The Inhibitory Action of Aniba Canelilla (H. B. K.) Mez. Extracts on the Corrosion of Carbon Steel in Hydrochloric Acid Medium
The Inhibitory Action of Aniba Canelilla (H. B. K.) Mez. Extracts on the Corrosion of Carbon Steel in Hydrochloric Acid Medium
Iuri Bezerra de Barros 0 2
Dayana Lacerda Cust?dio 0 2
M?nica Calixto de Andrade 0 2
0 Instituto Polite?cnico, Universidade do Estado do Rio de Janeiro - UERJ , Rua Bonfim, 25,CEP 28625- 570, Nova Friburgo, RJ , Brasil
1 Departamento de Qui?mica, Universidade Federal do Amazonas - UFAM , Av. Rodrigo Octa?vio, 6200, CEP 69077-000, Manaus, AM , Brasil
2 Valdir Flore?ncio da Veiga Junior
The use of eco-friendly corrosion inhibitors in metallurgical processing has increased interest due to the reduced environmental impact. Hence, the inhibitory effect of Aniba canelilla (Lauraceae) extract was studied in the corrosion of carbon steel in 1.0 mol?L-1 hydrochloric acid solution. This acid is used during the surface treatment of steel processing. The carbon steel protection was observed by varying the extract concentration from 50 to 300 mg?L-1. Polarization curves revealed that this extract acted as an adsorption inhibitor decreasing both anodic and cathodic current densities. A relatively high inhibition corrosion efficiency, close to 97%, was obtained with plant stem extracts by gravimetric measurements. Weight loss measurements showed that the extract remains active for at least 72 hours at room temperature. The adsorption process of this extract is properly represented by the Langmuir isotherm. Atomic force microscopy shows that inhibited acid medium produces a smooth surface.
Metallurgical industries use acids in thermomechanical
processing and surface treatment for pickling purposes.
Sulfuric and hydrochloric acids are used to remove scales
present in mild steel after exposure in high temperature
under oxidant environment. However, the acids must be
inhibited to reduce the dissolution of metallic substrate. In
this context, the search for corrosion inhibitors to protect
metallic surfaces in acidic media aims higher anti-corrosion
efficiency as well as the use of chemicals less aggressive
to the environment. The protective efficiency appears to
increase with the presence of oxygen, nitrogen, sulfur and ?
electrons in organic compounds that makes natural products
a promising source.1-5 Apparently, the inhibition efficiency
is linked to the polar functions that act as the reaction center
of the adsorption process.6
The environmental toxicity of organic corrosion inhibitors
has prompted the search for green corrosion products as
they are biodegradable and do not contain heavy metals nor
toxic compounds. Plant products can be inexpensive, readily
available and renewable,4 as well as environmentally friendly.
Lauraceae botanical family is known to have between its
metabolites several alkaloids, a natural product that present
at least one nitrogen atom in a heterocyclic ring.7Aniba
canelilla (H. B. K.) Mez. belongs to Lauraceae family,
and it is present in upland forests, occurring in Brazil in
the states of Par? and Amazonas. It is popularly known as
?casca preciosa? (precious bark in Portuguese language). A.
canelilla stem produces an essential oil that is rich in
1-nitro2-phenylethane.8-10 Moreover, antioxidant and cytotoxic
activities in Artemia salina were observed in this essential
oil.11 The isolated 1-nitro-2-phenylethane showed analgesic
activity.12 In addition to the essential oil, different isoquinoline
alkaloids as reticuline, coclaurine and noranicanine have
been reported in A. canelilla.13-14
A study with A. roseodora, also from Lauraceae family,
shows that the alkaloid anibine acts as a corrosion inhibitor.15
Investigation of the corrosion inhibition potential of Garcinia
kola, from the Clusiaceae or Guttiferae family, showed the
presence of alkaloids increases the anti-corrosion effects.16
In a previous study, we described the corrosion inhibition
of this extract obtained from Aniba canelilla, in carbon steel in
1.0 mol?L-1 H2SO4.17 The presence of alkaloids reticuline and
N-methylcoclaurine (see Figure 1) in this extract was observed
by direct electron spray ionization mass spectrometry. In the
present study, we evaluate the corrosion inhibition efficiency
of the extract in 1.0 mol?L-1 HCl by means of gravimetric,
electrochemical and microscopy techniques.
