Study of Synthesis and Corrosion Inhibition of Novel Mannich and Schiff Bases on Carbon Steel in Acid Solution

Article abstract of DOI:10.1134/S1070427218030242

In this paper, a Schiff base (SB-1) and derivatives (SB-2 and SB-3) was synthesized and characterized by IR and ¹H NMR methods, the corrosion efficiency and mechanism of carbon steel in 1: 1 hydrochloric acid was obtained by weight loss measure

Full text of DOI:10.1134/S1070427218030242

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2018, Vol. 91, No. 3, pp. 499−509. © Pleiades Publishing, Ltd., 2018.
VARIOUS TECHNOLOGICAL
PROCESSES
Study of Synthesis and Corrosion Inhibition of Novel Mannich
1
and Schiff Bases on Carbon Steel in Acid Solution
a
b
a
b
a,
Luoping Fu , Fei Yi , Bo Zeng , Chao Hu , and Jianbo Li *
a
College of Chemistry and Chemical Engineering, Southwest Petroleum University, Chengdu 610500, China
b
PetroChina Tarim Oilfield Company, Korle City, 841000, China
*
e-mail: jianboli121@outlook.com
Received March 2, 2018
Abstract—In this paper, a Schiff base (SB-1) and derivatives (SB-2 and SB-3) was synthesized and characterized
1
by IR and H NMR methods, the corrosion efficiency and mechanism of carbon steel in 1 : 1 hydrochloric acid
was obtained by weight loss measurements, atomic absorption spectrophotometry, electrochemical measurements,
atomic force microscopy studies and quantum chemical calculations. The results indicated that the inhibition ef-
ficiency was SB-3 > SB-2 > SB-1 at low concentration of inhibitors. Under high concentration, they have same
efficiency. The electrochemical measurements showed that the synthesized compounds is an efficient mix-type
inhibitors and its efficiency increased with the increase in inhibitor concentrations. The quantum chemical pa-
rameters were calculated using the density functional theory (DFT), and results showed that the inhibitor and the
metal surface interacted with the donor-acceptor to achieve the effect of corrosion inhibition.
DOI: 10.1134/S1070427218030242
INTRODUCTION
As we all known, the Schiff base and Mannich base
always use corrosion inhibition field [9‒12]. Schiff base
are organic compounds containing azomethine group
which resulted from condensation of a primary amine
with a carbonyl compounds (aldehyde or ketone), that is
much more than corrosion inhibition of the correspond-
ing amine and aldehyde as they have both heteroatom
and π electrons in their structures [13–15]. The π elec-
trons in the Schiff base molecule not only can locate
the unoccupied orbital of the transition metal, but also
can accept the electrons of the d orbital of the transition
metal to form feeding back metal-inhibitor bond [16].
Carbon steel is widely used in industry such as
construction material, storage tanks of chemical
reactors, oil and gas production and transportation
pipelines [1]. In the same way, hydrochloric acid
solution is extensively used in industrial-cleaning
processes, such as: acid descaling, acid cleaning, and
the oil well acidification and in petrochemical processes
[
2, 3]. One of the major problems in these sectors is the
damage caused by corrosion of carbon steel in acidic
environments. Therefore, using of inhibitors is the most
practical and cost-effective method to overcome this
lacunae [4]. The major of the well-known inhibitors are
organic compounds containing heteroatoms that can
provide lonely electron pairs, such as oxygen, nitrogen,
phosphorus, or sulfur, and aromatic rings, and multiple
bonds has been already examined to inhibit the corrosion
of carbon steel [5‒8].
The Mannich base is synthesized by Mannich
reactions, which consist of an amino alkylation of an
acid proton placed next to a carbonyl functional group
with formaldehyde and ammonia or any primary or
secondary amine [17]. Mannich base compounds have
been of interest in order to obtain efficient corrosion
inhibitors since they provide much greater inhibition
efficiency compared to corresponding amines and
aldehydes [18].
1
The text was submitted by the authors in English.
4
99

500
LUOPING FU et al.
EtOH
O
N
N
H
NH
NH
+
H N
NH2
2
Reflux
OH
OH
HO
SB-1
N
N
N
SB-2
OH
HO
O
O
O
,
H
H
N
N
N
N
Reflux
OH
HO
O
SB-3
N
N
OH
HO
Fig. 1. The preparation of SB-1, SB-2 and SB-3.
