Showing papers by "Belkheir Hammouti published in 2018"

Adsorption and Corrosion Inhibition Effect of 2-Mercaptobenzimidazole (Surfactant) on a Carbon Steel Surface in an Acidic Medium: Experimental and Monte Carlo Simulations

Abstract: Experimental electrochemical methods, combined with Monte Carlo simulations, have been employed to investigate the possibility of usi ng 1-decyl-2-(decylthio)-1Hbenzimidazole (T2) as corrosion inhibitor for mild steel in a 1 M HCl medium. This inhibitor was found to be of the mixed type. The re sults derived from EIS indicate that the charge transfer resistance has increased with t he increase in the inhibitor concentration. The inhibitory mechanism was explore d by the potential of zero charge (Epzc) measurement at the solution/metal interface. The inhibitor adsorption has followed Langmuir adsorption isotherm. Surface morp h logy results showed the compound adsorbed film on a mild steel surface. The molecule interactions with the mild steel surface were simulated based on Monte Ca rlo simulation approach using Fe(111) crystal surface as a representative metalli c surface.

Towards a Deeper Understanding of the Anticorrosive Properties of Hydrazine Derivatives in Acid Medium: Experimental, DFT and MD Simulation Assessment

Abstract: The corrosion inhibition properties of two compounds namely, 1,2-dibenzylidenehydrazine (C1) and 1,2-bis(1-phenylethylidene)hydrazine (C2) for mild steel (MS) in 1.0 M HCl were studied by using weight loss, electrochemical techniques, density functional theory (DFT), and molecular dynamic (MD) simulations. Experimental results show that both C1 and C2 behave as mixed-type inhibitors. Both inhibitors showed efficient binding with metal surface. With C1 exhibiting the highest inhibition efficiency, resulting in low double layer capacitance and a high polarization resistance. The mechanism of inhibition action of the studied compounds was discussed in the light of the DFT and MD simulations studies. MD simulation revealed a nearly flat configuration for the C1 molecule on the metal surface, with more negative interaction energy in comparison to C2. Theoretical results are in line with the experimental results.

4-(2-(2-(2-(2-(Pyridine-4-yl)ethylthio)ethoxy)ethylthio)ethyl)pyridine as New Corrosion Inhibitor for Mild Steel in 1.0 M HCl Solution: Experimental and Theoretical Studies

Abstract: The inhibition effect of 4-(2-(2-(2-(2-(pyridine-4-yl)ethylthio)ethoxy)ethylthio)ethyl)pyridine (P4E4P) on mild steel corrosion in 1.0 M HCl solution was investigated by quantum chemical calculations, electrochemical techniques, and weight loss measurements. The experimental results reveal that this compound has a good inhibiting effect and the inhibition efficiency, increased with the inhibitor concentration to reach 97% at 1 mM. The effect of temperature on the corrosion behavior of mild steel has been examined in the temperature range of 308–353 K. The inhibition efficiency increases with increasing inhibitor concentration, but decreases with increasing temperature. The adsorption of the inhibitor on mild steel surface obeyed the Langmuir adsorption isotherm. The kinetic and thermodynamic parameters for mild steel corrosion and inhibition adsorption, respectively, were determined and discussed. Potentiodynamic polarization suggested that it is a mixed type of inhibitor. Data obtained from EIS measurements were analyzed to model the corrosion inhibition process through the appropriate equivalent circuit model. Quantum chemical calculations were employed to study the electronic properties of P4E4P to ascertain the correlation between the inhibitory effect and the molecular structure. Both the experimental and theoretical results are in good agreement with each other in this regard and confirm that P4E4P is an effective inhibitor.

