J. Nig. Soc. Phys. Sci. 4 (2022) 214–222

Journal of the
Nigerian Society

of Physical
Sciences

The corrosion characteristics of SS316L stainless steel in a
typical acid cleaning solution and its inhibition by

1-benzylimidazole: Weight loss, electrochemical and SEM
characterizations

K. K. Adamaa, I. B. Onyeachub,∗

a Department of Chemical Engineering, Faculty of Engineering, Edo State University Uzairue, Edo State, Nigeria.
b Department of Industrial Chemistry, Faculty of Science, Edo State University Uzairue, Edo State, Nigeria.

Abstract

Acid cleaning, an inevitable industrial practice used to descale chemical reactors, usually causes serious corrosion attack on underlying alloy
substrates. Ameliorating this phenomenon requires the addition of effective corrosion inhibitors into the acid solution. Current global regulations
encourage environmentally-benign molecules as corrosion inhibitors. Consequently, 1-benzylimidazole has been investigated for its inhibitive
characteristics against the corrosion of SS316L stainless steel in a typical acid cleaning solution containing 2 % HCl + 3.5 % NaCl. Weight loss
measurements confirm that the corrosion inhibition property of 1-benzylimidazole increases with concentration but depreciates with increased tem-
perature. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) measurements confirm that 1-benzylimidazole
adsorb on the stainless steel surface to isolate its surface from the acid solution. 1-benzylimidazole is a mixed-type inhibitor with greater anodic
influence, and its adsorption enhances the formation and protectiveness of a passive film. Weight loss and the electrochemical measurements agree
to an average inhibition efficiency > 70 % at 1000 ppm. The inhibitor adsorbs via physisorption and obeys the Temkin isotherm model. SEM
surface characterization confirm the ability of 1-benzylimidazole to protect the surface microstructure of the stainless steel during the corrosion.

DOI:10.46481/jnsps.2022.596

Keywords: Corrosion inhibitor; Stainless steel; Acid cleaning; Imidazole; Polarization.

Article History :
Received: 18 January 2022
Received in revised form: 17 March 2022
Accepted for publication: 19 March 2022
Published: 29 May 2022

c©2022 Journal of the Nigerian Society of Physical Sciences. All rights reserved.
Communicated by: Edward Anand Emile

1. Introduction

Stainless steel is heavily deployed in the construction
of many reactors in the chemical industry. It exhibits good
corrosion resistance because it readily forms an iron/chromium-
enriched passive layer [1]. Unfortunately, the passive film

∗Corresponding author tel. no: +2348034917997
Email address: onyeachu.benedict@edouniversity.edu.ng (I.

B. Onyeachu )

formation is usually truncated by chloride ion-containing
corrosion environments because its products are transformed
into soluble chlorides [2]. The resultant effect is a localized
form of corrosion which diminishes the structural integrity of
many chemical reactors and shortens their span of usage. Acid
cleaning is a typical industrial process which exposes stainless
steel surfaces to chloride ion-induced corrosion. It involves the
use of dilute mineral acid (especially 2-5 % HCl) to remove
inorganic scales which grow on the surfaces of industrial

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Adama and Onyeachu / J. Nig. Soc. Phys. Sci. 4 (2022) 214–222 215

metallic equipment and diminish their performance. While
the metal surface is descaled, a simultaneous acid corrosion
attack on the underlying substrate usually ensues. The extent
of this corrosion is even aggravated by the seawater sources
used to prepare the acid solutions, since seawater is naturally
enriched with chloride ions, especially as NaCl [3, 4]. A
practical industrial approach to ameliorate this corrosion attack
is to add highly effective corrosion inhibitors into the acid
cleaning solution. Currently, most industries apply propargyl
alcohol-based inhibitors which are very toxic, both, to humans
and other environmental species [5].

