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The extract of Datura stramonium has been studied as a possible source of green inhibitor for corrosion of mild steel (MS) in HCl and H₂SO₄ media at different temperatures. The anticorrosion effect was evaluated by conventional weight loss studies, electrochemical studies viz., Tafel polarization, ac impedance, and SEM studies. The studies reveal that the plant extract acts as a good inhibitor in both the acid media and better in H₂SO₄ medium. Tafel polarization method indicate that the plant extract behaves as a mixed mode inhibitor. Double layer capacitance and charge transfer resistance values derived from Nyquist plots obtained from ac impedance studies give supporting evidence for the anticorrosive effect. The inhibitive effect may be attributed to the adsorption of the inhibitor on the surface of MS, following Temkin adsorption isotherm. Increase of inhibition efficiency with increase of temperature along with Ea values serve as a proof for chemisorption. SEM studies provide the confirmatory evidence for the protection of MS by the green inhibitor. The study reveals the potential of D. stramonium for combating corrosion which may be due to the adsorption of alkaloids and other phytoconstituents.

The inhibitory effect of some Schiff bases viz. N,N′-bis(2-hydroxybenzylidene)-1,3-diaminobenzene (SB1), N,N′-bis(4-bromobenzylidene)-1,3-diaminobenzene (SB2) and N,N′-bis(2-hydroxy-5-bromobenzylidene)-1,3-diaminobenzene (SB3) on the corrosion of aluminium alloy in 0.5 M HCl acid have been studied using weight loss measurements, potentiodynamic polarization and Scanning Electron Microscopy (SEM). The experimental results showed that these Schiff bases SB1, SB2 and SB3 efficiently inhibit the corrosion of aluminium alloy in 0.5 M HCl medium and found to follow almost similar corrosion inhibition pattern. The potentiodynamic polarization curves revealed that, all the studied Schiff bases are mixed type inhibitors with a predominantly cathodic action and their inhibition efficiencies increased with increasing inhibitor concentration. The adsorption of Schiff bases was found to follow Langmuir adsorption isotherm. SEM study revealed that these compounds protect the metal corrosion by adsorption on its surface to form a protective layer. The inhibition performance depends strongly on the type of functional groups substituted on the benzene ring.

The corrosion inhibition characteristics of 2,2′-bipyridine (BIPY) and 2,2′-bipyridine-3,3′-dicarboxylic acid (BIDA), on carbon steel in sulphuric acid solutions was studied using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques at 20°C, 30°C and 40°C. The results indicate that the organic compounds inhibit the corrosion of mild steel in H₂SO₄ solutions and the extent of inhibition increases with inhibitor concentration and decreases with temperature. A mixed-inhibition mechanism is proposed for the inhibitive effects of the compounds. The order of inhibition efficiency obtained was BIDA>BIPY. There is a good correlation between the quantum chemical parameters and experimentally determined inhibition efficiency of the inhibitors. The adsorption characteristics of the inhibitor were approximated by Temkin isotherm. Morphological study of the carbon steel electrode surface was undertaken by scanning electron microscope (SEM) and the interfacial species formed on the surface in the presence of inhibitors analyzed by Infrared spectroscopy.

Reinforced concrete is one of the widely used construction materials for bridges, buildings, platforms and tunnels. Though reinforced concrete is capable of withstanding a large range of severe environments including marine, industrial and alpine conditions, there are still a large number of failures in concrete structures for many reasons. Either carbonation or chloride attack is the main culprit which is due to depassivation of reinforced steel and subsequently leads to rapid steel corrosion. Among many corrosion prevention measures, application of corrosion inhibitors play a vital role in metal protection. Numerous range of corrosion inhibitors were reported for concrete protection that were also used commercially in industries. This review summarizes the application of natural products as corrosion inhibitors for concrete protection and also scrutinizes various factors influencing its applicability.

This work aims at synthesis and characterization of 2,2${}^{\prime }$-dibenzimidazolyl butane as an effective corrosion inhibitor of mild steel in sulfuric acid solution. A simple and efficient method for its synthesis in described. The chemical structure and surface morphology of 2,2${}^{\prime }$-dibenzimidazolyl butane were characterized by mass spectrometry (MS), Fourier transform infrared (FTIR), Raman, ¹H, ${}^{13}$C NMR spectroscopy and transmission electron microscopy (TEM). Its thermal decomposition and its variation in mass was studied by thermogravimetric analysis (TGA) coupled with differential thermal analysis (DTA). The molecular mass of 2,2${}^{\prime }$-dibenzimidazolyl butane was determined to be at 290g/mol and its degradation was achieved at 455^∘C. Then, the corrosion inhibition efficiency of 2,2${}^{\prime }$-dibenzimidazolyl butane was studied with various concentrations in 0.5 M H₂SO₄ solution for mild steel by the potentiodynamic polarization and the electrochemical measurements. According to the results of electrochemical impedance spectroscopy, the inhibition efficiency decreased with concentration and reached its maximum (95.5%) at 100ppm. The polarization measurements showed that the prepared inhibitor acts as a cathodic type inhibitor. The mass loss tests are in accordance with the results of electrochemical measurements.

