The Analysis Of Electrochemical Corrosion Behavior And Corrosion Inhibition For Different Metals In The Solution Containing Chloride Ion

The use of inhibitors is one of the most cost-effective and practical methods to protect metallic materials against corrosion in corrosive medium. The objective of this paper is to investigate the corrosive rate, corrosive products, surface image of Alloy 690, Cu and N80, and the inhibition mechanism for the inhibitor on the surface of metal using electrochemical experiment, Scanning electron microscope ?SEM? and X-ray photoelectron spectroscopy, etc. The results showed that when Ag₂SO₄ as inhibitor was added into NaCl solution, ?AgCl₂?- or ?AgCl₃?^2- between silver ion and chloride ion were formed to decrease activity of chlorine ion in corrosion solution. The adsorption of the complex compound would change the double-layer structure from two layers to three layers, inhibiting the anodic oxidation process of Alloy690. With the increase of concentration of Ag₂SO₄, equilibrium potential would rise, and capacitance of the solid/liquid interface would decrease. Better inhibition effect than other cases could be achieved when the concentration of silver sulfate and sodium chloride ratio equaled to 0.2. Thiourea and hexamethylenetetramine can form strong chemical bonds and adsorpt on the surface of Cu. It can slow down the corrosive rate effectively. The inhibition efficiency of thiourea added alone was only 67.28%, while the highest observed inhibition efficiency was 95.56% after compounding thiourea with hexamethylenetetramine. At the same time, Thiourea and hexamethylenetetramine also had good inhibition effect, the inhibitors results in stable films, inhibits the cathodic and anodic reactions in HC1 solution and reduces the diffusion coefficients of corrosive particles. Mannich base on N80 can increase the charge transfer resistance and prevent the occurrence of corrosion reaction in the acid solution, thereby reducing the corrosion rate of metal surface. When Mannich base is compound with sodium tungstate, the highest inhibition efficiency was 99.65%; consequently there was a good synergistic effect on N80. The adsorption of inhibitors on the surface of N80 was in accordance with the Langmuir adsorption model, and it mainly belonged to chemisorption. The process of adsorption on N80 surface was spontaneous and irreversible endothermic reaction.