2.1 Plant extract
Aniba canelilla stems were collected in the Adolpho
Ducke Forest Reserve (S 2?57?43??, W 59?55?38??, 120 m),
located in Manaus City (Amazonas State, Brazil). Voucher
samples are deposited at the herbarium of National Institute
of Amazonian Research (INPA). The stems were dried in
shade at room temperature. The plant material was extracted
with ethanol by refluxing for 8.0 hr using a Soxhlet device.
After extraction, the solvent was evaporated and dried to
produce a solid mass. The A. canelilla stem extract was
stored at low temperature (-4.0 ?C) until the corrosion tests.
2.2 Electrochemical measurement
The electrochemical measurements were conducted in a
thermostated three-electrode cell. A silver chloride electrode
(Ag/AgCl 3.0 M) was used as the reference electrode and
the counter electrode was a large area platinum wire. The
electrolyte was 1.0 mol?L-1 HCl prepared from concentrated
reagent analytical grade (Vetec Fine Chemicals Ltda, Brazil).
All experiments were performed in 200 mL of electrolyte
under non-stirred and naturally aerated conditions. The
temperature was controlled at 25.0 ? 0.2 ?C.
Carbon steel UNS G10200, hereafter termed C-steel,
was used as a working electrode. The electrodes were
prepared by embedding the steel rods in Teflon? polymer
and exposing a surface area of 0.33 cm2 to the electrolyte.
Previously to the measurements, the sample surfaces were
sanded with 600 grade emery paper under water flow, washed
with double-distilled water, degreased with ethanol and
dried with hot air. In all experiments, the C-steel electrode
reaches its stable corrosion potential after 1,800 s. After this
period, the electrochemical impedance spectroscopy (EIS)
measurement was performed over a frequency range from
20 kHz to 10 mHz at the corrosion potential with 8.0 mV
sine wave perturbation and 10 points per frequency decade.
Subsequently, the polarization curves were performed, from
the cathodic to the anodic direction, from -300 mV below the
corrosion potential up to 300 mV above it, with a scan rate of
1.0 mV?s-1. All electrochemical experiments were performed
in triplicate using a Gamry Reference 600 potentiostat. The
equivalent electric circuit5 used to model the electrochemical
reactions is exhibited in Figure 2.
The inhibition efficiency (?%) was calculated from
potentiodynamic polarization curves and electrochemical
impedance diagrams, as shown next in Eqs. (1) and (2).
jcorr,0 - jcorr # 100%
Rct - Rct,0 # 100%
where jcorr, 0 is the corrosion current density in the absence
of inhibitor, and jcorr is the corrosion current density in the
presence of inhibitor, obtained from Tafel plots, calculated as
presented in Eq. (3). In this equation, E is the applied potential,
j is the current density close to the corrosion potential, and
is the is the anodic and cathodic constant with units of V/
decade. Furthermore, the charge-resistance Rct obtained from
the EIS and fitted employing an equivalent electric circuit
was used to evaluate the inhibition effect. In Eq (2) where
Rct,0 is the resistance in the absence of inhibitor, and Rct is
the charge-resistance with inhibitor. The blank condition
was 1.0 mol?L-1 HCl (without inhibitor).
E = b $ log
2.3 Weight loss experiment
C-steel coupons (25.0 mm x 20.0 mm x 1.0 mm) were
used in the weight loss experiment after being abraded with
100 grade emery paper under water flowing, washed with
deionized water, degreased with ethanol, and dried in hot air.
