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(Calamansi) Citrofortunella Microcarpa Rind Extract As Plant Derived
Green Corrosion Inhibitor For Mild Steel In 1.0M Hcl
To cite this article: Gian Carlo E. Arguelles et al 2020 IOP Conf. Ser.: Mater. Sci. Eng. 778 012007
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26th Regional Symposium on Chemical Engineering (RSCE 2019) IOP Publishing
IOP Conf. Series: Materials Science and Engineering 778 (2020) 012007 doi:10.1088/1757-899X/778/1/012007
(CALAMANSI) CITROFORTUNELLA
MICROCARPA RIND EXTRACT AS PLANT
DERIVED GREEN CORROSION INHIBITOR
FOR MILD STEEL IN 1.0M HCl
Gian Carlo E. Arguelles, Mark Ceazar D. Torres, Brian James U. Wu, Jerry G.
Olay*, Renato C. Ong
Department of Chemical Engineering, College of Engineering, Adamson University,
900 San Marcelino, Ermita, Manila 1000, Philippines
*jerry.olay@adamson.edu.ph
Abstract. The inhibitive action of extracts from Citrofortunella microcarpa (Calamansi) peels
on mild steel in 1.0M HCl solution has been studied using the weight-loss method,
electrochemical method, and SEM-EDX analysis. The measurements showed that calamansi
peels have good inhibition properties. Weight loss results suggest that inhibitive efficiency
increases as the concentration increases. It was also found that the adsorption stabilizes at 72
hours and degrades at longer immersion times. SEM studies of the immersed mild steel showed
the decreasing extent of corrosion attack on mild steel at an increasing ratio of inhibitor, while
EDX analysis shows the reduction of the formation of corrosion products, suggesting the
formation of inhibitor film on the mild steel surface. The Calamansi peel extract inhibitor
obeys the Langmuir adsorption isotherm model and the mode of adsorption was found to be
physical and spontaneous. The results of the electrolysis technique have shown the favoring of
inhibition in cathodic reactions.
Keywords: Corrosion inhibitor, Inhibitive efficiency, Weight loss method, SEM, Adsorption
Isotherm.
Introduction
Corrosion is the material degradation by chemical reaction with their environment. This, in turn, can
lead to damage to steel structures, causing economic damages, and threatening our safety and the
environment (M'hiri et al., 2016). The use of corrosion inhibitors is a practical method to protect steel
from corrosion, especially when exposed to acidic solutions during different processes in the industry
(Patni, Agarwal, & Shah, 2013). Acids are also used in processing industries as inhibitors and for the
elimination of deposited scales from metallic surfaces (Hassan, Khadom, & Kurshed, 2016). From the
perspective of materials of construction and corrosion, Hydrochloric acid is one of the most
challenging common acids to handle. It is very corrosive to many alloys and metals used in industry
(Hmimou et al., 2012).
Numerous ways have been established for inhibiting corrosion. Utilization of inhibitors for the
regulation of corrosion of alloys and metals in contact with aggressive surroundings is among one of
the acceptable methods used to reduce and prevent corrosion. However, efficient inorganic inhibitors
such as phosphates, chromates and nitrites; and organic inhibitors such as polyamines, long-chain
carboxylates, imidazole, and derivative compounds; are not only costly to produce but are also toxic
and non-biodegradable. Due to this environmental and economic concern, much interest is being
poured into organic, eco-friendly corrosion inhibitor research. Sources such as food by-products, plant
parts, and extracts are being considered, as they are easily available, inexpensive, and are less harmful
to the environment. Inhibitors from plant sources contain compounds such as proteins, tannin,
alkaloids, etc. which work as potential inhibitors for many metals in acidic medium (Agarwal, 2014;
Hassan, Khadom, & Kurshed, 2016).
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Published under licence by IOP Publishing Ltd 1
26th Regional Symposium on Chemical Engineering (RSCE 2019) IOP Publishing
IOP Conf. Series: Materials Science and Engineering 778 (2020) 012007 doi:10.1088/1757-899X/778/1/012007
The present work aims to show corrosion inhibitive property of calamansi peel extract using
weight loss, electrochemical studies, and SEM-EDX analysis in 1M HCl for mild steel.
Citrofortunella microcarpa is among the most widely cultivated fruit crop in the Philippines. Citrus
fruits such as calamansi, are utilized mainly for its pulp and juice, the rest of the fruit, including the
rind, are considered waste products. If its potential use is as a corrosion inhibitor is explored, not only
can it possibly replace toxic, synthetic and organic inhibitors, but it also helps in the reduction of
environmental pollution.
