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Effect of amino acids containing sulfur on the corrosion of mild steel in phosphoric acid solutions polluted with Cl − , F − and Fe 3+ ions–behaviour near and at the corrosion potential
Author(s) -
Morad Mohamed Samir S,
Hermas Abo ElHagag A,
Aal Mohamed S Abdel
Publication year - 2002
Publication title -
journal of chemical technology and biotechnology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.64
H-Index - 117
eISSN - 1097-4660
pISSN - 0268-2575
DOI - 10.1002/jctb.588
Subject(s) - chemistry , phosphoric acid , adsorption , langmuir adsorption model , corrosion , inorganic chemistry , dielectric spectroscopy , electrochemistry , nuclear chemistry , organic chemistry , electrode
Research on non‐toxic inhibitors is of considerable interest in investigations into the replacement of hazardous classical molecules. This paper reports the action of four amino acids containing sulfur on the corrosion of mild steel in phosphoric acid solution with and without Cl − , F − and Fe 3+ ions near and at the corrosion potential ( E corr ) using both the polarization resistance method and electrochemical impedance spectroscopy (EIS). Both cysteine and N ‐acetylcysteine (ACC) showed higher inhibition efficiency than methionine and cystine. Adsorption of methionine onto a mild steel surface obeys the Frumkin adsorption isotherm and has a free energy of adsorption value (Δ G ° ads ) lower than those obtained in the presence of cystine, cysteine and ACC whose adsorption isotherms follow that of Langmuir. Both F − and Fe 3+ ions stimulate mild steel corrosion while Cl − ions inhibit it. The binary mixtures of methionine, cysteine or ACC with Cl − or F − ions are effective inhibitors (synergism) while the combinations of the amino acid with Fe 3+ or the ternary Cl − /F − /Fe 3+ mixture have low inhibitive action (antagonism). EIS measurements revealed that the charge transfer process mainly controls the mechanism of mild steel corrosion in phosphoric acid solution in the absence and presence of the investigated additives. The mechanism of corrosion inhibition or acceleration is discussed. © 2002 Society of Chemical Industry