Desenvolvimento de inibidores verdes de corrosão derivados de extratos vegetais

Abstract

Metallic materials and metallic alloys are widely used as materials in the most diverse areas, due to their advantages. Carbon steel, for example, is the most used metal alloy and one of the most produced materials in the world. In contrast, most metals and their alloys in their pure form are highly reactive and undergo corrosion, a thermodynamically spontaneous process, resulting in their deterioration. One of the most practical methods of protecting materials is the use of corrosion inhibitors. Some inhibitors, however, are potentially polluting and harmful to human health, which motivates the search for new formulations. The literature reports the use of natural products, called "green inhibitors", plant extracts stand out within this class of inhibitors. In this perspective, in the present work a survey was carried out regarding the applicability of plant extracts as green corrosion inhibitors and the development of these inhibitors from plant extracts from different sources: leaves of Eucalyptus globulus Labill, seaweed Sargassum vulgare and grains of Paullinia cupana (guaraná), in the protection of carbon steel 1020. In the prospection, databases of scientific articles and patents were consulted and the documents found were analyzed. The extracts were characterized by spectroscopic and chromatographic techniques, and their inhibition activities were evaluated by gravimetric and electrochemical techniques. 335 articles and 42 patents related to the subject were retrieved, most of the extracts being prepared from leaves for the protection of carbon steel in an acid medium. In the characterization of the extracts, types of bonds and compounds were identified, such as terpenes and phenolic acids, which demonstrate the possibility of using these extracts as inhibitors of corrosion. The techniques used showed that in all studied concentrations the extracts increased the resistance to charge transfer, caused potential displacement and decreased the parameters related to corrosion, reaching 89.97% of maximum anticorrosive efficiency. Furthermore, the adsorption of molecules, in the presence of extracts, on active sites on the carbon steel surface was of physisorption and obeyed the Frumkin adsorption isotherm. The proposed inhibitors are presented as nontoxic, cheap, available in nature in abundance and easy to extract, characterizing them as green corrosion inhibitors.