Materials and Methodology
Preparation of the Mild steel specimen
(0.16% C; 0.14% Si; 0.33% Mn; 0.005% S; 0.017% P; 0.0013; balance Fe) specimens of dimension
3.00x2.54x0.25 cm were used for weight loss and electrochemical studies. Before all measurements,
the specimens were polished using different grades of emery paper from 220 to 1200, washed with
distilled water and degreased with acetone and later dried.
Preparation of plant extract
The Citrofortunella microcarpa fruit peels were gathered then washed with running water, and then
shade dried. The dried fruit peels were powdered and 10g of the powder was soaked in 250mL of HCl
then boiled for 4 hours. The prepared solution was left overnight then filtered using a Buchner funnel
to remove impurities. The filtrate was then made to 250mL by adding 1M of HCl.
Preparation of Electrolyte
AR Grade HCl was mixed with distilled water until 1M HCl was acquired; 250mL 1M HCl solution
was prepared. These solutions; 1M HCl, 5:100, 10:100 and 15:100 were ratios in the volume of the
Citrofortunella microcarpa fruit peel solution to 1M HCl.
Weight loss method
Weighted steel specimens of dimension 3.00x2.54x0.25 cm were completely immersed in 100 mL of
electrolyte (1M HCl) with and without different concentrations of FL and LP extracts at room
temperature. To prepare different concentrations, different amounts of FL and LP extracts were added
to 1M HCl accordingly in v/v ratio. Specimens were immersed for 2, 4, 8, 16, 32, 64, 96 and 120
hours. Specimens were then retrieved, washed with water, dipped into acetone, air-dried and
reweighed. From the weight loss data, the corrosion rates (R) were calculated from Eq. (1):
To prepare different concentrations, different amounts of inhibitor extracts were added to 1M
HCl accordingly in v/v ratio. Specimens were immersed for 24, 48, 72, 96, and 120 hours. Specimens
were then retrieved, washed with water, dipped into acetone, air-dried and reweighed. The weight
measurements were used to determine the weight loss, rate of corrosion and inhibition efficiency. The
weight loss is defined by:
W = W0 -Wf
Where W the weight loss in grams, W0 is the weight before immersion, and Wf is the weight after
immersion. The corrosion rate in Mils per year (mpy) is defined by:
𝐾𝑊
𝑅(𝑚𝑝𝑦) =
𝐷𝐴𝑇
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26th Regional Symposium on Chemical Engineering (RSCE 2019) IOP Publishing
IOP Conf. Series: Materials Science and Engineering 778 (2020) 012007 doi:10.1088/1757-899X/778/1/012007
Where R is the corrosion rate in Mils penetration per year (mpy) it is equal to a thousandth of an inch.
It is used to gauge corrosion rates. K is a constant equal to 3.45x10⁶ for mpy, W is the weight loss in
grams, D is the density for steel in gm/cm³, A is the surface area, and T is the immersion period in
hours. The inhibition efficiency (η) was computed using:
𝑅0 − 𝑅𝑖
𝜂(%) = 𝑥100%
𝑅0
Where R0 is the corrosion rate in the absence of the inhibitor and Ri is the corrosion rate with
the presence of the inhibitor from the fruit peel extract (Kumar & Yadav, 2018).
Electrochemical measurements
Electrochemical techniques were used. Utilizing an electrolytic cell-based set-up, similar to
electroplating setup was used to measure weight loss due to electrochemical deposition. The power
supply used is Sanwa AC DC Converter Charger Model SCC-3A with a maximum output of 12 Volts
and 3 Amperes. Each set-up contained 50 ml of electrolyte (1M HCl). Mild steel with a surface area of
10.8 cm2 was used as the electrode. The electrode was polished using emery paper, washed with
acetone, rinsed with distilled water and then dried. Open circuit potential was established and then
recorded in 5 to 15-minute intervals, each with increasing inhibitor concentration.
Surface Analysis
The surface morphology of mild steel specimens was examined by SEM-EDX analysis. For these
studies, a mild steel specimen was immersed in the absence and presence of the inhibitor. Scanning
electron microscope images obtained from the JEOL 5300 Scanning Electron Microscope, equipped
with secondary and backscatter electron detectors, and an X-ray detector for energy dispersive
spectroscopy measurements. Samples were analyzed under 500x and 1000x magnification. Surface
micrographs were compared to determine the extent of corrosion damage (Kumar & Yadav, 2018).
EDX analysis was used to determine the formation of corrosion products, and the extent of the
mitigation of the formation of these products in the presence of the inhibitor.
Results and Discussions
Weight loss experiment
The variation of the corrosion rate (in mpy) of mild steel with an immersion time of 24 hrs in 1M HCl
solutions in the absence and presence of varying ratios of the inhibitor are shown in Table 1. A
decrease in the corrosion rate was observed from samples immersed at all varying concentrations of
inhibitor, and pure extract solution.
