Experimental and computational studies on hydroxamic acids as environmental friendly chelating corrosion inhibitors for mild steel in aqueous acidic medium

Article abstract of DOI:10.1016/j.molliq.2020.113651

In the present study, three hydroxamic acids (HAs) namely acetohydroxamic acid (AHA), benzohydroxamic acid (BHA) and oxalohydroxamic acid (OHA) were synthesized, characterized and used as inhibitors for mild steel corrosion in1 M HCl using chemical, electrochemical, surface and computational methods. Results of the studies show that the HAs act as effective corrosion inhibitors and their inhibition efficiencies follow the order: OHA (96.37%) > BHA (95.69%) > AHA (93.29%). EIS study showed that studied HAs act as interface type inhibitors. Polarization study revealed that HAs demonstrate mixed-type corrosion inhibitors characteristics and adsorb on the active sites of metallic surface. Adsorption of HAs on metal-1 M HCl interfaces followed the Langmuir adsorption isotherm model. Surface morphological analyses of inhibited and uninhibited metallic surface were carried out using SEM-EDX and XRD methods. DFT analyses showed that studied compounds act as chelating type of ligands. Effect of Keto-enol tautomerism and different possible conformational isomers on metallic corrosion inhibition was demonstrated. The conformational isomers in which >C=O and –OH (hydroxyl) groups present in same side behave as chelating ligands and form relatively more stable complex than that of conformational isomers in which >C=O and –OH groups present in opposite side. Experimental and DFT studies complimented each other well.

Full text of DOI:10.1016/j.molliq.2020.113651

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Experimental and computational studies on hydroxamic acids as
environmental friendly chelating corrosion inhibitors for mild
steel in aqueous acidic medium
Dakeshwar Kumar Verma, Akram Al Fantazi, Chandrabhan
Verma, Fahmida Khan, Ashish Asatkar, Chaudhery Mustansar
Hussain, Eno E. Ebenso
PII:
S0167-7322(20)32502-2
DOI:
https://doi.org/10.1016/j.molliq.2020.113651
MOLLIQ 113651
Reference:
To appear in:
Journal of Molecular Liquids
Received date:
Revised date:
Accepted date:
21 April 2020
14 June 2020
19 June 2020
Please cite this article as: D.K. Verma, A. Al Fantazi, C. Verma, et al., Experimental and
computational studies on hydroxamic acids as environmental friendly chelating corrosion
inhibitors for mild steel in aqueous acidic medium, Journal of Molecular Liquids (2020),
https://doi.org/10.1016/j.molliq.2020.113651
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Experimental and computational studies on hydroxamic acids as
environmental friendly chelating corrosion inhibitors for mild
steel in aqueous acidic medium
a
b
c
d
Dakeshwar Kumar Verma , Akram Al Fantazi , Chandrabhan Verma *, Fahmida Khan ,
e
f
g
Ashish Asatkar , Chaudhery Mustansar Hussain and Eno E. Ebenso *
a
Department of Chemistry, Govt. Digvijay Autonomous Postgraduate College, Rajnandgaon, Chhattisgarh,
INDIA, 491441
b
Department of Chemical Engineering, Khalifa University of Science and Technology, P.O. Box 2533, Abu
Dhabi, United Arab Emirates
c
Center of Research Excellence in Corrosion, Research Institute, King Fahd University of Petroleum and
Minerals, Dhahran 31261, Saudi Arabia
d
Department of Chemistry, National Institute of Technology Raipur, Raipur 492010, CG, India
e
Department of Chemistry, Govt. Gundadhur Postgraduate College, Kondagaon, Chhattisgarh, INDIA
f
Department of Chemistry and Environmental Science, New Jersey Institute of Technology, Newark, N J 07102,
USA
g
Department of Chemistry, School of Chemical and Physical Sciences and Material Science Innovation &
Modelling (MaSIM) Research Focus Area, Faculty of Natural and Agricultural Sciences, North-West
University, Private Bag X2046, Mmabatho 2735, South Africa
Corresponding Address: chandraverma.rs.apc@itbhu.ac.in (CV) & Eno.Ebenso@nwu.ac.za
(EEE)
1

