Evaluation of Leaf and Bark Extracts of Chrozophora Plicata as Corrosion Inhibitors for Mild Steel in HCl

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Madhanraj, P. K. Kasthuri This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6455610/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Metals and alloys are susceptible to corrosion, a severe occurrence that shortens the lifespan of metallic and alloyed items and lowers their value and efficiency. Developing affordable and environmentally friendly inhibitors from the many local plants found in Kanuvai, Tamilnadu, India, was the goal of this study. For the ethanolic extracts from leaves and barks, phytochemical screening was done. Flavonoids, phenolic chemicals, and polyphenols were identified as the main groupings. The effectiveness of the inhibitors was examined using electrochemical impedance spectroscopy as well as potentio-dynamic polarization curves. For CTL and CTB, the highest possible IE%s were 87.1% and 69.6%, respectively. Both extracts function as mixed type inhibitors, according to the results of the potentio-dynamic polarization (PDP) tests. An increase in polarization resistance is shown by the findings of electrochemical impedance spectroscopy (EIS) experiments, indicating the inhibitors' ability to inhibit. Competitive physio-sorption and chemisorption mechanisms are involved in the inhibitors' adsorption on the steel surface, which follows the Langmuir adsorption isotherm model. The influence of temperature on corrosion inhibition was examined using the EIS approach at temperatures between 298K and 328K. The findings verify that when temperature rises, the inhibition efficiency (IE%) of all inhibitors somewhat decreases. Both inhibitors' thermodynamic properties were computed. Corrosion Chrozophora Plicata leaves barks steel Figures Figure 1 Figure 2 Figure 3 Figure 4 1. INTRODUCTION Corrosion is an electrochemical process takes place between metallic materials and environment that causes degradation of metals, which results environment and process pollutions, eco- nomic losses and safety of process. Corrosion also leads serious problems such as changing physical appearance, mechanical properties and resistance of materials. The economics losses caused by corrosion is enormous, and has been estimated to be in the range of 1–5% of an industrialized country’s gross national product particularly in industrialized countries such as United States, Australia, Kuwait, Japan, Sweden, China and India [1, 2]. One of the most affected metals by corrosion is mild steel or its alloys which are the most important and widely used metals in various industrial and engineering applications due to their relatively low cost, high ductility, malleability, good mechanical resistance and easy availability [3, 4 ]. Before market, pickling and chemical cleaning applications are widely used to remove undesirable rust and scales. Concentrated HCl is one of the widely utilized agents for this aim [ 5 , 6 ]. In general, corrosion inhibitors that contain heteroatoms (such sulfur, oxygen, nitrogen, and phosphorus) can use their non-bonding electron pair to bind with the iron's unoccupied d orbital and prevent metal corrosion by creating a protective layer [ 6 , 7 ]. Additionally, by electrostatic attraction, molecules with polar groups and aromatic rings (such C = O, -NH 2 , -OH, etc.) can be easily adsorbed on the metal surface [ 8 , 9 ]. Despite having the aforementioned property and strong inhibition against harsh ions, certain commercial organic corrosion inhibitors lack two other characteristics (they may be costly and toxic) [ 10 – 12 ]. Finding a substitute that has all the desired qualities is therefore essential. Recently, green organic corrosion inhibitors, including plant extracts [ 12 ], expired drugs [ 13 ], and ionic liquids [ 14 ] with effective compounds, have been introduced as a substitution for toxic convectional corrosion inhibitors. Plant extracts, comprising leaf [ 15 ], fruit [ 16 ], and seed [ 17 ] extracts, are generally biocompatible, biodegradable, and cost-effective. Also, donor electron components such as aromatic groups, heteroatoms, and compounds with π electrons in plant extract can further confirm their potential to be used as potent corrosion inhibitors [18–21]. The root extract of Valeriana wallichii acts as mixed type inhibitor and recorded high efficiency as corrosion inhibitor for mild steel [ 22 ]. Extracts of both treated and untreated waste of date palm tree including fiber and leaflets recorded efficiency of 78–81% for carbon steel in the presence of gum Arabic solution [ 23 ]. Pongamia Pinnata was examined as a an eco-friendly corrosion Inhibitor for Mild Steel in 1N sulfuric acid medium, the efficiency of the extract was found to be 95% [ 24 ]. The assessment of plant extracts on steel corrosion has been the subject of extensive investigation. Nevertheless, relatively little study has examined how plant extracts affect mild steel's corrosion behavior. Therefore, the purpose of this study was to examine how well Chrozophora plicata leaf and bark extracts inhibited mild steel corrosion. 2. EXPERIMENTAL 2.1. Plant sample collection Leaves and barks of C. Plicata abbreviated as CTL and CTB, respectively, were collected in April/May 2024 from some areas around Coimbatore city, Tamil Nadu, India. Barks and leaves were rinsed thoroughly with tap water to get rid of soil particles followed by bi-distilled water. The barks were cut into small pieces and air-dried under shade at room temperature for two weeks. Samples were later ground to fine powder to give 400 g of barks and 200 g of leaves. 2.2. Extraction of plant samples Each sample was macerated in aqueous ethanol (ethanol: water, 80% v/v) at room temperature for 3 to 5 days with occasionally stirring. Extract was collected after each 36 h by decantation and fresh solvent was added to the residue. Collected extracts were filtered through Whatman No 1 filter paper, combined and concentrated to dryness under reduced pressure at 40°C using a rotary evaporator. The obtained concentrated extracts were weighed and stored in a refrigerator (− 4°C), until used for analyses. 2.3. Scanning and verification of extract 2.3.1. Phytochemical Screening of the Crude Extracts: The ethanolic extracts were subjected to preliminary phytochemical screening for different phytoconstituents (alkaloids, saponins, glycosides, flavonoids, tannins, triterpenes, anthraquinones and phenolic compounds) by adopting standard protocols [ 25 ]. 2.3.2. Determination of Total Phenolic and Flavonoid Contents: The total phenolic content (TPC) in the extracts were estimated calorimetrically using the Folin-Ciocalteau method with slight modification [ 26 , 27 ]. An aliquot of 0.5 mL of each plant extract (1mg/mL) was mixed with 2.5 ml of 0.2N Folin-Ciocalteau reagent (Sigma–Aldrich) for 5 min. 2.0 mL of 7.5% sodium carbonate solution were then added. The mixture was allowed to stand for 2 h at room temperature for colour development. E Gallic acid standards were used to produce the calibration curve which was analysed in the same way as the plant extract and total phenolic was expressed as Gallic acid equivalents (mg GAE /g of plant extract). 2.4. Steel samples Most of the equipment of the desalination plant are made of mild steel, the composition of this alloys is: (0.189% C, 0.175% Si, 0.572% Mn, 0.197% Cu, 0.058% S and Fe balance. The dimensions of samples which used throughout all tests are 2.0 × 2.0 × 0.08 cm. 2.5. Corrosion measurements 2.5.1. Mass loss measurements Before each test, the surfaces of all samples were abraded using emery papers of 1200, 800, 320 and 180 grades, then rinsed thoroughly with bi-distilled water, degreased and dried with acetone. Mass loss measurements were performed at 298K for 6, 12, 18 and 24 h. 2.5.2. Electrochemical tests The electrochemical experiments were performed by using a potentiostat Gamry interface 1000 No. 06094 USA directed by Framework 7.07 software. A cell with three electrodes was connected with the thermostat. A Pt electrode and saturated calomel electrode were used as auxiliary and reference electrodes, respectively. The same material was used for both gravimetric and electrochemical experiments. Potentiodynamic polarization (PDP) tests were performed at a scan rate of 1.0 mV/s. The polarization curves were attained from − 1000 mV to 1000 mV. The same device (Gamry interface 1000) was used to perform electrochemical impedance spectroscopy (EIS) measurements. The steady-state current at a corrosion potential was measured before the sine wave voltage (10 mV) peak to peak at frequencies ranging from 104 Hz to 10 − 3 Hz is superimposed on the rest potential. After an hour of contact at 298 K, computer programs automatically controlled the measurements made at rest potentials. Nyquist plots are used to create the EIS diagrams. Experiments were conducted at temperatures between 298 and 328 K to examine how temperature affects the efficiency of inhibitors. All tests were run three times to ensure reproducibility. 