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Natural-based corrosion inhibitors have gained great research interest thanks to their low cost and higher performance. In this work, the chemical composition of the methanolic extract of Ammi visnaga umbels (AVU) was evaluated by gas chromatography (GC) coupled with mass spectrometry (MS) and applied for corrosion inhibition of carbon steel (CS) in 1.0 mol/L HCl using chemical and electrochemical techniques along with scanning electron microscope (SEM) and theoretical calculations. A total of 46 compounds were identified, representing 89.89% of the overall chemical composition of AVU extract, including Edulisin III (72.88%), Binapacryl (4.32%), Khellin (1.97%), and Visnagin (1.65%). Chemical (Weight loss) and electrochemical (potentiodynamic polarization curves (PPC), and electrochemical impedance spectroscopy (EIS)) techniques revealed that investigated extract can be used as an effective corrosion inhibitor for carbon steel in 1.0 mol/L HCl solution. At a low dose of 700 ppm, the inhibitory action of AVU extract reached an inhibition efficiency of 84 percent. According to polarization tests, the investigated extract worked as a mixed inhibitor, protecting cathodic and anodic corrosion reactions. The EIS test showed that upon the addition of AVU extract to HCl solution, the polarization resistance increased while the double layer decreased. SEM images showed a protected CS surface in the inhibited solution. Quantum chemical calculations by Density Functional Theory (DFT) for the main components confirmed the major role of heteroatoms and aromatic rings as adsorption sites. Molecular dynamics (MD) simulation was used to study the adsorption configuration of the main components on the Fe(110) surface. Outcomes from this study further confirmed the significant advantage of using plant-based corrosion inhibitors for protecting metals and alloys.

Benzodiazepines are known for their variety of applications. Herein, the corrosion inhibition efficiency on carbon steel in 1 M HCl solution in the presence and absence of two synthesized benzodiazepines 4-(2-Oxopropylidene)-1-propargyl-1,2,4,5-tetrahydro-3H-1,5-benzodiazepin-2-one (PTB) and 1-decyl-4-(2-oxopropylidene)-1,2,4,5-tetrahydro-3H-1,5-benzodiazepine-2-one (DTB) was investigated using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) methods at various concentrations from 10−3 to 10−6 K. The obtained structures were characterized using NMR spectroscopy. Potentiodynamic polarization measurements showed that 1,5-benzodiazepine derivatives act as a mixed type inhibitor. The various parameters of activation determining the kinetic data such as energy, enthalpy and entropy of the inhibitors were evaluated and discussed. The adsorptive behavior of PTB and DTB followed Langmuir-type isotherm. The standard free energies of adsorption were negative due to better inhibition performance. DFT calculations at the B3LYP/6-31 + G (d,p) level of theory in polarizable continuum model reveal that the high inhibition of efficiency of DTB compared with PTB may refer mainly to the easy electron transfer from the former to the carbon steel surface.

A novel quinazoline derivative, 3-cyclopropyl-3,4-dihydroquinoline- 2(1H)-One (CPHQ), was successfully designed and synthesized. Then, its corrosion inhibition behavior on carbon steel (CS) surface in 1.0M HCl at different temperatures was investigated using chemical, electrochemical and theoretical techniques. The experiments confirmed that the studied inhibitor shows inhibition efficiency as high as 95% even at very low concentration of 5�10�3 M. To ascertain the nature of adsorption of CPHQ molecules on CS surface, Langmuir adsorption isotherm model was best fitted. From potentiodynamic polarization (PDP) calculations, it was concluded that the CPHQ acted as a mixed type corrosion inhibitor. Electrochemical impedance spectroscopy (EIS) studies revealed that increase in CPHQ concentration, resulted in an increase in the polarization resistance with a simultaneous decrease in the doublelayer capacitance values. PDP tests were also performed to understand the corrosion behavior of CS as a function of temperature without and with varying concentrations of CPHQ, at temperatures 303, 313, 323, and 333 K. It can be concluded that the corrosion inhibition effect was dependent on the concentration of the inhibitor and the solution temperature. In order to understand the basic insights of the action mode of CPHQ molecules, Density Functional Theory (DFT) method, and Molecular Dynamic (MD) simulations were also employed on the optimized structure of CPHQ.