In the present work, three different compounds,
EXPERIMENTAL
1
4
2
,5-bis(N,N)-o-hydroxyphenylimino-3-amine (SB-1),
-(bis-(2-((2-hydroxybenzylidene)ethyl)amino)butan-
-one (SB-2), bis(5,11)-(2-((2-hydroxybenzylidene)
Materials and Instruments
All chemicals used: salicylaldehyde, diethylenetri-
amine, methanal, acetone, and anhydrous ethanol were
of include analytical grade and obtained from Chengdu
Kelong Chemical Reagent Factory (China). The work-
ing electrode and specimens for weight loss experiments
were prepared from oil-well N80 steel sheets. The N80
steel sheets (50 mm × 25 mm × 2 mm) were abraded
with a series of emery papers (grade 400#–1200#), and
then successively washed with acetone and anhydrous
ethanol.
amino)ethyl)-1,15-bis(2-hydroxyphenyl)-2,5,11,14-
tetraazapentadeca-1,14-dien-8-one (SB-3), were syn-
thesized using salicylaldehyde, diethylenetriamine, ac-
etone, and formaldehyde. Spectral properties of those
1
compounds would be investigated using H NMR,
FTIR, and the inhibition effect of the synthesized com-
pound on mild steel in 1 : 1 hydrochloric acid solution
was investigated using weight loss measurement, atom-
ic absorption spectrophotometry, electrochemical mea-
surements and atomic force microscopy (AFM). Finally,
quantum chemical parameters such as the energy of the
highest occupied molecular orbital (EHOMO), the energy
of the lowest unoccupied molecular orbital (ELUMO), the
Synthesis of the Corrosion Inhibitors
Synthesis of the SB-1. 1,5-Bis(N,N)-o-hydroxy-
phenylimino-3-amine(SB-1) was synthesized according
to synthetic route in Fig. 1. Salicylaldehyd (0.06 mol)
and anhydrous calcium chloride (0.5 g) was mixed
with 50 mL ethanol. To the solution was added
diethylenetriamine (0.03 mol) and the mixture was
stirred for 8 h in 78°C. Afterwards, the product with
energy gap (ΔE ) were calculated using the density
functional theory (DFT), the absolute electronegativity
gap
(χ) and global hardness (λ) were further analyzed by the
corrosion inhibition mechanism of synthetic corrosion
inhibitors.
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STUDY OF SYNTHESIS AND CORROSION INHIBITION
501
hexane was washed, filtered, dried, 8.7 g yellow product
Corrosion rate r was calculated by using the follow-
SB-1 was obtained.
ing equation:
SB-1: 89% yield of yellow solid; IR (solid state),
–
1
v (cm ): v
(
(3430–2850), vC=N (1658), v
x
C–H
C=C(arom)
1
1609–1498), v–OH (1296), vAr–CH (771). H NMR
(
400 MHz, DMSO-d ), δ, ppm: 11.64 (s, 2H, C–OH),
8.52 (s, 2H, HN=C), 07.38 (m, 2H, Ar-H), 07.30 (m,
H, Ar-H), 06.84 (m, 2H, Ar-H), 06.83 (m, 2H, Ar-H),
6
where Δw is the weight loss of the N80 steel, g; s is the
total area of one specimen, cm ; and t is the immersion
time, h. The inhibition efficiency (η) of the inhibitors
was evaluated using the following equation:
0
2
0
2
3.65 (m, 4H, CH ), 03.33 (s, 1H, N–H), 02.86 (m, 4H,
2
CH2).
Synthesis of the SB-2 and SB-3. SB-2 is synthesized
by mixing SB-1 (0.03 mol), formaldehyde (0.03 mol),
acetone (0.03 mol), and 30 mL ethanol and refluxing at
where η and r are the corrosion rates of N80 steel in
absence and presence of inhibitors, respectively.
8
0°C for 5 h. The SB-2 was obtained by washing with
mineral ether, and vacuum drying to remove the impu-
rities. SB-3 was synthesized in the same way, and the
difference was that the amount of acetone in mixing was
halved (SB-1 0.03 mol, formaldehyde 0.03 mol, acetone
Atomic Absorption Spectrophotometry
The corrosion test was conducted using reference
weight-loss measurements. At 303 K the test specimen
with the measured surface area was placed in an acid
solution containing different amounts of corrosion
inhibitors. It was soaked for a certain period of time.
