Study Of Corrosion Inhibition For The Acid Pickling By Amino Acid Derivatives

In the current industrial cleaning,pickling is often used in rust removal,scale removal and other fields.Pickling is mainly based on inorganic acids,eontaining hydrochloric acid,sulphuric acid,phosphoric acid,sulfonic acid and so on.Although acid can remove corrosion products on metal surface,it will cause serious corrosion to equipment,and then cause serious economic losses.Corrosion inhibitors can effectively reduce the corrosion of metals in acidic media,so the choice of appropriate corrosion inhibitors becomes an indispensable part in industrial acid pickling.With the enhancement of people’s awareness of environmental protection,high efficiency,environmental friendliness and low toxicity have become an important topic in the research and development of corrosion inhibitors.In this paper,three amino acid derivatives(N-Glucosyl-Cysteine,N-Glucosyl-Glycine,N-Glucosyl-Methionine)were chosed to be as corrosion inhibitors,and the corrosion in lmol/L HCI and 0.5mol/L H2SO4 were studied by static weightloss measurement,polarization curve,electrochemical impedance spectroscopy(EIS)and scanning electron microscopy(SEM),the synergistic effect between corrosion inhibitor and halide ions was investigated.The inhibition mechanisms of inhibitors and synergistic inhibiton mechanism of inhibitor with halide ions for carbon steel in acidic media were discussed.The main conclusions were drawn as follows:(1)Three amino acid derivatives exerted excellent inhibition properties for carbon steel in lmol/L HCI solution and 0.5 mol/L H2SO4 solution,respectively,and the inhibition efficiency increased with increasing concentration of the inhibitors.At the same inhibitor concnetration and acid solution,the inhibition effect of three corrosion inhibitors followed the order N-Glucosyl-Cysteine<N-Glucosyl-Glycine<N-Glucosy 1-Methionine.The inhibition efficiency of N-Glucosyl-Methionine at lmmol/L reached the maxmium values:91.8%(lmol/L HCI)and 72.6%(0.5mol/L H2SO4),respectively.The inhibitors acted as mixed type inhibitors via suppressing both the anodic iron dissolution and cathodic hydrogen reduction processes simultaneously.The adsorption of three corrosion inhibitors on carbon steel surface obeyed Langmiur adsorption isotherm,and the adsorption belonged to the joint physisorption and chenisorption.Moreover,the inhibition efficiency of the three corrosion inhibitors was higher in 1 mol/L HCI solution than in 0.5mol/L H2SO4 solution which was due to the different anion(C1-and SO42-)in different acid solutions.(2)The results of synergistic inhibiton indicates that the special adsorption of halide ions on carbon steel surface led to the increase of the inhibition efficiency of inhibitors after the halide ions(KCl,KBr and KI)were added to 0.5mol/L H2SO4 solution.Under the same halide ions concentration,the synergistic effect of halide ions with inhibitors increased by the order:Cl-<Br<I-.(3)In 0.5mol/L H2SO4 solution,when the total concentration of inhitor and KI was fixed at 0.1mmol/L,the optimal concentration ratio of inhibitor and KI was determined as Cinhibitor:CCI=1(both Cinhibitor and CKI are 0.05mmol/L).The inhibition efficiencies of three corrosion inhibitors achieved great improvement compared to that without KI:66.9%-86.1%for N-Glucosyl-Cysteine,69.4%-87.2%for N-Ghicosyl-Glycine and 72.6%-89.4%for N-Glucosyl-Methionine.