Mild steel corrosion in HCl solution is an example of corrosion in acidic mediums. The ongoing research efforts to develop novel environmentally friendly corrosion inhibitors raise questions regarding their ability to effectively protect steel from corrosion. Herein, a series of experimental studies were conducted to explain the scientific mechanism of adsorption of four hydrazone derivatives (HDZs) namely, 2-((2,3-dimethylphenyl)amino)-N′-((1E,2E)-3-phenylallylidene)benzohydrazide (HDZ1) (E)-2-((2,3-dimethylphenyl)amino)-N′-(4-hydroxybenzylidene)benzohydrazide (HDZ2) (E)-2-((2,3-dimethylphenyl)amino)-N′-(1-phenylethylidene)benzohydrazide (HDZ3) and N′-cyclohexylidene-2-((2,3-dimethylphenyl)amino)benzohydrazide (HDZ4) on mild steel (MS) in 1.0 M HCl using chemical, electrochemical and surface characterization techniques. All results show that the inhibitor molecules form a stable layer on steel surface through chemical and physical interactions. HDZs adsorption onto the steel surface was found to follow Langmuir model. Furthermore, electrochemical results demonstrated that our developed inhibitors act as mixed-type inhibitors, with HDZ1 showing the highest polarization resistance and lowest corrosion current density. X-ray diffraction and scanning electron microscope were used to study corrosion products phases and surface morphology of MS samples. Our findings provide deeper insights into understanding the interaction mechanisms of HDZs with a steel surface and can be helpful to explore novel approaches to mitigate the steel dissolution.

Nowadays, a properly designed corrosion protection system, which is essential for large-scale practical application remains a big challenge. Herein, we report a combined experimental and theoretical study of the adsorption of a galactomannan polysaccharide, namely, Fenugreek gum (FG) on the mild steel (MS) surface in 1.0 M HCl by using electrochemical techniques, X-ray photoelectron spectroscopy (XPS), DFT, molecular dynamic (MD) simulations, radial distribution function (RDF) and mean square displacement (MSD). XPS results show that the FG forms a layer on steel surface. FG adsorption onto the steel surface was found to follow Langmuir model. The electrochemical results demonstrated that FG acts as mixed-type inhibitor. Scanning electron microscope (SEM) was used to examine the surface morphology of the samples. Our findings provide deeper insights into understanding the interaction mechanisms of FG with MS and can be helpful to explore novel approaches to mitigate the steel dissolution occurring at the acidic environment.

Nickel- aluminium bronze (NAB) is one of the well-known copper-based alloys; it is a well-recognized material in the marine environment thanks to its good corrosion and wear resistance along with its high strength. In this paper, the effect of film-forming potential on the electrochemical behavior of NAB alloy in 0.1 M Na2SO4 solution was evaluated. The study of the stability of passive films formed on NAB alloy was investigated using potentiodynamic and potentiostatic polarizations, Mott–Schottky (MS) and electrochemical impedance spectroscopy (EIS) analysis. The compositions of the passive films were determined by scanning electron microscope (SEM), UV–vis–NIR spectroscopy, and X-ray diffraction (XRD). All electrochemical tests revealed that the anodic potentials had a strong influence on passive films formed on NAB alloy. At intermediate frequencies above 450 mVSCE, the corrosion process is controlled by the adsorption/desorption process along with charge transfer and diffusion processes. Mott–Schottky analysis indicated that the donor density is in the range of 1021 cm−3 and increased with an increase in the film-forming potential. Moreover, the SEM analysis showed that the NAB alloy suffered a severe corrosion attack of the copper-rich α phase leading to the retention of the κ phases of the as-cast NAB in the passive films. The passive films were grown on the NAB alloy and displayed n-type semi-conductor behavior, which is entirely predictable from the main Cu and Al oxide in the film.

