Study Of Corrosion Inhibition For Carbon Steel In Acid Solution By Amino Acid

Amino acids are attractive as green acid corrosion inhibitor because they are non-toxic, biodegradable, low production costs and good soluble in aqueous media.Corrosion inhibition of amino acids was studied by weight-loss method. Three-component inhibitor including methionine, cetyltrimethylammonium bromide and potassium iodide has been developed. The optimally addition ratio and concentration are separately 20mg/L、10mg/L、20mg/L determined by orthogonal and parallel experiments. The three-component inhibitor for carbon steel in H2SO4 at 30℃had an inhibition efficiency of 98.21%. Polarization curves indicated the compound inhibitor acted as mixed-type inhibitor. Impedance testing showed that the compound inhibitor decreased corrosion rate by increasing the charge transfer resistance of metal surface. SEM showed that the carbon steel surface was smooth, which indicated the formation of protective film on metal surface.Four cysteine derivatives were synthesized and identified their structure by infrared spectroscopy. Comparing the inhibition efficiencies of the four inhibitor by weight-loss method, the order tends to decrease in the following: S-benzyl-cysteine> S-hexyl-cysteine> S-butyl-cysteine> S-octyl-cysteine. The inhibition efficiencies of the two former were above 98% at 800 mg/L. Polarization curves indicated that S-benzyl-cysteine and S-butyl-cysteine functioned as mixed-type inhibitor. S-hexyl-cysteine was cathodic inhibitor at low concentration and mixed-type inhibitor at high concentration. Impedance testing showed that the compound inhibitor decreased corrosion rate by increasing the charge transfer resistance of metal surface. SEM showed that the carbon steel surface was smooth.The amino acids studied obey Langmuir adsorption isotherm. The negative value of free adsorption energy implies the adsorption of inhibitors on the steel surface is spontaneous and exothermic.