Estudo da aplicação de azóis na inibição da corrosão do aço inoxidável ABNT 430 em meio ácido

Abstract

Corrosion is a natural process that occurs in metallic materials. In this work we studied the possible inhibitory effect of benzotriazole (BTAH), C6H4N3, benzimidazole (BZM) C7H6N2 and Indole C8H7N in different concentrations for stainless steel 430 that was immersed in H2SO4 or HCl 1 mol Lˉ¹. To achieve this objectives, it were employed techniques like: microstructural analysis, forced convection static system potentiodynamic polarization (employing the rotating disc electrode, RDE), electrochemical impedance spectroscopy (EIS), optical microscopy and scanning electron microscopy (SEM). The optical analysis of the stainless steel microstructure showed that the structure is ferritic with the presence of inclusions (iron, chromium and niobium oxides). The cathode potentiodynamic curves for the H2SO4 1 mol Lˉ¹ system showed that: the BTAH decreased the current density (j) with inhibitory efficiency of 55% and there were no significant change in the lowest concentration. The BZM and the Indole showed a dubious effect, i.e. in the most positive cathode regions they acted as inhibitors and in the most negative as catalysts for the hydrogen evolution reaction. For the cathodic study employing the forced convection in H2SO4 1 mol Lˉ¹ the registered inhibiting efficiencies were lower than those of the static system. The studies with the adsorption isotherm showed that only the indole follow the Langmuir`s isothems model in the H2SO4 1 mol Lˉ¹ with ∆G of the order 104 JmoLˉ¹, suggesting that it is an chemical specie iteration. In the HCl 1 mol Lˉ¹ medium it was found that: the BTAH decreases the current density in all studied concentrations, while for the 10ˉ³ mol.Lˉ¹ the best inhibitor efficiency was registered for the indole, probably it is due the protonation of indole, the presence of negative charges of adsorbed ions Clˉ must have supported the adsorption. For the cathotic with forced convection studies it were registered a reduction in the inhibitory efficiency for all the studied azoles when compared with the system in H2SO4 1 mol Lˉ¹. About the present number of nitrogen in azoles relating to inhibitory efficiency to the studied system, we conclude that the azoles adsorption depends on the medium and the chemical reactivity of this azole.