Corrosion Inhibition Mechanism of Mild Steel by Amylose-Acetate / Carboxymethyl Chitosan Composites in Acidic Media

*is article details an investigation on the mechanism of corrosion inhibition of mild steel using amylose-acetate-blended carboxymethyl chitosan (AA-CMCh) in acidic media in the context of kinetic and thermodynamic parameters. *e surface of mild steel was exposed to test solutions and evaluated using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). *e activation energy (Ea), free energy of adsorption (ΔG), enthalpy of activation (ΔHads), and entropy of activation (ΔSads) were determined in order to elucidate the mechanism of corrosion inhibition. *e results confirmed that AA could be improved using CMCh as a corrosion inhibitor. *e corrosion rate decreased from 1109.00 to 229.70mdd (79.29%), while corrosion inhibition increased from 35.13 to 89.72%. Sulfate acid (H2SO4) of 0.25M also helped in decreasing the corrosion rate from 2664.4 to 1041.67mdd (60.9%) while also in increasing corrosion inhibition from 56.94 to 68.31%.*e calculated values for ΔG, ΔHads, and ΔSads were −33.22 kJ·mol, −48.56 kJ·mol, and 0.0495 kJ·mol·K, respectively. *e mechanism of corrosion inhibition of mild steel in the acidic condition is dominated and precipitated by the formation of the Fe-chelate compound, which was confirmed by the SEM/EDS spectrum. *e reactions were spontaneous, exothermic, and irregular and takes place on the surface of mild steel.


Introduction
Mild steel is widely used for the fabrication of reaction vessels, storage tanks, and petroleum refineries.e usage of corrosive agents in industries, which are detrimental to metals, is unavoidable.To protect metallic surfaces from these agents, various strategies have been proposed and studied, such as cathodic protection, anodic protection, corrosion protection coating, and corrosion inhibitors.e use of inhibitors appears to be the more common due to its low cost, ease-of-procedure, and high efficiency [1,2].Many synthetic organics, extracted plants, and inorganic chemicals can be used as inhibitors to prevent mild steel from corroding.Inorganic compounds (e.g., sodium chromate, phosphate, and molybdate) have been proposed as corrosion inhibitors for mild steel in many forms of aqueous media.Karekar et al. [3] reported the use of zinc molybdate nanoparticles as a center nanocontainer for inhibiting the corrosion of mild steel.e zinc molybdate nanoparticles were embedded in a three-layer material consisting of polyaniline, benzotriazole, and polyacrylic acids.e highest corrosion inhibition was reported to be at 5% NaOH and 5% NaCl.However, inorganic compound harms the environment due to its release of toxins and carcinogens to the environment [2].
Extracted plants are widely used as green corrosion inhibitors for mild steel in many acidic media.Abrishami et al. [4] proposed the usage of zinc acetylacetonate-modified Urtica dioica leaf extract as an active corrosion inhibitor to protect mild steel in chloride solutions.
e proposed corrosion inhibitor reported excellent inhibition efficiency.Krishnan et al. [5] reported the usage of biogenic corrosion inhibition for the protection of mild steel.
Chitosan derivatives are currently being touted as a potential material for the protection of metal surfaces from corrosive agents due to their unique structural features, such as rich surface chemistry, biodegradability, bioactivity, biocompatibility, polycationic, and high molecular weight, and the fact that it is renewable [25,26].
ese organic compounds are incubated in acidic mediums at a pH of <6.5, producing a linear poly-base electrolyte with a highly positive charge density.
is phenomenon contributed to chitosan and its derivatives becoming highly biocompatible and biodegradable [27].Many chitosan derivatives have been used to inhibit corrosion in the acidic medium.Cheng et al. [28] reported an anodic corrosion inhibitor based on carboxymethyl chitosan (CMCh) to prevent corrosion on mild steel in an HCl solution.e results confirmed that the CMCh could potentially inhibit corrosion and be used as a control agent to address mild steel corrosion problems.Wan et al. [29] proposed carboxymethyl hydroxypropyl chitosan to inhibit corrosion on the surface of mild steel in a 1.0 M HCl solution.It could also be used as an anticorrosion material at a low concentration to obtain an inhibition efficiency of 95.3% in 1,000 ppm (by weight).Salomon et al. [30] utilized chitosan particle-modified silver nanoparticles to enhance the inhibition of corrosion.is was tested on a St37 steel and 15% H 2 SO 4 solution.e corrosion inhibitor based on chitosan-modified silver nanoparticles reported an inhibition efficiency >94%.Alsabagh et al. [31] developed corrosion inhibition based on natural polymer chitosan and used it on carbon steel in a 1.0 M HCl solution.e agent was found to increase the hydrophobic character of chitosan and further enhance its surface-active properties.e results demonstrated that corrosion inhibition was attained at an efficiency of 250 ppm.Umeron et al. [32] proposed another corrosion inhibitor based on natural polymer chitosan to protect the surface of mild steel and reported excellent efficiency (96%) at room temperature.e obtained efficiency in corrosion inhibition was generally due to the specific interaction between functional groups of -COOH and -NH 2 and the metal surface. is study investigates corrosion inhibition based on amylose acetate-modified carboxymethyl chitosan.e corrosion inhibition efficiency of AA-modified CMCh was used on the surface of mild steel in HCl and H 2 SO 4 media.
e corrosion inhibitions of AA-modified CMCh on the mild steel surface using kinetic and thermodynamic data were also investigated.
e morphological form of the corroding mild steel surface in the presence of AA-modified CMCh was analyzed using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX).e novelty of this work lies in the use of amylose acetateblended carboxymethyl chitosan as a green corrosion inhibitor for the protection of mild steel in both the HCl and H 2 SO 4 solutions.e benefit of this AA-modified CMCh is its high inhibition efficiency (>95%), low inhibitor concentration (in the ppm level), long working period (3 days), and strong bond(s) between the steel and inhibitor solution.

