Jackfruit Peel Extract as Environmentally Safe Inhibitor for Carbon Steel Protection in Acidic Solution

Jackfruit Peel Extract as Environmentally Safe Inhibitor for Carbon Steel Protection in Acidic Solution

Ira KusumaningrumRudy Soenoko Eko SIswanto Femiana Gapsari

Mechanical Engineering Department, Faculty of Engineering, MT Haryono 167 Malang, 65145 Indonesia

Corresponding Author Email: 
ira210371@gmail.com
Page: 
46-54
|
DOI: 
https://doi.org/10.14447/jnmes.v25i1.a07
Received: 
2 November 2021
|
Revised: 
29 December 2021
|
Accepted: 
5 January 2022
|
Available online: 
31 March 2022
| Citation

© 2022 IIETA. This article is published by IIETA and is licensed under the CC BY 4.0 license (http://creativecommons.org/licenses/by/4.0/).

OPEN ACCESS

Abstract: 

The addition of corrosion inhibitors into the acidic environment is an environmental modification to control the rate of corrosion. Organic compound inhibitors become an environmentally friendly alternative. In this study, research and analysis have been carried out on jackfruit peel extract as a corrosion inhibitor for AISI 1037 carbon steel protection in 1M HCl solution. Variation of inhibitor concentration is 200-3000 ppm. Corrosion rate measurements were performed by applying weight loss and potential polarization methods. The addition of inhibitor concentrations up to 1000 ppm increased the inhibitor efficiency up to 90.98%, but the efficiency decreased at concentrations of 2000 ppm and 3000 ppm. The adsorption inhibitors that occurred in this study was physical adsorption. It followed the Langmuir isothermal adsorption. The fungsional group of the film layer on the carbon steel surface indicated that the jack fruit peel extract compounds was adsorbed on the steel surface.

Keywords: 

corrosion, inhibitor, adsorption, thermodynamic parameter

1. Introduction

Corrosion is the destruction of a metal because it reacts with the environment [1]. Corrosion cannot be prevented but can be controlled. This can extend the life of the metal structure or components. Corrosion control can be done by selecting the right design and material, applying protective coating, cathodic or anodic protection and modifying the environment. The addition of corrosion inhibitors into the electrolyte solution is one of the modifications to the environment. Corrosion inhibitors are chemicals that are added to the corrosion system with low concentration. The addition aims to reduce the rate of corrosion without significantly altering the concentration of corrosive substances [2]. The use of inorganic inhibitors can have a detrimental effect on the environment and humans because it contains toxic substances. Therefore, organic compound-based inhibitors are the right choice and environmentally friendly.

Organic inhibitors are adsorbed type inhibitors. This type of inhibitor can reduce the rate of corrosion. It forms an adsorbent layer that is able to protect the metal surface from its corrosive environment. This is due to inhibitory compounds having heteroatomic structures such as N, O, P, S, and atoms having free electron pairs[3]. Elements with free electron pairs as ligands form complex compounds with metals. Organic inhibitors was widely used to control corrosion. This had been proven by many studies that use plants as corrosion inhibitors. Research was done on all parts of the plant. Thymus vulgaris [4], parsley/Petroselinum sativum [5], Hyptis suaveolens [6], Dryopteris cochleata [7], bamboo leaf [8], Urtica dioica [9], Sida acuta [10], Nicotiana tabacum [11], and Retama monosperma [12] is a plant whose leaves are used as corrosion inhibitors. Studies using fruits as corrosion inhibitors such as in Gingko Biloba [13], Chinese Gooseberry [14], Aqueous citrullus lanatus [15], Moroccan ammodavcus leucotrichus [16], red apple [17] and Myristica fragrans [18] were also conducted. Plant waste such as peels of lychee [19], melon [20], Musa paradisca [21], watermelon [22] and orange [23] were also used as corrosion inhibitor.

Utilizing fruit waste was an attempt to increase the role of nature in industry. This attempt can increase the economic value of the fruit waste. The watermelon peel extract had been used as corrosion inhibitor on mild steel in 1 M HCl solution and 0.5 M H2SO4. Concentrations vary from 0.1 g/l to 2.0 g/l [22]. Corrosion rate was tested using potentiodynamic polarization method and electrochemical impedance spectroscopy method. The same patterns were shown by both methods. The inhibitor efficiency increased as the concentration of watermelon peel extract was increased. Corrosion inhibition on mild steel was investigated where the melon peel extract was added into 1 M HCl with varied concentration between 0.05 g/l to 0.5 g/l and at varied temperatures of 295⁰K to 333⁰K [20]. The highest inhibitor efficiency was shown by the addition of 0.5 g/l into 1 M HCl solution.

