Interfacial phenomena and surface protection of N80-carbon steel in acidic environments using thiazolidinediones: An experimental and computational analysis

Abstract

In petrochemical engineering, a pressing challenge is the corrosion of N80 carbon steel (N80-CS) in strong acidic conditions like 15 wt% HCl, impacting both mechanical integrity and economic viability. Herein, the corrosive behavior of N80-CS in a 15 wt% HCl solution was evaluated with two thiazolidinediones, (Z)− 5-benzylidenethiazolidine-2,4-dione (BT) and 5-(4-fluorobenzylidene) thiazolidine-2,4-dione (FBT). The surface and interface phenomena were evaluated using electrochemical testing, Scanning electron microscope (SEM), atomic force microscopy (AFM), and computational modelling. Electrochemical impedance spectroscopy (EIS) revealed that, at optimum concentrations, the polarization resistance (Rp) manifested a notable increase from an initial 5.51 Ω cm2 to 80.46 and 39.64 Ω cm2 when BT and FBT were introduced, respectively. This corresponded to inhibition efficiencies of 93% for BT and 86% for FBT. This results in a substantial reduction in effective double layer capacitance due to the adsorption of inhibitor molecules. The Rp values of BT compound peaked at 158.02 Ω cm2 after a 24-hour immersion period, later declining to 82 Ω cm2 after 42 h, thus evidencing the enhanced stability of the inhibitor’s protective layer on the steel surface. The potentiodynamic polarization (PDP) technique validated that both compounds function as mixed-type corrosion inhibitors. Their adsorption followed the Langmuir adsorption isotherm model, indicating a mixed mechanism of protection via both physical and chemical interactions between the inhibitor molecules and the steel surface. SEM and AFM analyses further revealed significant alterations in the surface morphology and roughness of N80-CS, affirming the performance of these inhibitors. Ab initio Density Functional Theory (DFT) simulations further supported the experimental results, particularly explaining the superior performance of BT and its exceptional adsorption characteristics. This study confirms the anti-corrosive potential of thiazolidinediones and sets the groundwork for future research and improved inhibitor design.