Imidazole and its derivatives are nitrogen-based hetero-
cyclic compounds largely used for the production of numerous
cheap environmentally-safe drugs [6, 7]. In the past decade,
imidazole derivatives have been reported as formidable cor-
rosion inhibitors for various metals. Singh et al. [8] reported
that 2-(4-methoxyphenyl)-4,5-diphenyl-imidazole exhibited
93 % efficiency for the inhibition of J55 steel corrosion in
CO2-saturated brine solution. Ting et al. [9] reported that
4-phenylimidazole acted as a mixed-type corrosion inhibitor
for copper in sulphuric acid and provided 95.84 % efficiency;
adsorbing both by physical and chemical mechanisms. In
other reports [10], thiazole-4-carboxylic acid, 2-methyl-1,3-
thiazole-4-carboxylic acid, and some imidazole zwitterions
have been reported as highly efficient for carbon steel during
acid corrosion [11]. Particularly, dimethylbenzodiimidazole
(2,7-dimethyl3,6-dihydrobenzo[1,2-d;3,4-d’] diimidazole
acted as an anodic inhibitor for SS316L stainless steel in
0.5 M H2SO4 and provided 77 % at optimum concentration
[12]. Also, some synthesized dicationic imidazolium ionic
liquids were also reported for SS304 stainless steel in 0.5 M
H2SO4 solution whereby 92 % efficiency was recorded [13].
Apparently, not much work has been reported for imidazole
derivatives as stainless steel corrosion inhibitors. Even so, the
reported derivatives are expensively synthesized compounds
with cumbersome molecular structures that disturb their
adsorption. Identifying a cheap and simple-structure imidazole
derivative which can deliver high inhibition efficiency will be
very beneficial to the industry.

In the present work, 1-benzylimidazole has been identified
as a promising imidazole derivative for the inhibition of stain-
less steel acid corrosion. 1-benzylimidazole is a major pharma-
cological ingredient with environmentally-safe characteristics,
according to the Paris Commission (PARCOM) standard [14],
because it exhibits log Po/w = 1.93 and LD50 = 75 mg/kg [15].
As Figure 1 shows, 1-benzylimidazole has a simple structure
whereby a phenylmethyl group is attached to the imidazole ni-
trogen. Computational simulation previously revealed that this
simple structure enables 1-benzylimidazole to inherently ori-
ent in a flat position and achieve good metal surface coverage
during corrosion inhibition [16]. The most visible reports of 1-
benzylimidazole as corrosion inhibitor have been presented for
carbon steel [16, 17, 18] in acid solutions. The inhibitor exhib-
ited more anodic behaviour on the carbon steels, causing us to
suspect its ability to enhance anodic passivation when applied

for stainless steel. Furthermore, the inhibitor efficiency has not
been reported in a practical acid cleaning solution which con-
tains HCl + NaCl, and is usually conducted at elevated temper-
atures [3]. Filling this research gap will be highly beneficial
towards the development of greener corrosion inhibitors for in-
dustrial acid cleaning.

Consequently, we apply weight loss technique to screen
the effect of concentration and temperature on the perfor-
mance of 1-benzylimidazole as inhibitor against the corrosion
of SS316L stainless steel in 2 % HCl + 3.5 % NaCl solu-
tion. Thereafter, we employ electrochemical techniques like
electrochemical impedance spectroscopy (EIS) and potentiody-
namic polarization (PDP) to provide mechanistic interpretation
of 1-benzylimidazole performance at maximum concentration.
Scanning electron microscopy (SEM) was employed to probe
the extent of stainless steel surface damage by corrosion and its
mitigation by the 1-benzylimidazole.

2. Materials and method

2.1. Materials

All chemicals and reagents used in this work were pur-
chased from Sigma Aldrich and Fischer Scientific, respectively.
Stainless steel SS316L, having the elemental composition pre-
viously reported [19], was used. The bulk alloy bar was ma-
chined into corrosion test coupons with total surface area 24.89
cm2 and 1 cm2 , respectively, exposed for the weight loss and
electrochemical experiments. The test solution (2 % HCl + 3.5
% NaCl) was prepared by, firstly, diluting concentrated HCl (37
w/v%) with distilled water to obtain a 2 % HCl solution and,
secondly, preparing 3.5 % NaCl solution using the 2 % HCl
as solvent. Stock solution of 1-benzylimidazole was prepared
in isopropanol and calculated volumes were subsequently re-
trieved and made up to 200 mL with the acid solution, so as to
obtain working inhibitor concentrations of 200, 400, 800 and
1000 ppm. A thermostatic water bath was employed to main-
tain experimental temperatures.

