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Comparative study of the inhibition of extracts from the peel and seeds of Citrus Aurantium against the corrosion of steel in molar HCl solution
H. Elmsellem1, H. Bendaha2, A. Aouniti1, A. Chetouani1,3, M. Mimouni2, A. Bouyanzer1.
1Laboratoire de Chimie Appliquée et environnement (LCAE-URAC18), Faculté des Sciences, Université Mohammed Premier, Oujda, Morocco
2Laboratoire de la chimie des matériaux (LCM), Faculté des Sciences, Université Mohammed Premier, Oujda, Morocco
3Laboratoire de chimie physique, Centre Régionale des Métiers de l'Education et de Formation ''CRMEF'', Région de l'Orientale, 60000 Oujda, Morocco.
*Corresponding author. E-mail : ahmedchetouani70@hotmail.com Recieved 13 Mai 2017, Revised 24 Mai 2014, Accepted 24 Mai 2014
Abstract
The corrosion inhibition of mild steel in 1 M HCl solution with different concentrations of citrus Aurantium peel and seeds extracts were studied using Tafel extrapolation, weight loss measurements, and electrochemical impedance spectroscopy (EIS). It was found that citrus aurantium peel and seeds extracts acted as slightly cathodic inhibitors and inhibition efficiencies increased with the increase of extracts concentration. The adsorption of the molecules of the extracts on the mild steel surface was in accordance with the Langmuir adsorption isotherm. The results showed citrus aurantium peel and seeds extracts could serve as a corrosion inhibitor of the mild steel in hydrochloric acid environment.
Keywords: Mild steel,Citrus Aurantium, Extract, HCl, Corrosion.
1. Introduction
Green inhibitors like natural products from plant extracts and substances from other renewable sources are of the interest of the researchers who are interested in “green chemistry” or “eco- friendly” technologies. The literature contains a number of references on green corrosion inhibitors [1-8]. Most of the synthetic corrosion inhibitors present environmental risks that have been the cause to think about the use of certain natural products. Recently, plant extracts have also gained importance as a source acceptable to the environment, renewable and readily available for a wide range of inhibitors necessary. Plant extracts are considered an incredibly rich source of naturally synthesized chemical compounds that can be extracted by simple low-cost procedures. However, the synergistic and antagonistic effects often are expected with these mixtures of inhibitors that affect their efficiency of inhibition. Several surveys have been obtained using these extracts economic plants [9]. The extracts obtained from the leaves, peel, seeds, fruits and roots of plants include mixtures of organic compounds containing nitrogen, sulfur and oxygen and other [10-11] have been
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reported to function as effective inhibitors of metal corrosion in aggressive environments. The effectiveness of corrosion inhibition of these extracts is generally attributed to the presence in their composition, complex organic species such as tannins, alkaloids, flavonoids, polyphenolic compounds, nitrogen bases , glycosides and as well as their protein products of acid hydrolysis[12].
For centuries and today, Citrus have a great interest in scientific research. Among these citrus, we focused on the Citrus Aurantium. It is the family Rutaceae. In the scientific literature, researchers have used different parts of Citrus aurantium, such as peel[13], juice [14], flowers [15] leaves, [16]
seeds [17] ... Some have used these dry parts [18] and other have used fresh[19]. They also varied their studies according to the existing extraction type (steam distillation, maceration, Soxhlet extraction, micro-wave ...). The seeds are rich in citrus aurantium limonoids such as limonin and nomiline and other limonoids limonin derivatives and nomiline [20]. As for the peel is rich in flavanones and many polymethoxylated, which are very rare in other plants, including the most popular hesperetin and naringenin. And their glycosides such as hesperidin and naringin, and polymethoxylated respectively nobiletin and tangeretin [21].The purpose of this paper is to examine the corrosion inhibition effect of citrus Aurantium peel and seeds extract for mild steel in 1M HCl solution by gravimetric method and electrochemical techniques such as linear polarisation and impedance spectroscopy (EIS).
2.2. Plant Extract
Preparing sample:
Citrus aurantium is collected from orange located in the East of Morocco Oujda precisely in the period between December and March. The fruits are washed, peeled and the peel was dried in oven at 313 K for 24 hours. The fruit was cut into six parts in order to facilitate the separation of seeds. These are well washed, also dried in oven at 313 K for 48 hours, and finely the dried peel and dried seed are ground and stored in until to use.