Kinetic–Thermodynamic Properties of a Polyacrylamide on Corrosion Inhibition for C-Steel in 1.0 M HCl Medium: Part 2

Abstract: In this second part, the adsorption and thermodynamics properties of a polyacrylamide PA on corrosion inhibition of in 1.0 M HCl solution were analyzed by means of potentiodynamic polarization and electrochemical impedance spectroscopy techniques. Besides, the effects of temperature as well as the immersion time, on the inhibition efficiency, at 3 × 10−6 mol L−1 of PA, were also investigated. The adsorption data were modeled using six linearized forms of adsorption isotherms corresponding to Langmuir, Flory–Huggins, Temkin, Frumkin, Freundlich as well as the kinetic–thermodynamic model of El-Awady. The Langmuir model was first ruled out notwithstanding the highest value of linear regression coefficient and a slope close to unity. Secondly, it was found, according to both El-Awady and Flory–Huggins models, that exactly three molecules of water were replaced by one PA molecule. Thirdly, it was shown the presence of repulsive lateral interactions in the adsorbed inhibitory layer confirmed by the negative sign of the interaction parameters of Temkin and Frumkin isotherms. The effect of immersion period revealed significant improvement of the charge transfer resistance and accordingly the inhibiting efficiency which reach circa 96% after 6 h. The confrontation of thermodynamic (Kads, ΔrGads°) along with the kinetic parameters (A, Ea) showed that the adsorption of PA molecules onto C-steel surface involved both chemical and physical adsorption but predominantly chemisorption.

Anticorrosion Activity of a Polyacrylamide with High Molecular Weight on C-Steel in Acidic Media: Part 1

Abstract: The chemical structure of a polyacrylamide (PA), synthesized by inverse emulsion polymerization, was confirmed by FTIR and 1H NMR. The experimental conditions were conducted to produce high molecular weight of 1.4 × 106 g mol−1 determined by both gel permeation chromatography and viscosity average molecular weight methods. The efficiency of PA was evaluated, on corrosion inhibition of C-steel in 1.0 M HCl solution, by means of electrochemical impedance spectroscopy, potentiodynamic polarization (PP), and mass-loss (ML) measurements, and a very good concordance was obtained from the three techniques. The inhibiting efficiency increased up to 4 × 10−6 mol L−1 and dropped down afterward. The PP curves revealed that PA was of mixed-type, influencing predominantly the anodic process. The electrochemical interface was satisfactorily modeled with the electrical circuit (RS + Qdl/Rct) using CPE(α,Q) reflecting one-time constant. This fact, testifying the dominant character of charge transfer control of the C-steel corrosion process, was well described in both Nyquist along with Bode diagrams which take into account the frequency dependence, justifying the suitable choice of the electrical circuit. The adsorption of PA involved both physical and chemical interactions of non-protonated and protonated molecules with a deeper discussion on the suitable sites of protonation. The performance of PA was maintained if not slightly ameliorated in a more aggressive medium such as 0.5 M H2SO4 at 298 K. Two-time constants were needed to model the electrochemical interface (RS + Qdl/(Rct + RL/L)).

Biomimetic oxidation of catechol employing complexes formed in situ with heterocyclic ligands and different copper(II) salts

Abstract: In the present work, catecholase activity is presented. The complexes were prepared by condensation of the organic ligand pyrazolyl L 1 –L 4 and copper(II) ion in situ. The pyrazolyl compounds L 1 –L 4 used in this study are: L 1 is (3,5-dimethyl-pyrazol-1-ylmethyl)-(4-methyl-pyridin-2-yl)-pyrazol-1-ylmethyl-amine; L 2 is 1-{4-[(3,5-dimethyl-pyrazol-1-ylmethyl)-pyrazol-1-ylmethyl-amino]-phenyl}-ethanone; L 3 is 1-{4-[(3,5-dimethyl-pyrazol-1-ylmethyl)-[1,2,4]triazol-1-ylmethyl-amino]-phenyl}-ethanone, and L 4 is 2-[(3,5-dimethyl-pyrazol-1-ylmethyl)-[1,2,4]triazol-1-ylmethyl-amino]-6-methyl-pyrimidin-4-ol, and copper ions salts Cu(II) are (Cu(CH3COO)2, CuCl2, Cu(NO3)2 and CuSO4). In order to determine factors influencing the catecholase activity of these complexes, the effect of ligand nature, ligand concentration, nature of solvent and nature of counter anion has been studied. The best activity of catechol oxidation is given by the combination formed by one equivalent of ligand L 2 and one equivalent of Cu(CH3COO)2 in methanol solvent which is equal to 9.09 µmol L−1 min−1. The Michaelis–Menten model is applied for the best combination, to obtain the kinetic parameters, and we proposed the mechanism for oxidation reaction of catecholase.