Jackfruits (Artocarpus heterophyllus) are tropical fruit that grow in South Asia countries and Florida. In those countries, jackfruits are more popular as garden plants rather than plants for commercial plantation [24]. In Indonesia, jackfruits are eaten when both ripe or nearly ripe. However, the waste of the fruit has not been utilized maximally. Jackfruit peel contains some antioxidant compounds such as protocatechuic acid, chlorogenic acid, isovitexin, feruloyl derivative, artocarpin and luteolin [25].

In this study, jackfruit peel extract (JPE) was used as an environmentally friendly inhibitor. The JPE contains some antioxidant compounds which are able to inhibit oxidation reaction in corrosion process. This expected to reduce corrosion rate on AISI 1037 carbon steel. The inhibitor efficiency was investigated by performing corrosion rate test using both potentiodynamic polarization and weight loss methods.

The interaction between and surface of the steel and the inhibitor molecule can be understood using the adsorption isotherm..There are some types of adsorption isotherm equation which are often met as the adsorption pattern of a corrosion inhibitor. They are adsorption isotherm of Langmuir, Freundlich, Temkin and Frumkin. Determining adsorption isotherm model was conducted with linear curve plot based on the adsorption isotherm equations [26].

Langmuir equation:

$K_{a d s}=\theta /(1-\theta) C_{i n h}$

Frumkin equation:

$\log \frac{\theta}{1-\theta C_{i n h}}=\log K_{a d s}+b \theta$     (1)

Freundlich equation:

$\log \theta=\log K_{a d s}+n \log C_{i n h}$     (2)

Temkin equation:

$\exp (-2 \alpha \theta)=b x C_{i n h}$      (3)

$\theta$ is the fraction of surface coverage, $K_{a d s}$ is balance constant of adsorption-desorption, $C_{\text {inh }}$ is inhibitor concentration and $b$ is interaction parameter which can be calculated using slope of the linear regression equation. The value of $b$ which is more than zero indicates attraction of the adsorbed species. The resistance is indicated by the value of a which is less than zero. Based on the value of each R2 determinant coefficient, the adsorption isotherm pattern is appropriated.

Inhibition mechanism of an organic compound on carbon steel surface can be reviewed through thermodynamic parameters which are the changes in adsorption free energy $\left(\Delta \mathrm{G}^{0}\right.$ ads $)$, enthalpy of adsorption $\left(\Delta \mathrm{H}^{0}\right.$ ads $)$ and entropy of adsorption $\left(\Delta \mathrm{S}_{\text {ads }}^{0}\right)$. The thermodynamic parameter for the higher JPE inhibitor efficiency was shown in table 3 . The adsorption energy of inhibitor on the steel surface can be evaluated from the following equation [27]:

$\Delta \mathrm{G}_{a d s}^{\circ}=-R T \operatorname{Ln}\left(K_{a d s} \times A\right)$     (5)

absolute temperature $\left({ }^{\circ} \mathrm{K}\right)$ and $\mathrm{A}$ is the consentrasion of water in the acidic solution (55.5 in Molar or 1000 in $\mathrm{g} / \mathrm{L}$). If the value of around $-20 \mathrm{~kJ} \mathrm{~mol}^{-1}$; it indicate physisorption. However, around $-40 \mathrm{~kJ} \mathrm{~mol}^{-1}$, respectively indicate chemisorption [36]. The negative of enthalpy $\Delta \mathrm{H}^{0}$ ads signifies exothermic adsorption. The absolute magnitude of $\Delta \mathrm{H}^{0}$ ads for chemisorption is greater than physisorption. The of $\Delta \mathrm{H}^{0}$ ads estimation is illustrated below through the Langmuir isotherm and calculated using Van't Hoff equation [27]:

