Pectin as promising green corrosion inhibitor of aluminum in hydrochloric acid solution

Abstract The present article describes the use of promising green eco-friendly pectin natural polymer as successful corrosion inhibitor on the surface of aluminum metal in acidic media. The inhibition efficiency first increased linearly up to 2.0 g/L, and then it continues steady exponential increase until it reached plateau. The maximum inhibition efficiency obtained at 10 °C using pectin concentration = 8.0 g/L was ∼91%, whereas at 40 °C it severely declined to 31%. As pectin concentration increased, higher activation energy, enthalpy of activation and entropy of activation were obtained. In presence of 2.0 M HCl, the aluminum sheet showed longitudinal parallel grooves together with huge amount of irregular deep voids distributed along the sheet, whereas in the presence of inhibitor and acidic medium the number of deep voids diminished. The adsorption process was more favored at lower temperatures with larger negative standard free energy. Adsorption of pectin macromolecules on aluminum surface demonstrated proper Langmuir isotherm fit.