Surface morphological and impedance spectroscopic studies on the interaction of polyethylene glycol (PEG) and polyvinyl pyrrolidone (PVP) with mild steel in acid solutions

The inhibition of mild steel corrosion in aerated acid mixture of 0.5 N H₂SO₄ and 0.5 N HCl solution was investigated using potentiodynamic polarization studies, linear polarization studies, electrochemical impedance spectroscopy, adsorption, and surface morphological studies. The effect of inhibitor concentration on corrosion rate, degree of surface coverage, adsorption kinetics, and surface morphology is investigated. The inhibition efficiency increased markedly with increase in additive concentration. The presence of PEG and PVP decreases the double-layer capacitance and increases the charge-transfer resistance. The inhibitor molecules first adsorb on the metal surface following a Langmuir adsorption isotherm. Both PEG and PVP offer good inhibition properties for mild steel and act as mixed-type inhibitors. Surface analysis by scanning electron microscopy (SEM) and atomic force microscopy (AFM) shows that PVP offers better protection than PEG.     

Effect of Avogadro natural oil on the corrosion inhibition of mild steel in hydrochloric acid solution

The inhibition action of Avogadro natural oil on corrosion of mild steel in one molar hydrochloric acid solution was investigated by gravimetric and potentiodynamic polarization techniques. The surface morphology of as-corroded samples was assessed with high resolution scanning transmission electron microscopy equipped with energy dispersive spectroscopy (HR-STEM/EDS). From the results, the presence of Avogadro natural oil in the metal–acidic interface decreased the corrosion rate with all the exposure times. The inhibition efficiency (%IE) increases with the concentration of the inhibitor considered. Results obtained from gravimetric measurements indicate that the natural oil exhibited higher efficiencies of 93.26 % after 384 h of exposure time and 98.26 % recorded in the potentiodynamic polarization method, both at 4.5 g/v inhibitor addition. Equally, results from the linear polarization indicated higher potential value with an increase in the polarization resistance (R _p) and lower current density for the inhibited samples than the uninhibited mild steel sample. The inhibitive effect of this oil was explained in view of adsorption on the metal surface. The adsorption process follows the Langmuir adsorption isotherm.     

The litchi (Litchi Chinensis) peels extract as a potential green inhibitor in prevention of corrosion of mild steel in 0.5 M H2SO4 solution

The corrosion inhibition of mild steel in 0.5 M H₂SO₄ solution by the extract of litchi peel (Litchi chinensis) was studied by weight loss method, potentiodynamics polarization and electrochemical impedance spectroscopy (EIS). The results show that the litchi peels extract acts as mixed-type inhibitor. The inhibition of corrosion is found to be due to adsorption of the extract on metal surface, which is in conformity with Langmuir’s adsorption isotherm. UV–Vis, Fourier transform infrared (FT-IR) spectroscopy and Scanning electron microscopy (SEM) studies confirm that the inhibition of corrosion of mild steel occurs through adsorption of the inhibitor molecules.     

Study on the Inhibition of Mild Steel Corrosion by Cationic Gemini Surfactant in 1 M HCl

The cationic gemini surfactant 1,2-bis(N-tetradecyl-N,N-dimethylammonium)ethane dibromide (14-2-14) was synthesized using a previously described method. The surfactant was characterized using ¹H NMR. The corrosion inhibition effect of 14-2-14 on mild steel in 1 M HCl at temperatures 30–60°C was studied using weight loss measurements, potentiodynamic polarization measurements and electrochemical impedance spectroscopy. Morphology of the corroded mild steel specimens was examined using scanning electron microscopy (SEM). The results of the studies show that gemini surfactant is an efficient inhibitor for mild steel corrosion in 1 M HCl; the maximum inhibition efficiency (IE) of 98.06% is observed at surfactant concentration of 100 ppm at 60°C. The %IE increases with the increasing inhibitor concentration and temperature. The adsorption of inhibitor on the mild steel surface obeys Langmuir adsorption isotherm. SEM studies confirmed smoother surface for inhibited mild steel specimen.     