3. RESULTS AND DISCUSSION 3.1. Phytochemical Screening of the Crude Extracts The phytochemical screening of CTL and CTB revealed positive tests of phenolics, flavonoids, glycosides, tannins, steroids and Saponins and negative tests of alkaloids and anthraquinones. 3.2. Determination of Total Phenolic and Flavonoid Contents: The main classes of chemicals that function as principal antioxidants or free radical scavengers are polyphenols, which include flavonoids and phenolic compounds. Their capacity to give free radicals hydrogen atoms and their stability as radical intermediates are the foundations of their antioxidant activity. When it comes to absorbing and neutralizing free radicals, quenching singlet and triplet oxygen, or breaking down peroxides, these redox characteristics can be crucial [ 28 ]. Total phenolic contents are quantified as Gallic acid equivalents by reference to regression equation (y = 11.861x + 0.0001, R2 = 0.9929). Values of total phenols are expressed as means ± standard deviation for three replicate measurements. The total phenolic contents of CTL and CTB are 115.90 ± 0.25 mg 263.03 ± 0.06 GAE/g, respectively. Flavonoid content was calculated from the regression equation of the standard curve (y = 28.5655x + 0.1608, R2 = 9876) and expressed as mg quercetin equivalents (QE) per gram of dried plant extract. The leave extract of Chrozophora Plicata has high flavonoid content (77.03 ± 0.12), while the barks of Chrozophora Plicata contains only 3.28 ± 0.00 mg QE/g. 3.3. Mass loss measurements The influence of adding several concentrations of CTL and CTB to the corrosive medium were examined by using mass loss method at 298 K. The loss in the weight of steel pieces in uninhibited and inhibited seawater was determined. Eq. (1) was used to determine the corrosion rate in millimetres per year (mm y − 1 ): C RM = \(\:\frac{KxW}{Ax\:t\:x\:{\rho\:}}\) (1) where K = 8.76×104 was used as constant. W and t are the mass loss in grams and the exposure time in hours. According to ASTM G1-03 standard [ 29 ], the density of steel is 7.86 g cm − 3. The exposed area, A (in cm 2 ) was calculated from Eq. (2) [ 30 ]: A= \(\:\frac{\pi\:}{2}\) (D 2 – d 2 ) + lπD + lπd (2) where D, d and l are the diameter of mild steel pieces, the diameter of the hole for holding and the thickness, respectively. Equations 3 and 4 were used to calculate the inhibition efficiency inhibitor efficiency 𝐼𝐸 𝑀𝐿 % and the surface coverage (θ): \(\:ƞ\) WL (%) = C 0 WL – C WL / C 0 WL X 100 (3) θ = C 0 WL – C WL / C 0 WL (4) Where C WL ° and C WL are the corrosion rates without and with various concentrations of the inhibitors, respectively, θ is the degree of surface coverage of tested inhibitors. Table 1 summarizes the obtained results. The inhibition efficiency and the corrosion rates of the steel in presence of inhibitors were found to increase continuously with an increase in their concentration. The order of the inhibition efficiencies at the same concentration is CTL > CTB. The results support the hypothesis states that by increasing the concentration of inhibitors, the adsorption of inhibitors will be gradually increased, leading to a complete blockage of corrosion of active sites except 1-θ of exposed surface area. Table 1 Weight loss data of steel samples in uninhibited and inhibited at 298K. Inhibitors C (g/L) C(mg.cm − 2 .h -1 ) η WL % Ɵ Blank - 1.231 - - CTL 0.25 0.412 64.2 0.642 0.50 0.358 72.4 0.724 1.00 0.214 82.4 0.824 1.50 0.125 88.5 0.885 CTB 0.25 0.552 50.2 0.502 0.50 0.478 59.3 0.593 1.00 0.407 64.8 0.648 1.50 0.339 70.6 0.706 3.4. Stability of the inhibitors Weight loss tests were conducted in seawater with the optimal concentration of the inhibitors for different immersion lengths in order to evaluate the stability of the inhibitors' inhibitive layer and determine how long it would take for the inhibitors to reach the maximum IE%. Figure 1 presents the findings. It's clear that as immersion duration grows, IE% falls. The greatest efficacy was noted between one and six hours of immersion. There was a noticeable drop in efficacy when the immersion period was extended to 24 hours. These outcomes could occur from the inhibitor layer's instability or from the plant extracts' biodegradable nature over extended interaction [ 31 , 32 ]. 3.5. Electrochemical measurements 3.5.1. Potentiodynamic polarization curves Figure 2 shows the Tafel polarization plots of different concentrations of CTL and CTB, respectively. The kinetic factors viz. corrosion current density (Icorr), anodic Tafel slopes, cathodic Tafel slopes (bc) and corrosion potential (Ecorr) were attained from these plots and are given in Table 2 . Values of EI% were determined using Eq. 5: IE % = I 0 corr - I corr / I 0 corr x 100 (5) where I°corr and Icorr are corrosion current densities of the steel samples without and with the inhibitors, respectively. Table 2 's results show that as the concentration of the inhibitors increased, Icorr values gradually reduced. The values of the cathodic Tafel slopes, bc, and anodic Tafel slopes, ba, clearly differ, with the exception of the lowest concentration, suggesting that the addition of inhibitors has no effect on the mechanism of the proton discharge reaction. Table 2 Electrochemical parameters of steel at various concentrations of CTL and CTB in sea water and corresponding inhibition efficiency. Inhibitors Con. (g/L) -Ecorr (mV/SCE) Icorr (µA cm-2) Ba (mVdec -1 ) -bc (mV dec -1 ) IE I corr Blank - 461 1425 153 221 ---- CTL 0.25 472 574 175 212 59.4 0.50 508 426 185 184 70.5 1.00 519 268 169 190 80.9 1.50 538 176 172 194 87.1 CTB 0.25 481 731 170 175 49.6 0.50 494 611 169 182 57.2 1.00 512 529 187 196 63.9 1.50 482 437 173 180 69.6 Figure (2) reveals that all inhibitors suppressed both anodic and cathodic currents confirming mixed type inhibitor. IE% increases as the inhibitor concentration increases reaching a maximum values 87.1% and 69.6% for ATL and ATB, respectively. 3.5.2. Electrochemical impedance spectroscopy (EIS) The EIS experiments were performed in uninhibited and inhibited seawater to obtain more information about the corrosion inhibition mechanism of the mild steel. EIS results are showed as Nyquist plots in Fig. 3 . The semicircles of EIS experiments were slightly depressed compared to those derived from the theory of EIS. The imperfectness of capacitive loop is a common behaviour and it is attributed to the result of the heterogeneity, frequency dispersion and roughness of the steel surface [ 33 , 34 ]. Curves have been obtained after 60 minutes of soaking the electrodes in the required concentration (open circuit potential). It is clear from Fig. 3 that single capacitive loops have been obtained for all inhibitors indicating that the mild steel dissolution at metal/seawater interface is controlled by charge transfer process. The inhibition efficiencies, EI Rt (%) are displayed in Table 3 . Table 3 Electrochemical Impedance parameters for corrosion of the steel sample at various concentrations of the inhibitors at 298K. Inhibitors Con. (g/L) Rt (Ω.cm2) Q x 10 − 4 (S n Ω -1 cm -1 ) (10 4 ) C dl (µF/cm 2 ) EI Rt (%) Blank - 14 2.68 145.2 - CTL 0.25 35 2.36 58.1 89.6 0.50 38 1.96 36.5 62.4 1.00 68 1.74 22.8 80.6 1.50 109 1.64 6.7 87.1 CTB 0.25 25 2.54 64.2 51.6 0.50 29 2.36 45.2 56.3 1.00 40 2.12 31.4 66.5 1.50 49 1.95 11.8 72.4 In order to determine Rt values, the high frequency impedance was subtracted from the low frequency one as shown in Eq. 6: R t = Z re (at low frequency) – Z re (at high frequency) (6) C dl values (electrochemical double layer) were determined at the frequency f max , when the imaginary component of the impedance has a maximum value (-Z max ) by Eq. 7: 𝐶 𝑑𝑙 = 1 2𝜋𝑓 𝑚𝑎𝑥 /𝑅 𝑡 (7) The inhibition efficiency IE%(EIS) is determined by using Eq. 8: 𝐸𝐼% (𝐸𝐼𝑆) = R t o – R t / R t o x 100 (8) where 𝑅 𝑡 𝑜 and 𝑅 𝑡 and are the charge transfer resistance values without and with the presence of the inhibitor, respectively. Table 3 makes it clear that when all inhibitors are present, the resistance levels rise. This can be attributed to the molecules' ability to prevent rusting. Additionally, it is evident that while the inhibitor is present, Cdl values drop. This might be explained by a decrease in the local dielectric constant and/or an increase in the depth of the electric double layer [ 35 , 36 ], suggesting that inhibitor molecules are adsorbing at the metal contact. The constant replacement of water molecules by adsorption inhibitor molecules on the steel surface, which lowers the degree of iron oxidation, is probably the cause of the drop in Cdl values and the increase in Rt values and, consequently, the increase in IE% [ 37 , 38 ]. The EIS test findings and the polarization test results are in good agreement. 