Extraction :
The powdered of Citrus aurantium seeds or peel is brought to the Soxhlet extraction with a series of solvents of increasing polarity (hexane, chloroform, acetone, methanol, and water). The methanol extract was concentrated under reduced pressure until you have a solid. This will be the object of our study corrosion.
2.3. Solutions
The aggressive solutions of 1.0 M HCl were prepared by dilution of an analytical grade 37% HCl with double distilled water. The concentration range of green inhibitor employed was 0.1– 5 (g/l).
2.2. Weight loss measurements
Coupons were cut into 1.5× 1.5 × 0.05 cm3 dimensions having composition (0.09%P, 0.01 % Al, 0.38
% Si, 0.05 % Mn, 0.21 % C, 0.05 % S and Fe balance) used for weight loss measurements. Prior to all measurements, the exposed area was mechanically abraded with 180, 400, 800, 1000, 1200 grades of emery papers. The specimens are washed thoroughly with bidistilled water degreased and dried
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with ethanol. Gravimetric measurements are carried out in a double walled glass cell equipped with a thermostated cooling condenser. The solution volume is 100 cm3. The immersion time for the weight loss is 6 h at (308±1) K. In order to get good reproducibility, experiments were carried out in duplicate. The average weight loss was obtained. The corrosion rate (v) is calculated using the following equation:
𝒗 =𝑺.𝒕𝑾 (1)
where W is the average weight loss, S the total area, and t is immersion time. With the corrosion rate calculated, the inhibition efficiency (Ew) is determined as follows:
Ew % =𝑉0−𝑉𝑉0 X 100 (2)
where V0 and V are the values of corrosion rate without and with inhibitor, respectively.
2.3. Electrochemical tests
The electrochemical study was carried out using a potentiostat PGZ100 piloted by Voltamaster soft- ware. This potentiostat is connected to a cell with three electrode thermostats with double wall. A saturated calomel electrode (SCE) and platinum electrode were used as reference and auxiliary electrodes, respectively. Anodic and cathodic potentiodynamic polarization curves were plotted at a polarization scan rate of 0.5mV/s. Before all experiments, the potential was stabilized at free potential during 30 min. The polarisation curves are obtained from −800 mV to −200 mV at 308 K.
The solution test is there after de-aerated by bubbling nitrogen. Inhibition efficiency (Ep%) is defined as Equation3, where icorr(0) and icorr(inh) represent corrosion current density values without and with inhibitor, respectively:
𝐸𝑝% =icor 0 −icor (inh )
icor 0 x 100 (3)
The electrochemical impedance spectroscopy (EIS) measurements are carried out with the electrochemical system, which included a digital potentiostat model Voltalab PGZ100 computer at Ecorr after immersion in solution without bubbling. After the determination of steady-state current at a corrosion potential, sine wave voltage (10 mV) peak to peak, at frequencies between 100 kHz and 10 mHz are superimposed on the rest potential. Computer programs automatically controlled the measurements performed at rest potentials after 0.5 hour of exposure at 308 K. The impedance diagrams are given in the Nyquist representation. Inhibition efficiency (ER%) is estimated using the relation 4, where Rt(0) and Rt(inh) are the charge transfer resistance values in the absence and presence of inhibitor, respectively:
𝐸𝑅% =Rt inh −Rt (0)
Rt inh x 100 (4)
4 3. Results and discussion
Mild steel corrosion behavior in 1 M HCl was investigated in the absence and presence of citrus aurantium seeds extract with the help of weight loss and electrochemical techniques. It was seen that mild steel dissolution rate was very high in 1 M HCl alone but presence of inhibitor significantly decreased the corrosion rate of mild steel.
3.1. Weight loss measurements
Although there are many experimental techniques which can be used to evaluate the inhibitor efficiency of citrus aurantium peel and seeds extracts, weight loss is one of the simplest and frequently used methods. Using the experimental weight loss data, percentage inhibition efficiencies (EW %), were calculated in the classical way. Values of EW for all investigated percentages of citrus aurantium peel and seeds extracts in 1 M HCl are summarized in Table 1.
