Inhibition and mechanism of Terminalia catappa on mild-steel corrosion in sulphuric-acid environment

Mild-steel samples were immersed in 0.5 M H2SO4 having different concentrations of Terminalia catappa leaf-extract for investigating inhibition and mechanism of the leaf-extract on mild-steel corrosion in the testenvironment. Corrosion-rate measurements were obtained by potentiodynamic polarisation and gravimetric techniques and analysed for detailing sustainable corrosion-protection by the natural-plant in the test-environment. Results indicate potentiodynamic corrosion-rate correlated excellently (R = 99.25%, Nash-Sutcliffe efficiency (NSE) = 98.52%, ANOVA p-value = 0.0222) with function of the gravimetric corrosion-rate and the leaf-extract concentration. By the experimental and correlated results, inhibition effectiveness on mild-steel corrosion increased with increasing leaf-extract concentration up to the 8 g/L Terminalia catappa leaf-extract, which exhibited optimal inhibition efficiency, η = 99.99% (experimental model) or η = 95.45% (correlation prediction). Correlation prediction, potentiodynamic and gravimetric data followed the Langmuir and the Flory-Huggins adsorption isotherms with agreements of favourable adsorption/prevalent physisorption mechanism for the leaf-extract corrosion-protection of mild-steel in the test-environment