$\operatorname{Ln} K_{a d s}=-\Delta H_{a d s}^{\circ} / R T$      (6)

where $\mathrm{T}$ is the absolute temperature, and $\Delta H_{a d s}^{\circ}$ is the enthalpy of adsorption. If. $\Delta S_{a d s}^{\circ}<0$, that signifies the adsorption process occurence. The greater of $\Delta S_{a d s}^{\circ}$ value indicates the higher the adsorption will be. Its value can be calculated using equation:

$\Delta G_{a d s}^{\circ}=\Delta H_{a d s}^{\circ}-T \Delta S_{a d s}^{\circ}$     (7)

The adsorption process of inhibitor can be observed by activation parameters such as the activation energy $\left(E_{a}\right)$, the activation enthalpy $\left(\Delta \mathrm{H}^{\#}\right)$ and the activation entropy $\left(\Delta \mathrm{S}^{\#}\right)$ for corrosion in the absence and presence of inhibitor. the activation energy $\left(E_{a}\right)$ were calculated from Arrhenius equation [28]:

$i_{\text {corr }}=A \exp \frac{E_{a}}{R T}$      (8)

Where $\mathrm{i}_{\text {corr }}$ is the density of corrosion current, $A$ is the constanta of Arrhenius, and $R$ is the constanta of universal gas. The transition state equation was presented:

$i_{c o r r}=\frac{R T}{N h} \exp \left(\frac{\Delta S^{\#}}{R}\right) \exp \left(\frac{-\Delta H^{\#}}{R T}\right)$     (9)

Where N is constanta of Avogadro, h is the constanta of planck.

2. Experimental

2.1 The materials

The material protected in the experiment was AISI 1037 carbon steel with chemical composition of 0.37% C, 0.17%-0.37%Si, 0.35%-0.65% Mn, 0.025% P, 0.020% S, 0.25% Cr, 0.25% Ni, 0.25% Cu and Fe as the rest. The specimen dimension was 10 mm x 40 mm x 5 mm. It was abraded consecutively using emery paper with grade size of 600 to 1200.

1 M HCl solution was used as the electrolyte in the study. It was prepared by dissolving 83 ml of 38% HCl from Merck with aquades to obtain 1000 ml solution. JPE inhibitor was added into 1M HCl solution with varied concentration.

JP extraction was started by cleaning process of the peel from contaminants. Next, the clean JP was dried and ground to produce fine powder. The extraction stage was performed by maceration method using ethanol solvent. Filtrate from the extraction result was filtered and put into Erlenmeyer. Next, the filtrate was evaporated using rotary vacuum evaporator to produce thick extract.

2.2 Characterization of JP extract

Then, the functional group of the JPE was identified using Fourier transform infra red (FTIR) spectroscopy of Shimadzu 8400 S. After that, the JP powder was mixed with KBr salt to form pellets and later was used as test sample. The main compound identification was performed using mass spectrometer of triple quadrupole TSQ Quantum Access Max with ionization of ESI source (electrospray ionization) and operated using positive mode ionization. The condition of ESI ionization covered spray voltage of 3 kV and evaporation temperature of 275⁰C.

2.3 The test method

The corrosion rate measurement using weightloss method was performed by weighing the specimen before and after immersion process. The specimen was dipped into 250 ml corrosive media of 1 M HCl solution and was added by varied concentrations of inhibitor: of 200 ppm, 400 ppm, 600 ppm, 800 ppm, 1000 ppm, 2000 ppm and 3000 ppm. The specimen was immersed with variation of time of 1 hour to 96 hours (4 days). Corrosion rate (CR) in this method was calculated by applying weightloss data of the specimen during corrosion test [22] using the following equation:

$C R=87600 W / \rho A T$     (10)

where: CR is corrosion rate and W is lost weight.

The inhibitor efficiency (EI) was calculated using equation:

$E I=\left(\left(C R_{\text {blank }}-C R_{\text {inh }}\right) / C R_{\text {blank }}\right) 100 \%$     (11)

The weight of the specimen was measured using moisture balance Shimadzu MOC-120H with maximum capacity of 120 gram and readability of 0.001 gram. Corrosion rate was also measured using potentiodynamic polarization. The test was performed with Autolab PGSTAT 204 N and software Nova 1.11 Autolab to measure corrosion rate of AISI 1037 carbon steel in 1 M HCL with and without JPE inhibitor. JPE added into 1 M HCl was varied: 200 ppm, 400 ppm, 600 ppm, 800 ppm, 1000 ppm, 2000 ppm and 3000 ppm. Previously, the unexposed specimen surface was coated with epoxy resin previously.

