Engineering Chemistry, ISSN: 2813-6535, Vol. 9, pp 1-10

doi: 10.4028/p-ryFR6C

© 2025 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.

Submitted:
2024-11-19

Accepted:
2024-12-02

Online:
2025-03-10

Promising Organic Inhibitor of Salak (Salacca zalacca) Peel Extract on AISI 1040

Daffa Irsyad Darmawan , Muhammad Rifani , Muthia Putri Darsini Lubis , Hizkia Alpha Dewanto , Fredy Kurniawan e , Yusairie Mohd , Yunita Triana

Department of Material and Metallurgical Engineering, Institut Teknologi Kalimantan, Balikpapan 76127, Indonesia

Department of Chemistry, Institut Teknologi Sepuluh November, Surabaya 60111, Indonesia

Faculty of Applied Science, Universiti Teknologi MARA, Shah Alam, Selangor 40450, Malaysia

student.itk.ac.id, student.itk.ac.id, muthia_lubis@lecturer.itk.ac.id,

hizkia.ad@lecturer.itk.ac.id,

g*nita@lecturer.itk.ac.id

Keywords: AISI, Corrosion, Green, Inhibitors, Peel

Abstract

This study investigates the corrosion inhibition properties of Salak (Salacca zalacca) peel extract as a green inhibitor on AISI 1040 steel in a 1 M HCl acidic environment and focusing on secondary metabolites such as flavonoids and tannins. The qualitative phytochemical analysis showed antioxidant activity of the inhibitor extract was categorized as moderate with an IC50 value of 105.219 ppm . Functional group analysis using FTIR indicated that the flavonoids and tannins in the extract acted as antioxidants and inhibited corrosion growth. The weight loss test revealed the highest inhibition efficiency was achieved at a concentration of 200 ppm after 20 days of immersion. In the potentiodynamic polarization test, the corrosion rate was year at the same concentration and immersion time. These results suggest that Salak (Salacca zalacca) peel extract can effectively inhibit corrosion at spesific concentrations but its efficiency diminishes at higher concentrations.

Introduction

The original version of this paper is available on https://www.scientific.net/EC.9.1.pdf

Corrosion of metals is one of the matters with big losses in the world's industry [1], [2]. It can be seenthat the impact of corrosion on the domestic economy of various countries reaches of GDP. When damage is major, expensive maintenance and replacement is required for safe and reliable construction use, and even if the serviceability of the structure is not compromised, deterioration in appearance results in a decrease in the value of the construction.[3] Corrosion is generally known as material degradation, which is an event of damage or decrease in the quality of a material, especially metal, due to environmental reactions that provide an atmosphere for oxidation-reduction reactions [4]. A corrosion inhibitor is a chemical compound that, when added, can be attached to the material's surface and will be a protector against cove environments [5].
There are several ways to protect against corrosion, namely cathodic protection [6], and coatings [7] one of the effective alternative ways to protect against corrosion on metal surfaces is inhibitors (inorganic and organic) [8], [9]. The selection of inhibitors is not only based on their ability to inhibitor corrosion rates with high efficiency. Several methods have been used to reduce the corrosion rate ofcarbon steel corroded by acid solutions. Still, an effective use is the use of organic inhibitors [10-17], but also in terms of their level of toxicity when applied to industry against environmental pollution. For this reason, the use of inorganic inhibitors is limited, like that encouraging the development of alternative organic inhibitors or green inhibitors that are economical, easily renewable, biodegradable, and environmentally friendly from extracts of natural ingredients. Substances from natural sources exhibit antioxidants. Antioxidant compounds can be found in plantssuch as meat, roots, skin, stems, and leaves [18][22].