2.2. Methods

Prior to any experiment, the surface of the stainless steel
coupon was polished with #400, #600, #800 and #1000 grit sil-
icon carbide papers. This was performed with simultaneous
washing under running tap water, degreasing with acetone and
mechanical drying with warm air. Weight loss experiments, af-
ter 24 h immersion in the uninhibited and inhibited acid solu-
tions, were conducted, initially, at 25◦C. Using the optimum
inhibitor concentration, the effect of temperature (45 and 65◦C)
was investigated. The stainless steel coupons were retrieved
after 24 h immersion and cleaned according to the ASTM G1-
03 standard procedure [20]. The coupons were then re-weighed
and the weight difference (∆W) before and after immersion was
calculated based on Equation (1). From the weight loss, the cor-
rosion rate (CR) in millimeter per year (mpy) was calculated,
based on Equation (2); where A = total surface area of coupon

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Adama and Onyeachu / J. Nig. Soc. Phys. Sci. 4 (2022) 214–222 216

Figure 1: Structure of 1-benzylimidazole.

(24.89 cm2 ), ρ = density of SS316L stainless steel (8.0 g cm−3

), T = immersion time (24 h).

∆W = Wbefore − Wafter (1)

CR(mpy) =
∆W × 3.45 × 106

A ×ρ× T
(2)

The electrochemical experiments such as EIS and PDP
were conducted on a Gamry 600 potentiostat equipped with the
Echem Analyst software for data analysis. The electrochemical
set-up was a 3-electrode system which contained the stainless
steel as the working electrode, a graphite rod as counter elec-
trode and Ag/AgCl as the reference electrode. All measure-
ments were performed at the end of 1 hour free immersion to
ensure that the corrosion coupons attained steady-state open cir-
cuit potential [21]. The EIS measurement was conducted by ap-
plying ± 10 mV sinusoidal signal amplitude perturbation over
a frequency range of 105 Hz to 10−1 Hz. The PDP experiment
was conducted by polarizing the stainless steel from −0.25 V
(vs. open circuit potential) to +1.2 V vs. Ref. at a rate of 0.2
mV/s . The SEM surface characterization for the polarized in-
hibited and uninhibited electrode was achieved using the JEOL
JSM-6610 LV scanning electron microscope.

3. Results and discussion

3.1. Weight loss results

The weight loss, and associated corrosion rate, experienced
after 24 h immersion of the stainless steel coupons in 2 % HCl
+ 3.5 % NaCl solution at 25◦C without and with different 1-
benzylimidazole concentrations are presented in Figures 2a and
2b. In the acid solution without inhibitor, the stainless steel
loses an average of 0.0411 g after 24 h immersion, which cor-
responds to a corrosion rate of 30.20 mpy. In the presence of
1-benzylimidazole, the weight loss diminishes continually with
increasing inhibitor concentration. The least average weight
loss of 0.0109 g (or 8.01 mpy corrosion rate) was observed in
the presence of 1000 ppm, and approximated to 73.48 %, fol-
lowing Equation (3) and Figure 2c.

Figure 2: Results of (a) weight loss (b) corrosion rate and (c) inhibition effi-
ciency after 24 immersion of SS316L stainless steel in 2 % HCl + 3.5 % NaCl
solution without and with different concentration of 1-benzylimidazole at 25◦C

%I E∆W = 1 −
CRwith inhibitor

CRwithout inhibitor
× 100% (3)

This result can be interpreted by considering that the weight
loss experienced by the immersed coupons is caused by the
loss of surface atoms like Cr and Fe via oxidation into species
like Cr3+ , Fe2+ and Fe3+. On the other hand, organic inhibitors
impede corrosion by interacting the reactive electrons n their
heteroatoms and C = C functional groups with the d-orbitals
of metal atoms. These electron-rich sites donate electrons that
fill the d-orbitals in the metal atoms, thus, supressing their
oxidation. The resultant inhibitor adsorption increases the
hydrophobicity of the metal surface and isolates it from the
corrosion environment, as the schematic in Figure 3 elucidates.
The more inhibitor in the acid solution, the more metal surface

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Adama and Onyeachu / J. Nig. Soc. Phys. Sci. 4 (2022) 214–222 217

is covered and protected.