Experimental
2.1.Chemicals.All of the chemical used in this work were of analytical grade, and the solutions were prepared using deionized water.Chitosan, carboxymethyl chitosan, dioxane, acetate acid, and silicon carbide sand paper (100, 200, and 400 grades) were purchased from Sigma-Aldrich (St. Louis, USA), while monochloroacetate acid, isopropanol, methanol, ethanol, acetone, chloroform, chloride acid (HCl), and sulfuric acid (H 2 SO 4 ) were purchased from Merck (Darmstadt, Germany).Tapioca tuber and detergent 2 International Journal of Chemical Engineering were procured from the supermarket.e mild steel plate BJTP-24, with an area measuring 2.0 × 1.0 cm 2 , used in this work reported a chemical composition of C � 0.16%, Si � 0.19%, Mn � 4.8%, P � 0.16%, S � 0.22%, and balanced Fe.

Instruments.
e FT-IR spectra of amylase acetate were obtained using Spectrum FTIR GX infrared spectrophotometer (PerkinElmer).e surface morphologies of mild steel were imaged using the scanning electron microscopedispersive X-ray spectrum (SEM-EDS).e pH values of the solutions were measured using a pH meter ( ermo Scientific).e glassware used in this work was cleaned using distilled and deionized waters.

Amylose Isolation and Surface Modification.
e amylose powders were obtained from its cassava base via a simple extraction technique.e preparation of amylose was slightly modified from the one reported in Erna et al. [33].In brief, the cassava sample was first cleaned using fresh water to remove any soil or contaminant.e cleaned cassava was continuously shredded and directly mixed into fresh water to create a rough pulp. is rough pulp was then shaken and squeezed to obtain a suspension of amylose.e extracted amylose was carefully filtered using gauze to obtain a slurry amylose and carefully rinsed with fresh water several times to get a clean starch.is isolated starch was then air-dried at ambient temperature.
e dried starch was thoroughly crushed using a mortar and pestle and immediately purified using a dioxane solution for 4 h to remove any remaining acid(s).en, the purified starch was again dried at 80 °C and carefully dispersed in a solution of n-butanol.e obtained amylose was then sterilized using an autoclave for 2 h at a pressure of 15 psi and left to cool at 25 °C for 24 hrs.e sterilized amylose was collected via centrifugation (6,500 rpm and 10 min) and washed thoroughly using deionized water and absolute methanol thrice.
To modify the surface of amylose, ∼5 g of amylose was immediately acetylated with 25 mL of acetate acid glacial and manually stirred until the solution becomes homogeneous.
en, a mixture consisting of 0.2 mL sulfate acid and 5.0 mL acetate glacial was immediately added into the acetylated amylose and stirred for 1 h at 37 °C.A solution of 16.5 mL acetate acid anhydride was carefully added and stirred for another 44 hrs at 37 °C.
en, the final acetate-modified amylose was slowly deposited into 200 mL of isopropanol solution and stirred at room temperature.
e formed precipitation was then filtered and thoroughly washed with hot distilled water and then air-dried overnight at room temperature.
e modified amylose was directly characterized using a spectrum FTIR GX infrared spectrophotometer (PerkinElmer).

