Sustainable protection for mild steel (S235): Anti-corrosion effectiveness of natural Paraberlinia bifoliolata barks extracts in HCl 1 M

This study analyzed tannin extract from the bark of the tropical tree Paraberlinia bifoliolata as an anticorrosion agent for S235 mild steel immersed in a 1 M hydrochloric acid solution. A factorial experimental strategy was designed to analyze the effect of three key variables: temperature, immersion time and inhibitor level. We varied the temperature at three levels: 298, 313 and 328 K, while immersion time was determined at 4, 14 and 24 h. We adjusted the inhibitor concentration to 0.5, 1.0 and 1.5 g/L. Design Expert software was used for optimization and statistical analysis to discover the optimum conditions for corrosion prevention. Data revealed that corrosion inhibition reached its maximum efficacy of 75.2 % at a temperature of 298 K, after a 4 h immersion and with an inhibitor concentration of 1.5 g/L. The remarkable effectiveness of tannin extract was attributed to the creation of a monovalent protective barrier on the steel surface via a physical adsorption process. This adsorbed layer reduced the active sites accessible to corrosive agents while strongly limiting mass transfer at the metal-solution junction. In addition, Scanning Electron Microscopy analysis of the surface showed a significant reduction in surface porosity after application of the inhibitor. These observations support the idea of using tannin extract from Paraberlinia bifoliolata as an effective, environmentally-friendly corrosion inhibitor for mild steel in acidic environments. • The tannin extract from Paraberlinia bifoliolata bark enhances the corrosion protection of S235 mild steel in HCl. • The optimal formulation is obtained at a concentration of 1.5 g/L at 298 K for 4 h, corresponding to an inhibition efficiency of 75.2 %. • The tannin extract from Paraberlinia bifoliolata bark performs better than other compounds in preventing mild steel corrosion. • Scanning Electron Microscopy (SEM) images confirmed the effectiveness of the Paraberlinia bifoliolata inhibitor.