As temperature increases to 45 and 65◦C, Table 1 shows
that the weight loss and corrosion rate increase for, both, the
uninhibited and inhibited acid solutions. The corrosion inhi-
bition efficiency provided by the maximum concentration of
1000 ppm, initially, decreased rather moderately to 67.80 %
(45◦C) and, thereafter, quite drastically to 37.61 % (65◦C). Al-
though the presence of 1-benzylimidazole, somewhat, protected
the stainless steel at these elevated temperatures, the deprecia-
tion in inhibitor efficiency may be attributed to the competitive
mechanisms of increased surface dissolution and weakened in-
hibitor adsorption. Increased temperature promotes the transfer
of corrosive agents, especially the chloride ions, from solution
bulk to the metal surface, thus, promoting surface dissolution
rather than inhibitor adsorption. Also, elevated temperatures
could induce desorption of already adsorbed inhibitors from the
metal surface, indicating that 1-benzylimidazole adsorbs via a
physiosorption mechanism [22].

3.2. Adsorption isotherm
Adsorption isotherms provide adequate understanding of

the mode of interaction between an adsorbing corrosion in-
hibitor molecule and the metal substrate. They describe
whether inhibitor molecules adsorb on the metal surface as a
single layer of film, as multilayer, or if any repulsion exists
among inhibitor molecules [23]. In this research, the Lang-
muir, Temkin and Freundlich isotherms were employed to test
the mode of interaction of 1-benzylimidazole on the stainless
steel surface. The Langmuir isotherm predicts that the in-
hibitor adsorbs on the stainless steel surface as a monolayer.
The Temkin isotherm predicts that the inhibitor forms a multi-
layer with plausible inhibitor-inhibitor interaction. On the other
hand, the Freundlich isotherm depicts that the inhibitor is ad-
sorbing on a rough and heterogeneous surface. The linear forms
of the Langmuir, Temkin and Freundlich isotherms are, respec-
tively, presented as follows:

C
θ

=
1

Kad s
+ C (4)

θ = −
1

2α
ln C −

1
2α

Kad s (5)

log θ = log Kad s +
1
n

log C (6)

θ = surface coverage = %I E100 , Kad s = adsorption-desorption
equilibrium constant, C = inhibitor concentration (in ppm)
and the factor, α, accounts for the lateral interaction between
inhibitor and metal surface.

The value of n describes the feasibility of inhibitor adsorp-
tion; which is highly feasible when 0 < 1n < 1 but, respectively,
moderate or difficult when 1n = 1 or > 1 [24]. A plot of versus
C will yield the Langmuir isotherm curve, as shown in Figure
4a. The Temkin isotherm, Figure 4b, is described by the plot
of θ against ln C whereas the plot of log θ versus log C gives

Figure 3: Schematic representation to show how 1-benzylimidazole adsorption
increases the hydrophobicity of the stainless steel surface

the Freundlich isotherm, Figure 4c. Given that it displayed the
closest agreement between experimental plots and fitting line,
and because its correlation coefficient (R2) value was closest
to unity, the Freundlich isotherm most appropriately describes
the adsorption of 1-benzylimidazole on the SS316L stainless
steel. The adsorption equilibrium constant was calculated as
1.025 ppm mol−1 and, from this value, the Gibbs’ free energy
(∆Gad s = −RT ln(106 Kad s) ) was deduced as -34.29 kJ/mol and
the negative value of ∆G confirms that the inhibitor adsorption
was spontaneous and feasible.

3.3. Electrochemical results

Electrochemical measurements are capable of providing
mechanistic explanations to the corrosion inhibition behaviour
of 1-benzylimidazole on the SS316L stainless steel in the acid
solution. At the open circuit potential, a quasi-equilibrium
is established between the rates of oxidation and reduction
reactions taking place in the micro-cells forming anodic and
cathodic active sites on the alloy surface. By displacing the
alloy from its equilibrium potential, relevant electrochemical
parameters could be measured and related to the corrosion phe-
nomenon. Steady-state electrochemical techniques like EIS can
provide accurate information about the dielectric and charge
transfer phenomena at the alloy-acid solution interface. A more
aggressive technique like the PDP is able to provide details
about the corrosion potential, corrosion kinetics, passivation
and passivation breakdown/pitting corrosion phenomena.

