solution/interface [33].
Polarization curves
The polarization curves of C38 steel in 1.0 M HCl obtained with and without
various concentrations of used inhibitor is shown in Fig. 3. Electrochemical
parameters such as corrosion current density (Icorr), corrosion potential (Ecorr), Tafel
slope constants calculated from Tafel plots (-bc) and the inhibition efficiency (EI
%) were determined by Tafel extrapolation method and are given in Table 2. EI %
was calculated using Eq. (3):
123

Inhibitive effect of imidazopyridine derivative
2373
Table 1 Impedance parameters of C38 steel in 1.0 M HCl containing different concentrations of imi-
dazopyridine compound
Inhibitor
Concentration (M)
Rct (X cm2)
Fmax (Hz)
Cdl (lF/cm2)
ER (%)
Blank
P2
1
33.23
58.28
50.00
25.00
25.00
25.00
15.82
95.80
109.30
70.10
51.70
51.20
–
10-6
10-5
10-4
10-3
43.0
63.4
73.0
83.1
90.81
123.24
196.46
0.1
0.01
1E-3
1E-4
1E-5
P2
1M HCl
10-3
10-4
10-5
10-6
M
M
M
M
1E-6
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
E(mV/SCE)
Fig. 3 Polarization curves of C38 steel in 1.0 M HCl containing different concentrations of P2
Icorr ꢁ I
Icorr
EI % ¼
corrðinhÞ ꢃ 100
ð3Þ
where Icorr and Icorr(inh) are the corrosion current density values without and with
inhibitor, respectively.
It is seen that the addition of various concentrations of inhibitor affects the
polarization curves and consequently decreases Icorr significantly, due to increase in
the blocked fraction of electrode surface by adsorption. Cathodic curves gave rise to
parallel Tafel lines, indicating that the hydrogen evolution is activation controlled and
the reduction mechanism is not affected by the presence of inhibitor. These results
demonstrated that the hydrogen evolution reaction was inhibited and that the
inhibition efficiency increased with inhibitor concentrations. The maximum quantity
of the inhibitor reported in Table 1 corresponds to the optimum concentration of the
inhibitor. The presence of inhibitor does not cause any significant shift in the Ecorr
value. This implies that the inhibitor, P2, acts as a mixed-type inhibitor, affecting both
anodic and cathodic reactions [34]. According to Riggs and coworkers [35], if the
displacement in corrosion potential is more than 85 mV/SCE with respect to the
corrosion potential of the blank, the inhibitor can be considered as a cathodic or anodic
type, but the maximum displacement in the present case is less than 20 mV/SCE,
which indicates that P2 is a mixed-type inhibitor. According to Cao [36], if the shift in
123

2374
A. Ghazoui et al.
Table 2 Polarization data of C38 steel in 1.0 M HCl without and with addition of inhibitor at 308 K
Inhibitor
Concentration (M)
-Ecorr (mV/SCE)
-bc (mV/dec)
Icorr (lA/cm2)
EI (%)
Blank
P2
1
455.2
446.0
444.8
460.5
448.6
127.3
119.8
116.9
132.1
129.0
815.7
464.0
326.1
175.6
098.4
–
10-6
10-5
10-4
10-3
43. 1
58.8
79.4
90.9
Table 3 Gravimetric results of C38 steel in 1 M HCl at different concentration of each inhibitor at 6 h
and 308 K
Inhibitor
Concentration (M)
Wcorr (mg/(cm2 h))
Ew (%)
Blank
P2
1
1.14
–
1 9 10-6
1 9 10-5
5 9 10-5
1 9 10-4
5 9 10-4
1 9 10-3
0.6338
0.4249
0.3500
0.2842
0.1303
0.0940
44.4
62.7
69.3
75.1
88.6
91.7
Ecorr is negligible, the inhibition is most probably caused by a geometric blocking
effect of the adsorbed inhibitive species on the surface of corroding metal.
Gravimetric measurements
The effect of addition of P2 at different concentrations on C38 steel corrosion in
1.0 M HCl solution was studied by weight-loss measurement after 6 h of
immersion. Table 3 shows the values deduced of Wcorr and the inhibition efficiency
(Ew %) determined by the following equation:
ꢀ
ꢁ
Wcorr
Wcꢂorr
Ew % ¼ 1 ꢁ
ꢃ 100
ð4Þ
where Wcorr and Wcꢂorr are the corrosion rates of C38 steel in the presence and
absence of each inhibitor, respectively.
Table 3 clearly indicates a decrease in the corrosion rate in the presence of all
concentrations of this compound. This effect is hugely marked at higher
concentration of inhibitor. The presence of P2 gave a high inhibiting. This is
probably due to the presence of oxygen and nitrogen atom according to Every and
Riggs [37]; the organic compound containing the nitrogen and oxygen has better
inhibition efficiency, in acidic media.
Adsorption isotherms are usually used to describe the adsorption process. The
most frequently used isotherms include: Langmuir, Frumkin, Temkin Flory–
Huggins, Dhar–Flory–Huggins, Bockris–Swinkels. Adsorption of the organic
molecules occurs as the interaction energy between molecule and metal surface is
123

