A Study Of The Inhibition In Acid Solution By Amino Acids Containing Sulfur And Derivatives

Amino acids are attractive as corrosion inhibitors because they are non-toxic and aresoluble in aqueous media.The performance of two selected amino acids,namely cysteine and methionine assafe corrosion inhibitors for carbon steel in HCl solutions was evaluated by Tafelpolarization and impedance measurements.Results indicate that the inhibition efficiencywas not high,so orthogonal and parallel experiments should be taken. The inhibitionefficiency reached95.98%for the composite inhibitors with20mg/L cysteine,50mg/Lnaphthene base imidazoline quaternary ammonium salt and50mg/L HMTA. The pricewas low and eco-friendly to environment.Polarization results revealed that the compositeinhibitors act as mixed-type inhibitors with anodic predominance. Impedance testingshowed the concentrations of inhibitiors increased with the values of charge-transferresistance increasing, so the inhibition efficiency increased gradually.Three derivatives were synthesized and identified by infrared spectroscopy. Theinhibition efficiency depends on the their chemical structures.It increases following theorder,methionine sulfone<methionine sulfoxide<S-benzyl-cysteine. The inhibitionefficiency was82.53%、82.69%and89.57%with concentration of800mg/L,respectively. Polarization results revealed that these derivatives inhibitors act as mixed-type inhibitors. Methionine sulfone was anodic inhibitor at high concentration.Impedance testing showed the concentrations of inhibitiors increased with the values ofcharge-transfer resistance increasing, so the inhibition efficiency increased gradually.Adsorption of these inhibitors on carbon steel surface is found to obey the Langmuiradsorption isotherm.The parameters indicated a chemical adsorption.The negative valuesofΔ Gadsindicate the apontaneous adsorption of these inhibitors on carbon steel surface.SEM showed that the carbon steel surface was smooth,which confirmed theexistence of a protective adsorbed film on the carbon steel surface.