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GRAPHICAL ABSTRACT
2

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ABSTRACT
In the present study, three hydroxamic acids (HAs) namely acetohydroxamic acid (AHA),
benzohydroxamic acid (BHA) and oxalohydroxamic acid (OHA) synthesised, characterized
and used as inhibitors for mild steel corrosion in the electrolytic solution of 1M HCl.
Corrosion inhibition property of HAs was evaluated using several chemical, electrochemical,
surface and computational methods. Results showed that studies HAs act as effective
corrosion inhibitors and their inhibition efficiencies follow the order: OHA (96.37%) > BHA
(95.69%) > AHA (93.29%). EIS study showed that studied HAs act as interface type
inhibitors. Polarization study revealed that HAs demonstrate themselves as mixed type
corrosion inhibitors and they adsorb on the active sites of metallic surface. Adsorption of
HAs on metal-1M HCl interfaces followed the Langmuir adsorption isotherm model. Surface
morphological analyses of inhibited and uninhibited metallic surface were carried out using
SEM-EDX and XRD methods. DFT analyses showed that studied compounds act as
chelating type of ligands. Effect of Keto-enol tautomerism and different possible
conformational isomers on metallic corrosion inhibition was demonstrated. The
conformational isomers in which >C=O and –OH (hydroxyl ) groups present in same side
behave as chelating ligands and form relatively more stable complex than that of
conformational isomers in which >C=O and –OH groups present in opposite side.
Experimental and DFT studies well complimented each other.
Keywords: Tautomers as corrosion inhibitors, conformational isomers, chelating corrosion
inhibitors, Hydroxamic acid and Langmuir adsorption isotherm.
1
. Introduction
Corrosion is a process in which metallic materials undergo degradation through
chemical and/ or electrochemical reactions with the components of the surrounding
environment. Corrosion is a natural and spontaneous process in which a pure metal converts
in to its relatively more stable oxide, chloride, carbonate and sulphate etc. Though, complete
prevention of metallic corrosion is practically impossible however the rate of corrosive
dissolution and its adverse effect can be minimized using previously used methods of
corrosion mitigation such as alloying, dealloying, coatings, paintings, passivation and
corrosion inhibitors [1-4]. Basic requirements for a compound to be used as corrosion
inhibitor are shown in Fig.1. Use of synthetic corrosion inhibitors is one of the most effective
methods because of their ease of synthesis and high inhibition effectiveness. Most of the
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well-know corrosion inhibitors are heteroatoms (N, O, P, and S) and aromatic rings
containing compounds. Obviously, polar functional groups such as –OH, –OMe, –NH , –
2
NH–, –COOH, –CN, –O–, –NO , –CONH , –COOC H and –N=N– etc. [5-12] enhance the
2
2
2
5
solubility of organic inhibitors in polar electrolytes. Heteroatoms of the polar functional
groups also act as adsorption centers as they can transfer their non-bonding electrons to the
metallic d-orbitals through coordination boding [13-15]. Along with non-bonding electrons of
heteroatoms, multiple bonds of aromatic rings and side chain also favour the adsorption of
organic inhibitors on metallic surface through d-p bonding type of interactions. Problem of
the corrosive dissolution is even more severe during acid cleanings of metallic ores that
acquire the implementation of aggressive solutions such as HCl, H SO , HNO , NaCl and
2
4
3
H PO etc. Some of the common industrial cleaning processes are acid pickling, descaling,
3
4
acid descaling and oil-well acidification [15-20].
Hydroxamic acids (HAs) represent a special class of organic compounds that possess
several biological and industrial applications. Hydroxamic acid and its derivatives are
reported as potential biological agents toward anti-asthmatic and anti-inflammatory activities
[
21]. Additionally, HAs form highly stable complexes with transition metal cations due to the
presence of several electron rich (donor) oxygen and nitrogen heteroatoms. The HAs can be
regarded as chelating ligands as they possess at least two electron rich sites (non-bonding
and/or -electrons) that can form coordination bondings with the metallic d-orbitals [22,23].
Because of their high complexation ability, HAs are expected to possess high adsorption
tendency on metallic surface. Therefore, HAs can be used as one of the best alternatives to
traditional existing corrosion inhibitors that generally show low efficiency at relatively high
concentration. In view of this, some of the authors recently reported the corrosion inhibition
effect of hydroxamic acids [24, 25]. Because of their natural and biological activities, HAs
can be regarded as green and environmental friendly alternatives to the traditional toxic
corrosion inhibitors.
Herein, three hydroxamic acids (HAs) designated as AHA, BHA and OHA are used as
corrosion inhibitors for mild steel in 1 M HCl medium. Inhibition efficiencies of the HAs
were measured using chemical (weight loss), electrochemical (EIS and PDP), surface (SEM
and EDX) and density functional theory (DFT) methods. All the studied HAs showed
reasonably good protection efficiencies for mild steel in 1M HCl. DFT study is also carried
out to demonstrate the effect of different tautomeric forms o tested HAs on their protection
capability. Generally, HAs are represented as RC(O)N(OH)R' and different conformational
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isomers can be constructed for three studied HAs based on the orientation of R and R’. DFT
study was also performed for different conformations isomers of investigated HAs to
demonstrate the effect of relative orientation of different groups on the corrosion inhibition
performance. Outcomes of the study revealed that AHA, BHA and OHA act as chelating
ligands and form stable complexes with metallic surface. Protection efficiency of the tested
compounds was first of all investigated using weight loss method and supported by
electrochemical studies using potentiodynamic polarization and electrochemical impedance
spectroscopic methods. Surface morphology studies and adsorption behaviour of investigated
compounds was determined using SEM-EDS and XRD methods. DFT study was undertaken
in order to describe the nature metal-inhibitor interactions. DFT study also carried out to
demonstrate the effect of different tautomers and conformational isomers of AHA, BHA and
OHA on MS corrosion in 1M HCl. Several experimental and computational indices were
computed and described. The order of protection efficiencies of tested HAs derived from
chemical, electrochemical and surface investigations were well complimented by DFT
studies.
2
. Methods and Materials
2
.1. Synthesis of HAs
Acetohydroxamic acid (AHA) was synthesized as per the previously used method [26]. In
brief, 15 ml double distilled water, 12 ml ethanol and 7g crystalline hydroxylamine
hydrochloride were taken in a 500 ml round bottom flask. The mixture was allowed to stir
until the above reaction mixture becomes clear. After that, 20 ml of sodium hydroxide (10
mol/L) was added slowly. Temperature of the reaction mixture was maintained at 20°C. In
the above reaction mixture, ethyl acetate (0.1 mol) added gradually at room temperature and
kept in ice bath for cooling. To the above reaction mixture concentrated HCl was added to
decrease the pH level up to 6. After that, 100 ml ethanol was added to above reaction mixture
to get yellow colored precipitate. The precipitate was dissolved in a mixture of ethyl acetate
and acetone. After proper dissolution, the above reaction mixture cooled to room temperature
and kept overnight in freezer to get white crystals of acetohydroxamic. AHA showed the
melting point of 88°C±1. Similarly, BHA was prepared using the protocol described
previously [26]. 1.4 of hydroxylamine hydrochloride and 2.1 g sodium carbonate (anhydrous)
were dissolved in 50 ml ether. Above reaction was stirred to get a homogeneous reaction
mixture using a magnetic stirrer. At constant stirring, 2.8 g benzoyl chloride and 3.5 ml
double distilled water were added slowly. The above reaction mixture was stirred for 30
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minute. The residual solvents (mainly ether) were removed using rotatory evaporator and
resultant mixture was kept overnight to get crystalline raw material. Finally, crystallization of
the above crude material with ethyl acetate results in to the formation of pure BHA having
the melting point of 128°C ±1. For OHA synthesis, 9.0 g of hydroxylamine hydrochloride
and 7.1 g of diethyl oxalate were added drop-wise with proper shaking at 0°C for 25-30
minutes. The precipitate of raw OHA was obtained after some time that was crystallized in
double distilled water to give pure OHA having melting point of 161°C ±1[24]. The chemical
structure, IUPAC name, abbreviations, and FT-IR, 1H and 13C NMR characterization data of
investigated HAs are reported in Table 1 and their respective spectra are shown in Fig. S1.
2
.2. Test material and electrolyte
Mild steel sheet having chemical composition of (%) C = 0.18, O = 0.08, S = 0.06, P = 0.04,
Cr = 0.04 and reminder Fe was used for the preparation of test specimens for weight loss,
electrochemical and surface analyses. The metallic specimens were abraded using emery
papers of different (400-1200) grades, washed (with water), and degreased with acetone. The
analytical grade HCl (37% HCl MERCK) was used for the preparation of test electrolyte of 1
M HCl electrolytic. Protection efficiency of HAs was determined at their different
concentrations ranging from 20-80 ppm.
2
.3. Weight loss measurement
Weight loss or gravimetric study is one of most simple, reliable, effective, reproducible, and
cost-effective methods for the determination of inhibition efficiency of corrosion inhibitors
that does not require employment of any tedious process and expensive instruments. Several
useful indices including corrosion rate (ρ), surface coverage () and inhibition efficiency
(%η) can be derived using weight loss experimentation. Using weight loss technique,
protection efficiency of HAs was measured at their different concentrations in the
temperature range of 298–328 K. The weight loss tests were performed for the immersion
time of 6h. Weight loss experiments (at each concentration) were triply performed and
maximum observed standard derivations were less than 2%. The corrosion rates (ρ) values for
mild steel corrosion in acidic medium were calculated using the following equation [27]:
∆
푤
휌 = (1)
퐴푡
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2
where, ∆W, A and t represent the weight loss (in mg), the metallic surface area (in cm ) and
immersion time (6h), respectively. Using corrosion rate (ρ) values, the inhibition efficiency
(%η) was evaluated using following equation [27]:
ꢀ1
ꢀ1
−ꢀ2
%
휂 = ﴾
﴿ × ꢁ00
(2)
1
2
Where ρ and ρ represent the corrosion rate values for mild steel corrosion in 1M HCl with
and without HAs, respectively.
2
.4. Electrochemical analyses
Potentiostat Gamry Echem Analyst 5.0 Software G- 300 model was applied for
electrochemical studies. The instrument consists of platinum as a counter electrode, mild steel
as a working electrode and SCE as a reference electrode. The electrochemical studies were
performed after immersing the MS in 1M HCl for 30 minute in order to get open circuit
potential (OCP) established. For EIS study, an AC signal of 10 mV amplitude in the
frequency range of 100 kHz-0.01 mHz was employed. The Nyquist curves for MS corrosion
were fitted in suitable equivalent circuit (Fig. 6). The equivalent circuit consists of solution
resistance (R ), a charge transfer resistance (R ) and a constant phase element. The values of
s
ct
charge transfer resistance and inhibition efficiency (%η) at different concentrations of HAs
were derived using following equation [28]:
푅푐ꢂ (ꢃ푛ℎ)−푅푐ꢂ
%
휂 =
× ꢁ00
(3)
푅푐ꢂ (ꢃ푛ℎ)
In above equation, Rct(inh) and R represent the charge transfer resistances for MS corrosion
ct
with and without HAs, respectively. For polarization studies, MS potential allowed to scan in
-1
the potential range of -250 to +250 V at the constant scan rate of 1 mV s (with respect to the
potential of SCE) [21]. The obtained anodic and cathodic Tafel curves were extrapolated to
get the values of corrosion current densities (icorr) through which inhibition efficiencies (%η)
at several concentrations of HAs were calculated using following relationship [29]:
푖푐표푟푟−푖푐표푟푟(ꢃ푛ℎ)
%
휂 =
x ꢁ00
(4)
푖푐표푟푟
where, icorr and icorr (inh), represent the values of corrosion current densities for MS corrosion in
M HCl without and with HAs, respectively.
.5. SEM-EDS and XRD studies
1
2
The scanning electron microscope (SEM) coupled with electron dispersion X-ray
spectroscopy (EDS) analyses were carried out to support the electrochemical studies. For
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SEM-EDX analyses, MS surfaces are allowed to corrode freely in test electrolyte (1M HCl)
in the absence and presence of 80 ppm concentration of HAs. After 6h immersion time,
surfaces of the corroded specimens were examined using SEM-EDX methods. The ZEISS
EVO SEM 18 / INCA 250 EDS XMAX with a detector (20mm) Oxford model was employed
for SEM-EDS analyses. X-ray diffraction (XRD) analysis was carried out to determine the
nature of protective layer deposited on the surface of metal. The stretch samples collected
from the inhibited (80 ppm) and uninhibited metallic surfaces were used for XRD analysis.
The PAN Analytical, Netherland X-ray diffractometer was used for this purpose.
2
.6. DFT analyses
Density function theory (DFT) based quantum chemical calculations were performed to
support the experimental studies. Recently, DFT has emerged one of the most powerful
techniques to demonstrate the interactions between corrosion inhibitors and metallic surfaces.
In the present study, interactions of HAs and MS surface were demonstrated using Gaussian
0
9 and basis set of G-31 + G (d, p) basic. The DFT studies were performed on different
possible tautomeric and conformational isomers of HAs. Using DFT studies, energies of
frontier molecular orbital pictures (EHOMO and ELUMO) and different related indices were
derived using following relationships [30]:
IE  EHOMO
EA  ELUMO
1
(5)
(6)
1