Salak (Salacca zalacca) is a species of palm tree (family Aracaceae) native to Indonesia. Consumerslike snake fruit with thick flesh, a sweet taste, and small seeds [19]. However, the results of the phytochemical test showed that the bark of the Salak (Salacca zalacca) fruit contained flavonoids and tannins. The ethanol extract of Salak (Salacca zalacca) fruit peels has antioxidant activity with an IC50 value of 49,45 [20] The presence of flavonoids and tannins from the bark extract of the zalacca fruit is the basis for supporting the utilization of the peel waste in this study. In addition to bark, many studies have used organic extracts on carbon steel with an HCl environmentamong sunflower seeds [21], peppers [23], jackfruit banana skin [24], and orange and mango peels [25].
In this study, the inhibitor was extracted from the bark of the Salak (Salacca zalacca) fruit cultivated at KM 21 Karang Joang. It was used as a corrosion inhibitor on AISI 1040 steel in a 1M HCl environment. The contentof AISI specimens were confirmed using OES. The 1,1- diphenyl-2picrylhydrazyl (DPPH) test wasused to determine the antioxidant activity of salak fruit bark (Salacca zalacca). The Fourier Transform Infra-Red (FTIR) technique confirmed the extract's functional groups of antioxidant compounds. Furthermore, the effects of inhibitor concentration and immersion time on inhibitor performance were reviewed through weight loss corrosion testing methods and polarization measurements. In addition, surface observations of AISI 1040 steel macrostructures were analyzed using a Scanning Electron Microscope (SEM).

Research MethodologyInhibitors Preparation

The original version of this paper is available on https://www.scientific.net/EC.9.1.pdf

Salak fruit skin (Salacca zalacca) obtained from KM 21 Karang Joang, North Balikpapan District, Balikpapan City, was dried by sunlight exposure for seven days. Inhibitor preparation was carried out by the maceration method by inserting 500 grams of dried zalacca skin and pulverizing it with a blender and 3000 mL of ethanol into a 5000 mL container. Immersion was carried out for 3 x 24 hours. Then the extraction results are separated between the filtrate and residue. After that, the evaporator and oven are carried out [26]

Secondary Metabolite Identification Method

The original version of this paper is available on https://www.scientific.net/EC.9.1.pdf

At this point testing was carried out to identify secondary metabolites, namely phytochemicals and DPPH. Phytochemical testing was done to determine the secondary metabolites contained in the skin extract of salak (Salacca zalacca), the compounds to be known were flavonoids and tannins.
After knowing the secondary metabolites of phytochemicals, then proceed with DPPH. Testing the antioxidant activity with 1,1- diphenyl-2-picrylhydrazyl (DPPH) aims to determine the antioxidant activity of salak (Salacca zalacca) bark extract.

Electrolyte Solution Preparation

The original version of this paper is available on https://www.scientific.net/EC.9.1.pdf

1 M HCl is produced from which the molar is 10.32 M , then HCl is diluted in 1 liter of distilled water to obtain a 1 M HCl solution [27].

Weight loss Method

The original version of this paper is available on https://www.scientific.net/EC.9.1.pdf

The sample used is AISI 1040 steel with a size of as shown in Fig.1. This test was done with the aim of knowing the resulting weight loss in the sample when immersed in a corrosive medium, namely 1 M HCl . This test was done with various inhibitor concentrations ( 0 ppm , , and 500 ppm ) and Immersion time ( 10 days, 20 days, and 30 days) [27]. Corrosiontesting with the weight loss method with ASTM G31-21 standard was repeated three times [28].

Fig. 1 Weight loss Method

Fig. 1. Weight loss Method

Electrochemical Experimental

The original version of this paper is available on https://www.scientific.net/EC.9.1.pdf

The polarization test was conducted using an autolab to gather corrosion rate data for AISI 1040 steel. This method employs a three-electrode setup which includes an reference electrode, a platinum auxiliary electrode, and AISI 1040 steel working electrode. This configuration allows precise measurement of the electrochemical behavior of the steel in the corrosive environtment and providing valuable insight into the effectiveness of the corrosion inhibitor based on concentration and soaking time as shown in Fig. 2.

