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    Impact of carbon chain length on the adsorption kinetics of bis-mercapto-benzimidazole MB-Cn-MB (n = 2, 4, 6, 8, 10) at the Q235-steel/1 M HCl interface
    (Vserossiiskaya Assotsiatsiya Korrozionistov, 2023) Achnine, N.; Driouch, M.; Niouri, W.; Kadiri, M.; El Assiri, E. H.; Mousaif, A.; Haoudi, A.
    In the present work, we undertook a study on the effect of increasing the carbon chain from two to ten atoms on bolaform surfactants whose head was a mercapto-benzimidazole {MB-C-n-MB with n = 2, 4, 6, 8 & 10}. A comparative study of the inhibiting effect of MB-C2-MB and MB-C-8-MB at different concentrations was carried out by comparing three techniques, direct (gravimetric) and indirect (stationary {potentiodynamic polarization, PDP} and transient {electrochemical impedance spectroscopy, EIS}). The polarization curves were analyzed qualitatively by visual inspection and then quantitatively by fitting their data using three methods {Tafel-Fit, Stern-Fit or Wagner and Traud-Fit, and Rp-Fit} while those from the transient method were examined both by graphical inspection of Nyquist, Bode and Betova representations, then modeled and fitted using an appropriate equivalent electrical circuit, EEC. To overcome some ambiguities inherent to basic approximations of Tafel's method, discussed in this paper, the cathodic and anodic polarization curves were recorded separately with a potential sweep from low to high overvoltage, then adjusted using the Stern and Jena-Bonhoeffer model. Indeed, examination of the results showed that the approximations inherent in the Tafel treatment and the fitting procedure undertaken led to an overestimation of i(corr) value compared with its value estimated using the Stern model at each concentration of MB-C-2-MB and MB-C-8-MB. Also, we have exhaustively examined the ambiguities, little discussed in the contemporary literature, associated with the modeling, quantitative, and qualitative interpretation of impedance data containing more than one indistinguishable time constant. The inhibiting efficiencies derived from different techniques and methods undertaken showed that MB-C-8-MB was more effective than MB-C-2-MB. To develop an insight into the inhibition mechanism of MB-C-8-MB, six adsorption isotherms, commonly used in the literature, were adapted to the experimental data and critically discussed. The Langmuir model was discarded despite the good statistical parameters of fit, because it remains a hypothetical model that can in no way reproduce the reality of the studied interface. Finally, the polarization resistance values obtained from EIS results for the optimum concentration of 10(-3) M of the different surfactants studied showed that the inhibition efficiencies followed the trend {eta.%(MB-C-2-MB)= 84% < eta%(MB-C-4-MB) < eta%(MB-C-6-MB) < eta%(MB-C-8-MB) approximate to eta%(MB-C-10-MB)=96%}.