3.6. Adsorption study Adsorption study aims to discover the way by which the inhibitor molecules interact with the steel surface. Values of surface coverage, θ, at various inhibitor concentrations at 298K (Table 1 ) were employed to determine the adsorption isotherm. θ values were calculated by using Eq. 9: Ɵ= W corr o – W corr / W corr o (9) There are many models of adsorption isotherms such as, Freundluich, D-R, Temkin and Langmuir isotherms. Application of Eq. 10 gives straight lines with slope values of 1.044, and 1.056 for CTL and CTB respectively. Also, good correlation coefficient (R2 > 0.987) was obtained proving that the adsorption of the inhibitor molecules from seawater on the steel surface follows the Langmuir model. C inh / θ = 1/ k ads + C inh (10) With ∆G ads = −𝑅𝑇 𝑙𝑛 ( 𝐾𝑎𝑑𝑠 𝑥 999) (11) Values of equilibrium adsorption constant (K ads ) were determined from the intercept of Eq. 10 and ΔG ads values were calculated from Eq. 11. Results are shown in Table 4 . Table 4 Values of 𝐾 𝑎𝑑𝑠 and ∆𝐺 𝑎𝑑𝑠 for the adsorption process of CTL and CTB on mild steel at 298K. Inhibitor 𝐾 𝑎𝑑𝑠 ΔG ads CTL CTB 6.15 5.28 -21.5 -21.3 Table 4 's results show that the adsorption process is likely spontaneous because the adsorption free energy values are negative. According to previously published data, the process is most likely classified as chemisorption when the value of ∆𝐺𝑎𝑑𝑠 ∼ −40 kJ/mol or more negative, and as physio-sorption if ∆𝐺𝑎𝑑𝑠 ∼ −20 kJ/mol or less negative. The findings of this investigation indicate that both chemical and physical interactions occurred [39–41]. 3.7. Effect of temperature (EIS) technique was adapted to explore the effect of temperature on the inhibition process and to obtain some thermodynamic parameters of the corrosion process. EIS experiments were performed at temperature range of 298–328 K without and with the optimal concentration of the inhibitors (Fig. 4 ). Table 5 Effect of temperature on the adsorption of various inhibitors (1.50 g/L) in the carbon steel at different temperatures. Inhibitors T (K) Rt (Ω.cm2) Q x 10 − 4 (S n Ω -1 cm -1 ) C dl (µF/cm 2 ) EI Rt (%) Blank 298 12 2.68 142.2 - 308 9 2.74 116 - 318 6 2.94 128 - 328 5 3.25 83 - CTL 298 103 1.60 28 87.2 308 58 1.87 42 80.4 318 34 1.95 58 78.2 328 18 2.24 73 73.5 CTB 298 46 1.96 36 72.6 308 26 2.24 48 67.5 318 18 2.45 61 58.6 328 12 2.72 86 54.1 The findings in Table 5 demonstrate that in both inhibited and uninhibited medium, the values of charge transfer resistance (Rt) decrease with increasing temperature. Additionally, Table 5 shows that as the temperature rose, the IE% values in the presence of all inhibitors somewhat dropped. This is probably due to the possibility of high temperatures during the desorption process. These findings demonstrate that CTL is an effective inhibitor over the temperature range under study. Since its IE% dropped to just 54% at 328 K, it is evident that CTB efficiency is temperature dependant. Inhibitors derived from plants frequently exhibit this behavior [ 42 , 43 ]. 4. CONCLUSION CTL and CTB were applied to mild steel to prevent corrosion. The investigation was conducted using a variety of methods, including electrochemical measurements and weight loss. CTB exhibits moderate to poor inhibition efficacy, whereas CTL exhibits strong inhibition efficiency. According to the Langmuir adsorption model, the study shows that both CTL and CTB block the anodic and cathodic processes (mixed-typed inhibitor). The findings indicated that both inhibitors' effectiveness declined over time. Declarations Author Contribution 1-3: All authors reviewed the manuscprit References Verma C , Ebenso EE , Quraichi MA . Corrosion inhibitors for ferrous and non ferrous metals and alloys in ionic sodium chloride solutions: A review. J Mol Liq 2017;248:927–42 . Meng HY , Ma X , Zhu H , Li J , Li C , Cao D . Experimental and theoretical studies of benzothiazole derivatives as corrosion inhibitors for carbon steel in 1M HCl. Corros Sci 2016;112:563–75 . 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Salghi, IM. Chung, Y. El Aoufir, K. S Bhat, I. H. Ali, S. L. Gaonkar, M. I. Khan and H. Oudda, Journal of Adhesion Science and Technology, /doi.org/10.1080/01694243.2018.1554764. L. Bammou, M. Belkhaouda, R. Salghi, O. Benali, A. Zarrouk, H. Zarrok and B. Hammouti, Journal of the Association of Arab Universities for Basic and Applied Sciences, 16 (2014) 83. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Madhanraj","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA/klEQVRIiWNgGAWjYHACMxCRwMDA2MDAwGMDZDM2HiBeywGZNJCWBmK1AMEBm8MQGp963fbD2x783GGXxy92uPnzh5zzdmvbDwNtqbGJxmnFmbRyw94zycWSsxPbJA6cuZ287UwiUMuxtNwGXFoO5JhJ8LYdSNxwO7GN4WDP7WSzA0AtjA2HcWs5/8ZM8i9Qy/7bic0fDv47l2x2/iEBLTdyzKTBtkgnNkgc4DlgZ3aDkC03npVJy7YlJ84AOkziDE9ygtkNoC0J+PxyPnmb5Ns2u8T+2emPP1Tw2NmbnU9/+OBDjQ1OLRggEawygVjlIGBPiuJRMApGwSgYGQAABHZtBPloC3QAAAAASUVORK5CYII=","orcid":"","institution":"LRG College of Arts and Science For Women","correspondingAuthor":true,"prefix":"","firstName":"L.","middleName":"","lastName":"Madhanraj","suffix":""},{"id":443958095,"identity":"eac63c4a-dbdb-4e60-9494-88aad8e1bdec","order_by":1,"name":"P. K. Kasthuri","email":"","orcid":"","institution":"Government Arts College","correspondingAuthor":false,"prefix":"","firstName":"P.","middleName":"K.","lastName":"Kasthuri","suffix":""}],"badges":[],"createdAt":"2025-04-15 14:08:12","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6455610/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6455610/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":80800775,"identity":"8186425a-25ed-4ab2-a4fe-f18425f948bc","added_by":"auto","created_at":"2025-04-17 08:32:06","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":12207,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of immersion time on the inhibition efficiency, for mild steel in at 298K.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6455610/v1/287af8b77aa0217e77368607.png"},{"id":80801729,"identity":"7680cf4e-1460-4c4a-80a6-20343b3de7e1","added_by":"auto","created_at":"2025-04-17 08:40:07","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":194331,"visible":true,"origin":"","legend":"\u003cp\u003ePotentiodynamic polarization curves of steel in the presence of different concentrations of (A) CTL (B) CTB\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6455610/v1/9e516156aab5abe544fb1a39.png"},{"id":80801730,"identity":"12ac3fb8-98c7-42cc-941b-a0e7906ab0ae","added_by":"auto","created_at":"2025-04-17 08:40:07","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":92394,"visible":true,"origin":"","legend":"\u003cp\u003eNyquist diagrams for carbon steel electrode with and without (A) CTL and (B) CTB after 60 minutes of OCP.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6455610/v1/44257ee854bfc852e43b4722.png"},{"id":80800786,"identity":"e52bcaf5-7a99-44ea-9606-5d43dd506ca0","added_by":"auto","created_at":"2025-04-17 08:32:07","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":74779,"visible":true,"origin":"","legend":"\u003cp\u003eNyquist diagrams for mild steel at different temperatures for (A) CTL (B) CTB (C) Blank\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6455610/v1/a86962e0ac17d9541f789d25.png"},{"id":80837932,"identity":"aa255ee9-922c-4c13-afcb-8948e87a993f","added_by":"auto","created_at":"2025-04-17 15:16:52","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1303660,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6455610/v1/e4d6ac5a-a736-4155-ac8e-94cd4b21aa26.