Comparison of the corrosion inhibition performance of tannins extracted from stryphnodendron adstringens with that of commercial tannins extracted from black wattl (Acacia mearnsii)

Abstract

Large amounts of low-carbon steel are used globally in many industrial sectors, as this material is very versatile, economical, and effective. The major problem with this type of steel is its susceptibility to corrosion, especially if used in acidic media, which is quite common in industry. Therefore, several anticorrosion methods are used for protecting structures and equipment, and an economical and effective method for protection is the use of inhibitors. The current ecological awareness, together with more rigid sustainability legislation, has created opportunities for research on the use of organic, nontoxic inhibitors from renewable sources. Tannins have been studied as likely inhibitors of the corrosive process due to their ability to form stable tannin complexes with corrosion products on the metal surface. These compounds are composed of flavonoid units and are considered an innovative line of anticorrosion products. This study evaluated the corrosion inhibition performance of tannins extracted from Stryphnodendron adstringens (Mart. Coville.) (barbatimão), a tree species characteristic of the Brazilian Cerrado biome, compared with the corrosion inhibition performance of commercial tannins extracted from Acacia mearnsii (De Wild) (black wattle) and cationically modified in terms of the protection of (Society of Automotive Engineers International) SAE 1020 carbon steel in a medium of 0.1 molar hydrochloric acid. The electrochemical methods of potentiodynamic polarization, electrochemical impedance spectroscopy, and gravimetry were used to characterize the inhibitory effects of the tannins, together with Fourier transform infrared spectroscopy for analysis of the reaction product between the iron and tannins. The results obtained showed the mixed inhibitor character of the tannins from barbatimão, which achieved good results, with an inhibition efficiency of up to 79%, compared with 95% for the modified tannins from black wattle.