The working electrode was AISI 1037 carbon steel, the conter electrode was platinum and the reference electrode was Ag│AgCl. The scan rate was set at 0.100 V/s. The value of Open Circuit Potential (OCP) ranged from -0.44 V to -0.46 V using average OCP value. From the data, the inhibition efficiency value (%EI) [27] was calculated using the equation:

$E I=\left(\left(i_{\text {corr }}-i_{(\text {corr }) i}\right) / i_{\text {corr }}\right) 100 \%$     (12)

2.4 Surface analysis

The surface morphology of AISI 1037 carbon steel before and after immersion for 4 days in 1M HCl solution, without or with JPE inhibitor was analyzed using a scanning electron microscope (SEM) FEI Quanta FEG 650. Sample was sprinked on top of the stub with double sided carbon tape without sputter coating.

3. Results and Discussion

3.1 Characterization of JP extract

The identification of JPE functional group using FTIR produced some peaks with certain wavelength values. It is presented in Figure 1.

Figure 1. The results of Fourier transform infrared (FTIR) test on JPE functional group

Based on IR chart[29], the functional group bond of JPE was functional group of alkyl halides with C-Br stretch bond in wavenumber range of 690-515 cm-1 with intensity of 41.26% and C-Cl stretch in wavenumber range of <600-840 cm-1 with intensity of 66.22%,. The alkenes fungsional group with =C-H stretch group can read in wavenumber range 995-685 cm-1 and intensity of 70.69%. Aromatic functional group was found with C-H bond and wavenumber range of 900 - 675 cm-1 with intensity of 57.64% and C-C stretch bond in wavenumber range of 1500-1400 cm-1 and intensity 39.77 %. Besides that, aromatic functional group was found with C-N stretch bond in wavenumber range of 1335-1250 cm-1 and intensity of 46.33% or known as aromatic amines functional group. In range of 1250-1020 cm-1 and intensity of 23.61%, it was found aliphatic amines functional group with C-N stretch bond. alcohols functional group was found at wave range of 3500-3200 cm-1 and intensity of 10%.

The characteristics of compounds which are potential as antioxidant in JPE was identified using spectrometer MS, shown in spectrogram as presented in table 1. In the spectrogram, the compound with the highest abundance is artocarpin with molecule structures [28] shown in Figure 2.

Figure 2. Molecule structures of Artocarpin

3.2 Inhibitor performance

Inhibition performance could be observed from the inhibitor's ability to inhibit corrosion rate on AISI 1037 carbon steel. Based on the weight loss test, there was decrease in corrosion rate as the inhibitor concentration was increased. However, this happened only until the concentration of 1000 ppm. Above 1000 ppm, (at concentration of 2000 ppm and 3000 ppm) the corrosion rate increased. Thus, the inhibitor was efficient by the increase of the concentration up to 1000 ppm. The inhibitor became less efficient when the concentration was increased up to 2000 ppm and 3000 ppm such as shown by the graph in figure 3. It can be caused by the saturation binding conditions between the steel surface and the inhibitor molecules. The other cause was the removal of the protective layer due to interactions between the inhibitor with HCl or with the inhibitor itself [30]. It can called the competitive adsorption [31].

Increasing the concentration up to 1000 ppm had significantly reduced the dimension of the metal surface which had electrochemical reaction. The addition of JPE inhibitors into the HCl solution caused the adsorption of the inhibitor molecules on the metal surface by forming a protective layer. The metal was protected by this layer from its aggressive environment and the corrosion was fails [31].

Table 1. Identification of JPE compounds

No. Peak

Observed m/z

Calculated m/z

Formula

Compound

1

95,13

95,12

C6H6O; C6H5OH

Phenol

2

155,05

155,13

C7H6O4

Protocatechuic acid

3

309,07

309,23

C15H10O6

Luteolin

4

325.12

325.12

C15H10O7

Morin

5

335.09

335.32

C16H14O6

Artocarpanone

6

437.15

437.51

C26H28O6

Artocarpin

7

511,06

511,40

C21H20O10

Isovitexin

Figure 3. The JPE inhibitor efficiency on AISI 1037 carbon steel in 1 M HCl solution

Increasing the concentration up to 1000 ppm had significantly reduced the dimension of the metal surface which had electrochemical reaction. The addition of JPE inhibitors into the HCl solution caused the adsorption of the inhibitor molecules on the metal surface by forming a protective layer. The metal was protected by this layer from its aggressive environment and the corrosion was fails [31].