Continuing to study the inhibition of corrosion, 5,5-diphenyl-2-thioxoimidazolidin-4-one (PTI) has been tested as a corrosion inhibitor for mild steel (MS) in an aggressive 1 M HCl solution by chemical and electrochemical techniques: weight loss, potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis, UV-Visible. Inhibitory efficacy increases with increasing inhibitor concentration and decreases with increasing temperature. The studied inhibitor is more efficient (99.2%) at 298 K at an optimal concentration of 1mM. The PDP study revealed that PTI behaved as mixed type of inhibitor. In addition, the PTI inhibitor obeys the single layer adsorption isotherm of Langmuir. The quantum chemical calculations, molecular dynamic (MD) simulation studies fairly well agreed with the experimental measurements.

The corrosion inhibition performance of novel synthesized thiosemicarbazide derivative namely, 2-isonicotinoyl-N-phenylhydrazinecarbothioamide (IPC) on the mild steel coupon surface in 1M hydrochloric acid solution is investigated by weight loss measurements. The adsorption parameters of the IPC on the mild steel coupon surface have been evaluated and the surface morphology of the tested mild steel is studied by scanning electron microscope (SEM) technique. The results of this study demonstrate a significant inhibitor (IPC) for mild steel and showed the highest inhibitive efficiency of 96.3% at 5mM as optimum studied inhibitor concentration. The adsorption of IPC molecules on a mild steel coupon surface is obeyed completely by the model of Langmuir adsorption isotherms. SEM has been applied to analyse the layer of IPC molecules which formed on a mild steel coupon surface as a protective layer. The inhibition efficiency (IE) of IPC from weight loss techniques and SEM analysis was harmonic with each other. The Density Functional Theory (DFT) computations have been applied to evaluate the adsorption sites of the IPC molecules and the quantum chemical calculations correlation of IPC molecules with methodological results are discussed. The energy of the highest occupied molecular orbital (EHOMO) shows a significant tendency of the IPC molecules to donate pairs of electrons to the iron atoms on the surface of mild steel. The energy of the lowest unoccupied molecular orbital (ELUMO) for IPS molecules reveals a high tendency to accept electrons from iron atoms on the surface of mild steel.

Corrosion inhibition mechanism of six 2-amino-5-alkyl-1,3,4-thiadiazole compounds, for metal surface corrosion was studied by combining quantum chemistry, molecular mechanics and molecular dynamics simulation methods. Molecular reactivity parameters such as $E_{\mathrm{\text{HOMO}}}$, $E_{\mathrm{\text{LUMO}}}$, Fukui index were obtained and revealed that the change in alkyl chain length has little influence on the reactivity of thiadiazole inhibitor molecules. Molecular mechanics calculation results show that the molecule with elongated alkyl chain could form self-assembled membrane with higher stability and coverage rate to prevent the diffusion of corrosive substances to metal surface. Molecular dynamics simulation revealed the -equilibrium adsorption behavior of these thiadiazole molecules on metal surface and the calculated results were in agreement with the experimentally determined inhibition efficiencies.

Nanostructured hybrid silica/epoxy films containing boehmite nanoparticles were investigated in the present work as pretreatments for AA2024 alloy. To produce the nanocomposite sol-gel films, boehmite nanoparticles prepared from hydrolysis/condensation of aluminum isopropoxide (AlI) were doped into another hybrid organosiloxane sol. The produced oxide nanoparticles have the capability to act as nanoreservoirs of corrosion inhibitors, releasing them controllably to protect the metallic substrate from corrosion. For this purpose the corrosion inhibitor, cerium nitrate, was introduced into the sol-gel system via loading the nanoparticles. The morphology and the structure of the hybrid sol-gel films were studied by Scanning Electron Microscopy (SEM). The corrosion protection properties of the films were investigated by Potentiodynamic Scanning (PDS) and Electrochemical Impedance Spectroscopy (EIS). The results show that the presence of boehmite nanoparticles highly improved the corrosion protection performance of the silica/epoxy coatings. Moreover, they can act as nanoreservoirs of corrosion inhibitors and provide prolonged release of cerium ions, offering a self-healing property to the film.

Chloride ions begin to erode concrete in early age. In this paper, the rule of diffusion coefficient and the development of effective porosity of early age concrete mixed corrosion inhibitor in different concentrations of salt solution are analyzed through coulomb electricity method and the effective porosity test. Results show that the chloride ion penetration resistance of early age concrete increase with increase of age, weaken with the increase of chloride ion concentration. Effective porosity decreases with the increase of age and the concentration of sodium chloride solution. Concrete mixed corrosion inhibitors can effectively reduce the coefficient of permeability, the early effect is better than the late.