Fig. 2 Schematic of three electrodes Electrochemical

Fig. 2. Schematic of three electrodes Electrochemical

Characterization

The original version of this paper is available on https://www.scientific.net/EC.9.1.pdf

Characterization testing was carried out to determine the functional groups content in Salak (Salacca zalacca) peel extract using Fourier Transform Infrared Spectroscopy (FTIR) to helped confirm the presence of key compounds such as flavonoids and tannins.ronScanning Electron Microscope with Energy Dispersive X-Ray ( SEM-EDX) test was carried out to observe the surface morphology of steel samples and allowing for a comparison of the extent surface damage with and without the application of inhibitors.

Results and Discussion

The original version of this paper is available on https://www.scientific.net/EC.9.1.pdf

Determination of Antioxidant Properties of Salak (Salacca zalacca) Peel Extract

The original version of this paper is available on https://www.scientific.net/EC.9.1.pdf

The results of the linear regression equation for the antioxidant activity of Salak (Salacca zalacca) peel extract was determined to be with a strong correlation coefficient of 0.91 , indicating a good fit of the data. Then, using the IC50 value is substituted for the y value as a free radical inhibitor value of so that the x value is obtained, which is the IC50 value. This provides a quantitative measure of the extract's antioxidant potential, helping to evaluate its effectiveness in reducing oxidative stress.

Table 1 Results of Measurement of Antioxidant Activity of 96% Ethanol Extract of Salak (Salacca zalacca) Peel with the DPPH method

Concentration (ppm) | Antioxidant Activity (%) | IC₅₀ (ppm) | Antioxidant Potential
0 | 0 | 105,219 | Medium
12,5 | 2,72
25 | 3,63
50 | 31,74
100 | 44,82 |  |

Qualitative Analysis of Secondary Metabolites of Salak (Salacca zalacca) Bark Extract

The original version of this paper is available on https://www.scientific.net/EC.9.1.pdf

Table 2 Phytochemical Test Results

Secondary Metabolites | Reactor | Results
Flavonoid | NaOH 1% + HCl 1% | +
Tanin | Lead (II) acetate (CH₃COO)₂ Pb 1% | +
Saponin | Aquadest + HCl | -
Alkaloid | HCl + dragendorf | -

Information:

: detected

: not detected

The phytochemical test results of the Salak (Salacca zalacca) bark extract revealed the presence of secondary metabolites specifically flavonoids and tannins which were detected through positive reactions in the assay. In contrast, the tests for alkaloids and saponins yielded negative results indicating their absence in the extract. These finding suggest that the corrosion inhibition properties of the extract may primarily be attributed to the flavonoid and tannins which are known for their antioxidant and metal-binding capabilities.

Analysis of Functional Groups in Salak (Salacca zalacca) Peel Extract

The original version of this paper is available on https://www.scientific.net/EC.9.1.pdf

Secondary metabolites in Salak (Salacca zalacca) peel extract play crucial role in the inhibition mechanism making it essential to analyze the constituent compounds involved. In this study, we conducted FTIR characterization was performed to identify these key secondary metabolite.Based on the FTIR result confirmed the presence of tannins and flavonoids which both are known to contribute the corrosion inhibition process due to their antioxidant properties and ability to form protective layers on metal surfaces.
Flavonoids contain several functional groups, including double bonds, single bonds, singlebonds, and O-H single bonds which contribute to their chemical reactivity. These functional groups play a significant role in the interaction of flavonoids with metal surfaces aiding in formation of a protetctive barrier against corrosion. Based on the molecular structure of the flavonoids detected in this assay suggest their potential effectiveness in the corrosion inhibiton process through antioxidant activity and adsorption onto metal surface.

Fig. 3 Structure of Flavonoid

Secondary metabolite compounds, namely tannins, contain functional groups such as and single bonds which contribute to their chemical properties. FTIR analysis confirmed the presence of tannins in Salak (Salacca zalacca) peel extract indicating their role in the inhibition mechanism in Fig. 4, tannin is a detectable compound.