Carbon steel is a commonly used alloy in petroleum refining equipment. Nonetheless, its weak corrosion resistance is a perpetual problem for these industries. In the present study, we manifest the usefulness of a novel 1,2,4-triazole derivative, namely 5-hexylsulfanyl-1,2,4-triazole (HST) in inhibiting the carbon steel (CS) corrosion in 1.0 M HCl using mass loss measurements, electrochemical, scanning electron microscopy coupled with X-ray detection (SEM-EDX), X-Ray diffraction (XRD) and computational techniques. We deduced from the gravimetric study that the optimal concentration of HST is 10−3 M. Its inhibition efficiency can reach 97 % based on electrochemical data. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) results suggest an increased impedance in the presence of HST and mixed nature of inhibitor action, respectively. The compound HST mitigates corrosion at the temperature range of 298 K–338 K, with an inhibition efficiency of 89 % at 338 K. Free Gibbs energy obtained from the Langmuir isotherm model suggests that the inhibitor molecules hinder the acid attack mainly by chemisorption. A computational study based on Density Functional Theory (DFT) and Molecular Dynamics (MD) simulations was performed in an attempt to identify the factors most associated with anti-corrosive properties of the tested compound.

Two new benzodiazepine derivatives namely, 1-ethyl-4-(2-oxopropylidene)-1,2,4,5-tetrahydro-2H-1,5-benzodiazepine-2-one (BZD-1) and 1-octyl-4-(2-oxopropylidene)-1,2,4,5-tetrahydro-2H-1,5-benzodiazepine-2-one (BZD-2) have been synthesized and used as corrosion inhibitors for carbon steel in acidic solution (1 M HCl). Corrosion inhibition evaluation was performed using weight loss, electrochemical techniques [potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS)], quantum chemical calculations, and molecular dynamic (MD) simulations. The results showed that both compounds are good corrosion inhibitors for carbon steel in 1 M HCl medium; their inhibition efficiency increased with inhibitor concentration. In addition, the results obtained from above methods reveal that BDZ-2 is an excellent inhibitor. It gives a maximum inhibition efficiency of 96.63% at 10−3 M and inhibits corrosion by adsorbing at the carbon steel surface. EIS measurements showed that the charge transfer resistance increases, whereas the double-layer capacitance decreases with the inhibitor concentration. Polarization studies showed that BDZ-1 and BDZ-2 are mixed type. The tested inhibitors have been adsorbed on the carbon steel surface according to Langmuir isotherm adsorption model. The experimental results are in reasonably close agreement with quantum chemical parameters calculated at DFT/B3LYB/3-21G and the molecular dynamic simulations results.

Lagerstroemia speciosa leaf extract (LSLE) was examined as corrosion mitigating agent against mild steel in 1 M HCl. The extract was characterized by GC–MS and FTIR. Weight loss (WL), potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), SEM- EDX, AFM, UV–Vis spectroscopy and DFT studies were performed to examine corrosion mitigation performance of LSLE. As revealed by WL the extract was above 94% efficient at the concentration of 500 ppm and 333 K. Adsorption of LSLE on mild steel surface is spontaneous and follows Langmuir isotherm model. Mixed type inhibition with anodic predominance was revealed by PDP results. EIS data revealed the formation of inhibitive film on metal surface by the active groups of the extract. SEM and AFM show a better morphological image and reduced surface roughness in the presence of LSLE. UV–Vis results indicate Fe-LSLE complex formation during corrosion reaction. DFT has been conducted to correlate the inhibition efficiency with the molecular structure of active species present in the extract. Quantum parameters and Molecular dynamic simulation helps in correlating the molecular structure and adsorption strength with inhibition efficiency. ANOVA statistical test was conducted to compare the inhibition efficiencies obtained by using different techniques and the data reveals that they are significantly not different.