The performance of JPE inhibitor was also shown by the result of potentiodynamic polarization test such as presented in Figure 4 and Table 2. The method was conducted to strengthen the data obtained from the weightloss method. The Tafel plot of AISI 1037 carbon steel with or without JPE inhibitor in 1 M HCl solution is displayed in Figure 5. The plot illustrates the significant shift of Ecorr with and without inhibitor. It is shown in values of 16.3 mV, 8.29 mV, 19.24 mV, 28.31 mV, 7.7 mV, 1.1 mV and 7.75 mV at the concentration of 200 ppm, 400 ppm, 600 ppm, 800 ppm, 1000 ppm, 2000 ppm and 3000 ppm. The values of Ecorr shift which are less than 85.0 mV confirm that the inhibitor is mixed [27]. This is also supported by the shift of the values of anodic.

Tafel slope (βa) or cathodic Tafel slope (βc), with or without inhibitor, where βa was at range of 110.85 mV/dec up to 407.32 mV/dec and βc was at range of 63.89 mV/dec to 135.21 mV/dec. The biggest shift was found at βa which indicates mixed inhibitor. However, the inhibitor tends to be anodic [32].

Figure 4. The Tafel plot of AISI 1037 carbon steel in 1 M HCl solution with or without the addition of JPE inhibitor

The two test methods of inhibitor performance show that there is the same trend of inhibition such as shown by the graph in figure 5. It illustrated the efficiency of JPE inhibitor in 1 M HCl solution at varied concentrations to protect AISI 1037 carbon steel using potentiodynamic polarization or weightloss method. In the image, there was trend similarity in which the inhibition efficiency increases as the concentration increases up to 1000 ppm. However, the efficiency decreases at the concentration of 2000 ppm and 3000 ppm. Inhibitor efficiency in weightloss method is lower than that in the potentiodynamic polarization method even though it has the same trend.

Figure 5. Diagram of JPE inhibitor efficiency on AISI 1037 carbon steel in 1 M HCl solution

This showed that during corrosion, the mass changes was equivalent to the change of current [33].

Table 2. The Result of Potentiodynamic Polarization Test on AISI 1037 Carbon Steel in 1 M HCl Solution With or Without The Addition of JPE Inhibitor

Concentration

Tafel slope

Ecorr (V)

Icorr (A)

Corrosion rate (mm/year)

EI (%)

ba (V/dec)

bc (V/dec)

Blank

0.098

0.069

-0.440

0.000382

 

 

200 ppm

0.407

0.135

-0.456

0.000081

0.94

78.73

400 ppm

0.111

0.064

-0.448

0.000076

0.88

80.15

600 ppm

0.310

0.153

-0.459

0.000073

0.85

80.82

800 ppm

0.168

0.106

-0.468

0.000062

0.72

83.71

1000 ppm

0.116

0.078

-0.447

0.000034

0.40

90.98

2000 ppm

0.198

0.089

-0.439

0.000065

0.75

83.07

3000 ppm

0.199

0.089

-0.447

0.000067

0.77

82.55

3.3 Adsorption isotherm and activation energy

Table 3. Thermodynamic Parameters of Inhibitor Adsorption of JPE Inhibitor for The Higher Inhibitor Efficiency

Concentration

Ppm

Kads

∆Gads

KJ mol-1

∆Hads

KJ mol-1

∆Sads

KJmol-1⁰K-1

1000

10.089

-22.995

-5.765

0.058

The corrosion inhibition mechanism of JPE can be defined by discovering the adsorption isotherm adsorption model on the steel surface. The linear curve plot of the inhibitor concentration of 200 ppm, 400 ppm, 600 ppm, 800 ppm, 1000 ppm, 2000 ppm and 3000 ppm is displayed in Figure 6. Langmuir adsorption isotherm pattern is displayed in curve (a) Freundlich, (b) Temkin and (c) Frumkin. The adsorption isotherm equations are as follows. Based on the value of each R2 determinant coefficient, the appropriate adsorption isotherm pattern at the concentration of 200 ppm, 400 ppm, 600 ppm, 800 ppm, 1000 ppm, 2000 ppm and 3000 ppm is Langmuir where it has Cinh big influence on the adsorption isotherm which is shown by R2 value reaching 0.988.

