Synergistic Effect Of Sulfonate Surfactant And MBT On Corrosion Inhibition Of Carbon Steel In 3.5%NaCl Solution

Carbon steel is widely used for its excellent performance,but it is easily corroded in the solution containing chloride ion.Adding corrosion inhibitor is a simple and cost-effective corrosion protection method,but single corrosion inhibitor often fails to meet the protection requirements.The synergistic effect between various corrosion inhibitors can improve the corrosion inhibitory effect.Although there are many synergistic studies on corrosion inhibitors,they are all focused on developing the best formulations.The research on the synergistic mechanism of corrosion inhibitors is still immature,and there is relatively little research on comparing intramolecular and intermolecular synergy.In this thesis,two sulfonate surfactants,CHT/COT,were synthesized,then docked with2-mercaptobenzothiazole?MBT?to synthesize two corrosion inhibitors,CHMT/COMT.Using electrochemical impedance,dynamic potential polarization curve,surface analysis and other research methods to study the intramolecular/intermolecular synergistic effect of MBT and CHT/COT on 45^#carbon steel in 3.5%NaCl;The quantum chemistry calculation and molecular dynamics simulation were used to study the adsorption characteristics of the two corrosion inhibitors acting on the metal surface when used alone and in synergy.The mechanism of synergy between the two corrosion inhibitors was analyzed through the adsorption configuration and binding energy.The main contents of the thesis were as follows:Using cyanuric chloride,n-hexylamine/n-octylamine,and aminoethanesulfonic acid as raw materials,two sulfonate surfactants were synthesized:2-n-hexylamine-4-sodium sulfamate-6-chloro-1,3,5-s-triazine?CHT?and 2-n-octylamine-4-sodium sulfamate-6-chloro-1,3,5-s-triazine?COT?;then reacted with MBT to synthesize two intramolecular synergistic corrosion inhibitors:2-n-hexylamine-4-?2-mercaptobenzothiazole?-6-sodium sulfamate-1,3,5-s-triazine?CHMT?and 2-n-octylamine-4-?2-mercaptobenzothiazole?-6-sodium sulfamate-1,3,5-s-triazine?COMT?.The structure of four compounds were characterized by ESI-MS,FT-IR and ¹H NMR methods.The surface activity of four compounds in 3.5%NaCl solution was tested by surface tension method.The results showed that CHT/COT/CHMT/COMT all have good surface activity.The corresponding equilibrium surface tensions of 3.5%NaCl solution added with CHT/COT/CHMT/COMT were 40.9 mN·m^-1,35.2 mN·m^-1,33.6mN·m^-1,31.3 mN·m^-1,respectively.The corresponding critical micelle concentrations?cmc?were 9.72mM,5.16 mM,4.82 mM,and 3.36 mM,respectively.The intramolecular/intermolecular synergistic effect of MBT and CHT/COT when used alone and in synergy for 45^#carbon steel in 3.5%NaCl solution were analyzed by electrochemical impedance and dynamic potential polarization tests.The electrochemical impedance test showed that the corrosion inhibition efficiency of MBT and CHT/COT when they worked alone or synergistic for 45^#carbon steel in 3.5%NaCl solution increased with increasing concentration;In the concentration range studied,both MBT and CHT/COT showed good intramolecular/intermolecular synergistic effect of corrosion inhibition.At 25°C,when the concentration of CHMT was 1.5 mM,the corrosion inhibition rate was 60.08%,and the intramolecular synergistic effect was most obvious;when 3.5 mM CHT+3.5 mM MBT was added,the synergy coefficient of the system was 2.23,the inhibition rate was 78.54%,and the intermolecular synergistic effect was the most obvious.At 25°C,when the concentration of COMT was 1.0 mM,the corrosion inhibition rate was 64.66%,and the intramolecular synergistic effect was most obvious at this time;when 7.0 mM COT+7.0 mM MBT was added,the system's synergy coefficient was 1.49,the inhibition rate was 93.46%,and the intermolecular synergistic effect was the most obvious at this time.The potentiodynamic polarization test showed that when MBT and CHT/COT were used alone and in synergy,they all behaved as a mixed corrosion inhibitor mainly based on the anode,that was,they mainly suppressed the metal corrosion by controlling the anode dissolution reaction.Analysis of the surface morphology and surface composition of carbon steel by SEM-EDX showed that both MBT and CHT/COT intramolecular and intermolecular synergies inhibited corrosion by film formation on the surface of carbon steel.The adsorption thermodynamics of the corrosion inhibitors were studied using electrochemical test data:the intramolecular and intermolecular synergy between MBT and CHT/COT were spontaneously adsorbed on the surface of carbon steel,and the adsorption was consistent with Langmuir isotherm.Elevated temperature was not conducive to adsorption,and the adsorption of the corrosion inhibitor on the surface of carbon steel was the result of the physical adsorption and chemical adsorption.The experimental results combined with quantum chemical calculation and molecular dynamics simulation showed that the intramolecular corrosion inhibition synergistic effect of MBT and CHT/COT was mainly reflected in the increase of adsorption sites,and the adsorption sites after intramolecular coordination were mainly distributed on the nitrogen atom of the thiazole ring,triazine ring,and aminoethanesulfonic acid.The mechanism of intermolecular synergy between corrosion inhibitor MBT and CHT/COT belonged to the reinforcement theory.In the 3.5%NaCl solution with MBT and CHT/COT added at the same time,CHT/COT and the corrosion medium Cl^-produced competitive adsorption,CHT/COT would preferentially adsorb to the surface of carbon steel,slowing the corrosion of Cl^-to carbon steel,and then MBT filled the pores of the protective film formed by CHT/COT on the surface of carbon steel,and formed a denser protective film on the surface of carbon steel to reduce corrosion.