Inhibitive effect of imidazopyridine derivative
2375
0.0012
0.0009
0.0006
0.0003
0.0000
Fig. 4 Langmuir adsorption
plot of P2 on C38 steel
in 1.0 M HCl
P2
0.0000
0.0003
0.0006
0.0009
C (mol / L)
higher than that between the H2O molecule and the metal surface. The simple
mechanistic picture of the adsorption process was proposed by Langmuir. Langmuir
isotherm assumes that:
•
•
•
The metal surface contains a fixed number of adsorption sites and each site holds
oneꢂadsorbate;
DGads is the same for all sites and it is independent of the surface coverage,
h = E %/100;
The adsorbates do not interact with one another, i.e., there is no effect of lateral
interaction of the adsorbates on DGꢂads [38, 39].
The Langmuir adsorption isotherm given a relatively simple mathematical
expression of C, the concentration of inhibitor, K, the adsorptive equilibrium
constant and h, may be written in the following rearranged form:
C
1
¼
þ C
ð5Þ
h
K
The adsorptive equilibrium constant leads to determinate the standard adsorption
free energy (DGꢂads) using:
1
DGꢂads
RT
K ¼
expðꢁ
Þ
ð6Þ
55:5
Figure 4 presents the relationship between C/h and C. The curve obtained yields a
straight line with slope almost equals unity (1.08). The strong correlation factor
R2 = 0.9998 suggests that the adsorption of P2 on metal surface obeys well the
Langmuir adsorption isotherm. The reciprocal of intercept of the straight lines C/h-
axis is K = 93843.84 L/mol. The standard free energy of adsorption (DGꢂads) value
deduced is -39.61 kJ/mol. Generally, values of DGꢂads up to -20 kJ/mol are con-
sistent with electrostatic interactions between the charged molecules and the metal
(physisorption) while those around -40 kJ/mol or higher are associated with
chemisorptions as a result of sharing or transfer of electrons from organic molecules
to the metal surface to form a coordinate type of bond (chemisorptions) [40, 41].
123

2376
A. Ghazoui et al.
The negative value of DGꢂads indicate the stability of the adsorbed layer on the
steel surface and spontaneity of the adsorption process and also chemical and
physical adsorption can occur together, but any adsorbed layers beyond the first
must be physically adsorbed.
Conclusions
On the basis of these results, the following conclusions may be drawn:
•
•
P2 inhibits the corrosion of C38 steel in 1.0 M HCl. The inhibition efficiency
depends on the molecular structure.
Impedance method indicates that imidazopyridine derivative adsorbs on C38
steel surface with increasing charge-transfer resistance and decreasing the
double-layer capacitance.
•
The inhibition efficiency increases with increasing inhibitor concentrations to
attain a maximum value of 91.7 % for inhibitor P2 at 10-3 M.
Polarization study shows that imidazopyridine act as a mixed-type inhibitor.
P2 adsorbs on the steel surface according to the Langmuir isotherm.
•
•
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