The thermodynamic parameter for the higher JPE inhibitor efficiency was shown in table 3. In Table 3, it shown that at the concentration of 1000 ppm was around -20 KJ/mol. This indicated that there was interaction between inhibitor molecules with adsorbed chlorin ion on carbon steel surface which forms protective layer through the physical adsorption [22]. The positive value of enthalpy indicated that the adsorption process of JPE was endothermic process and there was a regularity of energy, so that the corrosion process was slowed down [34].

Table 4 was shown activation parameters for both corrosion in the absence inhibitor and corrosion inhibition at 1000 ppm JPE inhibitor between 298⁰K – 318⁰K. The addition of JPE inhibitor in HCl 1 M solution decreased the reaction rate and it was needed higher energy of activation to trigger the reaction [35]. The increase of energy of activation could be observed from the physisorption occurrence. This was confirmed by the decrease in inhibitor efficiency if the temperature was increased [6].

Table 4 was shown activation parameters for both corrosion in the absence inhibitor and corrosion inhibition at 1000 ppm JPE inhibitor between 298⁰K – 318⁰K. The addition of JPE inhibitor in HCl 1 M solution decreased the reaction rate and it was needed higher energy of activation to trigger the reaction [35]. The increase of energy of activation could be observed from the physisorption occurrence. This was confirmed by the decrease in inhibitor efficiency if the temperature was increased [6].

Table 4. Activation Parameters for Both Corrosion in The Absence and Present JPE Inhibitor

Concentration

(ppm)

T

K

icorr

(A/cm2)

Ea

(KJ/mol)

∆S#

KJ/molK

∆H#

KJ/mol

Blank

298

0.00038

31.52

-0.27

28.97

308

0.00082

318

0.00084

1000

298

0.00004

102.66

-0.05

100.12

308

0.00021

318

0.00046

Figure 6. The linear curve plot of Langmuir, Freundlich, Temkin and Frumkin adsorption patterns at the concentration of 200 ppm, 400 ppm, 600 ppm, 800 ppm, 1000 ppm, 2000 ppm and 3000 ppm

3.4 Inhibitor adsorption mechanism

The adsorption of JPE inhibitor on the carbon steel surface can occur through physical, chemical or both mechanisms. Based on the result of potentiodynamic polarization and the thermodynamic parameters, the inhibitor adsorption of JPE on the carbon steel surface indicated physical adsorption. It was illustrated in Figure 7. This illustration described the way of JPE molecules could adsorb on the steel surface and prevent the corrosion.

Figure 7. Illustration of inhibition of JPE

In the physisorption, Chloride ions present in the corrosive solution can be adsorbed onto the positively charged carbon steel surface due to their electrostatic interactions. The active subtances in the JPE, such as artocarpin, protonated and reacted to chlorine ions that have been absorbed on the carbon steel surface. The transformation from the low stable chloro iron complex to a higher stable iron-inhibitor complex was the causes.

The formed of complex based on interactions of donor acceptor like interaction between O atoms of neutral species and p electrons. Besides that, the interaction between π electrons on cation species and the d orbital that vacant of iron was the other ones. The soluble of iron complex that formed was depended on the the hydroxyl group and inhibitor molecule. Subsequently, the hydroxyl group was replaced by the molecule of inhibitor. Thus, the mechanism of JPE inhibitor adsorption followed this react:

$\mathrm{Fe}^{2+}+\mathrm{mH}_{2} \mathrm{O}+\mathrm{nCl}^{-}+\mathrm{p}(\mathrm{JPE}) \rightarrow\left[\mathrm{Fe}(\mathrm{JPE})_{\mathrm{p}}(\mathrm{OH})_{\mathrm{m}}(\mathrm{Cl})_{\mathrm{n}}\right)^{2-\mathrm{m}-\mathrm{n}}+$$\mathrm{m}(\mathrm{H})^{+}$

The formation of FeOH+ and [FeClOH]- intermediates was the first reaction. The next, FeOH+ and [FeClOH]- was convert to γ-Fe2O3 and γ-FeOOH and formed oxide layer. The inhibitor molecules were reacting with [FeClOH]at the pores of oxide layer, and formed the stable complex [Fe(JPE)p(OH)m(Cl)n]2-m-n. The complex formed would adsorb at the surface of carbon steel and reduce corrosion rate [36].