Fabrication of Corrosion Inhibition Based on AA-Blended
CMCh.Carboxymethyl chitosan was prepared as per Pang et al. [34].In brief, ∼1.0 g of chitosan powder was mixed with 1.35 g of NaOH and immediately dissolved in 8.0 mL isopropanol containing 2.0 mL of distilled water.e mixture was then kept in a water bath at 60 °C.A mixture of 1.5 g of monochloroacetate in 2.0 mL isopropanol was dripped into the chitosan suspension and left for 4 h at ambient temperature.e reaction was stopped via the addition of a solution of 20 mL ethanol (70%).e obtained CMCh was then filtered and washed with ethanol several times, followed by air drying at room temperature.
To make the AA-modified CMCh, a mixture consisting of 200 mg/L CMCh in chloric acid (1.0 M) and 500 mg/L CMCh in sulfate acid (0.25 M) was immediately added into a sample bottle containing 1.0-5.0mg AA and then carefully stirred until its homogeneous.e CMCh modified with AA was applied on mild steel to analyze the mechanism of corrosion inhibition based on the kinetics and thermodynamics study.

Preparation of Mild Steel Plates.
A mild steel plate was prepared, measuring 1.0 × 2.0 cm 2 , and directly cleaned using SiC sand paper (grades 100, 200, and 400).e cleaned mild steel plate was then rinsed with distilled water, acetone, and ethanol several times.It was then immediately dried in an oven for 15 min at 40 °C.e dried mild steel was then weighed, and its weight was recorded.

Determination of Corrosion Rate of Mild Steel in Acidic
Media.∼200 mg/L and 500 mg/L of AA-functionalized CMCh were separately added into a solution of 1.0 M HCl and 0.25 M H 2 SO 4 , respectively.
en, mild steel specimens were directly immersed into HCl and H 2 SO 4 media for 3 days and a day, respectively.e steel coupons were carefully rinsed with chloroform and acetone several times.e washed steel coupons were thoroughly brushed and washed with distilled water and ethanol thrice, followed by drying in an oven at 60 °C.en, mild steel specimens were weighed again to compare its respective rates of corrosion.e determination of the corrosion rate of mild steel in acidic media without inhibitors was also conducted for the comparison purposes.e corrosion rate (g•cm −2 •h −1 ) was calculated using equation (1), where W 1 and W 2 are the weights of mild steel coupons before and after incubation, respectively, in a test medium.S represents the surface area of corroded steel (dm 2 ), while t represents the immersion time (h):

Determination of Inhibition Efficiency, Surface Coverage, and Adsorption-Free Energy
Values.e determination of inhibition efficiency was conducted using HCl and H 2 SO 4 solutions.A series of AA-functionalized CMCh concentrations, from 200 to 600 mg/L and 500 to 900 mg/L, were thoroughly poured into sample bottles containing HCl and H 2 SO 4 solutions, respectively.e prepared steel coupons were then incubated in the HCl and H 2 SO 4 solution and carefully rinsed with distilled water, acetone, and ethanol International Journal of Chemical Engineering and then dried in an oven for 15 min at 40 °C.e inhibition efficiency (IE%) was calculated using equation (2), while the surface coverage (θ) value was determined using equation (3), where CR blank and CR inh are the values of the corrosion rates of mild steel in the absence and presence of inhibitors, respectively.Meanwhile, the Langmuir isotherm adsorption curve was determined using equation ( 4), and the free energy of adsorption (ΔG o ads ) was investigated using equation (5), where K ads represents the equilibrium constant of the adsorption process and C represents the inhibitor's concentration(s).R represents the gas constant, while T represents the absolute temperature: ΔG o ads � −RT ln 55.5 K ads . (5)

