Comparative inhibition study of mild steel corrosion in hydrochloric acid by new class synthesised quinoxaline derivatives: Part i

Article abstract of DOI:10.1007/s11164-012-0719-2

7-Cchloro-3-(4-methoxystyryl)quinoxalin-2(1H)-one (CMOSQ) and 7-chloro-2-(4-methoxyphenyl)thieno(3.2-b)quinoxaline (CMOPTQ) have been investigated for mild steel corrosion in 1 M HCl at different concentrations using weight loss measurements, potentiodyna

Full text of DOI:10.1007/s11164-012-0719-2

Res Chem Intermed (2013) 39:1843–1855
DOI 10.1007/s11164-012-0719-2
Comparative inhibition study of mild steel corrosion
in hydrochloric acid by new class synthesised
quinoxaline derivatives: part I
K. Adardour
R. A. Belakhmima
C. Kalonji Mubengayi
•
R. Touir
M. Ebn Touhami
H. El Kafsaoui E. M. Essassi
•
Y. Ramli
•
•
•
•
•
Received: 19 December 2011 / Accepted: 7 July 2012 / Published online: 31 July 2012
Springer Science+Business Media B.V. 2012
ꢀ
Abstract 7-Cchloro-3-(4-methoxystyryl)quinoxalin-2(1H)-one (CMOSQ) and
-chloro-2-(4-methoxyphenyl)thieno(3.2-b)quinoxaline (CMOPTQ) have been
7
investigated for mild steel corrosion in 1 M HCl at different concentrations using
weight loss measurements, potentiodynamic polarization curves and electrochemi-
cal impedance spectroscopy methods. Generally, inhibition efficiency of the
investigated compounds was found to depend on inhibitor concentration and their
structures. Comparitive results showed that CMOPTQ was the best inhibitor and the
inhibition efficiency increased with increasing the concentration and attained 86 and
-
3
-3
8
7 % at 10 M of CMOPTQ and 10 M of CMOSQ, respectively. Potentiody-
namic polarization studies clearly reveal that these inhibitors act essentially as
cathodic-type inhibitors. The inhibition efficiency increases with immersion time
and reaches 95 % CMOPTQ at 24 h. The electrochemical impedance spectroscopy
result showed that these compounds act by formation of film.
Keywords Synthesised quinoxaline derivatives ꢀ Mild steel ꢀ Hydrochloric acid ꢀ
Corrosion inhibition
K. Adardour ꢀ R. Touir (&) ꢀ R. A. Belakhmima ꢀ M. Ebn Touhami ꢀ H. El Kafsaoui
Materials, Electrochemical and Environment Laboratory, Faculty of Science, University Ibn Tofail,
BP 133, Kenitra, Morocco
e-mail: touir8@yahoo.fr
Y. Ramli
Laboratoire Nationale de Contr oˆ le des M e´ dicaments, Direction du M e´ dicament et de la Pharmacie,
BP 6206, 10000 Rabat, Morocco
Y. Ramli ꢀ C. K. Mubengayi ꢀ E. M. Essassi
Laboratory of Heterocyclic Organic Chemistry, Faculty of Science, Mohammed V University,
Rabat, Morocco
E. M. Essassi
Institute of Nanomaterials and Nanotechnology, MAScIR, Rabat, Morocco
123