Table 1. Corrosion parameters for mild steel in 1 M HCl in absence and presence of different concentrations of citrus aurantium peel and seeds extracts obtained from weight loss measurements at 35° C for 6h.
Inhibitors Concentration
(g/l)
V
(mg.cm-2 h-1)
𝐄𝐰 (%)
1M HCl - 0.82 ---
Extract of
CITRUS AURANTIUM
SEEDS
0,1 0,21 74
0,5 0,12 85
1 0,07 91
2 0,06 93
3 0,05 94
5 0,04 95
Extract of
CITRUS AURANTIUM PEEL
0,1 0,19 77
0,5 0,12 78
1 0,14 83
2 0,13 84
3 0,07 91
5 0,05 94
3.1.3. Adsorption isotherm and standard adsorption free energy
Surface can be provided by adsorption isotherm. Several isotherms including Frumkin, Langmuir, Temkin isotherms are employed to fit the experimental data. It is found that the adsorption of studied inhibitors on steel surface obeys the Langmuir adsorption isotherm equation [22.23]:
𝐶
ϴ=𝑘1+ 𝑐 (5)
where C is the concentration of inhibitor, K the adsorption equilibrium constant and ϴ is the surface coverage and expressed by the ration E%/100.
The surface coverage values ϴ were tested graphically for fitting a suitable adsorption isotherm. The plot of C/ϴ versus C yielded a straight line with a slope 1.02. This was observed clearly proving that
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the adsorption of the citrus aurantium peel and seeds extracts from acid solutions on the mild steel surface obeys the Langmuir adsorption isotherm (Fig.2).
0 1 2 3 4 5
0 1 2 3 4 5 6
C inh/ (g/l)
Cinh(g/l)
seeds peel
Figure 2. Langmuir isotherm of steel in the 1M HCl in presence of citrus aurantium peel and seeds extracts at calculated by gravimetric method.
3.1. Potentiodynamic polarization curves
Fig. 3 presents potentiodynamic polarization curves for mild steel in 1 M HCl containing different concentrations of citrus aurantium peel and seeds extracts. It can be remarked that the cathodic branches exhibit well defined Tafel region. It is seen also that the inhibitors addition hindered the acid attack on mild steel. Indeed, an increase in their concentrations gives a decrease in current densities.
Figure 3. Tafel plot of mild steel with different concentrations of citrus aurantium seeds and peel extract in 1M HCl solution
-800 -700 -600 -500 -400 -300 -200 -3
-2 -1 0 1
2 SEEDS
Log I( mA / cm2 )
E (mV / SCE)
HCl 1M 0.1g/l 0.5g/l 1g/l 2g/l 3g/l 5g/l
-800 -700 -600 -500 -400 -300 -200 -3
-2 -1 0 1
2 PEEL
Log I( mA / cm2 )
E (mV / SCE)
HCl 1M 0.1g/l 0.5g/l 1g/l 2g/l 3g/l 5g/l
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The values of corrosion potential (Ecorr), anodic and cathodic Tafel slopes (βa and βc), corrosion current density (Icorr) and percentage inhibition efficiency (Ep %) are presented in Table 2.
As it is shown in Fig.3 and Table 2, cathodic polarisation curves rise to parallel Tafel lines, indicating that the hydrogen evolution reaction is activation controlled. Thus, the presence of citrus aurantium seeds extract does not affect the mechanism of this process. The addition of citrus aurantium seeds extract tested causes a decrease of the current density.
The results demonstrate that the hydrogen reduction is inhibited and that the inhibition efficiency increases with inhibitors concentration. The best efficiencies obtained in the presence of SEEDS and PEEL respectively are 95% and 94g/l at 5g/l. This result indicates that citrus aurantium peel and seeds extracts act as cathodic inhibitors.