Then a small amount of solutions was sampled to test
the iron ion concentration. Repeated corrosion, soaking,
and testing process, allowed calculating the corrosion
rate and inhibition efficiency. Corrosion rate r was
calculated by using the following equation:
0
.015 mol). The preparation of SB-2 and SB-3 is shown
in Fig. 1.
SB-2: 86% yield of rufous solid; IR (solid state), v
x
–1
(cm ): v
(3447–2837), vC=O (1713), vC=N (1630),
C–H
1
vC=C(arom) (1587–1453), v–OH (1272), vAr–CH (755). H
NMR (400 MHz, DMSO-d ), δ (ppm): 11.57 (s, 2H, C–
6
OH), 08.54 (s, 2H, HN=C), 07.38 (m, 2H, Ar–H), 07.29
(m, 2H, Ar–H), 07.12 (m, 2H, Ar–H), 06.86 (m, 2H, Ar–
H), 03.32 (m, 6H, CH ), 02.73 (m, 4H, CH ), 02.56(m,
2
2
2
H, CH ), 02.10 (m, 3H, CH ).
2
3
SB-3: yield: 53% of rufous solid; IR (Solid state),
–
1
v (cm ): v
(3443 2921), vC=O (1709), vC=N (1630),
x
C–H
v
(1585–1458), v–OH (1279), vAr–CH (756).
where t is the corrosion time, min; c 2+ is the iron ion
C=C(arom)
Fe
1
concentration in t moment, mg L–1; s is the total area of
H NMR (400 MHz, DMSO-d ), δ (ppm): 11.61 (s, 4H,
C–OH), 08.53 (s, 4H, HN=C), 07.30 (m, 4H, Ar–H),
0
4
0
6
2
one specimen, cm . The inhibition efficiency η of the
inhibitors was evaluated using the following equation:
7.09 (m, 4H, Ar–H), 06.88(m, 4H, Ar–H), 06.84 (m,
H, Ar–H), 03.68 (m, 12H, CH ), 03.00 (m, 4H, CH ),
2
2
2.65 (m, 8H, CH2).
Weight Loss Measurements
where r0 and r1 are the corrosion rates of N80 steel
corr
corr
in the absence and presence of inhibitors, respectively.
The weight loss experiments were performed in 1 :
HCl solution in the absence and presence of various
1
Electrochemical measurements
concentration of corrosion inhibitors. The freshly pre-
pared N80 steel specimens were immersed for 500 mL
of test solutions with different concentrations of corro-
sion inhibitors at 303 K. The weight loss was taken as a
difference in the weight of the N80 steel coupons before
and after immersion in different solutions.
Corrosion tests were conducted in a conventional
three-electrode cell assembled with an N80 steel rod
as the working electrode (WE), a saturated calomel
electrode (SCE) as the reference electrode, and a carbon
rod as the counter electrode (CE). Before started any
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502
LUOPING FU et al.
electrochemical measurements, the working electrode
was immersed in the 1 : 1 hydrochloric acid solution
for 30 min at 303 K under an open circuit potential to
reach a stale steady state [19]. In order to minimize
ohmic potential drop, the tip of the reference electrode
is positioned in very close proximity to the working
electrode (WE) surface by the use of a fine Luggin
capillary [20], as use to salt bridge. And the remaining
uncompensated resistance was also reduced by the
electrochemical workstation.
of steel specimens were taken in the range from 0 to
10 nm at room temperature.
Quantum Chemical Calculations
Recently, quantum chemical calculations were
largely used in corrosion inhibition investigations [22–
2
5]. The initial configuration is built using the Visualizer
3
module of Material Studio 6.1 software, using Dmol
module to optimize the molecular configuration. The
quantum chemical parameters of corrosion inhibitors
were calculated using Density Functional Theory (DFT)
In order to study the effect of synthesized compounds
on corrosion of N80 steel in 1 : 1 HCl solution, electro-
chemical impedance spectroscopy (EIS) of N80 steel
were carried out in the absence and presence of different
concentrations of inhibitors. EIS measurements were
[26]. According to the frontier molecular orbital theory,
EHOMO often represents the electron donating ability
of a molecule, and the higher the value, the greater
the tendency to give electrons to appropriate acceptor
molecules with low energy empty molecular orbitals.
