Extract of Silybum marianum (L.) Gaertn Leaves as a Novel Green Corrosion Inhibitor for Carbon Steel in Acidic Solution

In this work, leaves of Silybum marianum (L.) Gaertn were extracted by a one-step extraction method using ethanol as a solvent, and the Silybum marianum (L.) Gaertn extract (SMGE) was firstly employed as a green corrosion inhibitor for carbon steel in 0.5 mol/L H2SO4. The corrosion inhibition performance was studied using weight loss and electrochemical methods, and the anti-corrosion mechanism of SMGE is further analyzed through some surface characterizations and theoretical calculations. The results indicate that SMGE can act as a mixed-type corrosion inhibitor and possess superior corrosion inhibition performance for carbon steel in H2SO4 solution, and the optimum corrosion inhibition efficiency reached 93.06% at 800 ppm SMGE combined with 60 ppm KI. The corrosion inhibition efficiency increased with the rising inhibitor concentration. Surface characterizations illustrated that the inhibitor could physico-chemically adsorb on a metal surface, forming a hydrophobic, protective film.