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Evaluation of Leaf and Bark Extracts of Chrozophora Plicata as Corrosion Inhibitors for Mild Steel in HCl","fulltext":[{"header":"1. INTRODUCTION","content":"\u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eCorrosion is an electrochemical process takes place between metallic materials and environment that causes degradation of metals, which results environment and process pollutions, eco- nomic losses and safety of process. Corrosion also leads serious problems such as changing physical appearance, mechanical properties and resistance of materials. The economics losses caused by corrosion is enormous, and has been estimated to be in the range of 1\u0026ndash;5% of an industrialized country\u0026rsquo;s gross national product particularly in industrialized countries such as United States, Australia, Kuwait, Japan, Sweden, China and India [1, 2]. One of the most affected metals by corrosion is mild steel or its alloys which are the most important and widely used metals in various industrial and engineering applications due to their relatively low cost, high ductility, malleability, good mechanical resistance and easy availability [3, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Before market, pickling and chemical cleaning applications are widely used to remove undesirable rust and scales. Concentrated HCl is one of the widely utilized agents for this aim [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e6\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn general, corrosion inhibitors that contain heteroatoms (such sulfur, oxygen, nitrogen, and phosphorus) can use their non-bonding electron pair to bind with the iron's unoccupied d orbital and prevent metal corrosion by creating a protective layer [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Additionally, by electrostatic attraction, molecules with polar groups and aromatic rings (such C\u0026thinsp;=\u0026thinsp;O, -NH\u003csub\u003e2\u003c/sub\u003e, -OH, etc.) can be easily adsorbed on the metal surface [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Despite having the aforementioned property and strong inhibition against harsh ions, certain commercial organic corrosion inhibitors lack two other characteristics (they may be costly and toxic) [\u003cspan additionalcitationids=\"CR11\" citationid=\"CR9\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Finding a substitute that has all the desired qualities is therefore essential.\u003c/p\u003e \u003cp\u003eRecently, green organic corrosion inhibitors, including plant extracts [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e12\u003c/span\u003e], expired drugs [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e13\u003c/span\u003e], and ionic liquids [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e14\u003c/span\u003e] with effective compounds, have been introduced as a substitution for toxic convectional corrosion inhibitors. Plant extracts, comprising leaf [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e15\u003c/span\u003e], fruit [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e16\u003c/span\u003e], and seed [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e17\u003c/span\u003e] extracts, are generally biocompatible, biodegradable, and cost-effective. Also, donor electron components such as aromatic groups, heteroatoms, and compounds with π electrons in plant extract can further confirm their potential to be used as potent corrosion inhibitors [18\u0026ndash;21]. The root extract of Valeriana wallichii acts as mixed type inhibitor and recorded high efficiency as corrosion inhibitor for mild steel [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Extracts of both treated and untreated waste of date palm tree including fiber and leaflets recorded efficiency of 78\u0026ndash;81% for carbon steel in the presence of gum Arabic solution [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Pongamia Pinnata was examined as a an eco-friendly corrosion Inhibitor for Mild Steel in 1N sulfuric acid medium, the efficiency of the extract was found to be 95% [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e24\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe assessment of plant extracts on steel corrosion has been the subject of extensive investigation. Nevertheless, relatively little study has examined how plant extracts affect mild steel's corrosion behavior. Therefore, the purpose of this study was to examine how well Chrozophora plicata leaf and bark extracts inhibited mild steel corrosion.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e"},{"header":"2. EXPERIMENTAL","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Plant sample collection\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eLeaves and barks of C. Plicata abbreviated as CTL and CTB, respectively, were collected in April/May 2024 from some areas around Coimbatore city, Tamil Nadu, India. Barks and leaves were rinsed thoroughly with tap water to get rid of soil particles followed by bi-distilled water. The barks were cut into small pieces and air-dried under shade at room temperature for two weeks. Samples were later ground to fine powder to give 400 g of barks and 200 g of leaves.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Extraction of plant samples\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eEach sample was macerated in aqueous ethanol (ethanol: water, 80% v/v) at room temperature for 3 to 5 days with occasionally stirring. Extract was collected after each 36 h by decantation and fresh solvent was added to the residue. Collected extracts were filtered through Whatman No 1 filter paper, combined and concentrated to dryness under reduced pressure at 40\u0026deg;C using a rotary evaporator. The obtained concentrated extracts were weighed and stored in a refrigerator (\u0026minus;\u0026thinsp;4\u0026deg;C), until used for analyses.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Scanning and verification of extract\u003c/h2\u003e \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e \u003ch2\u003e2.3.1. Phytochemical Screening of the Crude Extracts:\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eThe ethanolic extracts were subjected to preliminary phytochemical screening for different phytoconstituents (alkaloids, saponins, glycosides, flavonoids, tannins, triterpenes, anthraquinones and phenolic compounds) by adopting standard protocols [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e25\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003e2.3.2. Determination of Total Phenolic and Flavonoid Contents:\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eThe total phenolic content (TPC) in the extracts were estimated calorimetrically using the Folin-Ciocalteau method with slight modification [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. An aliquot of 0.5 mL of each plant extract (1mg/mL) was mixed with 2.5 ml of 0.2N Folin-Ciocalteau reagent (Sigma\u0026ndash;Aldrich) for 5 min. 2.0 mL of 7.5% sodium carbonate solution were then added. The mixture was allowed to stand for 2 h at room temperature for colour development. E Gallic acid standards were used to produce the calibration curve which was analysed in the same way as the plant extract and total phenolic was expressed as Gallic acid equivalents (mg GAE /g of plant extract).\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e2.4. Steel samples\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eMost of the equipment of the desalination plant are made of mild steel, the composition of this alloys is: (0.189% C, 0.175% Si, 0.572% Mn, 0.197% Cu, 0.058% S and Fe balance. The dimensions of samples which used throughout all tests are 2.0 \u0026times; 2.0 \u0026times; 0.08 cm.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e2.5. Corrosion measurements\u003c/h2\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003e2.5.1. Mass loss measurements\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eBefore each test, the surfaces of all samples were abraded using emery papers of 1200, 800, 320 and 180 grades, then rinsed thoroughly with bi-distilled water, degreased and dried with acetone. Mass loss measurements were performed at 298K for 6, 12, 18 and 24 h.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section3\"\u003e \u003ch2\u003e2.5.2. Electrochemical tests\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eThe electrochemical experiments were performed by using a potentiostat Gamry interface 1000 No. 06094 USA directed by Framework 7.07 software. A cell with three electrodes was connected with the thermostat. A Pt electrode and saturated calomel electrode were used as auxiliary and reference electrodes, respectively. The same material was used for both gravimetric and electrochemical experiments. Potentiodynamic polarization (PDP) tests were performed at a scan rate of 1.0 mV/s. The polarization curves were attained from \u0026minus;\u0026thinsp;1000 mV to 1000 mV.