Table 3 FTIR result of Salak (Salacca zalacca) skin

Wavenummber (cm⁻¹) | Frequency Area (cm⁻¹) | Chemical Bonds | Functional Group
3340,23 | 3200-3600 | O-H | Fenol
3010,54 | 3010-3100 | C-H | Aromatic Ring
2923,99 | 2850-2970 | C-H | Alkana
2853,93 | 2850-2970 | C-H | Alkana
2171,87 | 2100-2260 | C≡C | Alkuna
1718,54 | 1690-1760 | C = O | Aldehid, Keton
1514,54 | 1500-1600 | C = C | Aromatic Ring
1376,48 | 1300-1470 | C – H | Alkana
1223,99 | 1180-1360 | C – N | Amina, Amida
1155,99 | 1050-1300 | C – O | Alkohol, Eter, Hydroxycarboxylic acid, Ester
921,09 | 675-995 | C – H | Alkena
815,99 | 675-995 | C – H | Alkena
770,66 | 675-995 | C – H | Alkena
1718,54 | 1690-1760 | C = O | Aldehid, Keton
1514,54 | 1500-1600 | C = C | Aromatic Ring

Performance Analysis of Corrosion InhibitorsInhibition Efficiency

The original version of this paper is available on https://www.scientific.net/EC.9.1.pdf

In Table 4, it can be seen that the inhibition efficiency from concentrations of 0 to 500 ppm by soaking for 20 days

Table 4 Inhibiton Efficiency

Inhibitor
Concentration (ppm)
Sample Number
Initial Weight (gr)
Final Weight (gr)

0
1
10,225
8,591

2
10,582
8,649

3
10,449
8,584

100
1
10,240
8,602

2
10,257
8,553

3
10,498
8,791

200
1
10,130
8,659

2
10,223
8,640

3
10,180
8,414

300
1
10,393
8,667

2
10,195
8,512

3
10,534
8,236

400
1
10,847
8,921

2
11,055
8,324

3
10,894
8,750

Fig. 4 Inhibition Efficiency of Salak (Salacca zalacca) peel Extract in 1 M HCl Solution (a) Variation ofConcentration (b) Variation of Soaking Time

Fig. 4. Inhibition Efficiency of Salak (Salacca zalacca) peel Extract in 1 M HCl Solution (a) Variation ofConcentration (b) Variation of Soaking Time

Based on data from the most optimum concentration variation, the highest inhibition efficiency was observed at a concentration of 200 ppm , which was while the efficiency dropped drastically at 500 ppm to the significant reduction in efficiency at higher concentrations can be attributed to the saturation of adsorption sites on the steel surface. Once these sites are saturated, excess inhibitor molecules may aggregate and disrupt the uniform protective layer causing the metal surface to be exposed of the corrosive medium. On the concentration of 200 ppm , the Fig. 5 above explains that the highest inhibition efficiency was obtained with variations in soaking time at the optimum concentration of 200 ppm at 20 days of immersion time of .

Corrosion Rate

The original version of this paper is available on https://www.scientific.net/EC.9.1.pdf

The corrosion rate in Fig. 5 decreased from year to less than year at concentrations of 100 and 200 ppm ; then, the corrosion rate increased to more than 0.2 mm /year at concentrations of 300,400 , and 500 ppm . There is a correlation between the corrosion rate and the corrosion current ( ) so that the decrease in the corrosion rate both without and with the addition of inhibitors at each concentration indicates that the presence of an inhibitor in Salak (Salacca zalacca) bark extract helps inhibit the corrosion rate.

Fig. 5 Tafel Curve of Salak (Salacca zalacca) Peel Extract (a) Variation of Concentration(b) Variation of Soaking Time

Fig. 5. Tafel Curve of Salak (Salacca zalacca) Peel Extract (a) Variation of Concentration(b) Variation of Soaking Time

The polarization test results mirrored those of the weight loss test, showing the lowest corrosion rate at the concentration rate of 0.025 mm /year at a concentration of 200 ppm . The polarization measurements were consistent with the weight loss test results. The lowest corrosion rate combined with the highest inhibition efficiency was observed at a concentration of 200 ppm and a 20-day immersion period.