 (IE  EA)  (E
 ELUMO
)
(7)
HOMO
2
2
1



(8)
1
1


 (IE  EA)  (E
 ELUMO )
(9)
HOMO
2
2
Fe  inh
N 
2
(  )
Fe
inh
(10)
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For the calculation of ΔN (fraction of electron transfer) values, work function of iron (4.88
eV) was used instead of electronegativity of iron. The lowest energy crystalline iron (110)
surface was selected for fraction of electron transfer (ΔN ) calculation.
1
10
3
. Result and discussion
.1. Weight loss measurements
3
Effect of AHA, BHA and OHA concentration on MS corrosion in 1M HCl at the different
temperatures is presented in Table 2. It can be clearly seen that protection efficiency of AHA,
BHA and OHA increases with increasing their concentrations and maximum increase was
observed at 80 ppm concentration. Obviously, increase in the AHA, BHA and OHA
concentration results consecutive raise in the surface coverage that result in to the
corresponding increase in their protection efficiency. Inhibition efficiencies of the HAs
followed the order: OHA (96.37%)> BHA (95.69%)> AHA (93.29%). Difference in
protection efficiencies of AHA, BHA and OHA can be explained on the basis of their
molecular structures. The higher protection efficiency of BHA as compared to AHA can be
explained on the basis of the presence of aromatic (phenyl) moiety instead of methyl group of
the AHA. Presence of three additional double bonds of the aromatic ring enhances the
effectiveness of BHA adsorption on MS surface due to d-p interactions. OHA contains
additional -CO-NH-OH moiety at the place of phenyl ring of BHA. The -CO-NH-OH of
OHA should be considered as more electron donor as compared to the aromatic ring of BHA
as former contains two oxygen and one nitrogen atoms and one double bond in the form of
carbonyl group that can form more strong complex with metallic d-orbital than that of the
three double bonds of latter. Careful observation (Table 2) showed that protection efficiencies
of the AHA, BHA and OHA decrease on increasing the temperature. Increase in temperature
may results into the fractionation, arrangement or/ and decomposition of the HAs molecules
that can adversely affect their protection power. More so, increase in kinetic energy of the
HAs at elevated temperature can also decrease the adsorption abilities of AHA, BHA and
OHA molecules [31].
3
.2. Adsorption isotherm
Adsorption isotherm analysis is one of the most important aspects of metal-corrosion
interactions. Langmuir adsorption isotherm is the most common and frequently used isotherm
models that can be presented using following relationship [32]:
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퐶
ꢄ
= 퐾 + ꢅ (11)