\u003c/p\u003e \u003cp\u003eThe same device (Gamry interface 1000) was used to perform electrochemical impedance spectroscopy (EIS) measurements. The steady-state current at a corrosion potential was measured before the sine wave voltage (10 mV) peak to peak at frequencies ranging from 104 Hz to 10\u0026thinsp;\u0026minus;\u0026thinsp;3 Hz is superimposed on the rest potential. After an hour of contact at 298 K, computer programs automatically controlled the measurements made at rest potentials. Nyquist plots are used to create the EIS diagrams. Experiments were conducted at temperatures between 298 and 328 K to examine how temperature affects the efficiency of inhibitors. All tests were run three times to ensure reproducibility.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"3. RESULTS AND DISCUSSION","content":"\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Phytochemical Screening of the Crude Extracts\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eThe phytochemical screening of CTL and CTB revealed positive tests of phenolics, flavonoids, glycosides, tannins, steroids and Saponins and negative tests of alkaloids and anthraquinones.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Determination of Total Phenolic and Flavonoid Contents:\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eThe main classes of chemicals that function as principal antioxidants or free radical scavengers are polyphenols, which include flavonoids and phenolic compounds. Their capacity to give free radicals hydrogen atoms and their stability as radical intermediates are the foundations of their antioxidant activity. When it comes to absorbing and neutralizing free radicals, quenching singlet and triplet oxygen, or breaking down peroxides, these redox characteristics can be crucial [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e28\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTotal phenolic contents are quantified as Gallic acid equivalents by reference to regression equation (y\u0026thinsp;=\u0026thinsp;11.861x\u0026thinsp;+\u0026thinsp;0.0001, R2\u0026thinsp;=\u0026thinsp;0.9929). Values of total phenols are expressed as means\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation for three replicate measurements. The total phenolic contents of CTL and CTB are 115.90\u0026thinsp;\u0026plusmn;\u0026thinsp;0.25 mg 263.03\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06 GAE/g, respectively.\u003c/p\u003e \u003cp\u003eFlavonoid content was calculated from the regression equation of the standard curve (y\u0026thinsp;=\u0026thinsp;28.5655x\u0026thinsp;+\u0026thinsp;0.1608, R2\u0026thinsp;=\u0026thinsp;9876) and expressed as mg quercetin equivalents (QE) per gram of dried plant extract. The leave extract of Chrozophora Plicata has high flavonoid content (77.03\u0026thinsp;\u0026plusmn;\u0026thinsp;0.12), while the barks of Chrozophora Plicata contains only 3.28\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00 mg QE/g.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e3.3. Mass loss measurements\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eThe influence of adding several concentrations of CTL and CTB to the corrosive medium were examined by using mass loss method at 298 K. The loss in the weight of steel pieces in uninhibited and inhibited seawater was determined. Eq.\u0026nbsp;(1) was used to determine the corrosion rate in millimetres per year (mm y\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e):\u003c/p\u003e \u003cp\u003eC\u003csub\u003eRM\u003c/sub\u003e = \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\frac{KxW}{Ax\\:t\\:x\\:{\\rho\\:}}\\)\u003c/span\u003e\u003c/span\u003e (1)\u003c/p\u003e \u003cp\u003ewhere K\u0026thinsp;=\u0026thinsp;8.76\u0026times;104 was used as constant. W and t are the mass loss in grams and the exposure time in hours. According to ASTM G1-03 standard [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e29\u003c/span\u003e], the density of steel is 7.86 g cm\u0026thinsp;\u0026minus;\u0026thinsp;3. The exposed area, A (in cm\u003csup\u003e2\u003c/sup\u003e) was calculated from Eq.\u0026nbsp;(2) [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e30\u003c/span\u003e]:\u003c/p\u003e \u003cp\u003eA= \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\frac{\\pi\\:}{2}\\)\u003c/span\u003e\u003c/span\u003e (D\u003csup\u003e2\u003c/sup\u003e \u0026ndash; d\u003csup\u003e2\u003c/sup\u003e)\u0026thinsp;+\u0026thinsp;lπD\u0026thinsp;+\u0026thinsp;lπd (2)\u003c/p\u003e \u003cp\u003ewhere D, d and l are the diameter of mild steel pieces, the diameter of the hole for holding and the thickness, respectively. Equations\u0026nbsp;3 and 4 were used to calculate the inhibition efficiency inhibitor efficiency \u0026#119868;\u0026#119864;\u003csub\u003e\u0026#119872;\u0026#119871;\u003c/sub\u003e % and the surface coverage (θ):\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\:ƞ\\)\u003c/span\u003e \u003c/span\u003e \u003csub\u003eWL\u003c/sub\u003e (%)\u0026thinsp;=\u0026thinsp;C\u003csup\u003e0\u003c/sup\u003e\u003csub\u003eWL\u003c/sub\u003e \u0026ndash; C\u003csub\u003eWL\u003c/sub\u003e / C\u003csup\u003e0\u003c/sup\u003e\u003csub\u003eWL\u003c/sub\u003e X 100 (3)\u003c/p\u003e \u003cp\u003eθ\u0026thinsp;=\u0026thinsp;C\u003csup\u003e0\u003c/sup\u003e\u003csub\u003eWL\u003c/sub\u003e \u0026ndash; C\u003csub\u003eWL\u003c/sub\u003e / C\u003csup\u003e0\u003c/sup\u003e\u003csub\u003eWL\u003c/sub\u003e (4)\u003c/p\u003e \u003cp\u003eWhere C\u003csub\u003eWL\u003c/sub\u003e\u0026deg; and C\u003csub\u003eWL\u003c/sub\u003e are the corrosion rates without and with various concentrations of the inhibitors, respectively, θ is the degree of surface coverage of tested inhibitors. Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e summarizes the obtained results. The inhibition efficiency and the corrosion rates of the steel in presence of inhibitors were found to increase continuously with an increase in their concentration. The order of the inhibition efficiencies at the same concentration is CTL\u0026thinsp;\u0026gt;\u0026thinsp;CTB. The results support the hypothesis states that by increasing the concentration of inhibitors, the adsorption of inhibitors will be gradually increased, leading to a complete blockage of corrosion of active sites except 1-θ of exposed surface area.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eWeight loss data of steel samples in uninhibited and inhibited at 298K.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eInhibitors\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eC (g/L)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eC(mg.cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e.h\u003csup\u003e-1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eη\u003csub\u003eWL\u003c/sub\u003e %\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eƟ\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBlank\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.231\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003eCTL\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.412\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e64.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.642\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.358\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e72.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.724\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.214\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e82.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.824\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.125\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e88.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.885\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003eCTB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.552\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e50.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.502\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.478\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e59.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.593\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.407\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e64.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.648\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.339\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e70.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.706\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003e3.4. Stability of the inhibitors\u003c/h2\u003e \u003cp\u003eWeight loss tests were conducted in seawater with the optimal concentration of the inhibitors for different immersion lengths in order to evaluate the stability of the inhibitors' inhibitive layer and determine how long it would take for the inhibitors to reach the maximum IE%. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e presents the findings. It's clear that as immersion duration grows, IE% falls. The greatest efficacy was noted between one and six hours of immersion. There was a noticeable drop in efficacy when the immersion period was extended to 24 hours. These outcomes could occur from the inhibitor layer's instability or from the plant extracts' biodegradable nature over extended interaction [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e32\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003e3.5. Electrochemical measurements\u003c/h2\u003e \u003cdiv id=\"Sec18\" class=\"Section3\"\u003e \u003ch2\u003e3.5.1. Potentiodynamic polarization curves\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e shows the Tafel polarization plots of different concentrations of CTL and CTB, respectively. The kinetic factors viz. corrosion current density (Icorr), anodic Tafel slopes, cathodic Tafel slopes (bc) and corrosion potential (Ecorr) were attained from these plots and are given in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Values of EI% were determined using Eq.\u0026nbsp;5:\u003c/p\u003e \u003cp\u003eIE % = I\u003csup\u003e0\u003c/sup\u003e\u003csub\u003ecorr\u003c/sub\u003e - I\u003csub\u003ecorr\u003c/sub\u003e / I\u003csup\u003e0\u003c/sup\u003e\u003csub\u003ecorr\u003c/sub\u003e x 100 (5)\u003c/p\u003e \u003cp\u003ewhere I\u0026deg;corr and Icorr are corrosion current densities of the steel samples without and with the inhibitors, respectively.\u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e's results show that as the concentration of the inhibitors increased, Icorr values gradually reduced. The values of the cathodic Tafel slopes, bc, and anodic Tafel slopes, ba, clearly differ, with the exception of the lowest concentration, suggesting that the addition of inhibitors has no effect on the mechanism of the proton discharge reaction.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eElectrochemical parameters of steel at various concentrations of CTL and CTB in sea water and corresponding inhibition efficiency.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eInhibitors\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCon. (g/L)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-Ecorr\u003c/p\u003e \u003cp\u003e(mV/SCE)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eIcorr\u003c/p\u003e \u003cp\u003e(\u0026micro;A cm-2)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eBa\u003c/p\u003e \u003cp\u003e(mVdec\u003csup\u003e-1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-bc\u003c/p\u003e \u003cp\u003e(mV dec\u003csup\u003e-1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eIE\u003csub\u003eI\u003c/sub\u003ecorr\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBlank\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e461\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1425\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e153\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e221\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e----\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003eCTL\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e472\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e574\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e175\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e212\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e59.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e508\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e426\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e185\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e184\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e70.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e519\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e268\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e169\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e190\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e80.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e538\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e176\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e172\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e194\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e87.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003eCTB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e481\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e731\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e170\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e175\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e49.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e494\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e611\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e169\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e182\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e57.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e512\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e529\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e187\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e196\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e63.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e482\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e437\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e173\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e180\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e69.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eFigure (2) reveals that all inhibitors suppressed both anodic and cathodic currents confirming mixed type inhibitor. IE% increases as the inhibitor concentration increases reaching a maximum values 87.1% and 69.6% for ATL and ATB, respectively.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section3\"\u003e \u003ch2\u003e3.5.2. Electrochemical impedance spectroscopy (EIS)\u003c/h2\u003e \u003cp\u003eThe EIS experiments were performed in uninhibited and inhibited seawater to obtain more information about the corrosion inhibition mechanism of the mild steel. EIS results are showed as Nyquist plots in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The semicircles of EIS experiments were slightly depressed compared to those derived from the theory of EIS. The imperfectness of capacitive loop is a common behaviour and it is attributed to the result of the heterogeneity, frequency dispersion and roughness of the steel surface [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. Curves have been obtained after 60 minutes of soaking the electrodes in the required concentration (open circuit potential).\u003c/p\u003e \u003cp\u003eIt is clear from Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e that single capacitive loops have been obtained for all inhibitors indicating that the mild steel dissolution at metal/seawater interface is controlled by charge transfer process. The inhibition efficiencies, EI\u003csub\u003eRt\u003c/sub\u003e (%) are displayed in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eElectrochemical Impedance parameters for corrosion of the steel sample at various concentrations of the inhibitors at 298K.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eInhibitors\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCon. (g/L)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRt\u003c/p\u003e \u003cp\u003e(Ω.cm2)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eQ x 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e(S\u003csup\u003en\u003c/sup\u003eΩ\u003csup\u003e-1\u003c/sup\u003ecm\u003csup\u003e-1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e(10\u003csup\u003e4\u003c/sup\u003e) C\u003csub\u003edl\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e(\u0026micro;F/cm\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eEI\u003csub\u003eRt\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e(%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBlank\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.68\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e145.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003eCTL\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e58.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e89.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e38\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.96\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e36.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e62.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e68\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.74\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e22.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e80.