Inhibitive assessment of 1-(7-methyl-5-morpholin-4-yl-thiazolo[4,5-d]pyrimidin-2-yl)-hydrazine as a corrosion inhibitor for mild steel in sulfuric acid solution

In this study, the inhibitive effect of synthesized 1-(7-methyl-5-morpholin-4-yl-thiazolo[4,5-d]pyrimidin-2-yl)-hydrazine (MMTPH) as a new corrosion inhibitor for mild steel in 0.5 M sulfuric acid medium is investigated employing potentiodynamic polarization, electrochemical impedance spectroscopy and linear polarization resistance techniques. The results show MMTPH reduces anodic dissolution, retards the hydrogen evolution reaction and its adsorption follows Langmuir’s adsorption isotherm. Any increase in temperature will in turn increase corrosion current densities; however, the presence of MMTPH hinders the rate. In solutions with inhibitor concentration of 200 ppm, temperature elevations as great as 30° (25–55 °C) result in a drop of about 45 % in inhibition efficiency (99–55 %). Thermodynamic adsorption parameters show that the MMTPH is absorbed by a spontaneous exothermic process and the adsorption mechanism is physical. Quantum chemical method shows that the MMTPH molecules can be directly adsorbed at the steel surface on the basis of donor–acceptor interactions between π-electrons of pyrimidine, N atoms of hydrazine and vacant d-orbitals of iron atoms.     

Electrochemical investigation of a schiff base synthesized by cinnamaldehyde as corrosion inhibitor on mild steel in acidic medium

The inhibiting effect of (NE)-4-phenoxy-N-(3-phenylallylidene) aniline (PAC) on the corrosion of mild steel in 1.0 M HCl has been studied by electrochemical impedance spectroscopy, and Tafel polarization measurements. The corrosion rate was also calculated theoretically in terms of mm per year and mil per year, using current density values of mild steel in 1.0 M HCl medium. It was found that PAC has a remarkable inhibition efficiency on the corrosion of mild steel especially at high temperatures. The values of E _a obtained in presence of a Schiff base were found to be lower than those obtained in the inhibitor-free solution. The increase of inhibition efficiency percent with temperature increase was associated with the transformation of physical adsorption into chemical adsorption. The thermodynamic functions of adsorption processes have been evaluated and discussed at each temperature. Scanning electron microscope observations of the electrode surface confirmed the existence of a protective adsorbed film of the inhibitor on the electrode surface.     

Extract sarampa wood (Xylocarpus Moluccensis) as an eco-friendly corrosion inhibitor for mild steel in HCl 1M

Plant extracts are currently being used as eco-friendly corrosion inhibitors. In this study, the inhibitive performance of Xylocarpus Moluccensis extract (XME) was used as an eco-friendly corrosion inhibitor for the first time. The extract was studied using electrochemical measurement on mild steel in 1M HCl. Results from FIR and phytochemical confirmed that Xylocarpus Moluccensis extract contains compound hydroxyl group, phenolic, and flavonoid content which can be used as a corrosion inhibitor. The inhibition efficiency was determined using Tafel polarization and electrochemical impedance spectroscopy and showed 68% efficiency in 500 ppm. Langmuir adsorption isotherm was used to determine the adsorption mechanism of XME. Surface characterization (AFM) was also used to study the surface morphology of protective film inhibitors.     

Evaluation of the inhibitive effect of essential oil of Lavandula multifida L., on the corrosion behavior of C38 steel in 0.5 M H2SO4 medium

The essential oil of the aerial parts of Lavandula multifida L., collected in Errachidia region (three samples) in southeast Morocco, was extracted by hydrodistillation and analyzed by GC and GC-MS. The oil was predominated by carvacrol (57.9–59.0%). L. multifida oil was tested as corrosion inhibitor of C38 steel in 0.5 M H₂SO₄ using weight loss measurements, electrochemical polarization, and EIS methods. The results obtained by measurements of weight loss showed that inhibition efficiency increases with inhibitor concentration to attain 72.2% at 2 g/l of oil at 298 K. Polarization curves revealed that L. multifida oil acts as mixed type inhibitor. The temperature effect on the corrosion behavior of steel in 0.5 M H₂SO₄ without and with the inhibitor at 2 g/l was studied in the temperature range from 303 and 343 K. The adsorption of inhibitor on the C38 steel surface was found to be a spontaneous process and to obey Langmuir’s adsorption isotherm. The associated activation energy has been determined.     