Inhibition Mechanism

The original version of this paper is available on https://www.scientific.net/EC.9.1.pdf

Fig. 6 Mechanism Inhibition

Fig. 6. Mechanism Inhibition

Salak (Salacca zalacca) peel extract is used to make corrosion inhibitors because Salak (Salacca zalacca) peel contains secondary metabolites that can stop corrosion growth. Flavonoids and tannins are secondary metabolites that play a role in this study.Flavonoids are plants that belong to the primary antioxidant class. They can end free radical reactionsby donating hydrogen or electrons to free radicals by turning them into a protective layer such as shown in Fig. 6. Flavonoidswith part of the hydrocarbon chain can prevent the metal surface from directly contacting the electrolyte because they are hydrophobic. Based on the results of the FTIR test, where Alkene C = C has hydrophobic properties. In addition, the functional groups of phenol and alcohol hydrogen bonds( O are hydrophilic functional groups. So that one end of the bond chain must be hydrophilic like OH so that this chain becomes a barrier for a corrosive environment for metals to come into direct contact. Then these functional groups undergo an adsorption process onto the metal surface to form aromatic groups so that the hydrophobic functional groups ( and ) will tend to reject water ions that react with the metal. Meanwhile, hydrophilic functional groups will tend to capture unwanted ions so they do not react with metals.

Fig. 7 Macrostructure Observation Results of AISI 1040 Steel (a) AISI 1040 Steel Without Treatment (b) AISI 1040 Steel with a Concentration of 0 ppm for 20 days of Soaking Time in 1 M HCl (c) AISI 1040 Steel with a Concentration of 200 ppm at 20 Days of Soaking Time in HCl 1 M
Tannins have the potential as corrosion inhibitors because of their properties which have complex compounds and polyphenolic compounds with structures that form macromolecules and contain hydroxyl groups (-OH), so they are able to absorb transition metals (Fig. 7). Tannins the complex compoundcan directly become a barrier (barrier) that will coat the metal and protect it from coming into direct contact with the solution. From the morphological results with 1000x magnification on AISI 1040 steel samples with and without inhibitors and without treatment can be seen in the following figure.

Fig. 7. Macrostructure Observation Results of AISI 1040 Steel (a) AISI 1040 Steel Without Treatment (b) AISI 1040 Steel with a Concentration of 0 ppm for 20 days of Soaking Time in 1 M HCl (c) AISI 1040 Steel with a Concentration of 200 ppm at 20 Days of Soaking Time in HCl 1 M Tannins have the potential as corrosion inhibitors because of their properties which have complex compounds and polyphenolic compounds with structures that form macromolecules and contain hydroxyl groups (-OH), so they are able to absorb transition metals (Fig. 7). Tannins the complex compoundcan directly become a barrier (barrier) that will coat the metal and protect it from coming into direct contact with the solution. From the morphological results with 1000x magnification on AISI 1040 steel samples with and without inhibitors and without treatment can be seen in the following figure.

Conclusion

The original version of this paper is available on https://www.scientific.net/EC.9.1.pdf

The results of the corrosion test using the weight loss method obtained the results with the highest inhibition efficiency concentrations of 200 ppm at . In the polarization test, the results with the lowest corrosion rate were obtained at a concentration of 200 ppm of year. The results in the corrosion test using the weight loss method obtained the highest inhibition efficiency with a 20 -day immersion time of . The Polarization test obtained the lowest corrosion rate at 20 days of immersion, which was year . The use of inhibitors of bark extract(Salacca zalacca) can reduce the corrosion rate of AISI 1040 steel in a 1 M HCl environment due to the influence of secondary metabolites, namely flavonoids and tannins, which act as protectors to prevent metals from interacting with electrolyte environments.

Acknowledgments

The original version of this paper is available on https://www.scientific.net/EC.9.1.pdf

Thank you for the facilities from Integrated Laboratory Kalimantan Institute of Technology and Research Center for Mining Technology, National Research and Innovation Agency (BRIN). Thank you for scientific suggestion and recommendation from Prof. Dr.rer.nat Fredy Kurniawan (Sepuluh November Institute of Technology) and Prof. Yusairie Mohd (Universiti Teknologi MARA, Shah Alam).