푎푑푠
where, Kads represent adsorption-desorption constant. In the present study, Langmuir
2
adsorption isotherm model was well fitted with correlation coefficient (R ) values close to
unity. Using K values, the standard free energy of adsorption (∆G ) values were calculated
ads
ads
using following equation [32]:
∆Gads = -RT ln (55.5 Kads)
(12)
Here, numerical value of 55.5 denotes the molar concentration of water and R is the gas
constant and T represents the absolute temperature.The values of Kads and ∆Gads at different
studied temperatures are presented in Table 3. High numerical values of Kads showed that
AHA, BHA and OHA have strong ability to adsorb on metallic surface. Negative values of
∆Gads revealed that AHA, BHA and OHA spontaneously adsorb on metallic surface using
-1
their electron rich centers. Literature survey reveals that ∆Gads value of -40 kJ mol or more
-1
negative is consisted with chemisorption while its value of -20 kJ mol or less negative is
consistent with physisorption mechanism [25,26]. Results presented in Table 3 showed that
adsorption of the AHA, BHA and OHA on MS surface obeyed the physiochemisorption by
means of minor supremacy of physisorption mechanism as values of ∆Gads for AHA, BHA
and OHA are more close to -20 kJ/mol as compared to the -40 kJ/mol[33-34].
3
3
.3. Electrochemical analysis
.2.1. Potentiodynamic Polarization (PDP)
Anodic and cathodic Tafel curves for MS corrosion in 1M HCl with and without AHA, BHA
and OHA at their different concentrations (40 - 80 ppm) are shown in Fig. 3 (a-c) and various
PDP parameters such as inhibition efficiency (%η), corrosion potential (E ), corrosion
corr
current density (i ), cathodic ( ) and anodic ( ) Tafel slopes are summarized in Table 4.
corr
c
a
From Fig.3 it can clearly seen that shape of anodic and cathodic curves are significantly
affected in the presence of AHA, BHA and OHA indicating that they exert remarkable
anticorrosion effect on both anodic and cathodic reactions [35,36]. More so, careful
observation of the results presented in table 4 showed that corrosion current density values
are much lower in the presence of AHA, BHA and OHA than that of in their absence. This
observation suggests that AHA, BHA and OHA effectively adsorb on the metallic surface
using their electron rich centers and block the active sites responsible for the corrosion [35-
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3
6]. Observation of the results also showed that presence of AHA, BHA and OHA did not
cause any significant shift in the value of corrosion potential (E ) indicating that AHA,
corr
BHA and OHA act as mixed type inhibitors [37-39]. The order of protection efficiencies of
AHA, BHA and OHA derived from PDP study was consistent with the order of protection
efficiency derived using weight loss method.
3
.2.2. Electrochemical impedance spectroscopy (EIS)
EIS is one of the most important electrochemical methods to demonstrate the interfacial
behaviours of corrosion inhibitors. Nyquist plots for MS corrosion in 1 M HCl at different
AHA, BHA, and OHA concentrations are shown in Fig. 4 (a-c). Nyquist plots represent a
single semicircle indicating that MS corrosion with and without AHA, BHA and OHA
involve a single charge transfer (SCT) mechanism. The SCT mechanism of MS corrosion in
1
M HCl with and without AHA, BHA and OHA was further reinforced by single maxima in
the Bode plots (Fig.5). Increase in the diameter of the Nyquist curves on increasing the AHA,
BHA and OHA concentration is attributed to the increase in the value of charge transfer
resistance due to AHA, BHA and OHA adsorption at the MS-1M HCl interfaces. This finding
suggests that AHA, BHA and OHA act as interface type inhibitors and their presence results
in to formation of protective film at metal-electrolyte interfaces [40]. Equivalent circuit used
for fitting of Nyquist curves is presented in Fig. 6[41]. The double-layer capacitance (C ) for
dl
MS corrosion can be presented as follows [42]:
ꢅꢆ푙 = 푌ꢇ(휔푚ꢈ푥)ꢉ−ꢄ(13)
where, n and Y represent the phase shift and exponent, respectively.  represents the angular
0
frequency. Different EIS parameters are summarized in Table 5. Increase in the value of Rct
and decrease in the values of C is attributed to the adsorption of AHA, BHA and OHA on
dl
metallic surface and increase in the thickness of electric double layer, respectively [43-45].
3
.4. SEM-EDS analyses
SEM images and EDX spectra of MS surfaces corroded in 1M HCl with and without AHA,
BHA and OHA are shown Fig. 7 (a-d) and Fig. 8 (a-d), respectively. It can be clearly seen
that morphology of the MS surfaces are much smoother in the presence of AHA, BHA and
OHA than that of in their absence. This observation reveals that AHA, BHA and OHA adsorb
on metallic surface and protect from corrosive degradation. The adsorption of the AHA, BHA
and OHA on MS surface was further supported by EDX spectral analyses. Increase in the
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intensity of EDX signal for oxygen and presence of additional signals for heteroatoms (Table
6
) in the presence of AHA, BHA and OHA validate the adsorption mechanism of corrosion
inhibition.
3
.5. X-ray diffraction (XRD) analysis
Recently, XRD has immersed as one of the potential tool for the identification of crystalline
phase and to identify the nature of protective layer deposited onto metallic surface. Fig. 9
represents the XRD patterns of the inhibited and uninhibited scratched samples. Fig. 9a
depicts the XRD pattern of scratched sample of mild steel surface in the presence of 1 M
HCl. The XRD pattern shows three peaks at 2 = 37.2, 43.5, 44.7 and 54.8 which is
resulted due to deposition of surface metallic oxides (Fe O and FeOOH) [31, 46]. Careful
3
4
observation (Fig. 9b-d) showed that XRD patterns of the scratched samples containing AHA,
BHA and OHA showed XRD peaks of little intensities. The decrease in intensities of XRD
patterns indicates the non-crystalline nature of deposit protective oxide layers.
3
.6. Quantum chemical calculations
DFT based quantum chemical calculation is one of the most significant and frequently used
computational methods to demonstrate the adsorption and interaction behaviour of corrosion
inhibitors [47-50]. Recall that several DFT based parameters such as ELUMO (Lowest
Occupied Molecular Orbital), EHOMO (Highest Unoccupied Molecular Orbital), dipole
moment (), energy gap (∆E), electron transfer fraction (∆N), global hardness (η) and
electronegativity () are computed from the keto and enol forms and some of the major
conformational isotherms of AHA, BHA and OHA and are presented in Table 7. From the
frontier molecular orbital picture it can be seen that HOMO and LUMO are localized over the
entire parts of the AHA, BHA and OHA molecules. This observation suggests that they act as
strong electron donor as well as strong electron acceptor. Obviously, HOMO defines the part
of inhibitor molecules responsible for electron donation and a higher value of EHOMO is
consistent with high electron donating ability. Conversely, LUMO defines the part of
inhibitor molecules responsible for electron acceptance and a lower value of ELUMO is
consistent with high electron accepting ability [51, 52]. Careful observation of the results
presented in Table 7 showed that AHA, BHA and OHA are associated with relatively high
values of EHOMO and lower values of ELUMO therefore they offer strong donor-acceptor
interactions with the metallic surface and act as effective corrosion inhibitors[53]. Frontier
molecular orbital pictures (HOMO and LUMO) for AHA, BHA and OHA are shown in Figs.
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1
0-12. DFT studies were carried out for keto and enol forms of the AHA, BHA and OHA
molecules along with some common conformational isomers. Different conformational
isomers are constructed based on the orientation of hydroxyl (-OH) attached with nitrogen
with respect to the carbonyl (>C=O) functional group as presented in Figs. 10-12.
It is important to mention that C-N bond of AHA Keto-I acquires the bond length of 1.37Å
which is relatively lesser as compared to the normal C-N bond length. The reduction in the C-
N bond length is might be due to resonance between carbonyl (>C=O) functional group and
unshared pair electrons of nitrogen. Intermolecular H-bonding between >C=O (carbonyl) and
–
OH (hydroxyl) groups can also plays a significant role in the reduction of C-N bond length.
The H-bond length in Keto-I form (AHA) was 1.96Å. In AHA Keto-II form (>C=O and –OH
present in the opposite side), observed C-N bond length was 1.40 Å. Similarly, C-N and H-
bonding acquire the bond lengths of 1.38 Å and 1.93 Å, respectively.
The OHA has two hydroxamic acid groups therefore theoretically three major conformational
isomers are possible as presented in Fig. 12. It important to notice that AHA, BHA and OHA
in their keto and enol forms do not show any remarkable change in the DFT parameters.
Similarly, different conformational isomers also did not show any remarkable change in their
values of DFT indices. However, careful observation of the DFT results presented in Table 7
showed that conformational isomeric forms of AHA, BHA and OHA in which >C=O and –
OH (hydroxyl) groups present in same side are more effective corrosion inhibitors than that
of their enol-tautomeric forms. This can be explained on the basis of complexation behaviour
of AHA, BHA and OHA with metallic d-orbital. Obviously, in keto-tautomeric form in which
>C=O and –OH (hydroxyl ) groups present in same side behave as chelating ligands and form
relatively more stable complex than that of the conformational isomeric forms of AHA, BHA
and OHA in which >C=O and –OH groups present in opposite side.
3
.7. Corrosion inhibition mechanism
It is well established that most of the organic compounds interact with metallic surface using
donor-acceptor or charge sharing mechanism. Mostly, they interact with physiochemisorption
mechanism. Physisorption is mostly occurs via the interaction between charge metallic
surface charged inhibitor molecules whereas chemisorption takes place through charge
sharing between metallic orbitals and inhibitor molecules. Several factors including
temperature, nature of metal and electrolyte, immersion time etc. affect the adsorption
behaviour of the inhibitor molecules. Nevertheless, adsorption of inhibitor molecules results
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into the formation inhibitive films that isolate the metal from corrosive environment [54]. It is
established that in acidic medium, adsorption of organic inhibitors containing heteroatoms in
their molecular structures proceeds through physisorption and finally chemisorption. The
compounds tested as corrosion inhibitors in the present study contain numerous electron rich
centers through which they can effectively adsorb and inhibit metallic corrosion. These
electron rich centers transfer their non-bonding and -electrons into surface metallic orbital
and form coordination bondings [55,56]. The adsorption behaviour of different tested
corrosion inhibitors is illustrated in Fig. 13.
4
. Conclusions
In the present study, corrosion inhibition effect of three hydroxamic acids namely
acetohydroxamic acid (AHA), benzohydroxamic acid (BHA) and oxalohydroxamic acid
(OHA) for mild steel corrosion is evaluated using chemical, electrochemical, surface and
DFT methods. Following conclusions were drawn:
1
2
. AHA, BHA and OHA act as effective corrosion inhibitors for mild steel in 1M HCl
. Their effectiveness followed the order: OHA (96.37%)> BHA (95.69%)> AHA
(93.29%).
3
. Potentiodynamic polarization study showed that AHA, BHA and OHA behaved as
mixed type corrosion inhibitors.
4
5
. EIS study showed that AHA, BHA and OHA behaved as interface type.
. Adsorption of AHA, BHA and OHA at the interface of MS and 1M HCl obeyed the
Langmuir adsorption isotherm model.
6
7
. DFT study suggests that AHA, BHA and OHA interact with donor-acceptor
interactions.
. In conformational isomeric forms of AHA, BHA and OHA in which >C=O and –OH
(hydroxyl) groups present in same side behave as chelating ligands.
Acknowledgements
Author Dr. Dakeshwar Kumar Verma thankful to principal govt. Digvijay College for
providing instrumental and basic facilities
5
. Conflict of interest
Authors declared no conflict of interest
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References
1
.
Singh, A., Ansari, K. R., Quraishi, M. A., Kaya, S. and Banerjee, P. The effect of an
N-heterocyclic compound on corrosion inhibition of J55 steel in sweet corrosive
medium, New Journal of Chemistry, 43 (2019)6303-6313.
2
.
Verma, C., Olasunkanmi, L.,Ebenso, E.E., & Quraishi, M.A., C. Verma, L.
Olasunkanmi, E.E. Ebenso,M. Quraishi, Substituents effect on corrosion inhibition
performance of organic compounds in aggressive ionic solutions: a review, Journal of
Molecular Liquids, 251 (2017) 100–118.
3
.
Dehghani, A., Bahlakeh, G., Ramezanzadeh, B. and Ramezanzadeh, M.Potential role
of a novel green eco-friendly inhibitor in corrosion inhibition of mild steel in HCl
solution: Detailed macro/micro-scale experimental and computational explorations,
Construction and Building Materials, 245 (2020) 118464.
4
5
.
.
Verma, C., Verma, D.K., Ebenso, E.E., & Quraishi, M.A., (2018). Sulfur and
phosphorus heteroatom-containing compounds as corrosion inhibitors: An overview.
Heteroatom Chemistry, e21437.
Solomon, M. M., Umoren, S. A., Quraishi, M. A., & Salman, M. (2019). Myristic
acid based imidazoline derivative as effective corrosion inhibitor for steel in 15% HCl
medium. Journal
of
Colloid
and
Interface
Science, 551,
47–
6
0. https://doi.org/10.1016/j.jcis.2019.05.004
6
7
.
.
Zhang, J. (2020). 2-(3H-Imidazol-4-yl)-ethylamine as a green corrosion inhibitor for
Q235 steel in hydrochloric acid. International Journal of Electrochemical
Science, 15(2), 1437–1449. https://doi.org/10.20964/2020.02.27.
Singh, A., Ansari, K. R., Haque, J., Dohare, P., Lgaz, H., Salghi, R., & Quraishi, M.
A. (2018). Effect of electron donating functional groups on corrosion inhibition of
mild steel in hydrochloric acid: Experimental and quantum chemical study. Journal of
the
Taiwan
Institute
of
Chemical
Engineers, 82,
233–
2
51. https://doi.org/10.1016/j.jtice.2017.09.021.
8
.
Salarvand, Z., Amirnasr, M., Talebian, M., Raeissi, K., & Meghdadi, S. (2017).
Enhanced corrosion resistance of mild steel in 1 M HCl solution by trace amount of 2-
phenyl-benzothiazole derivatives: Experimental, quantum chemical calculations and
molecular dynamics (MD) simulation studies. Corrosion Science, 114, 133–
1
45. https://doi.org/10.1016/j.corsci.2016.11.002.
1
5

