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Two novel bithienyl fluorobenzamidine derivatives namely, 4-([2,2':5',2''-terthiophen]-5-yl)-2-fluorobenzamidine hydrochloride salt (MA-1615), 5'-(4-amidino-3-fluorophenyl)-[2,2'-bithiophene]-5-carboxamidine dihydrochloride salt (MA-1740) were synthesized, characterized and their corrosion inhibition properties were evaluated by electrochemical methods for carbon steel (C-steel) in 1 M HCl. Experimental investigations revealed that the inhibition effectiveness of the investigated inhibitors (INHs) by the Tafel polarization method followed the order: MA-1740 (96.9%) MA-1615 (95.6%), demonstrating higher efficiency than inhibitors of similar structure reported in the literature. The investigated bithiophene derivatives exhibit mixed-type corrosion inhibition characteristics by blocking the active sites on the surface of C-steel. EIS study revealed that the INHs behave as interface-type corrosion inhibitors. UV-Visible spectrometric measurements confirmed a complex formation between the Fe

The adsorption action of polyethylene oxide (PEO) on copper surface in 3.5 wt.% NaCl solution was tested using electrochemical frequency modulation (EFM), atomic absorption spectrometry (AAS), UV- visible spectrometry and the morphology of copper surface was investigated by attenuated total reflectance spectroscopy (ATR-FTIR), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) techniques. Results obtained show that PEO is effective in preventing the corrosion of copper in NaCl solution. The adsorption of PEO onto copper surface was found to follow Langmuir isotherm model. ATR-FTIR, SEM and EDX spectroscopy techniques confirmed the adsorption of protective film of PEO on copper surface. Further, quantum chemical calculations were in agreement with inhibition efficiency (%I) of PEO that were obtained experimentally.

Theeffect of 6-[5-(4-methoxyphenyl) furan-2-yl] nicotinonitrile (MA-1160) as a new corrosion inhibitor for carbon steel (CS) in hydrochloric acid (HCl) solution was investigated using weight loss (WL), atomic absorption spectroscopy (AAS) and electrochemical measurements. The surface morphology of CS was tested using: scanning electron microscopy, atomic force microscope, attenuated total reflection–Fourier transform infra-red and ultraviolet–visible spectroscopy methods. The adsorption of MA-1160 on CS surface obeyed the model of Langmuir isotherm. Polarization data revealed that this inhibitor behave as mixed-type inhibitor. The spectroscopic measurements revealed the formation of a protective adsorbed layer on CS surface. Quantum chemical calculations were calculated and discussed using density functional theory method. The inhibition efficiency (% €) was 84% in WL, 86.4% in AAS, 86.0% in potentiodynamic polarization and 84.8% in EIS 86% at 21 µM. Thus, all the test methods gave good agreement with each other in % €.

The inhibitive action and adsorption behavior of cefotaxime drug on corrosion of copper in 0.1 mol L−1 HCl solutions was discussed using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), electrochemical frequency modulation (EFM), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) techniques. The results obtained from different electrochemical measurements revealed that the cefotaxime drug is a good inhibitor efficient in the studied concentration range. Polarization curves suggested that the inhibitor is a mixed-type inhibitor. EIS spectra showed that the addition of inhibitor increases the charge-transfer resistance of the corrosion process, and hence the inhibition performance improved. Results obtained from EFM method are shown to be in agreement with potentiodynamic and EIS measurements. The adsorption behavior of inhibitor on copper surface followed Langmuir adsorption isotherm. SEM and EDX examination of the copper surface revealed that cefotaxime drug prevented copper from corrosion by adsorption on its surface to form a protective film. Quantum chemical calculations were employed using DFT method to determine the possible active centers responsible for the adsorption of cefotaxime drug on the copper surface.

In this study, the effect of imidazole derivatives on the inhibition of aluminum corrosion in 0.5 M HCl has been studied using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and electrochemical frequency modulation (EFM) measurements. The results show that all imidazole derivatives are good inhibitors, and inhibition efficiency follows the order: B > A. Polarization curves demonstrated that the imidazole derivatives were of mixed-type inhibitors. The adsorption of each inhibitor on aluminum surface obeys Frumkin adsorption isotherm. Surface morphology studies were done using scanning electron microscopy (SEM) to characterize the film formed on aluminum surface. Quantum chemical calculations show that imidazole derivatives can adsorb on the aluminum surface through the nitrogen atoms as well as π-electrons in the imidazole ring.

Newly antipyrinyl derivatives 4 and 5 were synthesized from the reaction of enaminonitrile 3 with 1-nitroso-2-naphthol and salicyaldehyde, respectively, and used to protect mild steel dissolution in 1.0 M HCl solutions using weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy measurements. It was shown that these inhibitors act as good corrosion inhibitors for mild steel protection. The inhibition efficiencies were attributed to the simple blocking effect by adsorption of inhibitor molecules on the mild steel surface. The results showed that inhibitors acts as a mixed-type inhibitor. Relationship between molecular structure and their inhibition efficiency was elucidated by quantum chemical calculations.

