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Tetraethyl orthosilicate (TEOS) was used as a chemical precursor to deposit ultra-thin SiOxCy plasma polymer films onto mild steel surfaces for preventing the corrosion process. The structure--property relationships of the coatings were evaluated by X-ray Photo Spectroscopy (XPS), X-Ray Diffraction (XRD), Fourier Transform InfraRed spectroscopy (ATR-FTIR) and Energy Dispersive X-ray spectroscopy (EDX) completed with Scanning Electron Microscopy (SEM). The SEM micrographs confirmed a pinhole-free surface morphology of the low-pressure deposited plasma polymer films. The TEOS molecules become fragmented in the plasma by numerous collisions with energy-rich electrons and heavier particles. Recombination of fragments and condensation onto the steel substrate is responsible for the formation of organic SiO containing plasma polymer layers. Such thin layers consist of predominantly SiOx structures. Their properties are determined largely by the gap distance between the two samples used as electrodes in the plasma. The efficiency of the corrosion-protecting coating was compared with uncoated samples. The corrosion protection was determined by exposure of samples to 3.5% NaCl aqueous solutions. For this purpose, polarization and Electrochemical Impedance Spectroscopy (EIS) were used to monitor the corrosion. The optimal gap distance between the electrodes was determined for corrosion protection. The best protective efficiency reached more than 97% of the total protection as measured at room temperature. [ABSTRACT FROM AUTHOR]

[Display omitted] • Three novel cyano coumarin compound were synthesized and approved by FTIR, 1H NMR and Mass spectroscopy. • The synthesized inhibitors obeyed Langmuir adsorption mode with a chemical adsorption. • The metal was protected by the creation of a protective layer on the surface, according to SEM, EDX, and UV data. • The corrosion related to SRB can be controlled by the current organic coumarin inhibitors. New synthesized coumarin-buta-1, 3-diene conjugated dyes having donor–acceptor structure were prepared. The characterization of the synthesized dyes was approved by using IR, 1H NMR and Mass fragmentation analysis. The adsorption properties for the synthesized coumarin compounds were determined by experimental and theoretical methods. The corrosion inhibition effect of the synthesized coumarin dyes against steel in acid environment was investigated by plasma atomic emission spectrometer, weight loss and electrochemical methods. The highest corrosion efficiency was 97.62 % resulted from potentiodynamic polarization technique at the highest concentration for Dye 2 inhibitor. The adsorption mechanism of the inhibitors was investigated and thermodynamic parameters were calculated. The surface protection examination was carried out using scanning electron microscopy and the formation of the complex on the surface was approved using Energy dispersive X-ray spectroscopy and UV– visible spectroscopy. The quantum chemical calculations were used to confirm the donor–acceptor system of the synthesized coumarin compounds. The biological activity effect versus sulfate reducing bacteria was confirmed. The experimental and theoretical results assure that these current synthesized dyes have a good ability to protect the steel from corrosion by forming a protective layer on the surface. [ABSTRACT FROM AUTHOR]

• Three azo acetyl coumarin dyes are prepared and confirmed with FTIR, 1HNMR and mass spectroscopy. • The adsorption isotherm of prepared dyes obeyed Longmuir adsorption isotherm according to results obtained from ICPE. • The prepared dyes showed high ability to inhibit steel corrosion reaction as a mixed type inhibitors. • The prepared dyes showed high efficiency to inhibit the growth of SRB bacteria. The new azo acetyl coumarin derivatives were synthesized and characterized using Fourier-transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (1H NMR) and mass spectral studies. The ability for these three dyes to act as corrosion inhibitors for mild steel in 1.0 M HCl was confirmed by potentiodynamic polarization (PP) and electrochemical impedance spectroscopy (EIS). The state of mixed adsorption with the PP effect is shown. The azo acetyl coumarin derivatives showed the strongest corrosion inhibition of 85.29–93.01% at a corrosion of 7.5 × 10−4 M. Adsorption of the inhibitory molecules on the mild steel surface followed Langmuir adsorption isotherm. The adsorption phenomenon was verified using UV–Vis, scanning electron microscopy (SEM) and Energy dispersive X-ray spectroscopy (EDX) technique, whereas FTIR confirmed the presence of several functional groups containing heteroatoms. Also, quantum chemical parameters, inductively coupled plasma atomic emission spectroscopy, and the anti-bacterial effect of these new derivatives against sulfate reducing bacteria (SRB) were studied. All obtained results ensure that these derivatives can form an effective blocking layer and control the corrosion process. [ABSTRACT FROM AUTHOR]