The EIS results are presented in Figure 5, as the plots
of Nyquist (Figure 5a), absolute impedance (Figure 5b) and
phase angle (Figure 5c). The characteristic arcs displayed
by the stainless steel appear larger in the presence of 1-
benzylimidazole, compared with the size in the blank acid
solution. Larger arcs usually depict greater resistance to charge
transfer at the alloy-solution interface, i.e. greater corrosion
resistance. The result confirms the inhibitive property of
1-benzylimidazole for the stainless steel. The trend in the
Nyquist arc sizes is confirmed by the values of low-frequency
absolute impedance in Figure 5b. Clearer mechanism is

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Table 1: Weight loss, corrosion rate and inhibition efficiency of 316 stainless steel during corrosion after 24 h in 2 % HCl + 3.5 % NaCl solution at 25◦C, 45◦C and
65◦C

Parameter
25◦C 45◦C 65◦C

Weight
loss (g)

Corrosion
rate (mpy)

Weight loss
(g)

Corrosion
rate (mpy)

Weight
loss (g)

Corrosion
rate (mpy)

Without inhibitor 0.041 g 30.20 mpy 0.059 g 43.35 mpy 0.109 g 80.71 mpy
with 1000 rpm 0.011 g 8.01 mpy 0.019 g 13.96 mpy 0.068 g 50.35 mpy
Inhibition Effi-
ciency (% IE)

73.48 % 67.80 % 37.61 %

Figure 4: (a) Langmuir (b) Temkin and (c) Freundlich isotherm plots for the adsorption of 1-Benzylimidazole on 316 stainless steel during corrosion in 2 % HCl
+3.5 wt% NaCl solution

deduced from the phase angle plots in Figure 5c, whereby the
stainless steel clearly displayed two time constants at high
and low frequencies, compared with the single time constant

exhibited by the uninhibited alloy. The two time constants
depict two phenomena at the alloy-solution interface; namely
the phenomenon at a corrosion layer-solution interface (at high

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Adama and Onyeachu / J. Nig. Soc. Phys. Sci. 4 (2022) 214–222 219

Figure 5: EIS plots in formats of (a) Nyquist (b) absolute impedance (c) phase angle and equivalent circuit for SS316L stainless steel during corrosion in 2 % HCl
+ 3.5 % NaCl (d) without and (e) with 1-benzylimidazole.

Table 2: EIS parameters for corrosion of 316 stainless steel in 2 % HCl + 3.5 % NaCl solution without and with 1000 ppm of 1-benzylimidazole at 25◦C.

CPEdl CPE f
Conc. Rs(

Ωcm2
) Ydl

µFcm−2 sn−1
αdl Rct(

Ωcm2
) Y f

µFcm−2 sn−1
α f R f(

Ωcm2
) (Rp = R f + Rct)(

Ωcm2
) Goodness

of fit(
×10−3

) % IE
without
inhibitor

0.719 374 0.75 212 - - - 212 3.92 -

with
1000
rpm

0.877 110 0.85 685 57 0.83 80 765 2.29 72.29

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Adama and Onyeachu / J. Nig. Soc. Phys. Sci. 4 (2022) 214–222 220

Table 3: Polarization parameters for corrosion of 316 stainless steel in 2 % HCl 3.5 % NaCl solution without and with 1000 ppm of 1-benzylimidazole at 25◦C.

Sample Ecorr (mV) icorr
(
µA/cm2

)
βa
(mV/decade)

-βc
(mV/decade)

% IE

without
inhibitor

-277 161.30 89.73 132.60 -

with 1000 rpm -258 45.90 68.84 136.10 71.54

Figure 6: PDP plots for SS316L stainless steel during corrosion in 2 % HCl +
3.5 % NaCl without and with 1-benzylimidazole.

Figure 7: SEM surface morphology of SS316L stainless steel after polarization
in 2 % HCl + 3.5 % NaCl (a) without and (b) with 1-benzylimidazole.

frequency) and at a corrosion layer-substrate interface (at low
frequency) [25]. Compared with the single time constant for
the uninhibited stainless steel, the two time constants in the
presence of 1-benzylimidazole is due to the adsorbed corrosion
inhibitor layer which isolates the stainless steel substrate
from the acid solution. Consequently, the Figure 5d and 5e
were adopted as electrical models to interpret the corrosion
phenomena for the uninhibited and inhibited stainless steel,
respectively, after fitting experimental results using the Echem
Analysts software. The values of respective electrical elements
are detailed in Table 2.