Adsorption and corrosion inhibition of mild steel in hydrochloric acid solution by verbena essential oil

The inhibitive action of verbena essential oil (VEO) on the corrosion of mild Steel in 1 M HCl solutions in the temperature range 298 to 328 K was measured by use of the weight-loss method, potentiodynamic polarization, and electrochemical impedance spectroscopy. Results showed that VEO inhibited corrosion of C38 steel in 1 M HCl solution and that inhibition efficiency increased with increasing concentration of inhibitor but decreased proportionally with temperature. Potentiodynamic polarization studies suggested VEO is a mixed-type inhibitor, with the anodic type predominating. Nyquist plots were depressed semicircles with their centre below the real axis. Adsorption of VEO by the C38 steel surface followed the Langmuir adsorption isotherm. Kinetic data for dissolution were investigated.     

The effect of 2-aminoquinoline-6-carboxylic acid on the corrosion behavior of mild steel in hydrochloric acid

The inhibitive effect of 2-aminoquinoline-6-carboxylic acid (AQC) against mild steel corrosion in 1?M HCl solutions was investigated using conventional weight loss, potentiodynamic polarization, linear polarization and electrochemical impedance spectroscopy methods. The weight loss results showed that AQC is an excellent corrosion inhibitor since its efficiency increased with the concentration to attain 91.8?% at 500?mg?l^?1. Electrochemical polarization measurements revealed that AQC acted as a mixed-type inhibitor and the results of electrochemical impedance spectroscopy have shown that the change in the impedance parameters, charge transfer resistance and double layer capacitance, with the change in concentration of the inhibitor is due to the adsorption of the molecule leading to the formation of a protective layer on the surface of mild steel. The adsorption was assumed to occur on the steel surface through the active centers of the molecule. The inhibition action of AQC was discussed in view of Langmuir adsorption isotherm. Density functional theory calculations of quantum parameters were used to explain efficiency in relation with molecular structure.     

Impedance spectroscopic study of corrosion inhibition of Al-Pure by organic Schiff base in hydrochloric acid

A new corrosion inhibitor namely o-Chloroaniline-N-benzylidene (o-CANB) has been synthesized and its inhibitive performance toward the corrosion of Al-Pure in 1.0 M hydrochloric acid has been investigated. Corrosion inhibition was studied by chemical method (weight loss) and electrochemical techniques including polarization method and electrochemical impedance spectroscopy (EIS). The present study has shown that this inhibitor is good in acidic media and the inhibition efficiency up to >99% in 1.0 M HCl. Polarization measurement revealed that the investigated inhibitor is a mixed type with a predominant action on cathode. Impedance measurement showed that the charge transfer resistance (R_ct) increased and double layer capacitance (C_dl) decreased with an increase in the inhibitor's concentration. Obtained results about inhibition efficiency from weight loss, polarization study and EIS are in good agreement with each other. The adsorption of the inhibitor on the metal surface in the acid solution was found to obey Langmuir's adsorption isotherm.     

Green approach to corrosion inhibition of mild steel in hydrochloric acid medium using extract of spirogyra algae

In the present investigation, a fresh water green algae spirogyra is used as an inexpensive and efficient mild steel corrosion inhibitor. The study is carried out in 0.5?M HCl solution using weight loss measurements, scanning electron microscopy–energy-dispersive X-ray spectroscopy, X-ray diffraction, and Fourier transforms infrared (FT-IR) techniques. The maximum inhibition efficiency was found to be 93.03% at 2?g?L^?1. The adsorption of extract of spirogyra on mild steel surface obeys the Langmuir adsorption isotherm. Corrosion inhibition mechanisms were inferred from the temperature dependence of the inhibition efficiency as well as from calculation of thermodynamic and kinetic parameters which direct the process. FT-IR analysis of green algae spirogyra revealed the presence of hydroxyl, amino, and carbonyl groups, which are responsible for the adsorption on the mild steel surface. SEM analysis supported the inhibitive action of the spirogyra extract against the mild steel corrosion in acid solution.     