1844
K. Adardour et al.
H
N
O
H
H
N
Cl
O
Cl
O
2h
+
Δ
N
CH
3
N
OCH
3
OCH
3
Scheme 1 Synthesis of, 7-chloro-3-(4-methoxystyryl) quinoxalin-2-one (CMOSQ)
Introduction
Corrosion problems have received a considerable amount of attention because of
their attack on materials. Due to its prominent properties, hydrochloric acid is
widely used in industry, for example in acid pickling, acid cleaning and acid
descaling. The use of inhibitors is one of the most practical methods for protection
against corrosion. The corrosion inhibition of metals in acids by organic additives
has been studied in considerable detail [1–4].
Most of the efficient inhibitors used in industry are organic compounds which
mainly contain oxygen, sulphur, nitrogen atoms and multiple bonds in the molecule
through which they are adsorbed on the metal surface [5–12]. Moreover, many
N-heterocyclic compounds have been proved to be effective inhibitors for the
corrosion of metals and alloys in aqueous media [13–21].
A perusal of the literature reveals that 7-chloro-3-(4-methoxystyryl)quinoxalin-
(1H)-one (CMOSQ) and 7-chloro-2-(4-methoxyphenyl)thieno(3.2-b)quinoxaline
CMOPTQ) have not been investigated as corrosion inhibitors. Accordingly, this
2
(
work deals with the study of the corrosion inhibition properties of these compounds.
The choice of these products was based on the consideration that these compounds
contain p-electrons and heteroatoms such as N, O and S, which induce greater
adsorption of the inhibitor molecule onto the metallic surface compared with
compounds containing only nitrogen, oxygen or sulphur. The inhibition of these
compounds always depends upon the number of active adsorption centres that an
inhibitor molecule may have, as well as the charge density, molecular size,
adsorption mode, and its capability to form metallic complexes.
This paper aims to determine the inhibition efficiency of quinoxaline derivatives
via mild steel corrosion in 1 M HCl solution at different concentrations in order
to compare the effect of molecular structure. The effects of immersion time and
temperature were evaluated and discussed.
Experimental details
Synthesis and characterisation of quinoxalines derivatives
Quinoxalines derivatives have been prepared by a new method developed in our
laboratory. The synthesised compounds have been obtained with good yield (80 %)
and their synthesised schemas are presented in schemas 1 and 2:
1
23

Comparative inhibition study of mild steel corrosion in hydrochloric acid
1845
OCH3
N
N
laweson//toluene
0 mn
OCH3
3
S
Cl
N
Cl
N
H
O
Scheme 2 Synthesis of, 7-chloro-2-(4-methoxyphenyl)thieno[2,3-b]quinoxaline (CMOPTQ)
•
6.25 mmol of 7-chloro-3-methylquinoxaline-2-one is merged with 12.5 mmol of
the appropriate aldehyde for 2 h at the boiling temperature of the latter. At the
end of the reaction, the solid was allowed to cool and then heated to 100 ꢁC for
1
0 min in 50 ml of acetone. The product was filtered hot and washed with
acetone (Scheme 1).
•
4 mmol of 7-chloro-3-styrylquinoxalin-2-one undergoes sulfuration by Lawes-
son’s reagent 4 mmol, for 30 min at reflux of toluene. After evaporating the
solvent to dryness, the product is recrystallized in ethanol (Scheme 2).
1
13
These products have been purified and characterised by NMR H and NMR
analysis using a Brucker AMWB 300 spectrometer:
C
•
7-chloro-3-(4-methoxystyryl)quinoxalin-2-one: (CMOSQ)
1
RMN H (300 MHz, DMSO-d6) d (ppm): 7.45 (s, 1H), 7.50 (d, 2H, H Cl,
J = 8.4 Hz), 7.60 (d, 1H, CH ethylenique, 3J = 16.2 Hz), 7.78 (d, 2H, H Cl,
J = 8.4 Hz), 8.00 (s, 1H), 8.06 (d, 1H, CH ethylenique, 3J = 16.2 Hz), 12.64
3
3
(
s, 1H, NH).
1
3
RMN C (75.5 MHz, DMSO-d6) d (ppm) 112.55 (2xC), 115.56, 116.63, 123.82,
24.05, 128.29, 129.27, 129.69 (2xC), 131.73, 133.09, 138.25, 151.59, 153.96,
55.36.
1
1
•
7-chloro-2-(4-methoxyphenyl)thieno (2,3-b)quinoxaline: (CMOPTQ)
1
RMN H (300 MHz, TFA) d (ppm): 7.52 (d, 2H, 3J = 8.7 Hz), 7.86 (d, 2H,
J = 8.7 Hz), 7.96 (s, 1H), 8.32 (s, 1H), 8.52 (s, 1H)
3
1
13
C RMN (63 MHz, TFA) d (ppm): 108.91, 119.7, 126.5, 128.8 (2xC), 129.4,
23.0 (2xC), 137.9, 138.6, 140.7, 141.8, 141.9, 159.5, 169.1
Methods and experimental electrochemical conditions
Corrosion tests were performed on mild steel of the following percentage
composition: 0.09 % P; 0.38 % Si; 0.01 % Al; 0.05 % Mn; 0.21 % C; 0.05 % S
2
and the remainder iron. Mild steel rods were mounted in teflon (surface area 1 cm ).
The specimens’ surface was prepared by grinding with emery paper of different grit
sizes, rinsing with distilled water, degreasing in ethanol, and drying before use.
Solutions of 1 M HCl were prepared by dilution of analytical grade 37 % HCl with
distilled water.
For weight loss measurements, rectangular mild steel specimens of size
4 9 1 9 0.05 cm) were used as samples for corrosion tests. After having been
(
successively polished with emery paper (400–1,200 grade) and weighed, the
123