Journal Pre-proof
9
.
El Aoufir, Y., Lgaz, H., Bourazmi, H., Kerroum, Y., Ramli, Y., Guenbour, A.,
&Oudda, H. (2016). Quinoxaline derivatives as corrosion inhibitors of carbon steel in
hydrochloridric acid media: Electrochemical, DFT and montecarlo simulations
studies. Journal of Materials and Environmental Science, 7(12), 4330–4347.
1
1
0. Obot, I. B., Madhankumar, A., Umoren, S. A., &Gasem, Z. M. (2015). Surface
protection of mild steel using benzimidazole derivatives: Experimental and theoretical
approach. Journal of Adhesion Science and Technology, 29(19), 2130–2152.
1. Rbaa, M., Galai, M., Abousalem. A. S., Lakhrissi. B., Touhami. M. E., Warad. I.,
Zarrouk. (2019). Synthetic, spectroscopic characterization, empirical and theoretical
investigations on the corrosion inhibition characteristics of mild steel in molar
hydrochloric acid by three novel 8-hydroxyquinoline derivatives.Ionics,
https://doi.org/10.1007/s11581-019-03160-9.
1
1
2. Singh, A., Ansari, K. R., Quraishi, M. A., Kaya, S. and Banerjee, P. The effect of
anN-heterocyclic compound on corrosion inhibition of J55 steel in sweet corrosive
medium, New Journal of Chemistry, 43 (2019) 6303-6313.
3. Yildiz, M., Gerengi, H., Solomon, M. M., Kaya, E., &Umoren, S. A. (2018).
Influence of 1-butyl-1-methylpiperidinium tetrafluoroborate on St37 steel dissolution
behavior in HCl environment. Chemical Engineering Communications, 205(4), 538–
5
48.
4. Rani, B. E. A., &Basu, B. B. J. (2012). Green inhibitors for corrosion protection of
metals and alloys: An overview. International Journal of
Corrosion. https://doi.org/10.1155/2012/380217.
1
1
1
5. Lai, C., Guo, X., Wei, J., Xie, B., Zou, L., Li, X., … Wang, C. (2017). Investigation
on Two Compounds of O,O’-dithiophosphate Derivatives as Corrosion Inhibitors for
Q235 Steel in Hydrochloric Acid Solution. Open Chemistry, 15(1), 263–271.
6. Wang, J., Lin, Y., Singh, A., & Liu, W. (2018). Investigation of some porphyrin
derivatives as inhibitors for corrosion of N80 steel at high temperature and high
pressure in 3.5% NaCl solution containing carbon dioxide. International Journal of
Electrochemical Science, 13(12), 11961–11973.
1
7. Qiang, Y., Zhang, S., Tan, B., & Chen, S. (2018). Evaluation of Ginkgo leaf extract as
an eco-friendly corrosion inhibitor of X70 steel in HCl solution. Corrosion
Science, 133, 6–16. Leena, P., ZeinulHukuman, N. H., Biju, A. R., &Jisha, M.
(2019). Studies on methanolic extract of lepidagathiskeralensis as green corrosion
1
6

