Investigation of the protection effect of ginger, tea tree and grapefruit essential oil extracts on mild steel in 0.5M H2SO4 solution

Abstract

Utilization of plant extracts for the corrosion protection of metallic alloys has increased significantly in the last few years. Ginger (GII), tea tree (TT) and grapefruit (GP) essential oil extracts were evaluated for their corrosion protection effect on mild steel in 0.5 M H2SO4 media by potentiodynamic polarization, weight loss analysis, open circuit potential measurement, optical microscopy and ATF-FTIR spectroscopy. Corrosion rate from weight loss and polarization at 0% extract concentration decreased from 63.33 mm y−1 and 18.01 mm y−1 to values between 0.31 mm y−1 and 1.96 mm/y for weight loss, and 0.604 mm y−1 and 0.161 mm/y for polarization at optimal extract concentration. Generally, the extracts performed effectively with inhibition efficiency above 95%. The extracts displayed mixed-type inhibition properties though with significant effect on the cathodic plot while the anodic plots indicate activation control mechanism. Corrosion inhibition of GII extract obeyed the Langmuir and Frumkin isotherm model while TT extract inhibition adhered to Langmuir, Frumkin, Frundlich and Temkin isotherms. GP extract inhibition obeyed the Langmuir isotherm only. Correlation coefficient of the isotherms were generally above 0.9. Adsorption of the extracts aligned with chemisorption adsorption from thermodynamic calculations. Open circuit potential plots in the presence of the extracts/acid solution generally depict significant electropositive shift compared to the plot in the absence of the extracts which was relatively electronegative. Potential variations were observed on the plots of the extracts due to miniature active passive transit characteristics at the extract-metal interphase. ATF-FTIR spectroscopic data shows the functional groups in TT extract molecules adsorbed onto the steel exterior compared to GII and GP extract molecules which depict surface coverage from analysis of the wavelength and transmittance data. Optical image of mild steel after corrosion depicts significantly degraded exterior with corrosion pits. However, in the presence of the extracts the steel morphology was well protected.