1846
K. Adardour et al.
samples were immersed for 24 h in 100 ml of uninhibited and inhibited solutions at
room temperature in the air. At the end of immersion, the specimens were cleaned
-
4
according to ASTM G-81 and reweighed to 10 g for determining the corrosion
rate [22]. The inhibition efficiency (IE%) is defined as follows:
x0 ꢁ x
IE% ¼
ꢂ 100
ð1Þ
x0
where x and x are the corrosion rate values after immersion in solution without
0
and with inhibitor, respectively.
For electrochemical measurements, a conventional three-electrode glass cell with
a platinum counter electrode and a saturated calomel electrode (SCE) as reference
was used. A mild steel cylindrical rod of the same composition as the working
electrode was pressure-fitted into a polytetrafluoroethylene holder (PTFE) exposing
2
only 1 cm surface to the solution. All potentials were measured against SCE.
The potentiodynamic polarization curves were recorded by changing the
electrode potential automatically with a potentiostat type PGZ 100, at a scan rate
of 1 mV/s. Before each experiment, the working electrode was immersed in the test
cell for 30 min until reaching steady state.
The evaluation of corrosion kinetics parameters was obtained using a fitting by
Stern–Geary equation such as mentioned in our previous work [23]. The inhibition
efficiency was evaluated from the measured icorr values using the relationship:
0
i
ꢁ icorr
corr
IE% ¼
ꢂ 100
ð2Þ
0
corr
i
0
corr
where i
inhibitor, respectively.
and icorr are the corrosion current densities values without and with
The electrochemical impedance spectroscopy measurements were carried out
using a transfer function analyser (VoltaLab PGZ 100), with a small amplitude AC
signal (10 mV rms), over a frequency domain from 100 kHz to 10 mHz at room
temperature and in air atmosphere. The results were then analysed in terms of
equivalent electrical circuit using the Bouckamp program [24]. The inhibition
efficiency of the inhibitor was found from the relationship:
0
Rct ꢁ R
ct
IE% ¼
ꢂ 100
ð3Þ
Rct
0
where R and R are the charge transfer resistance values in the absence and the
ct
ct
presence of inhibitor, respectively.
Results and discussion
Corrosion weight loss tests
The addition of quinoxaline derivatives effect on mild steel corrosion in 1 M HCl
solution was studied using weight loss measurement at 24 h of immersion. Table 1
represents the corrosion rate and the inhibition efficiency values. It is noted that
1
23

Comparative inhibition study of mild steel corrosion in hydrochloric acid
1847
IE%
Table 1 Corrosion rate and
Compounds
Conc. (M)
00
Corrosion rate
(
inhibition efficiencies for mild
steel in 1 M HCl at various
concentrations of quinoxaline
derivatives
-2
-1
h )
mg cm
Blank solution
CMOPTQ
0.0574
0.0205
0.0164
0.0136
0.0125
0.0211
0.0165
0.0145
0.0138
–
64
71
76
78
63
71
75
76
-5
10
-4
5
1
1
9 10
-4
0
0
-3
-4
5 9 10
CMOSQ
-4
-3
-2
1
1
1
0
0
0
CMOPTQ and CMOPTQ are good corrosion inhibitors for mild steel in acidic
media. As the corrosion rate decreased, inhibition efficiency increased with
-
increasing concentration and reached a maximum at 10 M of CMOPTQ and at
3
-
2
1
0
M of CMOSQ.
The presence of CMOPTQ gives high inhibiting efficiencies and CMOSQ
somewhat lower efficiency. This is probably due to the presence of sulphur and
nitrogen atoms in the CMOPTQ molecule. According to Every and Riggs [25],
the organic compound containing the nitrogen and sulphur has better inhibition
efficiency in acidic media compared to the organic compound containing nitrogen or
sulphur.
Potentiodynamic polarization curves
The corrosion behaviour of mild steel in 1 M HCl solution in the presence of
quinoxaline derivatives was investigated by potentiodynamic polarization curves at
room temperature after 30 min of immersion. Figures 1 and 2 show the results
obtained. It is shown that all inhibitors suppressed the cathodic and anodic reactions.
It is clear that the increase of concentration gave rise to a consistent decrease in
anodic and cathodic current densities, indicating that these inhibitors act as a mixed
type inhibitor [26].
Table 2 represents the various electrochemical parameters such as corrosion
potential, Ecorr, corrosion current density, icorr, Tafel slopes, b and b and the
c
a
inhibition efficiencies values, %IE. It can be seen that all compounds decreased icorr
significantly at all the studied concentrations. The almost unchanged corrosion
potential and Tafel slopes in the presence of inhibitors indicate that the inhibition
effect is caused by geometrical blocking of the reaction sites of the metal surface by
adsorbed molecule species without changing the anodic and cathodic reaction
mechanisms [27]. Values of corrosion inhibition efficiency obtained for CMOPTQ
are greater than obtained for CMOSQ. The lesser value of inhibition efficiency for
CMOSQ as compared to CMOPTQ can be attributed to the lower electron densities
around the chemisorption center. Compounds can produce protonated species in
HCl medium by the reaction of the amino group with HCl. This reaction is easer in
123