Table 2. Tafel polarization parameters obtained at different concentrations of citrus aurantium seeds and peel extract
Inhibitors Concentration (g/l)
-Ecorr (mV/SCE)
Icorr
(μA/cm2)
-βc βa Ep
(%)
1M HCl - 464 1386 164 135 --
Extract OF CITRUS AURANTIUM SEEDS
0.01 465 781 159 114 43.65
0.5 478 419 175 103 69.77
1 481 295 180 102 78.72
2 483 225 170 99 83.77
3 483 192 177 102 86.15
5 484 114 162 92 91.77
Extract OF CITRUS AURANTIUM PEEL
0.01 482 689 152 129 50.29
0.5 486 348 175 121 74.89
1 487 305 173 117 77.99
2 487 240 176 97 82.68
3 486 219 171 95 84.20
5 491 126 162 96 90.91
3.2. Electrochemical impedance spectroscopy
The corrosion behaviour of steel, in acidic solution in the presence and absence of inhibitor, is investigated by the electrochemical impedance spectroscopy (EIS) at 308 K after 30 min of immersion. Fig. 4 show the EIS diagrams carried out at 298 K in acid solution with and without citrus aurantium peel and seeds extracts. The impedance parameters derived from these investigations are mentioned in Table 3.
The values of the polarization resistance were calculated by subtracting the high frequency intersection from the low frequency intersection [24]. Double layer capacitance values were obtained at maximum frequency (fm), at which the imaginary component of the Nyquist plot is maximum, and calculated using the following equation.
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Cdl=1/2πfmRt (7)
with Cdl Double layer capacitance (µF.cm-2); fm: maximum frequency (Hz) and Rt: charge transfer resistance (Ω.cm2).
Figure 4. Impedance curves with different concentrations of citrus aurantium seeds and peel extract in 1M HCl solution
Table 3. Impedance parameters for mild steel in 1.0 M HCl in the absence and presence of different concentrations of citrus aurantium peel and seeds extracts.
Inhibitor Concentration (g/l)
Rt
(Ω.cm2) Rb
(Ω.cm2)
fmax
(Htz)
Cdl
(µf/cm2) E (%)
1M HCl - 14.57 1.37 54.64 200 --
Extract of CITRUS AURANTIUM SEEDS
0.01 37.14 2.41 61.12 70.15 60.77
0.05 74.48 2.18 39.40 54.26 80.44
1 95.47 2.21 39.17 42.58 84.74
2 126.79 2.27 30.41 41.30 88.51
3 135.40 2.26 31.22 37.67 89.24
5 169.35 2.35 31.76 29.61 91.40
Extract of CITRUS AURANTIUM PEEL
0.01 30 2.26 60.47 87.78 51.43
0.05 84 2.42 48.15 39.37 82.65
1 86 3.03 48.89 37.87 83.06
2 117 2.72 49.62 27.43 87.55
3 126 2.72 48.98 25.80 88.44
5 181 2.66 39.66 22.18 91.95
0 25 50 75 100 125 150 175
0 25 50 75 100
Zr (.cm2)
-Zim (.cm2 )
HCl 1M 0.1g/l 0.5g/l 1g/l 2g/l 3g/l 5g/l
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From Fig.4, the obtained impedance diagrams (consist of one large capacitive loop), indicates that a charge transfer process mainly controls the corrosion of steel [25]. The general shape of the curves is very similar for all samples; the shape is maintained throughout the whole concentration, indicating that almost no change in the corrosion mechanism occurred due to the inhibitor addition [26]. The Rt values increased with the increase of the concentration of citrus aurantium peel and seeds extracts.
Values of double layer capacitance are also brought down to the maximum extent in the presence of inhibitors and the decrease in the values of Cdl follows the order similar to that obtained for Icorr in this study.
The results obtained from the polarization technique in acidic solution were in good agreement with those obtained from the electrochemical impedance spectroscopy (EIS) with a small variation.
4. Conclusion
In this work we have studied the corrosion inhibition of citrus aurantium peel and seeds extracts for mild steel in 1M HCl solution by gravimetric method and electrochemical techniques. The results obtained are in good agreement and are given as follows.
The inhibition efficiency of SEEDS and PEEL increases with the increase of inhibition concentration to reach 95% at 5g/l of SEEDS and 94% at 5g/L of PEEL. (small differences in their numerical values).
SEEDS and PEEL are adsorbed on the steel surface according to the Langmuir adsorption isotherm.
The polarization curves indicate that the extract of citrus aurantium peel and seeds extracts act as cathodic type inhibitors and the impedance data indicate that inhibition was achieved via adsorption.
The data obtained from the three different methods: potentiodynamic polarisation, EIS and weight loss, are in good agreements.
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