Journal Pre-proof
inhibitor for mild steel in 1M HCL. Journal of Electrochemical Science and
Technology, 10(2), 231–243.
1
1
8. Singh, A., Ansari, K. R., Kumar, A., Liu, W., Songsong, C., & Lin, Y. (2017).
Electrochemical, surface and quantum chemical studies of novel imidazole derivatives
as corrosion inhibitors for J55 steel in sweet corrosive environment. Journal of Alloys
and Compounds, 712, 121–133.
9. PreethiKumari, P., Shetty, P., & Rao, S. A. (2017). Electrochemical measurements for
the corrosion inhibition of mild steel in 1 M hydrochloric acid by using an aromatic
hydrazide derivative. Arabian Journal of Chemistry, 10(5), 653–663.
0. Reddy, A.S., Kumar, M.S., & Reddy, G.R., (2000). A convenient method for the
preparation of hydroxamic acids, Tetrahedron Letters, 41, 6285–6288.
1. Farkas, E., Enyedy, E. A., Csoka, H., (1999). A comparison between the chelating
properties of some dihydroxamic acids, desferrioxamine B and acetohydroxamic acid,
Polyhedron, 18, 2391–2398.
2
2
2
2. Farkas, E., Enyedy, E.A., Zekany, L., &Deak, G., (2001). Interaction between iron
(
II) and hydroxamic acids: oxidation of iron (II) to iron (III) by desferrioxamine B
under anaerobic conditions, Journal of Inorganic Biochemistry, 83, 107–114.
3. Alagta, A., Felhosi, I., &Kalman, E., (2007). Hydroxamic acid corrosion inhibitor for
steel in aqueous solution, Material Science Forum, 537–538, 81–88.
2
2
2
4. Telegdi, J., Rigo, T., &Kalman. E., (2005). Molecular layers of hydroxamic acids in
copper corrosion inhibition, Journal of Electroanalytical Chemistry, 582, 191–201.
5. Bahlakeh, G., Dehghani, A., Ramezanzadeh, B. And Ramezanzadeh, M. Highly
effective mild steel corrosion inhibition in 1 M HCl solution by novel green aqueous
Mustard seed extract: Experimental, electronic-scale DFT and atomic-scale MC/MD
explorations, Journal of Molecular Liquids, 293 (2019)111559
2
2
6. Verma, D.K., Khan, F., (2016). Corrosion inhibition of mild steel in hydrochloric acid
using extract of glycine max leaves, Research on Chemical Intermediates, 42, 3489–
3
506.
7. Singh, A., Ansari, K. R., Chauhan, D. S., Quraishi, M. A., Lgaz, H., & Chung, I. M.
2020). Comprehensive investigation of steel corrosion inhibition at macro/micro
(
level by ecofriendly green corrosion inhibitor in 15% HCl medium. Journal of Colloid
and Interface Science, 560, 225–236.
1
7

