Application of ginger and grapefruit essential oil extracts on the corrosion inhibition of mild steel in dilute 0.5 M H₂SO₄ electrolyte

Admixture of ginger and grapefruit essential oils (GPP) were studied for their corrosion inhibition properties on mild steel (MS) in 0.5 M H₂SO₄ solution by potentiodynamic polarization, open circuit potential measurement, electrochemical impedance spectroscopy, weight loss analysis and ATF-FTIR spectroscopy. Results from potentiodynamic polarization shows GPP significantly reduced the corrosion of MS from 8.430 mm/y at 0% GPP concentration to values between 1.979 mm/y and 0.565 mm/y. The corresponding inhibition efficiency values ranged from 76.52% to 93.5% and corrosion current density from 1.88 × 10⁻⁴ A/cm² to 5.36 × 10⁻⁵ A/cm². GPP displayed mixed-type inhibition at all GPP concentrations studied. The OCP plot at 0% GPP initiated at -0.495V compared to -0.443V and -0.451V at 1% and 3.5% GPP. At 9000s, the corresponding OCP values are -0.442V, -0.410V and -0.424V due to electropositive plot shift and passivation of MS surface at 1% and 3.5% GPP, though significant potential transients were present on the OCP plot at 1% GPP. The electrochemical impedance results indicate that the corrosion resistance of MS increased from 4.402 Ω cm² to 99.318 Ω cm² upon the addition of 3.5% GPP resulting in inhibition efficiency of 96%. Data from weight loss analysis shows decrease in corrosion rate from 184.48 mm/y to values between 8.94 mm/y and 6.25 mm/y. The corresponding inhibition efficiency values varies from 95.16% at 1% GPP to 96.61% at 3.5% GPP concentration. The ATF-FTIR results confirm the adsorption of GPP molecules on the surface of the carbon steel electrode.