References

The original version of this paper is available on https://www.scientific.net/EC.9.1.pdf

S. Prifiharni et al., "Extract sarampa wood (Xylocarpus Moluccensis) as an eco-friendly corrosion inhibitor for mild steel in HCl 1M," Journal of the Indian Chemical Society, vol. 99, no. 7, Jul. 2022, doi: 10.1016/j.jics.2022.100520.

P. C. Okafor, X. Liu, and Y. G. Zheng, "Corrosion inhibition of mild steel by ethylamino imidazoline derivative in CO2-saturated solution," Corrosion Science, vol. 51, no. 4, pp. 761768, Apr. 2009, doi: 10.1016/j.corsci.2009.01.017.

R. Landolfo, L. Cascini, and F. Portioli, "Modeling of metal structure corrosion damage: A state of the art report," Sustainability, vol. 2, no. 7, pp. 2163-2175, 2010, doi: 10.3390/su2072163.

M. G., & G. N. D. Fontana, Corrosion Engineering McGraw-Hill book Company. New York, 1987.

K. Hu, J. Zhuang, J. Ding, Z. Ma, F. Wang, and X. Zeng, "Influence of biomacromolecule DNA corrosion inhibitor on carbon steel," Corrosion Science, vol. 125, pp. 68-76, Aug. 2017, doi: 10.1016/j.corsci.2017.06.004.

C.G. Soares, "SPECIAL ISSUE ON IMAM 2007." [Online]. Available:

W. Xu et al., "Corrosion of rail tracks and their protection," Corrosion Reviews, vol. 39, no. 1. De Gruyter Open Ltd, pp. 1-13, Feb. 01, 2021. doi: 10.1515/corrrev-2020-0069.

I. Radojčić, K. Berković, S. Kovač, and J. Vorkapić-Furač, "Natural honey and black radish juice as tin corrosion inhibitors," Corrosion Science, vol. 50, no. 5, pp. 1498-1504, May 2008, doi: 10.1016/j.corsci.2008.01.013.

Z. D. I. Esih, "Technology of Corrosion Protection," 1990.

H. Ashassi-Sorkhabi and E. Asghari, "Effect of hydrodynamic conditions on the inhibition performance of l-methionine as a 'green' inhibitor," Electrochimica Acta, vol. 54, no. 2, pp. 162-167, Dec. 2008, doi: 10.1016/j.electacta.2008.08.024.

X. Li, S. Deng, G. Mu, H. Fu, and F. Yang, "Inhibition effect of nonionic surfactant on the corrosion of cold rolled steel in hydrochloric acid," Corrosion Science, vol. 50, no. 2, pp. 420-430, Feb. 2008, doi: 10.1016/j.corsci.2007.08.014.

J. Aljourani, M. A. Golozar, and K. Raeissi, "The inhibition of carbon steel corrosion in hydrochloric and sulfuric acid media using some benzimidazole derivatives," Materials Chemistry and Physics, vol. 121, no. 1-2, pp. 320-325, May 2010, doi: 10.1016/j.matchemphys.2010.01.040.

M. Finšgar, S. Fassbender, F. Nicolini, and I. Milošev, "Polyethyleneimine as a corrosion inhibitor for ASTM 420 stainless steel in near-neutral saline media," Corrosion Science, vol. 51, no. 3, pp. 525-533, Mar. 2009, doi: 10.1016/j.corsci.2008.12.006.

Q. B. Zhang and Y. X. Hua, "Corrosion inhibition of mild steel by alkylimidazolium ionic liquids in hydrochloric acid," Electrochimica Acta, vol. 54, no. 6, pp. 1881-1887, Feb. 2009, doi: 10.1016/j.electacta.2008.10.025.

M. Seter, M. J. Thomson, J. Stoimenovski, D. R. MacFarlane, and M. Forsyth, "Dual active ionic liquids and organic salts for inhibition of microbially influenced corrosion," Chemical Communications, vol. 48, no. 48, pp. 5983-5985, May 2012, doi: 10.1039/c2cc32375c.