• Raman, Infrared and NMR spectra were interpreted based on keto-thione tautomer of 6-Methyl-2-thiouracil molecule. • Polarization and impedance measurements were analyzed for corrosion inhibition efficiency of mild steel in HCl. • FMO and NBO calculations were to correlate the active sites with the inhibition efficiency. • Adsorption annealing simulations locate the best adhering geometry of the inhibitor to the metal surface. Raman (3500-100 cm−1) and FT-ATR (4000-360 cm−1) spectra of solid 6-Methyl-2-thiouracil (6M2TU) have been recorded in addition to 1H and 13C NMR along with Mass fragmentation patterns. Moreover, the hydroxy-thiole, keto-thiole, hydroxy-thione and keto-thione tautomer's stability were theoretically probed using (DFT) B3LYP/6-31G(d,p) calculations in favor of keto-thione in the gaseous phase by ~12-24.5 kcal/mol. Moreover, the monomer and dimer structures were verified by MS/MS spectral measurements owing to the recorded m/z peaks at 141.2 and 281.1, respectively. The inhibition efficiency of 6M2TU towards mild steel iron (MSFe) against 1.0 M HCl has been investigated with molar concentrations of 0.75-7.5 × 10−3 at 30±2°C using potentiodynamic polarization, impedance measurements and electrochemical frequency modulation. The entitled compound shows a superior inhibition capability against corrosion ranged from 72-94% was obtained. The polarization curves suggest a mixed-type inhibitor for 6M2TU obeying the Langmuir adsorption model while the impedance data ensures an increase in the charge transfer resistance upon its adsorption on the surface of FeMS. Natural bond orbital (NBOs) showed an effective charge transfer from the inhibitor to d -orbitals of the metal in the following order; LP (S) > LP (O) > LP (N 1) > π (C=S) > LP (N 3) > π (C 5 =C 6) > π (C=O). The calculated low Δ E g a p (4.21 eV) predicts that 6M2TU have an efficient inhibition efficiency. Finally, The kinetic parameter F number (5.369673 cm−1) and the potential function (V 3) was estimated at 454±19 cm−1 (1.30±1.05 kcal/mol) implementing B3LYP/6-31G(d,p) optimized SPs and the calculated torsion frequency at 133 cm−1. [Display omitted] Raman, infrared and NMR spectra were used to study the molecular conformational/tautomeric structures of 6-Methyl-2-thiouracil. Vibrational interpretations were suggested for keto-thione tautomer based on normal coordinate analysis. The corrosion its inhibition effect on iron mild steel in HCl was investigated using potentiodynamic polarization and electrochemical impedance measurements favors a dominant/minor chemical/physical adsorption mechanism. [ABSTRACT FROM AUTHOR]

Chromium (VI) coatings are highly toxic and carcinogenic; therefore, thea should be replaced by a new eco-friendly material that retains its effectiveness in terms of corrosion. Herein, thin silicon oxycarbide films as an eco-friendly anticorrosive coating were deposited on a low carbon steel substrate by a radio frequency capacitively coupled plasma technique using tetraethyl orthosilicate (TEOS) as a precursor. The corrosion performance of the coatings were evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in dependence on the gap distance between the plasma electrodes and the pH values at room temperature. The chemical bonding and morphological features of the deposited films were investigated by Fourier Transformer Infrared Spectroscopy in Attenuated Total Reflectance (ATR-FTIR) mode, X-Ray Diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDX) coupled with scanning electron microscopy (SEM). The I c o r r values were significantly decreased by reducing the gap distance and reached a minimum at 1 cm gap distance. It was reduced from 12 µA/cm2 for the blank sample to 0.714 µA/cm2 in treated sample at gap distance 1 cm and protective efficiency reached ~ 94% in the neutral solution. Nevertheless, the best protective efficiency achieved more than 99% of the total protection in alkaline medium as measured at room temperature for treated sample at gap distance 1 cm. [ABSTRACT FROM AUTHOR]

