Integrative Electrochemical and Quantum Chemical Evaluation of a Schiff Base Inhibitor for Acidic Corrosion of XC70 Steel

Abstract

A Schiff base compound, designated as L₃, was successfully synthesized and thoroughly analyzed through various characterization techniques, including Fourier-transform infrared (FT-IR) spectroscopy, and elemental composition analysis. Its corrosion inhibition properties for XC70 carbon steel in 1 M HCl solution were assessed using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) methods. The investigation examined the impact of both L₃ concentration and temperature on its performance. Results indicated a direct correlation between increased concentration and temperature and improved inhibition efficiency (IE%), which reached a maximum of 84% at 10^–4 M. PDP measurements revealed that L₃ functions as a mixed-type inhibitor, affecting both anodic and cathodic processes. EIS data demonstrated that rising L₃ concentrations enhanced the charge transfer resistance (R_ct) from 104.3 to 251.2 Ω cm², while reducing the double-layer capacitance (C_dl) from 108.6 to 63.64 µF cm^–2, suggesting strong inhibitor adsorption at the metal-solution interface. Thermodynamic parameters such as \(\Delta G_{{{\text{ads}}}}^{^\circ }\) , ΔH_a, E_a, and ΔS_a were calculated to clarify the inhibition mechanism, indicating that L₃ adsorption occurs via chemisorption. Furthermore, the adsorption behavior followed the Langmuir isotherm model. Finally, quantum chemical analyses were carried out to interpret how the electronic structure of L₃ influences its corrosion inhibition performance.