ELUMO indicates the ability of the molecule to accept
electrons, and the lower the value, the molecules are easy
to accept electrons [27, 28]. ΔEgap is the energy gap of
the EHOMO and ELUMO. According to relevant literatures
and calculates data, lower value of the energy gap will
favor good inhibition efficiency [29, 30]. The HASB
equation was introduced to study of the adsorption of
inhibitor molecules on the metal surface, ΔE represents
the fraction of electrons transferred from the inhibitor
molecule to the metal surface [31, 32], which were
calculated through those following equation [33–35]:
–
2
5
carried out in a frequency range of 10 –10 Hz with
amplitude of 5 mV at open circuit potential (OCP) [21].
Measurements were performed with a computer pro-
gram. The inhibition efficiency η obtained from the EIS
was calculated using the following equation:
where Rct(i) and Rct(0) are the charge transfer resistance in
the presence and absence of inhibitors.
The Tafel potentiodynamic polarization studies were
made in the potential range from –250 to +250 mV from
–
1
the OCP with a scan rate of 1 mV s . The corrosion
potential Ecorr, corrosion current Icorr, anodic Tafel
slope β and cathodic Tafel slope β were obtained by
a
c
extrapolation of anodic and cathodic regions of the
Tafel plots. The inhibition efficiency η obtained from
the following equation:
where χ and λ represent the absolute electronegativity
Fe
Fe
where I0
and I1
and absolute hardness of metal, respectively. Using
a theoretical value of χFe = 7 and λFe = 0 eV for the
calculation of the value of ΔE[36, 37].
represents the corrosion current
corr
corr
density values in the absence and presence of inhibitors
respectively.
Atomic Force Microscopy Studies
RESULTS AND DISCUSSIONS
Weight Loss Measurements
Atomic force microscopy was used for characterizing
the surface morphology and measuring surface
roughness in acid medium with different corrosion
inhibitors. The two and three dimensional AFM images
The corrosion tests were performed in 1 : 1 HCl
solution. Figure 2 shows the variation of the inhibition
efficiency with SB-1, SB-2, and SB-3 concentrations at
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STUDY OF SYNTHESIS AND CORROSION INHIBITION
503
Blank
SB-1
SB-2
SB-3
Fig. 2. Variation of the inhibition efficiency by different
Fig. 3. The corrosion rate curves of SB-1, SB-2, and SB-3
concentrations of the SB-1, SB-2 and SB-3.
with 1000 ppm.
2
+
3
0°C by gravimetric measurements, According Fig. 2,
and released Fe , which led to the increase in concen-
2
+
the corrosion inhibition efficiency were increased with
the increasing concentration of SB-1, SB-2, and SB-3.
At low concentrations, the performance of inhibitors are
ordered as: SB-3 > SB-2 > SB-1; at high concentrations,
they have same inhibition efficiencies.
tration of Fe thereby affecting the corrosion rate of
N80 steel. In contrast to the corrosion rate curves of
SB-2 and SB-3, the corrosion rate of SB-2 and SB-3
does not change with time, while the corrosion rate of
SB-1 decreases with time
Atomic Absorption Spectrophotometry
Electrochemical Measurements
Atomic absorption spectrophotometry was used to
determine the concentration of iron ion in the blank
solution and SB-1, SB-2, and SB-3 with 1000 ppm at
different time. The corrosion rate curves are shown in
Fig. 3.
Tafel polarization measurement. Figure 4 shows
the influence of the inhibitors concentration on the po-
larization curves of N80 carbon steel. The corrosion
kinetic parameters obtained from polarization measure-
ment method were recorded and summarized in Table 1.
It is clear from the Fig. 3 that adding inhibitors can
significantly decrease the concentration of iron ion in
corrosion system. In blank solution, the corrosion rate of
N80 steel in 1 : 1 hydrochloric acid corrosion medium
decreases with the increased of time, which is due to
The Tafel polarization results show that increasing
the SB-1, SB-2, and SB-3 concentration reduces both
the cathodic and anodic electric current density, and in-
creasing the corrosion efficiency. The anodic polariza-
tion curve for N80 steel in 1 : 1 HCl solution can be
separated into three regions: inhibited region (i), flat
region (ii), and uninhibited region (iii). In inhibited re-
+
N80 steel reacts in the corrosive medium: Fe + 2H =
2+
Fe + H ↑. In corrosion process, N80 steel dissolved
2
Fig. 4. Tafel polarization curves of N80 steel at various mass concentrations of SB-1, SB-2, and SB-3 (1 : 1 HCl, 30°C).