After this surface treatment, the samples were immersed in
acid media. Triplicate specimens were immersed in the acid
test solution for 24 hr at 25?C in the absence and presence
(0, 50, 100, 200 and 300 mg?L-1) of ethanolic Aniba canelilla
stem extract. After the immersion exposure, the specimens
were cleaned, washed with deionized water and ethanol,
dried in hot air. Weight loss was determined by gravimetric
tests using an analytical balance, Ohaus AS200, with 0.1 mg
precision. The inhibition efficiency ( %) was determined using
W0 - W
where W0 and W are the weight variation divided by the
area and time in hours in the absence and presence of the
The time and temperature effects on the corrosion rate
of steel coupons in 1.0 mol?L-1 HCl were examined. These
experiments were performed in the absence and presence
of 100 mg?L-1 of ethanolic Aniba canelilla stem extract for
24, 48 and 72 hr at 25.0 ?C; and during an immersion period
of 2.0 hr at 25, 35, 45 and 55 ?C.
2.4 Surface analysis
C-steel coupons (25.0 mm x 20.0 mm x 1.0 mm) of the
same alloy that was used in the electrochemical measurements
were abraded with 600 grade emery paper under water flow,
then washed with deionized water, degreased with ethanol,
and dried in hot air for surface analysis.
The samples were immersed in 1.0 mol?L-1 HCl in the
absence and presence of 100 mg?L-1 of ethanolic Aniba
canelilla steam extract at 25 ?C for 2.0 hr. The specimens
were cleaned with deionized water, dried with hot air, and
then observed with an atomic force microscope (AFM),
model Flex AFM with a C3000 controller (Nanosurf), in
tapping mode, with a silicon probe (Tap190Al-G).
A Fourier Transform-Infrared (FT-IR) spectrometer
Frontier (Perkin Elmer) equipped with the attenuated total
reflectance (ATR) module device was used to analyze the
Aniba canelilla extract. Typically, 32 scans were accumulated
to obtain each spectrum.
3.1 Potentiodynamic polarization curve
The open circuit potential (OCP) was monitored for
1,800 s of exposure in the absence and presence of Aniba
canelilla extract in the following concentrations 0, 50, 100,
200 and 300 mg?L-1 (Figure 3) at 25 ?C. Polarization curves
and impedance were performed after an OCP monitoring
phase. The potential variations during 1,800 s were small,
and the OCP of inhibited media was approximately 15 mV
above the non-inhibited acid.
In the potentiodynamic polarization curves (Figure 4),
the presence of Aniba canelilla extract leads to a decrease
in both anodic and cathodic current densities. These results
could be assigned to the adsorption of organic compounds
present in the extracts at the active sites of the surface, which
limit the metallic dissolution and the hydrogen evolution,
and consequently slows down the corrosive process. Similar
polarization results from different inhibitors were also ascribed
to the adsorption of compounds.3;15
The electrochemical parameters of corrosion potential
(Ecorr), corrosion current density (jcorr ), and anodic (?a) and
cathodic (?c) constants are shown in Table 1. They were
obtained by fitting the Tafel plots. Corrosion potential
variations higher than 85 mV relative to the blank condition
is considered to identify an inhibitor as having anodic or
cathodic action.18 However, no significant deviation was
observed in Ecorr, hence demonstrating that Aniba canelilla
3.2 Electrochemical impedance spectroscopy
Figure 5 illustrates the Nyquist plots of C-steel in a 1.0
mol?L-1 HCl with and without ethanolic Aniba canelilla
extract at 25.0 ?C. All diagrams present a high frequency
capacitive loop whose size increases with the inhibitor content.
Moreover, a small inductive loop exists for the non-inhibited
medium, probably related to adsorbed species. The steel
tested without inhibitor exhibits the smallest size diagram.
The |Zi| vs. frequency plot on a logarithmic scale
(Figure 6) provides an insight into the experiment system.
The slopes at low and high frequencies are +? and -?. At
higher frequencies we have a larger number of points, and
with these data the ? value was determined (Table 2). When
this value differs from unity, a constant phase element (CPE)
can be used to fit the impedance spectra. The parameter
can be calculated as shown in Eq. (
). This graphical method
is direct, not affected by the simultaneous fitting of other
parameters, and does not use the electrolyte resistance to
correct the modulus.
where Q is the magnitude of the CPE, with -1 ? ? ? 1,
and ? is the angular frequency. The capacitive loops have
depressed semi-circular appearance, 0.5 ? ? ? 1.0 , as a result
of the physical inhomogeneity or the roughness of the solid
surface.20-22 In Eq. (6) i is the imaginary number (i2 =-1). The
exponent value makes it possible to identify the behavior
of a CPE (0 ? ? ? 1) from that of an ideal capacitor ?=1.
