Analysis of Inhibitive Performance of N '‐[( E )‐Phenylmethylidene]Pyridine‐3‐Carbohydrazide on Corrosion of IS 2062 E250 Mild Steel in 0.5‐M Trichloroacetic Acid

The Schiff base N ′‐[( E )‐phenylmethylidene]pyridine‐3‐carbohydrazide (PPC) was investigated as a corrosion inhibitor for IS 2062 E250 mild steel in 0.5‐M trichloroacetic acid. The inhibition performance was evaluated using weight‐loss measurements, potentiodynamic polarization, and electrochemical impedance spectroscopy at different inhibitor concentrations and temperatures, supported by quantum chemical calculations. The study provides a systematic evaluation of PPC as a corrosion inhibitor in an aggressive organic acid medium and establishes an experimental–theoretical correlation to elucidate its inhibition mechanism. Thermodynamic parameters such as activation energy, enthalpy, entropy, and Gibbs free energy of corrosion indicate that the adsorption of PPC on the steel surface involves both physical and chemical interactions. The inhibition efficiency reached up to 97% in 0.5‐M trichloroacetic acid. Polarization studies show that PPC modifies both anodic and cathodic Tafel slopes, confirming mixed‐type inhibition behavior. Electrochemical impedance results demonstrate strong adsorption through the formation of a protective surface film following the Temkin adsorption isotherm. Density functional theory calculations support the experimental observations by identifying key electrophilic (C20, C18, N15, and O28) and nucleophilic (C18, C20, and C2) active sites responsible for strong metal–inhibitor interactions. The combined results confirm PPC as an efficient corrosion inhibitor for acidic environments.