Determination of Activation of Energy, Enthalpy, and
Entropy. e prepared steel coupons have been immersed in HCl and H 2 SO 4 solutions containing and not containing inhibitors.
en, the mild steel plates were placed in a thermostat at various temperatures from 28.4 to 60.0 °C.e steel plate was rinsed with distilled water, acetone, and ethanol.Afterwards, it was oven-dried for 15 min at 40 °C.
e activation energy (E a ) was determined using equation (6), where R represents the gas constant, CR represents the corrosion inhibition, K represents the preexponential factor, and T represents the absolute temperature.e values of E a were calculated from the linear regression between ln CR and 1/T.e activation enthalpy (ΔH o ads ) and entropy (ΔS o ads ) can be calculated using equation (7): 2.9.Surface Analysis of Mild Steel.e prepared mild steel plates measuring 2.0 × 1.0 cm 2 were incubated in HCl and H 2 SO 4 in the absence/presence of inhibitor under optimum conditions for 3 days.ereafter, the mild steel specimens were removed, washed with distilled water, degreased with acetone, and then dried at room temperature.e steel specimens were mechanically cut into 1.0 cm 2 chips and then immediately analyzed with SEM and EDX.SEM was performed at a voltage of 5 kV and 5kx magnification on a LEO 1450 VP instrument.e chemical compositions were analyzed using an EDX detector.e attached functional groups on the mild steel surface were investigated using FT-IR spectroscopy equipment (PerkinElmer instrument).

Characterization of Amylose-Acetate.
e acetatemodified amylose powder for corrosion inhibition is shown in Figure 1.
e acetate-functionalized amylose powders are traditionally prepared using the acetylating method.e synthesis of AA involved mixing sulfuric and acetate acids and directly acetylate them via stirring.e powders of acetate functionalized amylose were clearly white.FTIR spectrum of the amylose-acetate is detailed in Figure 2. e O-H stretch peak at 3493.24 cm −1 is from the amylose molecules.
e peaks at 1745.65 cm −1 to 1236.42 cm −1 represent a carbonyl (COOH) group of the acetate.ese peaks confirmed the occurrence of esterification between amylose and acetate molecules.

Effect of Inhibitor Concentrations.
In order to determine the best condition for the corrosion inhibition response, the inhibitor loading was optimized to include both AA and AA-CMCh.
e inhibition efficiency response of corrosion studies based on AA towards mild steel in an acidic medium is shown in Figure 3.In the HCl solution, the inhibition efficiency response gradually increased alongside AA's concentration from 100 to 400 mg/L (Figure 3(a)), while in the H 2 SO 4 solution, the inhibition efficiency response also increased alongside AA loading from 100 to 400 mg/L (Figure 3(b)).
e increasing inhibition efficiency alongside inhibitor concentration is assumed to be due to the adsorption of inhibitor molecules on the surface of mild steel [35].With further increase in AA concentration from 400 to 600 ppm in HCl solution and 400 to 500 ppm in H 2 SO 4 solution, the responses of inhibition efficiency decreased because the inhibitor has been fully adsorbed onto the mild steel's surface.
is confirms that the carboxylic group (COOH) of AA and iron (Fe) of mild steel has bonded.e inhibitor molecules could form a film layer and act as a barrier between mild steel and corrosive media.e optimal AA concentration in HCl and H 2 SO 4 solutions, at 400 ppm, was used for further experiments.
e effect of the CMCh : AA ratio towards the inhibition efficiency of mild steel in HCl and H 2 SO 4 solution is illustrated in Figure 4.It can be seen that the inhibition efficiency signal increases alongside the CMCh : AA volume loading changed from 1 : 18 to 8 : 4 w/w in the HCl solution (Figure 4(a)).When CMCh : AA changed from 8 : 4 to 9 : 2 w/w, the signal of inhibition efficiency significantly declined.
e optimum ratio of CMCh : AA was found at 8 : 4 w/w, with its value of inhibition efficiency at 88.86%. is ratio (8 : 4 w/w) contributed to the interaction energy between the mild steel's surface and thin layer of inhibitor being higher than the interaction energy between the surface of mild steel and water, and consequently, the inhibition efficiency was found to be quite significant.
As can be seen in Figure 4(b), the inhibition efficiency response stabilized when CMCh : AA volume loading changed from 5 : 36 to 30 : 16 w/w in an H 2 SO 4 solution.When the ratio of CMCh : AA volume changed from 30 : 16 to 35 : 12 w/w, the inhibition efficiency response increased.
e CMCh : AA volume loading changed again from 35 : 12 to 45 : 4 w/w (Figure 4(b)), and the response of inhibition e ciency gradually reduced in response to this change.is means that the interaction energy between the mild steel's surface and thin layer of the inhibitor took place slowly, with the thin layer of the inhibitor being unable to prevent attacks of the sulfuric ion on the mild steel's surface. is resulted in increased corrosion on the surface [36].
erefore, the optimum ratio of CMCh : AA in H 2 SO 4 solution at 35 : 12 w/w was utilized for the subsequent evaluation of corrosion inhibition.

