Eco-friendly Chlorella vulgaris extracts for corrosion protection of steel in acidic environments

Abstract

This study evaluates the potential of Chlorella vulgaris sp. extracts as eco-friendly corrosion inhibitors for API 5L 42 Steel in a 1M HCl acidic environment, offering sustainable alternatives for industrial applications. Two corrosion inhibitors were obtained through solvent extraction methods: M1 (methanol) and M2 (methanol/chloroform). The extracts were characterized using infrared spectroscopy, the analysis revealed hydroxyl, methyl and vinyl groups as the most representative. The effect of corrosion inhibition was study by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The results show significant reductions in corrosion current density and increases in charge transfer resistance, with M2 achieving the highest protection efficiency of 91.20 % and a charge transfer resistance of 501.80 Ω at a 120 ppm concentration, while M1 reached 88.22 % efficiency with a charge transfer resistance of 102.30 Ω. Uv–Vis measurements were performed to determine the electronic transitions of the metal-inhibitor system for each of the extracts. ANOVA highlighted the significant influence of biomass concentration on corrosion resistance. The adsorption of M1 and M2 extracts on the carbon steel surface obeyed the Langmuir isotherm and Gibbs free energy calculations indicated a physisorption mechanism for both extracts. Surface morphology analysis by Scanning electron microscope (SEM) revealed less pitting and reduced surface roughness as inhibitor concentration increased. These findings underscore the potential of Chlorella vulgaris extracts, particularly M2 at 120 ppm, as effective and sustainable corrosion inhibitors for steel in acidic environments.