Study On Corrosion Inhibition Effect For Copper In Sodium Halide Solutions

The electrode potential of copper is more positive. It is commonly used as amaterial in the field of industry, military and civilian owing to its excellent electricaland thermal conductivities, mechanical workability and good corrosion resistance.Although the copper is behind hydrogen in the activity sequence table, and it is notactive. However it still can be severely corroded in corrosive system of chloride ions,sulphates, nitrates. Use of corrosion inhibitors is a simple, economical method to protectfrom corrosion. The application of corrosion inhibitor are in the development of new,high efficiency, low consumption, low toxicity and environmental protection, whichhas become a valuable subject.In this paper,2-mercaptobenzothiazole is the corrosion inhibitor of copper in0.6mol/L pH=13sodium halide solutions. This paper mainly applyed weight-lossexperiment, electrochemical test, surface morphology analysis to study corrosioninhibition effect of2-mercaptobenzothiazole. In addition, this paper also studies thecorrosion behavior of copper in neutral and alkaline sodium halide solutions. The mainresults are as follows:For alkaline sodium halide solutions, corrosion inhibition efficiency of2-mercaptobenzothiazole increases with the concentration increasing. When the bestconcentration is reached, the corrosion inhibition efficiency decreases with theconcentration continuous increasing. For alkaline NaF solution, the optimal inhibitioneffect is91.35%when the concentration of7.5mmol/L; For alkaline NaCl solution, theoptimal inhibition effect is95.45%when the concentration of corrosion inhibitor is7.5mmol/L; For alkaline NaBr solution, the optimal inhibition effect is92.76%whenthe concentration of corrosion inhibitor is15mmol/L; For alkaline NaI solution, theoptimal inhibition effect is98.24%when the concentration of corrosion inhibitor is15mmol/L.The good inhibition performance of2-mercaptobenzothiazole attributes to theprotective adsorption film of inhibitor molecules formed on copper/solution interface.This chemisorption between these compounds and copper are accordance withLangmuir adsorption isotherm. And the chemical adsorption plays an important role.For alkaline NaF, NaCl, NaBr solutions, after the inhibitor is added in the system, thecorrosion potential is moved in the positive direction. So that2-mercaptobenzothiazole belongs to mixed-type inhibitors with anodic predominance; For alkaline NaI solution,after the inhibitor is added in the system, the corrosion potential is moved in thenegative direction. So that2-mercaptobenzothiazole belongs to mixed-type inhibitorswith cathode predominance.Potentiodynamic polarization curve of copper in the neutral sodium halide solutiontest results show that the polarization curve, in accordance with the order of NaF, NaCl,NaBr, NaI, the corrosion potential more negative, the greater the corrosion currentdensity, that is, the greater the degree of corrosion. AC impedance test results confirmthe results above, in accordance with the order of NaI, NaBr, NaCl, NaF, radius ofimpedance arc increases significantly, the charge transfer resistance Rct increasessuccessively, and the charge transfer process is inhibited, that is, the resistance ofcorrosion electrochemical reaction is greater.Potentiodynamic polarization curve test results of copper in the alkaline sodiumhalide solution show that the polarization curve, in accordance with the order of NaF,NaCl, NaBr, NaI, the corrosion potential more negative, the greater tendency ofcorrosion. However, compared with the situation of copper in neutral sodium halidesolutions, the distribution of potentiodynamic polarization curves is relativelyconcentrated in alkaline sodium halide solution. And there is little difference among thecorrosion potential and current density of each curve. Ac impedance test results showthat the impedance arc of alkaline sodium halide solutions are very small, thedistribution is relatively concentrated, there is little difference among impedanceparameter values of each system. It shows that copper suffered serious corrosion, but itcan not indicate in which solution copper suffered more corrosion through the acimpedance test.