Table 1: Inhibition efficiency for different concentration extracts for the corrosion of mild steel in 1M
HCl obtained from weight loss measurement
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26th Regional Symposium on Chemical Engineering (RSCE 2019) IOP Publishing
IOP Conf. Series: Materials Science and Engineering 778 (2020) 012007 doi:10.1088/1757-899X/778/1/012007
Figure 1: Effect of immersion time on corrosion rate
In Figure 1, variations of corrosion rate at different concentrations, and different immersion times are
shown. Corrosion rates were observed to be lowest at 72 hours, indicating the stabilization of the
adsorption. However, a notable corrosion rate increase can be observed for succeeding immersion
times of 96, and 120 hours. This shows that peak adsorption of the inhibitor was achieved for an
immersion time of 72 hours. The increase in corrosion rate during extended periods of immersion,
show the deterioration of the adsorbed layer on the mild steel surface.
Electrochemical measurements
Table 2: Weight loss of mild steel using electrolytic cell set up
Table 2 shows data obtained from the cathodic and anodic reaction of mild steel subjected to direct
electric current by an external power supply. It can be that both electrodes lost weight at all three-time
points. It was also observed that the anode lost significantly more weight than the cathode. The weight
loss in the cathode is lowest in 10g concentration at a value of 0.0018, 0.0039, and 0.0059 for a run
time of 5, 10, and 15 minutes respectively, which implies that the inhibition favors the cathodic
reaction at 10g, although anodic reaction have significantly more weight loss, it was observed that the
increase of inhibitor concentration resulted to a decrease in weight loss, implying the inhibitive effect
of the solution favoring the cathodic reaction.
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26th Regional Symposium on Chemical Engineering (RSCE 2019) IOP Publishing
IOP Conf. Series: Materials Science and Engineering 778 (2020) 012007 doi:10.1088/1757-899X/778/1/012007
Adsorption Isotherm
At constant temperature, the testing of adsorption isotherm was obtained from the degree of surface
coverage (Ө) and the concentration of the inhibitor in the acid solution. In this case, the adsorption of
the inhibitor molecule replaces every single gaseous free (oxide-free) site on the surface of the metal.
The inhibitor replaces the adhered water molecule forming a film.
where x is the number of water molecules displaced by a single inhibitor molecule on a space. At the
reaction's equilibrium, the rate of adsorption is equal to the rate of desorption, and at this point,
adsorption isotherm plots can be gathered through the given surface coverage as a function of
concentration. The equation for the Ө is defined as 𝜃 = %IE/100. The surface coverage data were
obtained using the inhibition efficiencies from the weight loss experiments. Then, a suitable adsorption
isotherm (Figure 2-3) was obtained using the data.
The Freundlich adsorption isotherm was applied to investigate its mechanism by the following
equation:
1
𝜃 = 𝐾𝐶 𝑛
where θ is the amount of solute per weight of solid, C is the concentration of inhibitor, K is a specific
constant, and 1/n is the adsorption strength. The linearized equation will be:
1
log 𝜃 = log 𝐾 + log 𝐶
𝑛
The data points for the Freundlich isotherm are obtained from the weight loss data and are
presented in Table 3.
Table 3: Data for plotting Freundlich Adsorption Isotherm
From the plot in Figure 2, a non-linear relationship among the parameter can be observed,
meaning that the adsorption of the inhibitor does not obey the Freundlich Isotherm.
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26th Regional Symposium on Chemical Engineering (RSCE 2019) IOP Publishing
IOP Conf. Series: Materials Science and Engineering 778 (2020) 012007 doi:10.1088/1757-899X/778/1/012007
Figure 2: Freundlich adsorption plot for mild steel in 1M HCl
The Langmuir adsorption isotherm was also applied to investigate its mechanism by the
following equation:
𝐶 1 1
= +𝐶 ; 𝐾= ∆𝐺𝑎𝑑𝑠
𝜃 𝐾
𝐶𝐻2𝑂 𝑒 𝑅𝑇
Figure 3: Langmuir adsorption plot for mild steel in 1M HCl
The adsorption parameters for the Langmuir adsorption isotherm are estimated and given in
Table 4. Figure 3 shows that the adsorption process follows the Langmuir adsorption isotherm as the
correlation coefficient (R2 ) obtained 0.9997 is close to unity.