1848
K. Adardour et al.
100
10
1
-
5
1
1
5
1
0
0
0,1
-4
-4
×10
-3
0,01
0
blank solution
1E-3
-1,0
-0,9
-0,8
-0,7
-0,6
-0,5
-0,4
-0,3
-0,2
-0,1
0,0
E(v/sce)
Fig. 1 Potentiodynamic polarization curves for mild steel in 1 M HCl containing different
concentrations of CMOPTQ
1
00
1
0
1
0
.1
-4
1
0
-
4
5
×10
-
3
1
0
0
.01
-
2
1
0
blank solution
1
E-3
-1.0
-0.9
-0.8
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
E(v/sce)
Fig. 2 Potentiodynamic polarization curves for mild steel in 1 M HCl containing different
concentrations of CMOSQ
the case of the presence of sulphur. The better performance of CMOPTQ over
CMOSQ is also due to the greater surface area which leads to more adsorption on
the metal surface, thereby exhibiting a better inhibitory effect. This result is a good
match with the results obtained from weight loss tests.
1
23

Comparative inhibition study of mild steel corrosion in hydrochloric acid
1849
Table 2 Electrochemical parameters and inhibition efficiencies for mild steel in 1 M HCl containing
different concentrations of inhibitors
Compounds
Conc.
M)
E
corr
(mV sce
i
corr
b
a
b
(mV dec )
c
IE%
–
-1
-2)
-1
)
-1
(
)
(lA cm
(mV dec
Blank
00
10
-456
289.5
65.5
-146.4
solution
-
5
CMOPTQ
-437
-429
-452
-455
-429
-510
-446
-467
78.57
52.54
40.99
39.45
75.96
63.16
42.26
40.50
228
453
367
447
357
442
328
245
-124
-123
-129
-120
-129
-124
-162
-204
73
82
86
87
74
78
85
86
-
4
4
5
1
1
9 10
-
4
0
0
-
3
-
CMOSQ
5 9 10
-
-
-
4
3
2
1
1
1
0
0
0
4
00
00
00
00
0
blank solution
-
5
1
1
5
1
0
0
-
4
3
2
1
-
4
×10
-
3
0
0
100
200
300
400
500
600
2
Z (Ω.cm )
Re
Fig. 3 Nyquist diagrams for mild steel in 1 M HCl at Ecorr containing different concentrations of
CMOPTQ
Electrochemical impedance spectroscopy (EIS) measurements
Figures 3 and 4 show Nyquist plots for mild steel in 1 M HCl solution in the
presence of different concentrations of quinoxaline derivatives. It is clear that all of
the impedance spectra obtained in the absence and in the presence of inhibitors
consist of one depressed capacitive loop corresponding to one time constant. It is
obvious that the addition of the inhibitors results in an increase in the semicircular
capacitive loop diameter. These observations clearly bring out the fact that the mild
steel corrosion in 1 M HCl is controlled by a charge transfer process and the
corrosion inhibition occurs through the adsorption of the inhibitors on mild steel
123