The EIS spectra were analyzed using the equivalent
circuit (Figure 2), where RS represents the ohmic resistance
of the solution and Rct the charge transfer resistance whose
value measures the electron transfer across the surface and
is inversely proportional to corrosion rate.
The impedance parameters, including Rct, Q and ? obtained
from fitting the recorded EIS data using the equivalent
circuit of Figure 2, are listed in Table 3, along with the
percentage of inhibition efficiency (%). It is clear that the
Rct values increase with inhibitor concentration increase. The
adsorption of some molecules present in the extract onto the
metal/solution interface may justify these results. Indeed,
this hypothesis is corroborated by the anodic and cathodic
polarization curves, and the corrosion potential results. The
inhibition efficiency values (%), calculated from Rct data
in the absence and presence of the extract, for the highest
concentration was 82.0?1.9 %.
3.3. Weight loss
The results of weight loss measurements for the corrosion
of C-steel in 1.0 mol?L-1 HCl without and with ethanolic
Aniba canelilla extract in different concentrations (0, 50,
100, 200 and 300 mg?L-1) for 24 hr, at 25.0 ?C, are depicted
in Table 4. Again, the percentage of inhibition efficiency
% increases with the extract concentration, but shows no
significant change in concentrations higher than 100 mg?L-1,
reaching an efficiency around 97%.
The results of the weight loss measurements for the
corrosion of C-steel in 1.0 mol?L-1 HCl without and with
100 mg?L-1 of ethanolic Aniba canelilla extract for different
immersion times (24, 48 and 72 hr) are provided in Table 5.
These tests demonstrate the stability of the extract versus
time exposure. The C-steel corrosion rate was reduced
with the addition of the extract for all immersion times. It
is noted a slight variation in the efficiency % with time,
from 96.00% to 96.95% after 24 and 72 hr of immersion,
indicating that the inhibition efficiency remains after long
periods of immersion.
The effects of temperature on the corrosion of C-steel
in 1.0 mol?L-1 HCl without or with 100 mg?L-1 of ethanolic
Aniba canelilla extract ranging from 25 to 55 ?C after 2.0 hr
of immersion time are presented in Figure 7. The corrosion
rates of the steel in both media increased with the temperature.
The inhibition efficiency of the ethanolic Aniba canelilla,
which modifies on 0 and 100 mg?L-1 weight loss evaluations,
shows a slight increase with temperature.
1.181 ? 0.032 0.036 ? 0.004
0.575 ? 0.024 0.023 ? 0.001
Moreover, the apparent activation energy for C-steel
corrosion in pure HCl solution and in inhibiting acid media
was determined from an Arrhenius-type plot according to
log Wcorr = 2.30-3 E$Ra $ T + log A
where Wcorr is the corrosion rate, Ea is the apparent activation
energy, A is the pre-exponential factor, T is the absolute
temperature and R is the molar gas constant. Arrhenius plots
of (log Wcorr) vs. (1 / T) for C-steel in 1.0 mol?L-1 HCl both
in the absence and presence of the ethanolic Aniba canelilla
extract are shown in Figure 7.
The apparent activation energy obtained for the corrosion
process in the free acid solution was found to be 38.3 kJ?mol-1,
and 60.0 kJ?mol-1 in the presence of the inhibitor. The energy
barrier for the corrosion reaction increased in the inhibitor
presence. An increase in inhibition efficiency with rise in
temperature and lower activation energy in the presence
of inhibitor suggests a chemisorption mechanism. On the
other hand, a decrease in inhibition efficiency with rise
of temperature, with an analogous increase in corrosion
activation energy in the presence of inhibitor compared to
the situations with its absence, is frequently interpreted as
being a formation of an adsorption film of physical nature.23-25
Here, we observed the higher activation energy in the
presence of inhibitor and also noticed a slight growth on the
inhibition efficiency with increasing temperature. Due to the
great diversity of molecules present in the Aniba canelilla
extract, the inhibition mechanism is most likely complex,
involving both chemical and physical processes, as shown
by the polarization curves in Figure 4. A similar behavior
was observed with the seed extract of Retama monosperma
(L.), which is rich in alkaloids.26
3.4. Adsorption isotherm
The fitting of the obtained data to the Langmuir isotherm
is illustrated by plotting according to Eq. (8). In this equation,
C is the concentration, ? the occupied fraction of surface
and K the adsorption constant (Figure 8). The adjustment
of the Langmuir adsorption isotherm was very good, with a
correlation factor r2 close to 0.996. This behavior suggests
that compounds present in the ethanolic Aniba canelilla
extract were adsorbed onto the C-steel surface according to
a Langmuir adsorption isotherm, indicating the absence of
interaction forces amongst adsorbed molecules.