Journal Pre-proof
2
2
8. Verma, C., Quraishi, M. A., Ebenso, E. E., Obot, I. B., & El Assyry, A. (2016). 3-
Amino alkylated indoles as corrosion inhibitors for mild steel in 1M HCl:
Experimental and theoretical studies. Journal of Molecular Liquids, 219, 647–660.
9. Verma, D.K., Khan, F., I. Bahadur, I., Salman, M., Quraishi, M.A., Ebenso, E.E., &
Verma, C., (2018). Inhibition performance of Glycine max, Cuscuta reflexa and
Spirogyra extracts for mild steel dissolution in acidic medium: Density functional
theory and experimental studies, Results in Physics, 10, 665–674.
3
0. Ahmed, M. H. O., Al-Amiery, A. A., Al-Majedy, Y. K., Kadhum, A. A. H.,
Mohamad, A. B., &Gaaz, T. S. (2018). Synthesis and characterization of a novel
organic corrosion inhibitor for mild steel in 1ꢀM hydrochloric acid. Results in
Physics, 8, 728–733.
3
3
1. Verma, D.K., & Khan, F., (2016). Green approach to corrosion inhibition of mild
steel in hydrochloric acid medium using extract of spirogyra algae, Green Chemistry
Letters and Reviews, 9 (1), 52-60.
2. Singh, A., Ahamad, I., & Quraishi, M. A. (2016). Piper longum extract as green
corrosion inhibitor for aluminium in NaOH solution. Arabian Journal of Chemistry, 9,
S1584–S1589.
3
3
3. Fiori-Bimbi, M. V., Alvarez, P. E., Vaca, H., &Gervasi, C. A. (2015). Corrosion
inhibition of mild steel in HCL solution by pectin. Corrosion Science, 92, 192–199.
4. Dutta, A., Saha, S. K., Adhikari, U., Banerjee, P., &Sukul, D. (2017). Effect of
substitution on corrosion inhibition properties of 2-(substituted phenyl) benzimidazole
derivatives on mild steel in 1 M HCl solution: A combined experimental and
theoretical approach. Corrosion Science, 123, 256–266.
3
3
3
5. Singh, A., Ansari, K. R., Kumar, A., Liu, W., Songsong, C., & Lin, Y. (2017).
Electrochemical, surface and quantum chemical studies of novel imidazole derivatives
as corrosion inhibitors for J55 steel in sweet corrosive environment. Journal of Alloys
and Compounds, 712, 121–133.
6. Yadav, M., Kumar, S., Tiwari, N., Bahadur, I., &Ebenso, E. E. (2015). Experimental
and quantum chemical studies of synthesized triazine derivatives as an efficient
corrosion inhibitor for N80 steel in acidic medium. Journal of Molecular Liquids, 212,
1
51–167.
7. Singh, A., Lin, Y., Ansari, K. R., Quraishi, M. A., Ebenso, E. E., Chen, S., & Liu, W.
2015). Electrochemical and surface studies of some Porphines as corrosion inhibitor
(
1
8

Journal Pre-proof
for J55 steel in sweet corrosion environment. Applied Surface Science, 359, 331–
3
39.
3
3
8. Zhang, D., Tang, Y., Qi, S., Dong, D., Cang, H., & Lu, G. (2016). The inhibition
performance of long-chain alkyl-substituted benzimidazole derivatives for corrosion
of mild steel in HCl. Corrosion Science, 102, 517–522.
9. Abd El-Lateef, H. M., Abo-Riya, M. A., &Tantawy, A. H. (2016). Empirical and
quantum chemical studies on the corrosion inhibition performance of some novel
synthesized cationic gemini surfactants on carbon steel pipelines in acid pickling
processes. Corrosion Science, 108, 94–110.
4
0. Abd El-Lateef, H. M., &Tantawy, A. H. (2016). Synthesis and evaluation of novel
series of Schiff base cationic surfactants as corrosion inhibitors for carbon steel in
acidic/chloride media: Experimental and theoretical investigations. RSC
Advances, 6(11), 8681–8700.
4
4
4
4
1. Lgaz, H., Salghi, R., Jodeh, S., &Hammouti, B. (2017). Effect of clozapine on
inhibition of mild steel corrosion in 1.0 M HCl medium. Journal of Molecular
Liquids, 225, 271–280.
2. Hassannejad, H., &Nouri, A. (2018). Sunflower seed hull extract as a novel green
corrosion inhibitor for mild steel in HCl solution. Journal of Molecular Liquids, 254,
3
77–382.
3. Alvarez, P. E., Fiori-Bimbi, M. V., Neske, A., Brandán, S. A., &Gervasi, C. A.
2018). Rolliniaoccidentalis extract as green corrosion inhibitor for carbon steel in
(
HCl solution. Journal of Industrial and Engineering Chemistry, 58, 92–99.
4. Bedair, M. A., El-Sabbah, M. M. B., Fouda, A. S., &Elaryian, H. M. (2017).
Synthesis, electrochemical and quantum chemical studies of some prepared
surfactants based on azodye and Schiff base as corrosion inhibitors for steel in acid
medium. Corrosion Science, 128, 54–72.
4
4
5. Solomon, M. M., Gerengi, H., &Umoren, S. A. (2017). Carboxymethyl
Cellulose/Silver Nanoparticles Composite: Synthesis, Characterization and
Application as a Benign Corrosion Inhibitor for St37 Steel in 15% H SO
2
4
Medium. ACS Applied Materials and Interfaces, 9(7), 6376–6389.
6. Chugh, B., Singh,A. K., Thakur, S., Pani, B., Lgaz, H., Chung, I. M., Jha, R., and
Ebenso, E. E. (2020). Comparative investigation of corrosion-mitigating behaviour of
thiadiazole-derived bis-schiff bases for mild steel in acid medium: experimental,
1
9

