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Free Content Interfacial Behavior of Cysteine between Mild Steel and Sulfuric Acid as Corrosion Inhibitor

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Interfacial behavior of cysteine (Cys) between mild steel and sulfuric acid solution as a corrosion inhibitor has been studied with electrochemical AC (alternating current) and DC (direct current) techniques at (25.0±0.1) . The AC impedance results were evaluated using equivalent circuits in which a constant phase element (CPE) has been replaced with double layer capacitance (Cdl) to represent the frequency distribution of experimental data. Changes in impedance parameters (charge transfer resistance and double layer capacitance) indicated that cysteine molecules acted by accumulating at the metal/solution interface. The fractional coverage of the metal surface () was determined using AC impedance results and it was found that the adsorption of cysteine on the mild steel surface followed a Langmuir isothermmodel with a standard free energy of adsorption (G0ads) of -35.1 kJ·mol-1.  To clarify the type of interaction between mild steel surface and cysteine molecules with a molecular orbital approach, electronic properties, such as, the highest occupied molecular orbital (HOMO) energy, the lowest unoccupied molecular orbital (LUMO) energy, and the frontier molecular orbital coefficients have been calculated. Energy gaps for the interaction of mild steel surface and cysteine molecules (ELUMOFe-EHOMOCys and ELUMOCys-EHOMOFe) were used to determine whether cysteine molecules acted as electron donors or electron acceptors when they interacted with the mild steel surface. The local reactivity was evaluated through the condensed Fukui indices. Theoretical calculations were carried out using the density functional theory (DFT) at B3LYP level with the 6-311++G(d,p) basis set for all atoms by Gaussian 03W program.
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Keywords: AC impedance; Corrosion inhibitor; Cysteine; Interface; Quantumchemical calculation

Document Type: Research Article

Publication date: 15 August 2008

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  • Acta Physico-Chimica Sinica, founded in 1985, is sponsored by the Chinese Chemical Society and organized by the College of Chemistry and Molecular Engineering, PekingUniversity. Since 1997, Acta Physico-Chimica Sinica has been indexed in SCI of ISI (US). Acta Physico-Chimica Sinica is devoted to reporting new and original experimental and theoretical basic research of interest to physical chemists, biophysical chemists, and material physical chemists. Manuscripts that are essentially reporting data, applications of data, or reviews of the literature are not suitable for publication in Acta Physico-Chimica Sinica.
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