1850
K. Adardour et al.
4
3
2
1
00
00
00
00
0
Blank solution
-
4
1
0 M
-
4
5×10
M
-
3
1
1
0
0
M
M
-
2
0
100
200
300
400
500
600
2
ZRe(Ω.cm )
Fig. 4 Nyquist diagrams for mild steel in 1 M HCl at Ecorr containing different concentrations of
CMOSQ
Fig. 5 Equivalent circuit model
represents the metal/solution
interface
surface. The impedance diagrams obtained are not perfect semicircles and this
difference has been attributed to frequency dispersion [28].
In order to obtain accurate results, the analysis of complex plane plots was done
by fitting the experimental results to the equivalent circuit given in Fig. 5, which has
been used previously to model the mild steel/acid interface [29–32]. The circuit
consists of solution resistance, R , in series with the parallel combination of charge
s
transfer resistance, R , and a constant phase element, CPE, used in place of double
ct
layer capacitance, C , to represent the not ideal capacitive behaviour of the double
ct
layer more clearly. Various parameters obtained from these complex plane plots are
given in Table 3.
It is apparent that the charge transfer resistance value of mild steel in uninhibited
1
M HCl solution changes significantly after the addition of the inhibitors. The
inhibition efficiency of CMOSQ is lower than that of CMOPTQ which is somewhat
expected when considering the presence of the C=S group in CMOPTQ. This result
is a agreement with that obtained by Muzaffer Ozcan et al. [33] in the case of mild
steel corrosion inhibition in phosphoric acid.
1
23

Comparative inhibition study of mild steel corrosion in hydrochloric acid
1851
Table 3 Impedance data and inhibition efficiencies for mild steel in 1 M HCl at different concentration
of inhibitors
-1
)
2
-2
Compounds
Conc. (M)
00
E
corr (mV sce
R
ct (X cm )
C
ct (lF cm
)
IE%
Blank solution
CMOPTQ
-490
-464
-471
-478
-480
-422
-473
-485
-509
60
280
387
499
520
255
309
450
499
912
39
–
79
85
88
89
77
81
87
87
-5
10
-4
5
1
1
9 10
40
-4
-3
-4
0
0
36
26
CMOSQ
10
197
-4
5
1
1
9 10
51.53
-3
0
0
35.40
35.38
-2
Immersion time effect
Figures 6 and 7 show the impedance spectra obtained for mild steel after different
-
in aerated 1 M HCl solution in the presence of 10 M of
3
immersion times at E
corr
-
2
CMOPTQ or 10 M of CMOSQ, respectively. It is clear that all impedance spectra
obtained consist of one depressed capacitive loop and that its diameter is
significantly changed with immersion time. In addition, the presence of inhibitors
increases the impedance but does not change other aspects of the behaviour. The
characteristic evolution of the parameters with time is summarized in Table 4. It is
noted that that R values increased when C values decreased with increasing of
ct
ct
immersion time. The decrease in the C which can result from a decrease in local
ct
dielectric constant and/or an increase in the thickness of the double layer was
attributed to the inhibitor molecules adsorption on the metal surface [34]. However,
it is known that, in acidic media, the halide ions facilitate the adsorption of organic
inhibitors through intermediate bridges between the metal surface and the positively
charged inhibitor. Thus, if the inhibiting effect is due to the protonated species, a
synergistic increase in inhibition efficiency should be observed in the presence of
-
the halide ions [35]. In our case, more ions (Cl ions) adsorbed when the immersion
time increased.
Temperature effect
The temperature influence on the corrosion kinetic process in free acid and in the
presence of adsorbed inhibitor leads to the obtaining of more information on the
electrochemical behaviour of metallic materials in aggressive media.
Table 5 presentzx the corrosion rate values for mild steel in 1 M HCl in the
-
3
-2
presence of 10
M of CMOPTQ and 10
M of CMOSQ determined by
potentiodynamic polarization curves at various temperatures ranges (303–333 K).
It is well known that the corrosion rate increases with increasing of temperature in
acidic media. Apparently, the results obtained postulate that the inhibitor function
through adsorption on a metallic surface by blocking their active sites to form a
123

1852
K. Adardour et al.
1000
1
2
4
6
1
2
h
h
h
h
2 h
4 h
8
6
4
2
00
00
00
00
0
0
200
400
600
800
1000
1200
1400
2
Z Re ( Ω.cm )
-3
Fig. 6 Nyquist diagrams for mild steel in 1 M HCl containing 10
immersion times
M of CMOPTQ at various
6
5
4
3
2
1
00
00
00
00
00
00
0
1
2
4
6
1
2
h
h
h
h
2 h
4 h
0
100
200
300
400
500
600
700
800
900
2
Z Re ( Ω.cm )
-2
Fig. 7 Nyquist diagrams for mild steel in 1 M HCl containing 10 M of CMOSQ at various immersion
times
screen onto the mild steel surface from the acidic solution. As the temperature
increases, the desorption rate manifests parallel to the adsorption rate; the surface
becomes less protected and then the inhibitors gradually lose their effectiveness.
1
23