The influence of Cephapirin drug on the corrosion of carbon steel (CS) in 2 M HCl solutions has been examined by mass loss (ML), and electrochemical methods. The results demonstrated that Cephapirin drug acts as good inhibitor for CS corrosion. The inhibition efficiency increased as the concentration of the drug increases. Potentiodynamic polarization (PDP) studies showed that Cephapirin is mixed-type inhibitor. The electrochemical impedance spectra (EIS) studies reveal that the process of inhibition is through charge transfer. The adsorption of the drug on metal surface obeyed Temkin adsorption isotherm. The surface analysis of the CS was investigated using Attenuated total reflectance spectroscopy (ATR-FTIR) and UV–visible reflectance spectroscopy. Surface analysis of CS confirmed the existence of a protective adsorbed film of the drug on the metal surface. The quantum chemical calculations of the drug molecule in aqueous phase were done using density functional theory (DFT) method and discussed to correlate the theoretical and experimental data. The inhibition efficiency of Cephapirin drug obtained by chemical and electrochemical methods was in good correlation with each other.

Inhibition of QD36 steel corrosion in 0.5 M HCl solution by aniline derivatives was studied using chemical (weight loss), potentiodynamic polarization and electrochemical frequency modulation measurements. The adsorption process of studied aniline derivatives on steel surface obeys the Langmuir adsorption isotherm. The values of activation energy (E*a), adsorption equilibrium constant (Kads), free energy of adsorption (ΔGads°, adsorption enthalpy (ΔHads°) and adsorption entropy (ΔSads°)were calculated and discussed. Potentiodynamic polarization measurements showed that aniline derivatives are mixed-type inhibitors. The results obtained by EFM technique were shown to be in agreement with other chemical and electrochemical techniques. Scaning electron microscope (SEM) was used to study the surface morphology of the QD36 steel in 0.5 M HCl solution in the absence and presence of inhibitors. Further, theoretical calculations were carried out and relations between computed parameters and experimental inhibition efficiency were discussed.

Corrosion inhibition of carbon steel in HCl by azo dye derivatives (ADD) was investigated using chemical and electrochemical techniques. Results obtained indicate that ADD inhibited the corrosion of carbon steel in the acid medium. Inhibition efficiency increases with increase in ADD concentration and is synergistically enhanced on addition of iodide and bromide ions. By fitting the obtained experimental data with the Langmuir adsorption model and the Arrhenius equation, some thermodynamic and kinetic parameters for the corrosion process were estimated, and the values support the results obtained. Some quantum chemical parameters and the Mulliken charge densities for ADD were calculated by the MNDO semi-empirical method to provide further insight into the mechanism of inhibition of the corrosion process.

Inhibition of carbon steel corrosion in 2 M hydrochloric acid (HCl) solution by thiophene azo dye derivatives were studied using weight loss, electrochemical frequency modulation (EFM), and atomic absorption techniques. The experimental data suggest that the inhibition efficiency increases with increasing inhibitors concentration in presence of 103 μM potassium iodide (KI). This is due to synergistic effect. Thus, the experimental results suggested that the presence of these anions in the solution stabilized the adsorption of inhibitors molecules on the metal surface and improved the inhibition efficiency. The results of EFM experiments are a spectrum of current response as a function of frequency. The corrosion rate and Tafel parameters can be obtained with measurement by analyzing the harmonic frequencies. The adsorption of the inhibitors on metal surface obeys the Langmuir adsorption isotherm. The surface of metal examined using Fourier transform infrared and ultraviolet spectroscopy. Quantum chemical calculations were carried out and relations between computed parameters and experimental inhibition efficiency were discussed.

The effect of some furfural hydrazone derivatives (I -V) as corrosion inhibitors for C-steel in 3M H 3 PO 4 solution in which M indicates mol/l has been studied using weight-loss and galvanostatic polarization techniques. A significant decrease in the corrosion rate of C-steel was observed in the presence of the investigated compounds. This study revealed that, the inhibition efficiency increases with increasing the inhibitor concentration, and the addition of iodide and thiocynate ions enhances it to a considerable extent. The effect of temperature on the corrosion behavior of C-steel was studied in the range from 30-60°C with and without 5×10 -6 M investigated compounds using weight-loss method. Apparent activation corrosion energy (E a *) and other thermodynamic parameters for the corrosion process were calculated and discussed. The polarization measurements show that the investigated compounds act as mixed-type inhibitors, but the cathode is more polarized when an external current was applied. The adsorption of these compounds on the surface of C-steel in 3 M H 3 PO 4 obeys Frumkin's adsorption isotherm. The mechanism of inhibition was discussed in the light of the chemical structure of the investigated compounds.

The inhibition effect of hydroxyethylcellulose (HEC) on 1018 c-steel corrosion in 3.5% NaCl solution was investigated by using potentiodynamic polarization, electrochemical frequency modulation (EFM) and electrochemical impedance spectroscopy (EIS) techniques. The potentiodynamic polarization studies suggested that HEC acts as a mixed-type inhibitor. Data obtained from EIS were analyzed to model the corrosion inhibition process through equivalent circuit. Results obtained from EFM technique were shown to be in agreement with potentiodynamic and EIS techniques. The adsorption behavior of HEC on steel surface follows the Langmuir adsorption isotherm. Thermodynamic parameter (ΔG°(ads)) and activation parameters (Ea(*), ΔH(*) and ΔS(*)) were calculated to investigate mechanism of inhibition. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis system were performed to characterize the film formed on the metal surface. DMol(3) quantum chemical calculations were performed to support the adsorption mechanism with the structure of HEC molecule.