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

Authors: Olugbenga Adeshola Omotosho; Joshua Olusegun Okeniyi; Adeoluwa Barnabas Oni; Thomas Oluwafemi Makinwa; Omokolade Bamidele Ajibola; Ekundayo Oluwademilade Jacob Fademi; Chukwunonso Ezekiel Obi; Cleophas Akintoye Loto; Abimbola Patricia Idowu Popoola

Addresses: Mechanical Engineering Department, Covenant University, Ota 112001, Nigeria ' Mechanical Engineering Department, Covenant University, Ota 112001, Nigeria ' Mechanical Engineering Department, Covenant University, Ota 112001, Nigeria ' Mechanical Engineering Department, Covenant University, Ota 112001, Nigeria ' Mechanical Engineering Department, Covenant University, Ota 112001, Nigeria ' Mechanical Engineering Department, Covenant University, Ota 112001, Nigeria ' Mechanical Engineering Department, Covenant University, Ota 112001, Nigeria ' Mechanical Engineering Department, Covenant University, Ota 112001, Nigeria ' Chemical and Metallurgical Engineering Department, Tshwane University of Technology, Pretoria 0001, South Africa

Abstract: 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 test-environment. 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.

Keywords: Terminalia catappa; mild steel corrosion; corrosion inhibition; corrosion mechanism; sulphuric-acid environment; potentiodynamic polarisation; gravimetric technique; correlation analysis; adsorption isotherms; sustainable corrosion protection.

DOI: 10.1504/PIE.2016.083924

Progress in Industrial Ecology, An International Journal, 2016 Vol.10 No.4, pp.398 - 413

Received: 26 Mar 2016
Accepted: 02 Nov 2016
Published online: 26 Apr 2017 *

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