Inhibition of mild steel corrosion in 5 % HCl solution by 5-(2-hydroxyphenyl)-1,2,4-triazole-3-thione

A new corrosion inhibitor, namely 5-(2-hydroxyphenyl)-1,2,4-triazole-3-thione (5-HTT), has been synthesized and its influence on corrosion inhibition of mild steel in 5 % HCl solution has been studied using weight loss method and electrochemical measurements. Potentiodynamic polarization measurements clearly reveal that the investigated inhibitor is of mixed type, and it inhibits the corrosion of the steel by blocking the active site of the metal. Changes in impedance parameters were indicative of adsorption of 5-HTT on the metal surface, leading to the formation of protective films. The degree of the surface coverage of the adsorbed inhibitors was determined by weight loss measurements, and it was found that the adsorption of these inhibitors on the mild steel surface obeys the Langmuir adsorption isotherm. The effect of the temperature on the corrosion behavior with addition of 5 × 10^?4 M of the inhibitor was studied in the temperature range 30–60 °C. The reactivity of this compound was analyzed through theoretical calculations based on density functional theory to explain the different efficiency of these compounds as a corrosion inhibitor.     

Inhibition effect of horehound (Marrubium vulgare L.) extract towards C38 steel corrosion in HCl solution

The corrosion inhibition properties of horehound (Marrubium vulgare L.) extract (HE) in 1 M hydrochloric acid medium was carried out using electrochemical methods (polarization curve and electrochemical impedance spectroscopy). Experiments were performed by concentration of the inhibitor and temperature effect. The results showed variation in inhibition performance of this plant extract. The Langmuir model was tested to describe the adsorption behavior of the inhibitor on the C38 steel surface. Some thermodynamic functions of dissolution processes were also determined.     

Corrosion inhibition of mild steel in acidic medium by butyl alcohol

The corrosive behavior of mild steel in 1 M H₂SO₄ solutions contaminated with 3.5 % recrystallized sodium chloride at specific concentrations of butyl alcohol was investigated using potentiodynamic polarization and weight loss technique. The results obtained showed butyl alcohol to be an efficient inhibitor in the acid environment with general decrease in corrosion rate as the concentration of the alcohol increases. The adsorption of the inhibitor on the mild steel obeys the Langmuir adsorption isotherm. The thermodynamic parameters of adsorption deduced reveal a mixed interaction with the steel surface and spontaneous adsorption of butyl alcohol.     

Inhibitive effect by extract of Mentha rotundifolia leaves on the corrosion of steel in 1 M HCl solution

An extract of Mentha rotundifolia leaves (EMRL) was tested as a corrosion inhibitor of steel in 1 M HCl using electrochemical impedance spectroscopy, Tafel polarization methods, and weight loss measurements. The inhibition efficiency of the extract of Mentha rotundifolia leaves was calculated and compared. We note good agreement between these methods. The results obtained revealed that the inhibitor tested differently reduced the kinetics of the corrosion process of steel. Its efficiency increases with the concentration and attained 92.87 % at 35 %. The effect of temperature on the corrosion behavior of steel in 1 M HCl was also studied in the range 298 and 338 K. The thermodynamic data of activation were determined. Mentha rotundifolia extract is adsorbed on the steel surface according to a Langmuir adsorption model.     

