An investigation on the protective film formation on the carbon steel surface in the 1 M hydrochloric acid solution containing mulberry trunk – water extract

The Mulberry trunk - water extract (MTWE) demonstrates an effective corrosion inhibitor for carbon steel in a 1 M hydrochloric acid (HCl) solution. To achieve this, electrochemical measurements (PD, LPR, EIS) and surficial characterizations (SEM, AFM, XPS) are used and combined with FTIR and LC-MS/MS for analyzing components in the inhibitor. The electrochemical results indicate that MTWE acts as a mixed type inhibitor, achieving the highest efficiency of 96.83% at 3500 ppm, with cathodic protection being more dominant. Simultaneously, EIS and LPR results show MTWE contributes to increased corrosion resistance of steel in the highly acidic environment, with R total increasing from 7.19 ± 0.007 (0 ppm) to 43.54 ± 0.022 (3500 ppm) Ω.cm 2 . Additionally, SEM and AFM results show morphological and topological features of steel surfaces after immersion in the solution with the inhibitor are improved clearly. Furthermore, FTIR is applied to analyze the changes of functional groups on the metal surfaces before and after being inhibited, combined with XPS to confirm the presence of organic compounds on the inhibited system, with new peaks of N 1s, O 1s, and C 1s. Finally, the results from LC-MS/MS identifies 42 flavonoids, phenolic acids, and fatty acids in MTWE, which adsorb onto the steel surface through physiochemical adsorption to form a protective film.