Avaliação de extratos de chás verde e branco como inibidores de corrosão para o aço-carbono 1020 em solução de HCl 1mol/L

Abstract

The carbon steel remains one of the most versatile materials in terms of industrial application at present, despite the immense competition that has been suffering for decades from other materials. Given this range of applications in several environments, corrosion studies involving carbon steel is particularly important because, as a metallic material, it tends to be deteriorated in corrosive environments, leading to a loss in their property and extensive damage. The use of corrosion inhibitors is one of the most popular methods used to protect the metal against corrosion. Various inhibitors are used to prevent or reduce corrosion of carbon steel, depending on the environment to which the material is exposed. Although effective, many of these inhibitors are toxic, causing problems to humans and the environment, and many studies have been performed in order to replace them by environmentally non-aggressive products. Among these new types of inhibitors we highlight the organic compounds derived from natural products that act as good corrosion inhibitors due to the presence of heteroatoms in their structures. In this dissertation, we evaluated the inhibitory action of aqueous and alcoholic extracts of leaves of green and white teas (Camellia sinensis) on corrosion of 1020 carbon steel in HCl solution 1 mol/L, employing total immersion (TI) and electrochemical assays (Potentiodynamic Polarization - PP and Electrochemical Impedance Spectroscopy EIS). It was found that the two types of extracts of both teas act as good corrosion inhibitors in the studied medium. The results obtained from PP showed that all the studied extracts acted as mixed inhibitors. Moreover, it was noted an increase in the capacitive loop at high frequencies, obtained from EIS technique, whenever the extracts were present in the acid solution. These results, together with those observed by TI and scanning electron microscopy (SEM) experiments, confirmed the presence of a protective film adsorbed on the surface of the carbon steel specimen, probably formed by the antioxidant compounds in the extracts. Additionally, the use of an experimental design 22 with center point evaluated the influence of the parameters volume of extract (V) and extraction time (t), on the inhibition efficiency (E.I.) obtained from the results of the tests performed. It has shown that there is a general trend that higher E.I. values would be obtained using larger V and smaller t.In general, it can be said that among the used tea, green tea provide the best conditions for obtaining greater (E.I.) and aqueous medium was most suitable for best results