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e109\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.64\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e6.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e87.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003eCTB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.54\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e64.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e51.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e45.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e56.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e31.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e66.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e49\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.95\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e11.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e72.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eIn order to determine Rt values, the high frequency impedance was subtracted from the low frequency one as shown in Eq.\u0026nbsp;6:\u003c/p\u003e \u003cp\u003eR\u003csub\u003et\u003c/sub\u003e = Z\u003csub\u003ere\u003c/sub\u003e (at low frequency) \u0026ndash; Z\u003csub\u003ere\u003c/sub\u003e (at high frequency) (6)\u003c/p\u003e \u003cp\u003eC\u003csub\u003edl\u003c/sub\u003e values (electrochemical double layer) were determined at the frequency f\u003csub\u003emax\u003c/sub\u003e, when the imaginary component of the impedance has a maximum value (-Z\u003csub\u003emax\u003c/sub\u003e) by Eq.\u0026nbsp;7:\u003c/p\u003e \u003cp\u003e\u0026#119862;\u003csub\u003e\u0026#119889;\u0026#119897;\u003c/sub\u003e= 1 2\u0026#120587;\u0026#119891;\u003csub\u003e\u0026#119898;\u0026#119886;\u0026#119909;\u003c/sub\u003e/\u0026#119877;\u003csub\u003e\u0026#119905;\u003c/sub\u003e (7)\u003c/p\u003e \u003cp\u003eThe inhibition efficiency IE%(EIS) is determined by using Eq.\u0026nbsp;8:\u003c/p\u003e \u003cp\u003e\u0026#119864;\u0026#119868;%\u003csub\u003e(\u0026#119864;\u0026#119868;\u0026#119878;)\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;R\u003csub\u003et\u003c/sub\u003e\u003csup\u003eo\u003c/sup\u003e \u0026ndash; R\u003csub\u003et\u003c/sub\u003e / R\u003csub\u003et\u003c/sub\u003e\u003csup\u003eo\u003c/sup\u003e x 100 (8)\u003c/p\u003e \u003cp\u003ewhere \u0026#119877;\u003csub\u003e\u0026#119905;\u003c/sub\u003e\u003csup\u003e\u0026#119900;\u003c/sup\u003e and \u0026#119877;\u003csub\u003e\u0026#119905;\u003c/sub\u003e and are the charge transfer resistance values without and with the presence of the inhibitor, respectively.\u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e makes it clear that when all inhibitors are present, the resistance levels rise. This can be attributed to the molecules' ability to prevent rusting. Additionally, it is evident that while the inhibitor is present, Cdl values drop. This might be explained by a decrease in the local dielectric constant and/or an increase in the depth of the electric double layer [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e36\u003c/span\u003e], suggesting that inhibitor molecules are adsorbing at the metal contact.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eThe constant replacement of water molecules by adsorption inhibitor molecules on the steel surface, which lowers the degree of iron oxidation, is probably the cause of the drop in Cdl values and the increase in Rt values and, consequently, the increase in IE% [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. The EIS test findings and the polarization test results are in good agreement.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003e3.6. Adsorption study\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eAdsorption study aims to discover the way by which the inhibitor molecules interact with the steel surface. Values of surface coverage, θ, at various inhibitor concentrations at 298K (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) were employed to determine the adsorption isotherm. θ values were calculated by using Eq.\u0026nbsp;9:\u003c/p\u003e \u003cp\u003eƟ= W\u003csub\u003ecorr\u003c/sub\u003e\u003csup\u003eo\u003c/sup\u003e \u0026ndash; W\u003csub\u003ecorr\u003c/sub\u003e / W\u003csub\u003ecorr\u003c/sub\u003e\u003csup\u003eo\u003c/sup\u003e (9)\u003c/p\u003e \u003cp\u003eThere are many models of adsorption isotherms such as, Freundluich, D-R, Temkin and Langmuir isotherms.\u003c/p\u003e \u003cp\u003eApplication of Eq.\u0026nbsp;10 gives straight lines with slope values of 1.044, and 1.056 for CTL and CTB respectively. Also, good correlation coefficient (R2\u0026thinsp;\u0026gt;\u0026thinsp;0.987) was obtained proving that the adsorption of the inhibitor molecules from seawater on the steel surface follows the Langmuir model.\u003c/p\u003e \u003cp\u003eC\u003csub\u003einh\u003c/sub\u003e / θ\u0026thinsp;=\u0026thinsp;1/ k\u003csub\u003eads\u003c/sub\u003e + C\u003csub\u003einh\u003c/sub\u003e (10)\u003c/p\u003e \u003cp\u003eWith ∆G\u003csub\u003eads\u003c/sub\u003e= \u0026minus;\u0026#119877;\u0026#119879; \u0026#119897;\u0026#119899; ( \u0026#119870;\u0026#119886;\u0026#119889;\u0026#119904; \u0026#119909; 999) (11)\u003c/p\u003e \u003cp\u003eValues of equilibrium adsorption constant (K\u003csub\u003eads\u003c/sub\u003e) were determined from the intercept of Eq.\u0026nbsp;10 and ΔG\u003csub\u003eads\u003c/sub\u003e values were calculated from Eq.\u0026nbsp;11. Results are shown in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eValues of \u0026#119870;\u003csub\u003e\u0026#119886;\u0026#119889;\u0026#119904;\u003c/sub\u003e and ∆\u0026#119866;\u003csub\u003e\u0026#119886;\u0026#119889;\u0026#119904;\u003c/sub\u003e for the adsorption process of CTL and CTB on mild steel at 298K.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eInhibitor\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026#119870;\u003csub\u003e\u0026#119886;\u0026#119889;\u0026#119904;\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eΔG\u003csub\u003eads\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCTL\u003c/p\u003e \u003cp\u003eCTB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6.15\u003c/p\u003e \u003cp\u003e5.28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-21.5\u003c/p\u003e \u003cp\u003e-21.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e's results show that the adsorption process is likely spontaneous because the adsorption free energy values are negative. According to previously published data, the process is most likely classified as chemisorption when the value of ∆\u0026#119866;\u0026#119886;\u0026#119889;\u0026#119904; \u0026sim; \u0026minus;40 kJ/mol or more negative, and as physio-sorption if ∆\u0026#119866;\u0026#119886;\u0026#119889;\u0026#119904; \u0026sim; \u0026minus;20 kJ/mol or less negative. The findings of this investigation indicate that both chemical and physical interactions occurred [39\u0026ndash;41].\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003e3.7. Effect of temperature\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003e(EIS) technique was adapted to explore the effect of temperature on the inhibition process and to obtain some thermodynamic parameters of the corrosion process. EIS experiments were performed at temperature range of 298\u0026ndash;328 K without and with the optimal concentration of the inhibitors (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eEffect of temperature on the adsorption of various inhibitors (1.50 g/L) in the carbon steel at different temperatures.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eInhibitors\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eT (K)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRt\u003c/p\u003e \u003cp\u003e(Ω.cm2)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eQ x 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e(S\u003csup\u003en\u003c/sup\u003eΩ\u003csup\u003e-1\u003c/sup\u003ecm\u003csup\u003e-1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eC\u003csub\u003edl\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e(\u0026micro;F/cm\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eEI\u003csub\u003eRt\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e(%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003eBlank\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e298\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.68\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e142.