3.5 Adsorption layer

The characteristics of the adsorption layer on the specimen surface can be studied through its functional groups. Based on the comparison between the IR spectra of the JPE and the IR spectra of the adsorption layer, the characteristics of the adsorption layer were almost the same as the characteristics of the JPE. However, the wavenumber of functional groups of the adsorption layer shifted from the wavenumber of functional groups of JPE. This shown in figure 8.

Figure 8. The shift of the wavenumber of functional group of JPE until it was adsorbed on AISI 1037 carbon steel surface

The aromatic wavenumber shifted from of 1426.06 cm-1 to 1449.2 cm-1 and from 1518.64 cm-1 to 1526.35 cm-1. The alcohols wavenumber shifted from of 3414.5 cm-1 to 3439.6 cm-1. The shifts also occur in the wavenumber of the carboxylic acid, anhydrides, and alkenes fungsi functional groups. The wavenumber of the carboxylic acid shifted from 2932.36 cm-1 to 2942 cm-1, the anhydrides wavenumber shifted from 1742.36 cm-1 to 1846.51 cm-1, and the alkenes wavenumber shifted from 1644 cm-1 to 1638.21 cm-1. The shift of wavenumber did not change the functional groups because it was still in the wavenumber range.

3.6 The analysis of metal surface

The Surface morphology of AISI 1037 carbon steel before and after immersion in 1 M HCl without or with JPE inhibitor was provided by SEM result. The change of surface morphology was shown at figure 9 presented the smooth surface before the process of corrosion (Figure 9 a). Pits and cracks appear after immersion in 1 M HCl (Figure 9 b). They decrease after the addition of an inhibitor (figure 9 c-f). This shown that the addition of JPE inhibitor in acidic environment caused a reduction of corrosion rate.

Figure 9 The images of Scanning Electron spectroscopy of AISI 1037 carbon steel surface in 250x before corrosion (a), after immersion in 1 M HCl (b), after immersion in 1 M HCl with JP extract inhibitor 200 ppm (c), after immersion in 1 M with JPE inhibitor 600 ppm (d), after immersion in 1 M HCl with JPE inhibitor 1000 ppm (e), after immersion in 1M HCl with JPE inhibitor 3000 ppm

3.7 The comparison on inhibitor eficiency

The other fruit peel extract as corrosion inhibitors was used to compare the inhibitory ability of JPE compared to other fruit peel extracts. This can be observed from the inhibitor efficiencies. Some of them were garlic peel [38], garcinia indica peel [39], Musa paradisia peel [21], calamansi peel [40], grapefruit peel [41], cumcumber peel [42], pumpkin peel [43], carica papaya peel [44], punica granatum peel [45], aqueous brown onion peel [46], musa acuminate fruit peel [47], banana peel [48], lemon peel [49], longan peel [50], lychee peel [19], mangifera indica peel [51], almond peel [52], mango peel [53], orange peel [53], musa sapientum peel[54], sweet melon peel [20], green pea peel [55], mangosteen peel [56] and watermelon peel [22]. The comparison is shown in the figure 10.

Figure 10. The comparrison of inhibition efficiency of JPE and the others

4. Conclusion

JPE could be used as environmentally friendly inhibitor for AISI 1037 carbon steel in HCl solution. The functional groups in antioxidant compound molecules could be identified through FTIR spectrum of the extract. The result of mass spectroscopy indicated antioxidant compounds where the highest abundance was found in artocarpin. In this study, the most efficient inhibitor was found when the inhibitor concentration of 1000 ppm was added into 1 M HCl solution. The inhibitor efficiency achieved 90.98% using potentiodynamic polarization method. Adsorption occurred at concentration of 200 ppm up to 3000 ppm followed Langmuir pattern. The value of free energy and the activation energy indicated physical adsorption. The IR spectra of protective layer formed by the inhibitor indicated that the JPE was maybe adsorbed on the surface of AISI 1037 carbon steel.

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