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 91 No. 3 2018

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LUOPING FU et al.
Table 1. Polarization parameters of N80 steel at various mass concentrations of SB-1, SB-2, and SB-3(1 : 1HCl, 30°C)
Compounds
Blank
ρ, ppm
βa, V dec–1
βc, V dec–1
Ecorr, V
Ecorr, μA cm–2
η, %
9.748
9.732
12.168
14.494
21.144
9.303
9.427
7.556
13.723
3.553
6.245
7.451
4.648
2.574
8.740
7.279
4.567
4.912
7.928
6.993
6.914
6.692
7.238
10.369
–0.3736
–0.3976
–0.4111
–0.4427
–0.4430
–0.4079
–0.4243
–0.4570
–0.4565
–0.4083
–0.4551
–0.4558
–0.4248
1545
431.5
176.2
132.54
75.4
333.4
110
88.12
55.26
271.2
98.8
4
6
8
00
00
00
72.1
88.6
91.4
95.1
78.4
92.9
94.3
96.4
82.4
93.6
95.7
96.8
SB-1
SB-2
SB-3
1
000
4
6
8
00
00
00
1
000
4
6
8
00
00
00
17.170
20.908
66.55
48.8
1
000
gion, the anodic potential is basically linear with the
corrosion current density. In flat region, the potential
slightly increases with the anodic current, and a rela-
tive flat is observed at this stage. The results show that
the corrosion resistance of the inhibitor molecules on
carbon steel surface reaches equilibrium. In uninhibited
region, the current density increases rapidly with the in-
crease in potential, which is due to the deformation of
the adsorbed layer of the inhibitor molecules [38, 39]. It
is apparent from Fig. 5 that the nature of the polarization
curves remained the same in the absence and presence
of inhibitors, but the curves shifted toward lower cur-
rent density and corrosion potential in the presence of
inhibitors. Therefore, it can be concluded that inhibitor
molecules delay the corrosion process without chang-
ing the corrosion process mechanism of carbon steels
in a corrosive medium. In addition, there is no obvious
tendency for the value offset of β , β , and Ecorr, and
were less than 85 mV. Therefore, the inhibitors were de-
fined as mixed-type inhibitors, affecting the retardation
of both anodic and cathodic reactions [40, 41]. The re-
sult obtained in this method was in good agreement with
conventional weight loss method and atomic absorption
spectrophotometry.
Electrochemical impedance spectroscopy. Nyquist
and Bode plots of N80 steel in 1 : 1 HCl solution in the
absence and presence of different mass fraction of SB-
1, SB-2, and SB-3 are depicted in Figs. 5 and 6. As can
be seen from the Nyquist and Bode plots, all impedance
diagrams were characterized by single capacitive loop
at higher frequency range and Bode plots corresponding
them show only one time constant. Meanwhile, we can
observe the depressed and anomalistic semicircles that
may be attributed to the frequency dispersion effects
and other forms of interfacial impedance [42]. As it
is shown in the Fig. 5, for three inhibitors there is only
one low capacitance semicircle with its center is lower
a
c
Ecorr values in the absence and presence of the inhibitors
Fig. 5. Nyquist plots of N80 steel at various mass concentrations of SB-1, SB-2, and SB-3 (1 : 1 HCl, 25°C).
