Avaliação em comparação da eficiência dos inibidores (comercial e DMcT) para aço carbono 1007 em meio de água do mar sintética

Abstract

In this work, we studied the corrosion protection efficiency of low carbon steel in synthetic sea water containing inhibitors (commercial and 2,5-dimercapto-1, 3,4 - thiadiazol-DMcT-) at different concentrations. From the analysis of optical emission spectrometer, metallography and microhardness, it was possible to classify the steel sample as low carbon. From the results obtained from the Nyquist diagram, it can be concluded that there is a significant increase in the charge transfer resistance (Rct) values of steel in the presence of higher concentrations of inhibitors. High Rct values were obtained for the steel in synthetic sea water containing 200 ppm of both inhibitors when subjected to an exposure time of 20 h, indicating the coating of the steel by inhibitor film which was confirmed by SEM. Furthermore, in the polarization curves was observed a shift of the corrosion potential to more positive values for the concentration of 200 ppm as compared to the other concentrations. At this concentration, DMcT inhibitor performance was superior to the commercial, obtaining a value of inhibitor efficiency around of 99%. From these results, we can say that the DMcT with concentration of 200 ppm is quite promising as inhibiting corrosion of low carbon steel. As for this commercial inhibitor concentration is not recommended due to high toxicity presented by their constituents. Then, the concentration for commercial inhibitor more suitable is of 100 ppm. The theoretical data of the proposed circuit is adjusted to the experimental data obtained by EIS for both inhibitors, yielding a chi square of 10-2 and 10-3 for the commercial inhibitor and DMcT, respectively. These values are considered acceptable for a good fit and the circuit presented a physical meaning consistent with the realized analyzes. The DMcT has certain advantages compared to other commonly used inhibitors such as low cost, low toxicity to the environment, besides, it is fungicide and bactericide. Therefore, it is a material promising as an inhibitor for corrosion of low carbon steel, even at higher concentration than those used for commercial inhibitor.