Table 4: Adsorption Parameters of inhibitor extracts in 1M HCl obtained from Langmuir adsorption
isotherm
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26th Regional Symposium on Chemical Engineering (RSCE 2019) IOP Publishing
IOP Conf. Series: Materials Science and Engineering 778 (2020) 012007 doi:10.1088/1757-899X/778/1/012007
From the intercept of the line on the vertical axis, the specific constant K is calculated. The
value of the standard free energy of adsorption is determined using the equation:
∆𝐺𝑎𝑑𝑠 = −2.303𝑅𝑇 log(55.5𝐾)
The spontaneity of the adsorbed layer and the spontaneity of the adsorption process itself are
attributed to the negative value of ΔGads. The mode of adsorption was found to be physisorption since
it is generally attributed to ΔGads near -20kJ/mol, which indicates electrostatic interactions between the
charged metal surface and the inhibitor.
SEM-EDX analysis
Figure 4: SEM images of (1) dry mild steel (2) mild steel immersed in 1M HCl (3) mild steel
immersed in 5:100 (4) mild steel immersed in 10:100 (5) mild steel immersed in 15:100 (6) mild steel
immersed in extract solution at x1000 magnification.
Figure 4 shows the SEM micrographs of mild steel specimens immersed in different concentrations of
inhibitor solution under 1000x magnification. In comparison, it can be observed that samples
immersed in the presence of the organic inhibitor have surfaces that are less corroded compared to the
surface of dry mild steel. The extent of apparent surface damage is observed to decrease as inhibitor
concentration increases. SEM study shows that the inhibitor acts as a good corrosion inhibitor by the
adsorption on the mild steel surface.
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26th Regional Symposium on Chemical Engineering (RSCE 2019) IOP Publishing
IOP Conf. Series: Materials Science and Engineering 778 (2020) 012007 doi:10.1088/1757-899X/778/1/012007
Figure 5: EDX Spectrum for dry mild steel, mild steel immersed in 1M HCl, and mild steel immersed
in inhibitor solution
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26th Regional Symposium on Chemical Engineering (RSCE 2019) IOP Publishing
IOP Conf. Series: Materials Science and Engineering 778 (2020) 012007 doi:10.1088/1757-899X/778/1/012007
The EDX analytical technique was used for the elemental analysis and the determination of the
specimen composition. From Figure 5, an oxygen peak was observed to appear for the specimen
immersed in pure 1M HCl, this indicates the formation of corrosion products. The specimen
immersed in the inhibitor solution was observed to have a lower oxygen peak indicating the inhibition
from the formation of iron oxides through strong adsorption of the inhibitor on the mild steel surface.
Conclusion
SEM studies showed the decreasing extent of corrosion attack on mild steel at an increasing ratio of
inhibitor, suggesting the formation of inhibitor film on the mild steel surface. EDX spectra analyses
show a significant decrease in the oxygen peak, in inhibited solution, indicating the inhibition of
formation of corrosion products such as metal oxides.
Weight loss results suggest that inhibitive efficiency increases with the increment of inhibitor
ratio. The maximum inhibition efficiency value of 91.57% attained at pure calamansi inhibitor.
Immersion time studies show that the inhibition efficiency peaks and stabilizes at the 72-hour mark
and notably decreases in inhibition efficiency afterward. Corrosion rates were also observed to
increase past the 72-hour mark, indicating the weakening of the adsorptive film on the mild steel
surface at extended periods of immersion.
The adsorption of Citrofortunella microcarpa inhibitor solution to mild steel at 1M HCl obeys
the Langmuir Adsorption Isotherm, attributed to spontaneous physical adsorption onto the metal
surface, this is concluded based that ΔGads of -20kJ/mol and less negative is associated to physical
adsorption.
Electrochemical results show the favoring of inhibition of cathodic reactions, and that the
increase in inhibitor ratio would result in a decrease in weight loss. All results suggest that
Citrofortunella microcarpa rind extract solution acts as a good corrosion inhibitor for mild steel in 1M
HCl.
Recommendation
Corrosion inhibitor concentration and time of immersion could still be increased for improved
analysis. In this study, Citrofortunella microcarpa rind is used as an additive to HCl which is then
used as a dissolution medium, it is recommended to explore the possibility of identifying, and isolating
the inhibitive components in the rind to synthesize a primary coating, before subjecting the sample to
immersion in acidic medium. The application of potentiodynamic polarization techniques is
recommended, to determine the type of inhibitor, and for a more in-depth analysis of corrosion
parameters. It is also recommended to employ other testing methods to support weight loss and surface
analysis data, as well as adsorption isotherm modeling.
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26th Regional Symposium on Chemical Engineering (RSCE 2019) IOP Publishing
IOP Conf. Series: Materials Science and Engineering 778 (2020) 012007 doi:10.1088/1757-899X/778/1/012007
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