Determination of Activation Energy.
e activation energy (E a ) of the system in the presence of AA-CMCh was determined using the Arrhenius equation.e Arrhenius plots for mild steel in 1 M HCl with 400 ppm inhibitor is shown in Figure 5.
e E a value determined from the Arrhenius plots in the presence of AA-CMCh was 98.089 kJ•mol −1 . is high value of E a in the presence of an inhibitor was due to the high-energy barrier of the corrosion rate [37], con rming the formation of a complex compound between the inhibitor and Fe ion of mild steel.

Adsorption Isotherm.
e performance of the AA-CMCh as a successful corrosion inhibitor is mainly due to their adsorption ability on the surface of mild steel.is ability has been utilized to determine its mechanism of corrosion inhibition.
e Langmuir adsorption isotherm from a plot of C/θ against C at 28 °C is shown in Figure 5. e value of the correlation coe cient for AA-CMCh is close to one, which implies that the adsorption of AA-CMCh on the mild steel's surface is well tted to the Langmuir adsorption isotherm.
e calculated K ads and ΔG values are 10496 kJ•mol −1 and −33.22 kJ•mol −1 , respectively.ese values demonstrated that the adsorption types of inhibitors on mild steel surfaces are chemical adsorption.e Langmuir adsorption isotherms from a plot of C/θ against C in 1 M HCl solution at 40 °C and 60 °C were also plotted ( gure not shown).
e K ads and ΔG values at 40 °C were 7650 kJ•mol −1 and −33.722 kJ•mol −1 , respectively, while the   K ads and ΔG values at 60 °C were found to be 1773 kJ•mol −1 and −31.831 kJ•mol −1 , respectively.Generally, the obtained values of the ∆G ads were within −33.22 kJ•mol −1 to −33.83 kJ•mol −1 .e ∆G ads values are ∼−33 kJ•mol −1 or more negative, suggesting chemisorption, where charge sharing or charge transfer from an organic compound to the mild steel surface takes place to form a coordinate-type metallic bond [24,38].e thermodynamic performance for the corrosion of the mild steel surface in 1 M HCl at multiple concentrations of AA-CMCh composites was obtained from a plot of log(CR/T) versus 1/T and calculated using equation (7).e values of activation enthalpy (∆H) and activation entropy (∆S) were −48.56 kJ•mol −1 and 0.0495 kJ•mol −1 •K −1 , respectively.
e negative value of ΔH indicates the exothermic nature of the activated-complex formation from the reactants for the rate-determining step of the steel association process.e positive values of ΔS demonstrate irregularity of the adsorbed inhibitors on the mild steel surface [39]. is implies that the activated complex in the rate-determining step represents a dissociation instead of an association process [32].

Potentiodynamic Polarization Studies.
e performance of potentiodynamic polarization for mild steel in an HCl solution (1.0 M) at multiple concentrations of inhibitors at 301 K after 60 min of immersion time is shown in Figure 6.
e current anodic and cathodic response decreased as the AA-CMCh loading increased from 100 to 400 ppm due to the large amounts of inhibitor on the electrode's surface and also the moving corrosion potential towards increased negativity. is resulted in the classi cation of the inhibitor as the mixed type.
e electrochemical parameters, i.e., corrosion potential (E corr ), anodic and cathodic Tafel slope (ß c , ß a ), corrosion current density (i corr ), and inhibition e ciency (IE) obtained from the corresponding polarization curves, are shown in Table 1.In the proposed corrosion inhibitor, the IE (%) was calculated using the following equation:  International Journal of Chemical Engineering  International Journal of Chemical Engineering inhibition efficiency (%) where i 0 corr and i corr ′ represent the corrosion current densities without and with the addition of inhibitors, respectively.e results con rmed that the inhibition e ciency response increased, while the corrosion current density decreased when the addition of inhibitors concentration increased.
is implies that the inhibitor adsorption on the mild steel's surface and the adsorption process is enhanced and increased inhibition e ciency.
3.6.Surface Characterization: SEM and EDX.In order to determine the e ectiveness of the formatted thin layer of the inhibitor on the mild steel's surface, the treated mild steel was imaged using an SEM.SEM images of the mild steel surface in the presence/absence of CMCh in HCl and H 2 SO 4 solutions are shown in Figures 7 and 8.In the presence of AA at their respective optimum concentrations (400 ppm) in HCl (Figure 7(a)) and H 2 SO 4 solutions (Figure 8(a)), a smooth surface of mild steel can be seen (Figures 7(a . is implies that the AA-CMCh is more e ective in inhibiting corrosion on mild steel's surface compared to the AA inhibitor.is feature probably contributed to the homogeneity and biocompatibility of the AA-CMCh composites on the mild steel's surface.Generally, a smoother surface of the mild steel specimen denote that the AA-CMCh has adsorbed onto the mild steel's surface and protected specimens from direct acid attacks. e EDX spectra of the mild steel and control specimen in HCl solution is shown in Figure 9. e surface of mild steels as a control specimen before treatment (Figure 9(c)) and the presence of AA-CMCh (Figure 9(b)) exhibit a smooth and uniform surface.
e morphology in the presence AA was slightly damaged and rough (Figure 9(a)).
is con rmed that the mild steel surface is well protected from acidic attacks and prevented from corroding.Table 2 shows the percentage of atomic contents in the inhibitor and control specimens.e EDX spectrum in the presence of AA-CMCh con rmed that the concentration of the Cl ion is    International Journal of Chemical Engineering higher than that of the presence of AA, whilst the concentration of C in the control specimen prior to treatment was lower than that of the treated specimen due to the inhibitor absorbed onto the mild steel's surface.e concentration of Fe and O from the inhibitor of AA is not significantly different than the inhibitor of AA-CMCh (Table 2).Generally, both AA and AA-CMCh inhibitors are able to inhibit the mild steel specimen from a direct attack by the Cl ion, which protects the mild steel surface from an aggressive environment.

