Determination of inhibitor effectiveness of some amino acids in water solutions

In this study, the inhibition effect of some amino acids on the corrosion of stainless steel in wt %0,5 HCl solution were investigated at 20oC, 40oC, 50oC, 60oC. The corrosion rate of stainless steel was determined with the use extrapolation of the Tafel slope of the cathodic polarization curves method and Lineer polarization resistance method. İnhibition effect of each substance was calculated from the experimentally determined corrosion rate values. Inhibitor efficiency of amino acids of acceptable efficiency values at 20oC were determined at temperatures other than 20oC such as 40oC, 50oC, 60oC. Inhibitor efficiency at 60oC was found to be % 68 for solution containing 1000 ppm L-methionin, %68 for 3000 ppm L-cystin, %60 for 3000 ppm L-cysteine hydrochloride monohydrat , %60 for 2000 ppm N-acetyl-L-cysteine at 60oC. Maximum inhibitor effect was for the amino acids containing sulphur in its structure. vii With the consideration of the effect of inhibitors are being due to the adsorption of inhibitors at the metal surface, adsorption were in accordance with the Langmuir and Freundlich isoterms. In addition, the type of adsorption is determined by calculating the activation energies. The results were as follows; Ea =59234 J/mol for 2000ppm L-methionine , Ea=70160 J/mol for 1000ppm L-cystine, Ea=72108 J/mol for 3000ppm L- cysteine hydrochloride monohydrate, Ea = 49043 J/mol for 2000 ppm N-acetyl-L-cysteine, Ea = 22626 J/mol for the corrosion without inhibitor. The activation energy in the absence of inhibitor is lower than the activation energy in the presence of inhibitor which indicates that inhibitor enables protection against corrosion of stainless steel. Keywords : Inhibitors, amino acids, corrosion, stainless steel