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e308\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.74\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e116\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e318\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.94\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e128\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e328\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e83\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003eCTL\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e298\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e103\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e87.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e308\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e58\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.87\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e42\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e80.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e318\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e34\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.95\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e58\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e78.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e328\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e73\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e73.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003eCTB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e298\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e46\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.96\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e72.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e308\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e67.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e318\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e61\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e58.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e328\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.72\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e86\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e54.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eThe findings in Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e demonstrate that in both inhibited and uninhibited medium, the values of charge transfer resistance (Rt) decrease with increasing temperature. Additionally, Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e shows that as the temperature rose, the IE% values in the presence of all inhibitors somewhat dropped. This is probably due to the possibility of high temperatures during the desorption process. These findings demonstrate that CTL is an effective inhibitor over the temperature range under study. Since its IE% dropped to just 54% at 328 K, it is evident that CTB efficiency is temperature dependant. Inhibitors derived from plants frequently exhibit this behavior [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e42\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e43\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. CONCLUSION","content":"\u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eCTL and CTB were applied to mild steel to prevent corrosion. The investigation was conducted using a variety of methods, including electrochemical measurements and weight loss. CTB exhibits moderate to poor inhibition efficacy, whereas CTL exhibits strong inhibition efficiency. According to the Langmuir adsorption model, the study shows that both CTL and CTB block the anodic and cathodic processes (mixed-typed inhibitor). The findings indicated that both inhibitors' effectiveness declined over time.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003e1-3: All authors reviewed the manuscprit\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eVerma C , Ebenso EE , Quraichi MA . Corrosion inhibitors for ferrous and non ferrous metals and alloys in ionic sodium chloride solutions: A review. J Mol Liq 2017;248:927\u0026ndash;42 . \u003c/li\u003e\n\u003cli\u003eMeng HY , Ma X , Zhu H , Li J , Li C , Cao D . Experimental and theoretical studies of benzothiazole derivatives as corrosion inhibitors for carbon steel in 1M HCl. Corros Sci 2016;112:563\u0026ndash;75 . \u003c/li\u003e\n\u003cli\u003eDutta A , Saha SKr , Adhikari U , Banerjee P , Sukul D . Effect of substitution on corrosion inhibition properties of 2-(substituted phehyl)benzimidazole deriva- tivces on mild steel in 1M HCl solution: A combined experimental and theoretical approach. Corros Sci 2017;123:256\u0026ndash;66 . \u003c/li\u003e\n\u003cli\u003eEl-Taib Heakal F , Deyab MA , Osman MM , Elkholy AE . Performance of Centaurea cyanus aqueous extract towards corrosion mitigation of carbon steel in saline formation water. Desalination 2018;425:111\u0026ndash;22 .\u003c/li\u003e\n\u003cli\u003e[5] Ansari KK , Quraishi MA , Singh A . Corrosion inhibition of mild steel in hy- drochloric acid by some pyridine derivatives: an experimental and quantum chemical study. J Ind Eng Chem 2015;25:89\u0026ndash;98 . \u003c/li\u003e\n\u003cli\u003eObot IB , Ankah NK , Sorour AA , Gasem ZM , Haruna K . 8-Hydroxyquinoline as an alternative green and sustainable acidizing oilfield corrosion inhibitor. Sust Mater Technol 2017;14:1\u0026ndash;10 .\u003c/li\u003e\n\u003cli\u003eOuakki, M., Galai, M. \u0026amp; Cherkaoui, M. Imidazole derivatives as efficient and potential class of corrosion inhibitors for metals and alloys in aqueous electrolytes: A review. J. Mol. Liq. 345, 117815 (2022). \u003c/li\u003e\n\u003cli\u003eKhadom, A. A., Abd, A. N. \u0026amp; Ahmed, N. A. Xanthium strumarium leaves extracts as a friendly corrosion inhibitor of low carbon steel in hydrochloric acid: Kinetics and mathematical studies. S. Afr. J. Chem. Eng. 25, 13\u0026ndash;21 (2018).\u003c/li\u003e\n\u003cli\u003eHamed, S., Yop, K., Verma, C., Quraishi, M. A. \u0026amp; Ebenso, E. E. 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Oudda, Journal of Adhesion Science and Technology, /doi.org/10.1080/01694243.2018.1554764. \u003c/li\u003e\n\u003cli\u003eL. Bammou, M. Belkhaouda, R. Salghi, O. Benali, A. Zarrouk, H. Zarrok and B. Hammouti, Journal of the Association of Arab Universities for Basic and Applied Sciences, 16 (2014) 83.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Corrosion, Chrozophora Plicata, leaves, barks, steel","lastPublishedDoi":"10.21203/rs.3.rs-6455610/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6455610/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eMetals and alloys are susceptible to corrosion, a severe occurrence that shortens the lifespan of metallic and alloyed items and lowers their value and efficiency. Developing affordable and environmentally friendly inhibitors from the many local plants found in Kanuvai, Tamilnadu, India, was the goal of this study. For the ethanolic extracts from leaves and barks, phytochemical screening was done. Flavonoids, phenolic chemicals, and polyphenols were identified as the main groupings. The effectiveness of the inhibitors was examined using electrochemical impedance spectroscopy as well as potentio-dynamic polarization curves. For CTL and CTB, the highest possible IE%s were 87.1% and 69.6%, respectively. Both extracts function as mixed type inhibitors, according to the results of the potentio-dynamic polarization (PDP) tests. An increase in polarization resistance is shown by the findings of electrochemical impedance spectroscopy (EIS) experiments, indicating the inhibitors' ability to inhibit. Competitive physio-sorption and chemisorption mechanisms are involved in the inhibitors' adsorption on the steel surface, which follows the Langmuir adsorption isotherm model. The influence of temperature on corrosion inhibition was examined using the EIS approach at temperatures between 298K and 328K. The findings verify that when temperature rises, the inhibition efficiency (IE%) of all inhibitors somewhat decreases. Both inhibitors' thermodynamic properties were computed.\u003c/p\u003e","manuscriptTitle":"Evaluation of Leaf and Bark Extracts of Chrozophora Plicata as Corrosion Inhibitors for Mild Steel in HCl","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-17 08:32:02","doi":"10.21203/rs.3.rs-6455610/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"90ad2843-9e72-4bd2-8809-fafa0d30735f","owner":[],"postedDate":"April 17th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-04-17T15:08:44+00:00","versionOfRecord":[],"versionCreatedAt":"2025-04-17 08:32:02","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6455610","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6455610","identity":"rs-6455610","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}