The elements Rs, Rct and CPEdl represent the solution re-

sistance, charge transfer resistance and double layer capaci-
tance, respectively. The use of constant phase element (CPE),
rather than pure capacitor, in the model is to account for sur-
face roughness of the corroding alloy [26]. The Rct is equiva-
lent to the corrosion resistance of the corroding metal while the
CPEdl elements, Ydl and n, describe the admittance of charge
into the double layer and the roughness of the alloy surface (αdl
), respectively. In Figure 5e, the characteristic of the adsorbed
inhibitor layer is characterized by the R f and CPE f elements
(Y f and α f ) which, respectively, describe the porosity of the
adsorbed layer and the charge capacitance at the layer-solution
interface. From Table 2, the lower Ydl values obtained in the
presence of 1-benzylimidazole confirms that the inhibitor ad-
sorption reduces the accumulation of corrosion-inducing aque-
ous species at the stainless steel surface and, thus, lowers the
rate of charge transfer at the alloy surface-solution interface.
As Table shows, the inhibitor adsorption impacts a total resis-
tance (Rct + R f ) of 765 Ωcm2, compared with the value of 212
Ωcm2 recorded for the blank solution. This gives an inhibition
efficiency of 72.29 %, based on the Equation (7). Furthermore,
the αdl value is also higher in the presence of inhibitor, which
indicates that the inhibitor adsorption minimizes the roughness
of the alloy surface due to the corrosion attack.

%I EEIS = 1 −
Rtotal(with inhibitor)

Rtotal(without inhibitor)
× 100% (7)

%I EPDP = 1 −
icorr(with inhibitor)

icorr(without inhibitor)
× 100% (8)

In Figure 6, each PDP curve shows an activation-controlled
cathodic arm representing the dominant H+ reduction in the
acid solution. The anodic arm is characterized by an active re-
gion, a region of passivation and a region of passivation break-
down. The active region is attributed to the oxidation and dis-
solution of surface elements like Fe and Cr, the passivation po-
tential region depicts the formation of protective oxides and hy-
droxides of Fe and Cr [27], whereas the region of passivation
breakdown indicates potential regions where protective passive
layer is broken, especially locally by chloride ions.

Extrapolating the PDP plots around ± 10 mV of the
cathodic-anodic potential transition enabled the deduction of
corrosion current density (icorr ), corrosion potential (Ecorr ),
anodic (βa ) and cathodic (βc) Tafel constants [28]. The E corr
indicates the thermodynamic tendency to corrode in the solu-
tion and the most preferable active sites of corrosion inhibitor
interaction with the corroding surface, while the icorr is a mea-
sure of the corrosion rate.

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By Table 3, the presence of 1-benzylimidazole in the acid
solution slightly shifts the E corr towards more anodic poten-
tial and lowers the i corr value from 161.30 µ A cm−2 to 45.90
µAcm−2; which amounted to an inhibition efficiency of 71.54 %
according to Equation (8). It is reported that 1-benzylimidazole
exists as a cationic species in acidic solution [17]. Therefore,
the greater inclination of 1-benzylimidazole to adsorb on an-
odic sites of the stainless steel strongly suggests the existence
of pre-adsorbed anions on the anodic sites containing Fe2+ and
Cr3+, which eventually attract the cationic inhibitor towards the
anode. Such phenomenon was also reported elsewhere for 1-
benzylimidazole in CO2 + H2S-saturated NaCl solution [16].
This anodic preference is a stronger inclination towards more
protective passivation, as confirmed by Figure 6; where the in-
hibitor shifts passivation current to lower values. Although the
inhibitor does not affect the passivation potential (and passiva-
tion mechanism), it strongly modifies the passive film formed
into a more protective one. This means that 1-benzylimidazole
adsorption encourages the formation of Fe and Cr oxides and
hydroxides. Nevertheless, the inhibitor appears not too pro-
tective once the passive film is deteriorated. This is feasible
because the adsorbing inhibitor molecules and nucleating cor-
rosion products would experience some structural mismatch
which are easily targeted for localized attack and collapse.

3.4. SEM results

The surface morphologies of the stainless steel, after po-
larization in the acid solution without and with 1000 ppm of
1-benzylimidazole, are presented in Figure 7a and 7b, respec-
tively. In the absence of inhibitor, Figure 7a, the stainless steel
surface exhibits a rough morphology with patches of passive
products around the surface. In the presence of inhibitor, Fig-
ure 7b, the passive products appear to agglomerate into a more
continuous and denser layer which provides more surface cov-
erage for the alloy surface. This justifies the findings from elec-
trochemical measurements that the adsorption of 1- benzylimi-
dazole could facilitate the formation of passive layer. At some
points, however, some shallow cracks could be observed in the
Figure 7b. These are likely points where localized corrosion oc-
curs when the alloy is polarized beyond the passivation region.

