Study Of Corrosion Inhibitors On The Corrosion Inhibition Performance And Mechanism Of Purple Copper For Heat Exchangers

Copper has good corrosion resistance,machinability,thermal conductivity and other properties,mainly used in heat exchangers,due to the presence of a large number of Cl^-in its use environment,resulting in the corrosion of purple copper damage,and finally lead to damage to equipment.Among the many anti-corrosion methods,adding corrosion inhibitors is a cost-effective method,and the compounding of corrosion inhibitors is also one of the main research directions at present.Therefore,it is important to study the effect of corrosion inhibitors on the corrosion behavior of purple copper in simulated seawater solution and the corrosion inhibition mechanism of corrosion inhibitors.In this thesis,the electrochemical corrosion behavior of copper in 3.5%NaCl solution was firstly investigated by immersion and macroscopic electrochemical methods combined with scanning electron microscopy（SEM）,energy spectrum analysis（EDS）and X-ray diffraction analysis（XRD）;secondly,macroscopic electrochemical methods combined with SEM were used to investigate the corrosion behavior of benzotriazole（BTA）,polyepoxysuccinic acid（PESA）and sodium tungstate（Na₂WO₄）on the corrosion behavior of copper in 3.5%NaCl solution when the three corrosion inhibitors were used alone,on the basis of which BTA and PESA,BTA and Na₂WO₄ were combined to form a compound corrosion inhibitor,and the effect of the compounding ratio on the corrosion inhibition effect was investigated by micro-area electrochemistry（SVET）.Finally,Langmuir adsorption isotherms were used to investigate the corrosion inhibition mechanism of single and compound corrosion inhibitors.The corrosion rate of copper in NaCl solution increases with the increase of NaCl concentration,and decreases with the increase of soaking time.According to the surface morphology analysis,it can be seen that the surface of copper in 3.5%NaCl solution with the increase of immersion time corrosion pits gradually increased,corrosion products increased.The corrosion product analysis results show that the corrosion products of purple copper in NaCl solution are mainly alkaline copper chloride and alkaline copper carbonate.By adding BTA,PESA and Na₂WO₄ to the 3.5%NaCl solution,the experimental results showed that as the concentration of the three corrosion inhibitors in the solution increased,the charge transfer resistance Rct and passivation film resistance Rf showed an increasing trend,the radius of the capacitive arc increased,and the corrosion inhibition effect was obvious.The adsorption behavior of BTA,PESA and Na₂WO₄ on the surface of copper is in accordance with the Langmuir adsorption isotherm equation,the adsorption process of BTA and PESA on the surface of copper is chemical adsorption,and the adsorption process of Na₂WO₄ on the surface of copper is physical adsorption.The corrosion inhibition mechanism of BTA can form a composite protective film by chemical bonding on the surface of the specimen;the corrosion inhibition mechanism of PESA is that the oxygen atoms in the polar groups of the molecule form a ring-like compound by adsorbing metals through lone pairs of electrons to form a protective film;the corrosion inhibition mechanism of Na₂WO₄ is that WO₄^2-moves to the anode and forms a dense film by electrostatic gravitational force and van der Waals force with Cu²⁺.Good synergistic effect of corrosion inhibition was produced between BTA and PESA,BTA and Na₂WO₄.The best compounding ratio of BTA and PESA was 1:2,the charge transfer resistance value was the largest,and the corrosion inhibition effect was obvious,the SVET results showed that the electrochemical activity of copper was the weakest,the anode current density was the smallest,and the corrosion products on the surface of copper substrate was the least,so the corrosion inhibition effect was the best at this time.The compounding ratio of BTA与Na₂WO₄ is 2:1,the charge transfer resistance value is the largest,and the corrosion inhibition effect is obvious.SVET results show that the electrochemical activity of purple copper is the weakest,the anodic current density is the smallest,and the corrosion products on the surface of purple copper substrate are the least,and the corrosion inhibition effect is the best at this time.