Journal Pre-proof
theoretical,
and
surface
study.
ACS
Omega,
https://dx.doi.org/10.1021/acsomega.9b04274.
4
7. Obot, I. B., Madhankumar, A., Umoren, S. A., &Gasem, Z. M. (2015). Surface
protection of mild steel using benzimidazole derivatives: Experimental and theoretical
approach. Journal of Adhesion Science and Technology, 29(19), 2130–2152.
8. Gaussian 09, Revision A.02, Frisch MJ, Trucks GW, Schlegel HB, Scuseria GE,
Robb MA, Cheeseman JR, et al. Gaussian, Inc., Wallingford CT; 2009.
4
4
9. El Aoufir, Y., Lgaz, H., Bourazmi, H., Kerroum, Y., Ramli, Y., Guenbour, A.,
&Oudda, H. (2016). Quinoxaline derivatives as corrosion inhibitors of carbon steel in
hydrochloridric acid media: Electrochemical, DFT and montecarlo simulations
studies. Journal of Materials and Environmental Science, 7(12), 4330–4347.
5
5
5
5
5
5
0. Hadisaputra, S., Purwoko, A. A., Ilhamsyah, I., Hamdiani, S., Suhendra, D., Nuryono,
N., &Bundjali, B. (2018). A combined experimental and theoretical study of (E)-ethyl
3
-(4-methoxyphenyl)acrylate as corrosion inhibitor of iron in 1 M HCL
solutions. International Journal of Corrosion and Scale Inhibition, 7(4), 633–647.
1. Khalaf, M. M., Tantawy, A. H., Soliman, K. A., &Abd El-Lateef, H. M. (2020).
Cationic gemini-surfactants based on waste cooking oil as new ‘green’ inhibitors for
N80-steel corrosion in sulphuric acid: A combined empirical and theoretical
approaches. Journal of Molecular Structure, 1203.
2. Dehghani, A., Bahlakeh, G., Ramezanzadeh, B., &Ramezanzadeh, M. (2019).
Potential of Borage flower aqueous extract as an environmentally sustainable
corrosion inhibitor for acid corrosion of mild steel: Electrochemical and theoretical
studies. Journal of Molecular Liquids, 277, 895–911.
3. Salarvand, Z., Amirnasr, M., Talebian, M., Raeissi, K., &Meghdadi, S. (2017).
Enhanced corrosion resistance of mild steel in 1 M HCl solution by trace amount of 2-
phenyl-benzothiazole derivatives: Experimental, quantum chemical calculations and
molecular dynamics (MD) simulation studies. Corrosion Science, 114, 133–145.
4. Pournazari, S.,Moayed, M. H., & Rahimizadeh, M. (2013) Pages 20-31, In situ
inhibitor synthesis from admixture of benzaldehyde and benzene-1,2-diamine along
with FeCl catalyst as a new corrosion inhibitor for mild steel in 0.5 M sulphuric acid.
3
Corrosion Science, 71, 20-31.
5. Abd El-Lateef, H. M., Soliman, K. A., &Tantawy, A. H. (2017). Novel synthesized
Schiff Base-based cationic gemini surfactants: Electrochemical investigation,
2
0

Journal Pre-proof
theoretical modeling and applicability as biodegradable inhibitors for mild steel
against acidic corrosion. Journal of Molecular Liquids, 232, 478–498.
5
6. Khalaf, M. M., Tantawy, A. H., Soliman, K. A., & Abd El-Lateef, H. M. (2020).
Cationic gemini-surfactants based on waste cooking oil as new ‘green’ inhibitors for
N80-steel corrosion in sulphuric acid: A combined empirical and theoretical
approaches. Journal
of
Molecular
Structure, 1203. https://doi.org/10.1016/j.molstruc.2019.127442.
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Greenness : Non toxic to living
organisation and environment
Inhibitor molecule should posses
bulky groups extended pi bonds
and active site
Should contain functional groups
containing heteroatom like P, N, O,S
General requirements of
inhibitor
Cost effective, Biodegredable,
Renewable and Non toxic
Availibility to cover large surface
area of metal surface
Solubility of inhibitor molecule
Figure 1: Schematic illustrations of basic requirrements of corrosion inhibitors.
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0
2
4
6
8
10
0
.10
.08
10
2
4
6
0 ppm
0 ppm
0 ppm
OHA
8
0
80 ppm
6

0.06
4
0
.04
.02
2
0
0
20
30
40
50
Log C (ppm)
60
70
80
0
2
4
6
8
10
10
0
.12
.10
.08
.06
.04
.02
2
4
0 ppm
0 ppm
60 ppm
0 ppm
(
BHA)
0
8
6
4
2
0
8
0


0
0
0
20
40
60
80
Log C (ppm)
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0
2
4
6
8
10
0.12
0.10
0.08
0.06
0.04
0.02
10
2
4
6
8
0 ppm
0 ppm
0 ppm
0 ppm
AHA
8
6

4
2
0
20
30
40
50
Log C (ppm)
60
70
80
Figure 2: Langmuir plots of Log C (ppm) vs Log (/1-) for adsorption of OHA, BHA and
AHA molecules on MS surface in 1M HCl.
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Figure 3: Potentiodynamic polarization curves for mild steel in molar concentration of
hydrochloric acid (1 M HCl) and different concentrations (40-80 ppm) of (a) OHA, (b) BHA
and (c) AHA at room temperature.
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0
2
4
6
8
10
10
0
0
2
4
6
8
140
120
100
14
1
8
6
4
2
0
10
Blank
4
6
8
0 ppm
0 ppm
0 ppm
(A)
1
2
0
8
6
4
2
0
1
8
5
10
15
20
25
O
1
2
3
4
5
)
Z real
(
 cm2
6
80
60
40
20
0
4
2
0
0
20 40 60 80 100 120 140 160 180 200
2
Z
( cm )
real
0
2
4
6
8
10
10
0
0
2
4
6
8
1
1
1
40
14
1
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4
2
0
10
Blank
1
2
0
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2
0
4
6
8
0 ppm
0 ppm
0 ppm
(B)
1
20
00
8
5
10
15
20
25
O
1
2
3
4
5
)
Z real
(
 cm2
6
80
60
40
20
0
4
2
0
0
20
40
60
80 100 120 140 160 180
2
Z
( cm )
real
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0
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10
10
0
2
4
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8
100
14
12
10 10
Blank
4
6
8
0 ppm
0 ppm
0 ppm
(C)
8
1
0
8
6
4
2
0
6
4
80
60
40
20
0
8
6
4
2
0
2
250
5
10
15
20
O
1
2
3
4
5
Z real
(
 cm2
)
0
20
40
60
80
100
120
140
2
Z
( cm )
real
Figure 4: Nyquist plots for mild steel in molar concentration of hydrochloric acid (1 M HCl)
and different concentrations (40-80 ppm) of (a) OHA, (b) BHA and (c) AHA at room
temperature.
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