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STUDY OF SYNTHESIS AND CORROSION INHIBITION
505
Table 2. Values of the equivalent circuit required for fitting the EIS for 1 : 1 HCl in the absence and presence of different
concentrations of SB-1, SB-2 and SB-3 and corresponding inhibition efficiency
–
5
–2
Q, 10 F cm
Corrosion
inhibitors
ρ, ppm
R, Ω cm2
R1, Ω cm2 C , 10 F cm
–5
–2
R, Ω cm2
η, %
dl
Y0, μΩ–1 Sn cm–2
n
SB-1
SB-2
SB-3
Blank
0.817
0.7069
0.6904
0.6968
0.7329
0.8262
0.771
3.494
2.5990
0.9957
0.539
0.5619
0.3579
0.6263
0.6553
0.6820
0.7562
0.6958
0.8551
0.7544
0.7777
0.7562
0.7281
0.6959
0.7172
0.7509
0.01061
0.09535
0.04879
0.04875
0.04974
8.04
46.61
3.733
3.734
3.661
3.571
53. 85
2.347
1.215
5.768
5.266
53. 85
3.188
2.778
5.125
4.529
20.44
29.95
177.8
424.3
552.4
19.71
92.51
279.9
357.9
427.8
19.71
136.8
312.7
366.9
530.3
4
6
8
00
00
00
31.7
88.5
95.2
96.2
1
000
Blank
0.2599
1.172
4
6
8
00
00
00
0.1994
0.189
25.62
78.7
88.9
94.5
95.4
0.0028
0.6466
0.7877
0.8262
1.161
0.7488
20.37
0.1783
0.2152
1.172
1
000
Blank
22.84
8.04
4
6
8
00
00
00
0.3004
0.1897
0.4827
0.1924
11.92
85.6
93.7
94.6
96.3
0.7743
0.5836
0.7716
24.77
10.02
1
000
22.06
than the real axis. The Nyquist plots for three inhibitors
were found to be similar, which was explained by the
fact that the mechanism of the corrosion process of three
inhibitors are identical, but the Nyquist plots semicircles
in presence of the three inhibitors is bigger than that in
blank solution. This effect was more pronounced with
increasing inhibitors concentration. This implies that the
presence of inhibitors strengthens the inhibitive film [43].
Fig. 6. Bode plots of N80 steel at various mass concentrations of SB-1, SB-2, and SB-3 (1 : 1 HCl, 25°C).
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506
LUOPING FU et al.
Cdl
Q
Cdl
Rs
Rct
Rs
R1
Rct
R2
Q
Fig. 7. Electrochemical equivalent circuits used to fit of EIS measurements.
Figure 7 shows the electrical equivalent circuit dia-
gram model to fit the experimental results, which con-
solution of different inhibitors are shown in Fig. 8. In
the new polished specimen, from the Fig. 8a of the 2D
and 3D figures show that the surface roughness is very
good. In the absence of inhibitors specimen, it is clearly
shown in Fig. 8b the N80 steel is getting cracked due to
the acid attack on the N80 steel surface. From Fig. 8a
it can be seen that the surface roughness decreases and
corrosion occurs. Comparing the 2D and 3D images of
Figs. 8c–8e it can be seen that the surface roughness is
the best when adding the inhibitor SB-1 and SB-2, and
SB-3 is relatively unevenness.
sists of a solution resistance (R ), constant phase ele-
s
ment (Q), double layer capacitance (C ), membrane
dl
resistance (R and R ) and charge transfer resistance
1
2
(
Rct). The fitted EIS parameters calculated and listed in
Table 2 demonstrate that with the addition of inhibitors
the C value decreases. This fact is due to the addition
dl
of inhibitors that increase the double layer on the metal
surface. The value of R increases with increasing the
ct
inhibitors concentration indicating that SB-1, SB-2, and
SB-3 could enhance the charge transfer resistance and
reduce the double layer capacitance. It shows that the
adsorption process of inhibitor molecules at the metal
solution interface inhibits the corrosion of iron [44, 45]
and form a protective film at the metal surface.
Quantum Chemical Calculations
The quantum chemical parameters calculated by
DFT (Fig. 9, Table 3) give the optimized geometry of
the synthesized inhibitors atoms.
Lastly, according to electrochemical fitting data, at
low concentrations, the experimental descending order
of the corrosion inhibition for N80 steel was SB-3 >
SB-2 > SB-1, this is because the SB-3 molecular
structure has more benzene rings and carbon nitrogen
double bonds relative to SB-2 and SB-1. At high
concentrations, they have same corrosion inhibition
performance due to the molecular volume varied in
the order SB-3 > SB-2 > SB-1. Small molecules can
better contact with the metal surface achieving better
inhibition efficiency.
In general, the reactivity of inhibitors is related to
their frontier molecular orbital distribution, including
the highest occupied molecular orbital (HOMO) and
the lowest unoccupied molecular orbital (LUMO).