Inhibitory effect of Acacia hamulosa methanolic extract on the corrosion of mild steel in 1 M hydrochloric acid

Abstract: The flora of Saudi Arabia comprises about 18 species of Acacia species including Acacia hamulosa Benth. The methanolic extract of the flowering tops of A. hamulosa was tested for its radical scavenging activity toward 2,2-diphenyl-1-pricylhydrazyl (DPPH) radical and the activity was compared with L-ascorbic acid, quercetin and Trolox as standards. The total phenolic content was determined using Folin-Ciocalteu method. In addition the methanolic extract has been evaluated as a corrosion inhibitor for steel in 1 M HCl solution by means of weight loss measurements, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS). Tafel polarization study revealed that extract of Acacia hamulosa acts as a cathodic type inhibitor. Inhibition was found to increase with increasing concentration of the extract of Acacia hamulosa . Values of inhibition efficiency calculated from weight loss, Tafel polarization curves, and EIS are in good agreement. The effect of temperature on the corrosion behaviour of mild steel in 1 M HCl with addition of extract was also studied and thermodynamic parameters were determined and discussed. KEY WORDS : Acacia hamulosa , Extract, Polyphenols, Antioxidant corrosion, Electrochemical study Bull. Chem. Soc. Ethiop. 2018 , 32(2), 323-335. DOI: https://dx.doi.org/10.4314/bcse.v32i2.11

Hydrogen effect modeling on Ziegler-Natta catalyst and final product properties in propylene polymerization

Abstract: Hydrogen, as chain transfer agent, effects on kinetic of propylene polymerization; consequently variation of hydrogen concentration leads to change final product properties and also activates site of used catalyst. This phenomenon is one of the most important process variables is to adjust the final product properties and optimize the operating conditions. This work has attempted to present a mathematical model that cable to calculate the most important indices of end used product, such as melt flow index , number and weight average molecular weight and poly dispersity index. The model can predict profile polymerization rates determining important kinetic parameters such as the activation energy, lumped deactivation reaction initial reaction rate and deactivation constant. The mathematical model was implemented in Matlab/Simulink environment for slurry polymerization in laboratory scale. The modeling approach is based on polymer moment balance method in the slurry semi-batch reactor. In addition, in this work have provided a model that calculating fraction activated sites catalyst via hydrogen concentration. The model was validated by experimental data from lab scale, reactor. The experimental and model outputs were compared; consequently, the errors were within acceptable range. KEY WORDS : Mathematical modeling, Propylene polymerization, Kinetics study, Hydrogen response, population balance Bull. Chem. Soc. Ethiop. 2018 , 32(2), 371-386. DOI: https://dx.doi.org/10.4314/bcse.v32i2.15

Experimental and Theoretical Studies on Inhibition of Carbon Steel Corrosion by 1,5-Diaminonaphthalene

Abstract: The aim of this study is to investigate the inhibition efficiency of 1,5-diaminonaphthalene (NDA), for mild steel corrosion in 1 M HCl solution. For this purpose, weight loss, electrochemical impedance spectroscopy and potentiodynamic measurements were realized. The effect of NDA on the mild steel corrosion was also studied by quantum chemical calculations. Increasing inhibitor concentration led to significant reduction in the corrosion rate of mild steel, with inhibitor efficiency value above 90%. The corrosion behavior of steel in 1 M HCl without and with the inhibitor at various concentrations was studied at the temperature range of 308–348 K. Potentiodynamic polarization showed that the inhibitor acts as mixed type. The Nyquist plots showed that increasing NDA concentration, polarization resistance increased and double-layer capacitance decreased, involving increased inhibition efficiency. The adsorption of NDA on the mild steel surface was well described by the Langmuir adsorption model. In addition, quantum chemical calculations based on density function theory and molecular dynamic simulations are done to support the accuracy of experimental results.