Comparative inhibition study of mild steel corrosion in hydrochloric acid
1853
-2
Table 4 Electrochemical impedance parameters for mild steel in 1 M HCl solution with 10 M of
-
CMOSQ and 10 M of CMOPTQ, separately at different immersion times
3
-1
2
-2
Compounds
Immersion time (h) E (mV sce
)
R
ct (X cm )
C
ct (lF cm
)
IE%
Blank solution
1/2
1
-490
-490
-499
-519
-526
-549
-562
-495
-501
-518
-560
-569
-576
60
912
56.10
–
88
89
91
92
92
93
88
93
93
94
95
95
-2
10
M of CMOSQ
520
2
524.15
709.55
742.26
768.77
815
33.89
32.72
30.37
26
4
6
1
2
1
2
4
6
1
2
2
4
19.54
36.38
27.55
27.48
25.43
20.21
12.28
-3
10
M of CMOPTQ
499
802.31
912.99
989.31
2
4
1,244.71
1,295.66
Table 5 Electrochemical
parameters for mild steel in 1 M
-
2
)
Compounds
Blank solution
Temperature (K)
i
corr (lA cm
-3
HCl containing 10 M of
-
CMOPTQ and 10 M of
2
303
313
392
639
CMOSQ at various temperatures
3
3
23
33
1,628
3,293
-2
0
1
M of CMOSQ
303
40.50
3
3
3
13
23
33
76.93
144.56
215.03
39.45
-3
0
1
M of CMOPTQ
303
3
3
3
13
23
33
60.27
168.49
225.57
However, the corrosion reaction of mild steel in 1 M HCl depends on
temperature. The dependence of the chemical reaction rate constant K on the
temperature T is expressed by the Arrhenius law:
ꢀ
ꢁ
Ea
icorr ¼ K exp ꢁ
ð4Þ
RT
where icorr is the corrosion current density, K the Arrhenius pre-exponential factor,
T the absolute temperature and R is the universal gas constant.
The logarithm plots of corrosion current density versus reciprocal temperature
-
1
T
are given in Fig. 8. The plots obtained are straight lines and the slope of each
123

1854
K. Adardour et al.
8
8
7
7
6
6
5
5
4
4
3
.5
.0
.5
.0
.5
.0
.5
.0
.5
.0
.5
Blank solution
-2
1
1
0
0
M of SMOSQ
-3
M of SMOPTQ
2.95 3.00 3.05 3.10 3.15 3.20 3.25 3.30 3.35
1
000/T (K)
-
Fig. 8 Arrhenius plots for mild steel in acidic medium containing 10 M of CMOPTQ and 10
3
-2
M
of CMOSQ
one gives its activation energy E . The calculated activation energy values E are
a
a
-
1.31, 52.62 and 47.48 kJ/mol in the absence and the presence of 10 M of
3
6
-
2
CMOPTQ and 10 M of CMOSQ, respectively. The change in the apparent
activation energy values may be explained by the modification of the corrosion
process mechanism in the presence of adsorbed inhibitor molecules [36].
The literature [36–38] mentions that the apparent activation energy E values in
a
the presence are higher than these in the absence of an inhibitor. Other studies [39,
4
0] showed that in the presence of inhibitor the apparent activation energy values
were lower than those in the absence of the inhibitor. However, in our study, Ea
decreases in the presence of CMOPTQ and CMOSQ concentration indicating their
chemisorptions on a metallic surface.
Conclusion
Quinoxalines derivatives, namely, 7-chloro-3-(4-methoxystyryl)quinoxalin-2(1H)-
one (CMOSQ) and 7-chloro-2-(4-methoxyphenyl)thieno(3.2-b)quinoxaline (CMO
PTQ), have proved to be good inhibitors for the mild steel corrosion in 1 M HCl.
These inhibitors act as cathodic-type inhibitors. The inhibition efficiencies were
found to increase with an increase in inhibitor concentration and with immersion
times. The electrochemical parameters obtained calculated from EIS show the same
trend as those estimated from potentiondynamic polarization and weight loss
measurements. The decrease in activate energy values E in the presence of
a
inhibitors indicate their chemisorptions on a metallic surface.
1
23

Comparative inhibition study of mild steel corrosion in hydrochloric acid
1855
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