4. Conclusion

The corrosion characteristics of a chemical reactor alloy
SS316L stainless steel, and its inhibition by 1-benzylimidazole,
have been investigated in 2 % HCl + 3.5 % NaCl solution (a
typical solution used for industrial acid cleaning). The addition
of 1-benzylimidazole into the test solution significantly low-
ered the rate of corrosion of the alloy, wherein an optimum in-
hibitor concentration of 1000 ppm yielded inhibition efficiency
greater than 70 %. The 1-benzylimidazole acted more like an
anodic-type inhibitor which improved the characteristics of the
passive film formed on the alloy surface. The adsorption of 1-
benzylimidazole followed the Temkin isotherm and protected
the stainless steel surface from localized corrosion, based on
SEM characterization.

References

[1] J. Beddoes, J.G. Parr, “Introduction to Stainless Steels”, 3rd ed. (1999),
ASM International, Materials Park, Ohio, USA.

[2] Z. Zeng, N. Sakoda, T. Tajiri, S. Kuroda, “Structure and corrosion be-
haviour of 316L stainless steel coatings formed by HVAF spraying with
and without sealing”, Surface and Coatings Technology 203 (2008) 284.

[3] I.B. Onyeachu, M.M. Solomon, “Benzotriazole derivative as an effec-
tive corrosion inhibitor for low carbon steel in 1 M HCl and 1 M HCl
+ 3.5wt.% NaCl solutions”, Journal of Molecular Liquids 313 (2020)
113536.

[4] I.B. Obot, A. Meroufel, I.B. Onyeachu, A. Alenazi, A.A. Sorour, “Cor-
rosion inhibitors for acid cleaning of desalination heat exchangers:
Progress, challenges and future perspectives”, Journal of Molecular Liq-
uids 296 (2019) 111760.

[5] S.A. Thakur, G.P. Flake, G.S. Travlos, J.A. Dill, S.L. Grumbein, S.J.
Harbo, M.J. Hooth, “Evaluation of propargyl alcohol toxicity and car-
cinogenicity in F344/N rats and B6C3F1/N mice following whole-body
inhalation exposure”. Toxicology 314 (2013) 100.

[6] W.H. Beggs, F.A. Andrews, G.A. Sarosi, “Action of imidazole-containing
antifungal drugs”, Life Sciences 28 (1981) 111.

[7] P. Lindberg, P. Nordberg, T. Alminger, A. Brandstorm, B. Wallmark, “The
mechanism of action of the antisecretory agent omeprazole”, Journal of
Medicinal Chemistry 29 (1986) 1327.

[8] A. Singh, K.R. Ansari, A. Kumar, W. Liu, C. Songsong, Y. Lin, “Elec-
trochemical, surface and quantum chemical studies of novel imidazole
derivatives as corrosion inhibitors for J55 steel in sweet corrosive envi-
ronment”, Journal of Alloys and Compounds 712 (2017) 121.

[9] T. Yan, S. Zhang, L. Feng, Y. Qiang, L. Lu, D. Fu, B. Tan, “Investigation
of imidazole derivatives as corrosion inhibitors of copper in sulfuric acid:
combination of experimental and theoretical researches”, Journal of the
Taiwan Institute of Chemical Engineers 106 (2020) 118.

[10] M. Talari, S.M. Nezhad, S.J. Alavi, M. Mohtashamipour, A. Davoodi, S.
Hosseinpour, “Experimental and computational chemistry studies of two
imidazole-based compounds as corrosion inhibitors for mild steel in HCl
solution”, Journal of Molecular Liquids 286 (2019) 110915.

[11] J. Wang, D. Liu, S. Cao, S. Pan, H. Luo, T. Wang, H. Ding, B.B. Mamba,
J. Gui, “Inhibition effect of monomeric/polymerized imidazole zwitteri-
ons as corrosion inhibitors for carbon steel in acid medium”, Journal of
Molecular Liquids 312 (2020) 113436.

[12] C. Cardona, A.A. Torres, J.M. Miranda-Vidales, J.T. Pérez, M.M.
González-Chávez, H. Herrera- Hernández, L. Narváez, “Assessment of
Dimethylbenzodiimidazole as Corrosion Inhibitor of Austenitic Stainless
Steel Grade 316L in Acid Medium”, Int. J. Electrochemical Science 10
(2015) 1966.

