Studies On Corrosion Inhibition For Zinc In Nitric Acid Solution

Content:The corrosion velocity of zinc was studied using the weight-loss method in 0.5mol·dm-3 nitric acid, which added many kinds of compound. Then some kinds of compounds which provide certain corrosion inhibition effect, have been choosed in 0.5mol·dm-3 nitric acid solution.In these compounds sodium dodecylbenzene sulfonate and sodium dodecyl sulfonate were selected as research object. Their corrosion inhibition action for zinc was studied at different temperatures in 0.5mol·dm-3 nitric acid by adsorption theory, electrochemical methods (potentiodynamic polarization and impedance spectroscope method) and quantum mechanics theory, and the mechanism of corrosion inhibition action was analyzed. Moreover synergistic effects of benzotriazole and sodium dodecyl sulfonate (or thiourea and sodium dodecyl sulfonate) for zinc were investigated in order to enhance corrosion inhibition effective of sodium dodecyl sulfonate, which mainly restrained the corrosion of zinc in mixed inhibitors. The results indicated that the single molecule layer of these compounds adsorbed on the surface of zinc and almost followed Langmiur isothermal equation. Both of adsorption procedures was exothermic reaction and the adsorption ability and corrosion inhibition efficiency decreased with increasing temperature. They are all electrochemical admixture type inhibitor. The corrosion current was decreased in different degree and activate enegy were heightened. Zinc was protected by increasing the film's resistance, decreasing the film's capacitance and increasing the film's surface coverage after appending benzotriazole or thiourea with sodium dodecyl sulfonate in 0.5mol·dm-3 nitric acid. The molecular structure parameters of these compounds were obtained via DFT-B3LYP/3-21g quantum chemical calculation of Gaussian 2003, it was concluded relation between paramenters of inhibitor structure and effective of corrosion inhibition.A composite and excellent corrosion inhibitor was composed by orthogonal method. The corrosion inhibition action of this composite corrosion inhibitor has been evaluated by using weight-loss method, electrochemical methods (potentiodynamic polarization and impedance spectroscope method) and scanning electron microscopy techniques. The corrosion rate of zinc in 0.5mol·dm-3 nitric acid has been determined with different concentration of 0.5mol·dm-3 nitric acid, different temperature, different time and different velocity of flow. The result of electrochemical methods shown that they are all electrochemical admixture type inhibitor and zinc was protected by increasing the film's resistance, decreasing the film's capacitance and increasing the film's surface coverage after appending this composite corrosion inhibitor. The SEM photos indicated that no signal of pit corrosion and intercrystalline corrosion was found under different corrosion condition. It shows that the composite corrosion inhibitor is an excellent corrosion inhibitor on the surface of zinc in 0.5mol·dm-3 nitric solution.