Study on the corrosion inhibition effects of flavonoid derivatives on aluminium in hydrochloric acid

Corrosion inhibitors are substances that, even in small amounts, can effectively reduce the rate of metal degradation in corrosive environments. Flavonoids, a major class of plant-derived compounds, are considered eco-friendly due to their natural origin and diverse biological activities. This study examines the corrosion inhibition potential of three flavonoid derivatives: Naringenin (NRNG), Morin Hydrate (MNHD), and 6-Hydroxyflavone (6-HFN) on aluminium in hydrochloric acid solution. A combination of experimental techniques was employed, including Potentiodynamic Polarization (PDP), Electrochemical Impedance Spectroscopy (EIS), gravimetric analysis, Atomic Absorption Spectroscopy (AAS), Fourier Transform Infrared Spectroscopy (FTIR), and two-dimensional microscopy. PDP results indicated that current density increased with rising inhibitor concentration. EIS analysis revealed high inhibition efficiencies: 95.19 % for 6-HFN, 90.37 % for MNHD, and 82.35 % for NRNG. Gravimetric data confirmed that the adsorption of all three inhibitors followed the Langmuir adsorption isotherm, indicating monolayer adsorption. The adsorption mechanism for the three inhibitors was found to be a mixed-type. The calculated activation energy increased with inhibitor concentration but remained below the blank value (85.837 kJ·mol⁻¹), suggesting efficient inhibition. The negative Gibbs free energy values indicated a spontaneous adsorption process, while the positive enthalpy changes (less than the blank value of 83.205 kJ·mol⁻¹) suggested an endothermic and chemisorption-driven process. Microscopic analysis showed that inhibitor-treated aluminium experienced uniform corrosion, in contrast to the localized corrosion seen in uninhibited samples, highlighting the protective role of these flavonoid derivatives.