Structure-activity relationship of pyrazole-based corrosion inhibitors for carbon steel in HCl: combined experimental and theoretical study

The corrosion inhibition performance of two newly synthesized pyrazole-based derivatives, P6 (bis-pyrazole) and P8 (pyrazolyl-thiadiazine), toward carbon steel in 1.0 M HCl was systematically investigated using combined experimental and theoretical approaches. Electrochemical and gravimetric results revealed high inhibition efficiencies exceeding 95% at 5 × 10⁻⁴ M, with P6 exhibiting superior performance. This enhanced performance is attributed to its stronger adsorption affinity and more stable interaction with the steel surface. Polarization measurements revealed predominantly anodic inhibition behavior, although both anodic and cathodic reactions were affected, while impedance analysis confirmed the formation of a protective adsorbed film. Surface characterization (SEM, EDX, and AFM) further supported the development of a compact and homogeneous protective layer. Thermodynamic analysis suggested a mixed adsorption mechanism involving electrostatic and chemical interactions. Computational studies (DFT and Monte Carlo simulations) corroborated the experimental findings, demonstrating strong adsorption on the Fe (110) surface.