Ci = C + K1
The two dimensional AFM images of C-steel surface
are shown in Figure 9. The Figure 9A shows that the C-steel
surface before immersion seems smoother and still holds some
abrading scratches on the horizontal direction. As for Figure
9B, the C-steel surface after immersion in 1.0 mol?L-1 HCl
for 2.0 hr was damaged strongly as compared with Figure
9A. Figure 9C exhibits that there is a protective effect due
to an adsorbed film on the steel surface in the presence of
100 mg?L-1Aniba canelilla extract.
The three-dimensional AFM images are shown in Figure
10. It can be seen from Figure 10A that the C-steel surface
before immersion seems smooth compared to the C-steel
surface after immersion in uninhibited 1.0 mol?L-1 HCl for
2.0 hr. The maximum height of roughness of sanding C-steel
sample (Figure 10A) and C-steel in 1.0 mol?L-1 HCl without
inhibitor (Figure 10B) was calculated to be 1.17 nm and
20.4 nm, respectively. It is clearly shown in Figure 10B that
C-steel sample is attacked by the hydrochloric acid. However,
in the presence of higher concentration of inhibitor, the
average roughness was reduced to 16.9 nm (Figure 10C). The
roughness profile of the AFM images across the diagonals
of the sample observed area is presented in Figure 11. The
acid attacks the metal producing a rougher surface, as can
be seen by comparing the sanded and corroded profiles of
Figure 11. Nonetheless, it is evident that in the presence of
inhibitor (100 mg?L-1) the corrosion of the sample was quite
reduced and the smooth profile also reveals this behavior.
3.6. FT-IR analyses
The plant stem extract was analyzed by FT-IR spectroscopy
(Figure 12). The peak at 3348 cm-1 can be assigned to the
stretching mode of O-H and/or N-H. The peaks at 2920 and
2851 cm-1 can be assigned to aliphatic C-H groups. The peaks
at 1270 and 1119 cm-1 can be assigned to C-N linkage in
aromatic and aliphatic systems. The FT-IR peaks at 1704,
1607, 1516 and 1455 cm-1 correspond to C=O, R2C=N and
C=C. Moreover, Chauhan et al.27 and Abboud et al.28 also
The Aniba canelilla (Lauraceae) extract is an efficient
inhibitor on carbon steel in hydrocloric acid medium (1.0
mol?L-1 HCl) at 25 ?C. Moreover:
1. The results found in polarization measurements
suggest that the inhibitor compound adsorbs on
carbon steel surface. A concentration-dependent
reduction of both the anodic and cathodic current
densities was observed.
2. EIS confirms the behavior seen in the polarization
curves, showing an inhibition efficiency gain with
increasing extract concentration.
3. The adsorption process followed a Langmuir
adsorption isotherm from weight loss measurements.
Moreover, a high inhibition efficiency, close to
97%, was obtained with the plant stem extracts by
4. AFM analyses confirmed the protective effect of
inhibited solutions by the smooth profile of the
samples submitted to inhibited hydrochloric media.
5. The inhibitory efficiency of the extract remained
stable at least up to 72 hours at room temperature.
The authors acknowledge the financial support provided
by the Brazilian Agencies FAPERJ (E26/110.644/2012),
CAPES and CNPq. We also thank Mr. Emandro V. da Costa
for obtaining the AFM images.
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