Mechanism of Inhibition.
e adsorption of AA-blended CMCh on mild steel can be clearly defined by considering the chemisorption processes.
e specific mechanism of corrosion inhibition of AA-CMCh to the surface of mild steel coupons is detailed in the following equations: Fe + AA-CMCh ⟷ Fe(AA-CMCh) ads (9) Fe(AA-CMCh) ads ⟷ Fe 2+ + AA-CMCh + ne − (10) AA-CMCh aq + H 2 O ads ⟷ AA-CMCh ads + H 2 O aq (11) e chemisorption of AA-CMCh on mild steel is denoted by the donor-acceptor interactions between the lone pair of the electron from the carbonyl and amine groups of AA-CMCh with the d-orbitals of Fe. e value of free energy from the AA-CMCh adsorption was −33 kJ•mol −1 or more negative.is confirms that the adsorption mechanism of the AA-CMCh on the surface of the mild steel coupon was chemically adsorbed.
e inhibition of corrosion begins by the displacement of water molecules by the inhibitor's capacity toward specific adsorption of the inhibitor on the metal's surface [40].

Conclusions
e corrosion inhibition mechanism based on carboxymethyl chitosan/amylose-acetate composites used to protect mild steel in an acidic medium was successfully investigated.e AA-CMCh base inhibitor showed excellent inhibition performance in the case of mild steel in a 1 M HCl solution.e inhibiting efficiencies decreased in the order of AA-CMCh > AA.
e inhibitor adsorptions on the mild steel's surface are chemically adsorbed, while the corrosion inhibition mechanism on the mild steel's surface was spontaneous, exothermal, and irregular and took place due to the formation of the Fe-chelate compound on the surface of the mild steel specimen.e adsorption of the inhibitors on the mild steel specimen in acidic media solution comports with that of the Langmuir adsorption isotherm.e negative values of the ∆G ads and ∆H indicated that the adsorption reaction took place spontaneously and exothermally.

Figure 2 :
Figure 2: FT-IR spectrum of amylose modi ed with acetate.

Figure 1 :
Figure 1: Powder of the amylose functionalized with acetate.

Figure 3 :
Figure 3: E ect of amylose-acetate concentration on the inhibition e ciency for mild steel in 1.0 M HCl solution (a) and 0.25 M H 2 SO 4 solution (b).

Figure 4 : 2 R 2 Figure 5 :
Figure 4: E ect of CMCh : AA concentration on the inhibition e ciency of mild steel in solution of 1.0 M HCl (a) and 0.25 M H 2 SO 4 (b) for 3 days.

Figure 8 :
Figure 8: SEM micrographs of the mild steel surface in 0.25 M H 2 SO 4 with AA (a) and AA-CMCh (b).

Figure 7 :Figure 9 :
Figure 7: SEM images of mild steel surfaces in 1 M HCl with AA (a) and AA-CMCh (b).

Table 1 :
Electrochemical parameters obtained from polarization measurement in 1.0 M HCl in the presence and absence of a di erent concentration of AA-CMCh.

Table 2 :
Percentage atomic contents of elements measured using the EDX technique.