Protection of Steel Against Corrosion in 4% HCl Solution Using Thyme Extract

In this paper, the efficiency of the thyme extract as a "green" corrosion inhibitor for two types of steel in a 4% HCl solution was investigated. Measurements were performed without inhibitors and at different inhibitor concentrations (0.5, 1.0 and 1.5 g/L) and different exposure times (2, 4, 6, 8, 24, 48 and 168h). The responses in the study - corrosion rate (Km−), depth corrosion indicator (π) and inhibitor efficiency (z) were analyzed using the statistical software MINITAB 21. In the absence of inhibitors, the corrosion rate (Km−) was significantly higher, while in the presence of the extract there was a decrease in Km− and a proportional increase in the inhibition efficiency z. The maximum values of inhibition efficiency reached ~90–97% under optimal conditions (for steel 2 the inhibition efficiency reached 96.8% at a inhibitor concentration of 1.0 g/L and a time of 2h, while for steel 1 the inhibition efficiency reached 93.99% at an inhibitor concentration of 0.5 g/L and a time of 48h). Such a high efficiency suggests that a protective film has formed on the surface of the steel and that the thyme extract can be used as a corrosion inhibitor in aggressive acidic environments, such as HCl solution