D. Gopi, K. M. Govindaraju, and L. Kavitha, "Investigation of triazole derived Schiff bases as corrosion inhibitors for mild steel in hydrochloric acid medium," Journal of Applied Electrochemistry, vol. 40, no. 7, pp. 1349-1356, Jul. 2010, doi: 10.1007/s10800-010-0092-z.

E. Kowsari, M. Payami, R. Amini, B. Ramezanzadeh, and M. Javanbakht, "Task-specific ionic liquid as a new green inhibitor of mild steel corrosion," Applied Surface Science, vol. 289, pp. 478-486, Jan. 2014, doi: 10.1016/j.apsusc.2013.11.017.

D. Bizuayehu, M. Atlabachew, and M. T. Ali, "Determination of some selected secondary metabolites and their invitro antioxidant activity in commercially available Ethiopian tea (Camellia sinensis)," SpringerPlus, vol. 5, no. 1, Dec. 2016, doi: 10.1186/s40064-016-2056-1.

N. Moonrungsee, N. Peamaroon, A. Boonmee, S. Suwancharoen, and J. Jakmunee, "Evaluation of tyrosinase inhibitory activity in Salak (Salacca zalacca) extracts using the digital image-based colorimetric method," Chemical Papers, vol. 72, no. 11, pp. 2729-2736, Nov. 2018, doi: 10.1007/s11696-018-0528-1.

M. S. M. Saleh, M. J. Siddiqui, S. Z. M. Soad, S. Murugesu, A. Khatib, and M. M. Rahman, "Antioxidant and -glucosidase inhibitory activities and gas chromatography-mass spectrometry profile of salak (Salacca zalacca) fruit peel extracts," Pharmacognosy Research, vol. 10, no. 4, pp. 385-390, Oct. 2018, doi: 10.4103/pr.pr_7_18.

H. Hassannejad and A. Nouri, "Sunflower seed hull extract as a novel green corrosion inhibitor for mild steel in HCl solution," Journal of Molecular Liquids, vol. 254, pp. 377-382, Mar. 2018, doi: 10.1016/j.molliq.2018.01.142.

M. J. B. Kabeyi and O. A. Olanrewaju, "Biogas Production and Applications in the Sustainable Energy Transition," Journal of Energy, vol. 2022, pp. 1-43, Jul. 2022, doi: 10.1155/2022/8750221.

M. M. Kamel, A. A. S. Fouda, S. M. Rashwan, and O. Abdelkader, "Paprika extract: a green inhibitor for mitigating carbon steel disintegration in 1 M HCl pickling solution," Green Chemistry Letters and Reviews, vol. 14, no. 4. Taylor and Francis Ltd., pp. 598-609, 2021. doi: 10.1080/17518253.2021.1985173.

G. Ji, S. Anjum, S. Sundaram, and R. Prakash, "Musa paradisica peel extract as green corrosion inhibitor for mild steel in HCl solution," Corrosion Science, vol. 90, pp. 107-117, Jan. 2015, doi: 10.1016/j.corsci.2014.10.002.

J. C. da Rocha, J. A. da Cunha Ponciano Gomes, and E. D'Elia, "Aqueous extracts of mango and orange peel as green inhibitors for carbon steel in hydrochloric acid solution," Materials Research, vol. 17, no. 6, pp. 1581-1587, Nov. 2014, doi: 10.1590/1516-1439.285014.

Q. Liu et al., "A novel green reinforcement corrosion inhibitor extracted from waste Platanus acerifolia leaves," Construction and Building Materials, vol. 260, Nov. 2020, doi: 10.1016/j.conbuildmat.2020.119695.

A. Berrissoul et al., "Evaluation of Lavandula mairei extract as green inhibitor for mild steel corrosion in 1 M HCl solution. Experimental and theoretical approach," Journal of Molecular Liquids, vol. 313, Sep. 2020, doi: 10.1016/j.molliq.2020.113493.

"ASTM-G31-72-1999-".

This ePub file was created using machine-generated methods and automated software to convert the source text into an ePub format and may contain formatting inconsistencies from the original version. Formatting may vary depending on the device used.