The effect of some triazole derivatives as inhibitors for the corrosion of mild steel in 5 % hydrochloric acid

Corrosion inhibition by triazole derivatives (n-MMT) on mild steel in 5 % hydrochloric acid (HCl) solutions has been investigated by weight loss and electrochemical methods. The results obtained revealed that these compounds performed excellently as corrosion inhibitors for mild steel in HCl solution. Potentiodynamic polarization studies showed that they suppressed both the anodic and cathodic processes and inhibited the corrosion of mild steel by blocking the active site of the metal. The effect of temperature on the corrosion behavior of mild steel in 5 % HCl with the addition of different concentrations of the inhibitors was studied in the temperature range from 303 to 333 K. The associated activation corrosion and free adsorption energies were determined. The adsorption of these compounds on the mild steel surface obeys the Langmuir adsorption isotherm. The effect of molecular structure on the inhibition efficiency has been investigated by quantum chemical calculations. The electronic properties of inhibitors were calculated and are discussed.     

Aqueous extract of <Emphasis Type="Italic">Argemone mexicana</Emphasis> roots for effective protection of mild steel in an HCl environment

The inhibition effect of aqueous Argemone mexicana root extract (AMRE) on mild steel corrosion in 1 M HCl has been studied by weight loss, Tafel polarization curves, electrochemical impedance spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy techniques. Results indicate that inhibition ability of AMRE increases with the increasing amount of the extract. A maximum corrosion inhibition of 94 % is acknowledged at the extract concentration of 400 mg L^?1. Polarization curves and impedance spectra reveal that both cathodic and anodic reactions are suppressed due to passive layer formation at the metal–acid interface. It is also confirmed by SEM micrographs and FTIR studies. Furthermore, the effects of acid concentration (1–5 M), immersion time (120 h) and temperature (30–60 °C) on inhibition potential of AMRE have been investigated by the weight loss method and electrochemical techniques. An adsorption mechanism is also proposed on the basis of weight loss results, which shows good agreement with the Langmuir isotherm.     

Corrosion inhibition and adsorption behavior of imidazoline salt on N80 carbon steel in CO2-saturated solutions and its synergism with thiourea

The inhibition and adsorption behavior of 2-undecyl-1-sodium ethanoate-imidazoline salt (2M2) and thiourea (TU) on N80 mild steel in CO₂-saturated 3 wt.% NaCl solutions was studied at 25?°C, pH 4, and 1 bar CO₂ partial pressure using electrochemical methods. It was found that inhibition efficiency (η%) increased with increase in 2M2 concentration but decreased with increase in TU concentration with optimum η% value at 20 mg l^?1 TU. The data suggest that the compounds functioned via a mixed-inhibitor mechanism. The inhibition process is attributed to the formation of an adsorbed film of 2M2 and TU via the inhibitors polycentric adsorption sites on the metal surface which protects the metal against corrosion. A synergistic effect was observed between TU and 2M2. Potential of unpolarizability, E _u, was observed in the presence of 100 mg l^?1 TU which was shifted positively in the presence of 2M2–100 mg l^–1 TU blends, which suggests that the presence of 2M2 stabilized the adsorption of TU molecules on the surface of the metal. The adsorption characteristics of 2M2 were approximated by Langmuir adsorption isotherm.     

Inhibition effect of environmentally benign Karanj (Pongamia pinnata) seed extract on corrosion of mild steel in hydrochloric acid solution

The inhibition of the corrosion of mild steel in hydrochloric acid solution by the seed extract of Karanj (Pongamia pinnata) has been studied using weight loss, electrochemical impedance spectroscopy, potentiodynamic polarization, and linear polarization techniques. Inhibition was found to increase with increasing concentration of the extract. The effect of temperature, immersion time, and acid concentration on the corrosion behavior of mild steel in 1 M HCl with addition of extract was also studied. The adsorption of the extract on the mild steel surface obeyed the Langmuir adsorption isotherm. Values of inhibition efficiency calculated from weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy are in good agreement. Polarization curves showed that Karanj (P. pinnata) seed extract behaves as a mixed-type inhibitor in hydrochloric acid. The activation energy as well as other thermodynamic parameters for the inhibition process was calculated. The adsorbed film on mild steel surface containing Karanj (P. pinnata) seed extract inhibitor was also measured by Fourier transform infrared spectroscopy. The results obtained showed that the seed extract of Karanj (P. pinnata) could serve as an effective inhibitor of the corrosion of mild steel in hydrochloric acid media.