It is apparent from the Table 3 that the EHOMO values
increase in the order of SB-1 < SB-2 < SB-3 indicating
that the inhibitors provide electrons to the metal surface
in the order of SB-3 > SB-2 > SB-1. Comparatively,
the LUMO energies have also same regularity which is
SB-1 < SB-2 < SB-3. In addition, the energy gap ΔEgap
values decrease in the order of SB-1 > SB-2 > SB-3
indicating that the stability of the compounds formed
on the metal surface obeys the order of SB-3 > SB-2 >
SB-1. ΔN > 0 represents that the corrosion inhibitors
molecule provides electrons to the surface of the metal,
Atomic Force Microscopy Studies
The two and three dimensional AFM images of
polished, uninhibited, and inhibited carbon steel in acid
Table 3. Quantum chemical parameters of SB-1, SB-2 and SB-3
Compound
SB-1
EHOMO, eV
–5.03917
–4.72283
–4.62868
ELUMO, eV
–1.97777
–1.97592
–1.92451
ΔEgap
χ, eV
λ, eV
ΔN
3.06140
2.74692
2.70417
3.50847
3.34938
3.27660
1.53070
1.37346
1.35208
1.14050
1.32899
1.37691
SB-2
SB-3
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 91 No. 3 2018

STUDY OF SYNTHESIS AND CORROSION INHIBITION
507
(
a)
1
07 nm
25.6 nm
μm
–
1
0
1
07 nm
1
0
8
8
6
6
4
4
2
–
158.1 nm
2
1
0 μm
8
8
8
6
6
6
4
4
4
2
2
2
0
10.0 μm
(
b)
9
94.8 nm
μm
6
5.8 nm
10
9
94.8 nm
1
0
8
8
6
6
4
4
2
–
863.3 nm
2
1
0 μm
(
4
c)
92.3 nm
0
0
0
10.0 μm
μm
–
19.2 nm
92.3 nm
1
0
4
1
0
8
8
6
6
4
4
2
–
531.7 nm
2
1
0 μm
(
d)
10.0 μm
4
63.4 nm
μm
0
.0 nm
1
0
4
63.4 nm
1
0
8
8
6
6
4
4
2
–
463.4 nm
2
1
0 μm
8
6
4
(e)
2
10.0 μm
6
68.8 nm
μm
10
–
9.9 nm
8
68.8 nm
1
0
8
8
6
6
4
4
2
–
688.6 nm
2
1
0 μm
8
6
4
2
0
10.0 μm
Fig. 8. AFM two-dimensional and three-dimensional images of carbon steel surface; (a) polished carbon steel, (b) carbon steel exposed
in blank solution, (c, d ,e) carbon steel exposed in 1 : 1 HCl respectively containing 1000 ppm SB-1, SB-2, and SB-3.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 91 No. 3 2018

508
LUOPING FU et al.
excellent inhibition efficiencies for the corrosion of
SB-1
carbon steel in 1 : 1 hydrochloric acid solutions and the
efficiency increased with the increase in the dosage of
the inhibitors. At low concentrations, the performance
of inhibitors is in the order: SB-3 > SB-2 > SB-1, at high
concentrations they are of the same inhibition efficiency.
(2) It was found that the corrosion rate of carbon
steel in 1 : 1 hydrochloric acid solution decreased
gradually with the increase in time by atomic absorption
spectrophotometry. The corrosion rate of carbon steel
can be obviously reduced by adding inhibitors.
SB-2
(3) Electrochemical measurements indicated that
three inhibitors are mix-type inhibitors. The inhibiting
efficiencies obtained by polarization and EIS are in
good agreement.
(4) Quantum chemical calculation results show that
the inhibitor mainly acts to form a stable coordination
bond, acting on the metal surface through the interaction
of benzene rings, imines, nitrogen, and oxygen atoms
with metal surfaces. The inhibition efficiency of the
inhibitors mainly depends on the electron supplying
capacity of the inhibitor molecules, which also explains
the fact that corrosion efficiencies of synthesized
corrosion inhibitors of carbon steel in 1 : 1 HCl decrease
in the order of SB-3 > SB-2 > SB-1 at low concentrations.
SB-3
ACKNOWLEDGMENTS
The authors would like to acknowledge for the
financial support and the research facilities provided by
Southwest Petroleum University, Institute, Chengdu,
China.
Fig. 9. Optimized molecular structure (left), frontiers orbitals
distribution HOMO (center) and LUMO (right) of the tested
inhibitors.
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are mainly distributed in the conjugated systems such
as benzene ring and imine group, and the HOMO
orbitals are mainly distributed on the heteroatom such
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