Utilização da Ipomoea pes-caprae (L.) Br. Convolvulaceae em sistema microemulsionado na inibição à corrosão do aço carbono

Abstract

The problems related to corrosive action have a direct impact on the industry financial sector, environment and safety, which increases the necessity to fight such problem in the most effective way possible, associating the efficiency of inhibition to natural products that are able to minimize environment impacts. In this context, this study uses microemulsion systems (SME), SME with fraction of Tannins (SME-T) and SME with fractions of both Tannins and Saponins (SME-TS) as well as free-form Tannins and Saponins with corrosive inhibitors of the carbon steel AISI 1018 under the influence of a 3.5% NaCl corrosive mean. The corrosive inhibition efficiency and its mechanisms were investigated through polarization curves and adsorption isotherms. The tannin and saponin fractions showed maximum inhibition efficiencies of 80.82% (75 ppm) and 50.21% (200 ppm) in a 1mVs-1 scan speed. The microemulsion system SME shows maximum efficiency of 59.56% (50 ppm). However, with the solubilization of the Tannins (5.0x10-5 g) the inhibition efficiency reached 65.67% (100 ppm of the SME-T) and with the solubilization of the Tannins and Saponins in the proportion of 1:1 (7.6x10-5 g) performed a 81.30% (75 ppm) maximum efficiency to the SME-TS. Regarding the absorption process, the results of all the tested inhibitors adjust to the Langmuir isotherm. Observing the energy values of Gibbs, it was understood that the interfacial film formation happens spontaneously and it is resulting from the physic interactions between the inhibition molecules with other active metal sites. Considering the scan speed study in the electrochemical analysis, it was observed that the speed of 1 mVs-1 led to better results of corrosive inhibition efficiency of the carbon steel when compared to the speed of 10 mVs-1. In spite of that, the tannins and saponins solubilization in the microemulsion systems was feasible regarding the decrease in the use of vegetal material, and the systems represent a good alternative inhibitor to does not harm the environment, which is easy to find, low-cost, renewable and non-toxic.