Evaluation of 1,4-Benzothiazines in Steel Corrosion Inhibition in 15% HCl: Experimental and Theoretical Perspectives

Corrosion inhibitors are essential for metal protection. In this study, the efficacy of 1,4-Benzothiazine derivatives, particularly ethyl 3-hydroxy-2-(p-tolyl)-3,4dihydro-2H-benzo[b][1,4]thiazine-3-carboxylate (EHBT) and 2-(4-chlorophenyl)-1,4benzothiazin-3-one (CBT), was examined for carbon steel corrosion inhibition in 15 wt.% HCl. Techniques such as Electrochemical Impedance Spectroscopy (EIS), Potentiodynamic Polarization (PDP), weight loss measurement, and Scanning Electron Microscopy assessed the inhibitors' performance. Results showed inhibitor efficiency increased with concentration, with CBT and EHBT achieving up to 97% and 98% effectiveness respectively. Both acted as mixed inhibitors, reducing anodic and cathodic reactions. Adsorption of these molecules onto the steel surface was consistent with the Langmuir isotherm model, suggesting physical and chemical interaction. SEM analysis confirmed the protective layer formation by 1,4-Benzothiazine derivatives. Additionally, Quantum Chemical Calculations and Molecular Dynamics simulations provided insights into their interaction mechanisms on the Fe(110) surface. This research highlights the potential of 1,4-Benzothiazine derivatives in corrosion protection and paves the way for their further development.