• Raman, ATR-IR and Mass spectra of 4,5-Dicyanoimidazole (DCI) have been recorded. • Electrochemical impedance spectroscopy was used to evaluate DCI inhibition efficiency. • Polarization measurements were used to account for anodic and cathodic reactions of DCI. • FMO and NBO calculations were carried to correlate DCI molecular structure to experimental findings. Raman (3500-50 cm−1) and FT-ATR/FT-infrared (3500-500/4000-200 cm−1) spectrum of 4,5-Dicyanoimidazole (DCI) were recorded and analyzed by normal coordinate analysis calculations. In addition, we have studied the molecular structure of DCI by means of B3LYP Density Functional Theory (DFT) using 6-31g(d) basis set. Aided by computational outcomes, all vibrational bands were assigned quantitatively to their corresponding fundamentals. The corrosion inhibition efficiency of DCI towards mild steel in 1.0 M HCl has been investigated experimentally and theoretically. Electrochemical impedance spectroscopy, electrochemical frequency modulation and polarization measurements along with thermodynamic predictions were assigned to both the anodic and cathodic inhibition. DCI-metal interactions and charge reallocation were analyzed in terms of Frontier molecular orbital (FMO) and Natural bond orbital (NBO) analysis. Global reactivity descriptors; ionization potential (IP), electron affinity (A), electronegativity (χ), chemical potential (µ), chemical hardness (η), and electrophilicity index have been calculated and assigned to the inhibition efficiency. Good correlation between the theoretical calculations and experimental measurments has been achieved. The results are compared with similar molecular systems whenever appropriate. Raman and infrared spectral and computational study of 4,5-Dicyanoimidazole were adapted with electrochemical measurements to account for structural and corrosion inhibition relationship. The findings verify that the investigated molecule has high inhibition efficiency toward corrosion of mild steel in 1 M HCl. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• Polarization measurements and impedance spectra were reported for some triazole derivatives as corrosion inhibitors for Al in HCl. • FMO and NBO calculations were used to relate the molecular structure to the inhibition efficiency. • Adsorption annealing simulations were performed to locate the best adhering geometry of inhibitors to the metal surface. The corrosion inhibition of three triazole derivatives; p-tolyl-1H-1,2,3-triazol-5-ol (Z1), 4-Chlorophenyl-1H-1, 2, 3-triazol-5-ol (Z2) and Methyl-4-(5‑hydroxy-1H-1, 2, 3-triazol-1-yl) benzoate (Z3) towards aluminum metal in 1.0 M HCl have been investigated using potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), B3LYP Density Functional Theory (DFT) and adsorption annealing simulations. The electrochemical findings exhibit an inhibition efficiency increase in the order: Z3 > Z2 > Z1 with a maximum inhibition efficiency (74.7%) obtained at 500 ppm from Z3. Both anodic (βa) and cathodic (βc) Tafel constants was significantly affected by adding inhibitors to the corrosion medium proposing a mixed type nature. The adsorption of the inhibitors on the metal surface was found to be a spontaneous process and obeyed Langmuir isotherm. The conformational scan along with annealing adsorption simulations showed a dihedral angle between the triazole ring and the phenyl ring of only 30° which promotes optimal surface coverage. Global reactivity descriptors, Fukui indices, atomic charges and NBO analysis showed that the priority of charge reallocation form inhibitor MOs to the metal surface is easier in the order: Z3 > Z2 >Z1 which reveal good agreement to the electrochemical measurements. Based on DFT results, an inhibition mechanism was proposed. Molecular structure of some triazole derivatives were investigated in the context of their inhibition efficiency to the corrosion of Al in HCl. The FMO and NBO were used to account for the direction of electron flow within the investigated molecules and hence reallocation onto the metal surface. Electrochemical measurements were compared and assigned to the molecular structure outcomes. [Display omitted] [ABSTRACT FROM AUTHOR]