[13] M.T. Zaky, M.I. Nessim, M.A. Deyab, “Synthesis of new ionic liquids
based on dicationic imidazolium and their anti-corrosion performances”,
Journal of Molecular Liquids 290 (2019) 111230.

[14] Paris Commission (PARCOM) (2006). Protocols on Methods for the Test-
ing of Chemicals Used in the Offshore Oil Industry. Paris, France.

[15] 1-benzylimidazole, Material Safety Data Sheet,
www.caymanchem.com/msdss/70510m.pdf (Retrieved 16 th January,
2022).

[16] I.B. Onyeachu, D.I. Njoku, S. Kaya, B. El Ibrahimi, C.F Nnadozie,
“Sour corrosion of C1018 carbon steel and its inhibition by 1-
benzylimidazole: electrochemical, SEM, FTIR and computational
assessment”, Adhesion Science and Technology (2021) 1. DOI:
10.1080/01694243.2021.1938474.

[17] A. Ismail, H.M. Irshad, A. Zeino, I.H. Toor, “Electrochemical corrosion
performance of aromatic functionalized imidazole inhibitor under hydro-
dynamic conditions on API X65 carbon steel in 1M HCl Solution”, Ara-
bian Journal of Science and Engineering 44 (2019) 5877.

[18] H. Kumar, T. Dhanda, “Experimental and theoretical (MDS and FMO)
study of 1-Benzylimidazole for mild steel in 0.1 N H 2 SO 4 at normal and
elevated temperatures: An efficient anti-pitting and anti-cracking agent”,
Journal of Molecular Structure 1231 (2021) 129958.

[19] I.B. Obot, M.M. Solomon, I.B. Onyeachu, S.A. Umoren, A. Meroufel,
A. Alenazi, A.A. Sorour, “Development of a green corrosion inhibitor for
use in acid cleaning of MSF desalination plant”, Desalination 495 (2020)
114675.

[20] ASTM-G 01-03, Standard practice for preparing, cleaning, and evaluation
corrosion test specimens, ASTM Book of Standards (Re-approved 1997).

221



Adama and Onyeachu / J. Nig. Soc. Phys. Sci. 4 (2022) 214–222 222

[21] I.B. Onyeachu, M.M. Solomon, S.A. Umoren, I.B. Obot, A.A. Sorour,
“Corrosion inhibition effect of a benzimidazole derivative on heat ex-
change tubing materials during acid cleaning of multistage flash desali-
nation plants”, Desalination 479 (2020) 114283.

[22] C.C. Ahanotu, I.B. Onyeachu, M.M. Solomon, I.S. Chikwe, O.B.
Chikwe, C.A. Eziukwu, “Pterocarpus santalinoides leaves extract as a
sustainable and potent inhibitor for low carbon steel in a simulated pick-
ling medium”, Sustainable Chemistry and Pharmacy 15 (2020) 100196.

[23] O.A. Akinbulumo, O.J. Odejobi, E.L. Odekanle, “Thermodynamics and
adsorption study of the corrosion inhibition of mild steel by Euphorbia
heterophylla L. extract in 1.5 M HCl”, Results Mater. 5 (2020) 100074.

[24] S. Chaudhary, R.K. Tak, “Natural corrosion inhibition and adsorption
characteristics of Tribulus terrestris plant extract on aluminium in hy-
drochloric acid environment”, Biointerface Research in Applied Chem-

istry 12 (2022) 2603.
[25] A. Espinoza-Vazquez, F.J. Rodriguez-Gomez, “Caffeine and nicotine in 3

% NaCl solution with CO2 as corrosion inhibitors for low carbon steel”,
RSC Advances 6 (2016) 70226.

[26] C.H. Hsu, F. Mansfeld, “Technical note: concerning the conversion of the
constant phase element parameter Y o into a capacitance”, Corrosion 57
(2001) 747.

[27] H.H. Strehblow, “Passivity of metals studied by surface analytical meth-
ods, a review”, Electrochimica Acta 212 (2016) 630.

[28] M. Stern, A.L. Geary, “Electrochemical polarization, 1. A theoretical
analysis of the shape of polarization curves”, The Electrochemical So-
ciety 104 (1957) 751.

222