Inhibitory action of Vernonia amygdalina extract (VAE) on the corrosion of carbon steel in acidic medium

Olamide Olawale,Alewo Opuada Ameh,Adesoji Adeolu Adediran,Segun Isaac Talabi,Geraldine Chika Nwokocha

doi:10.5599/jese.353

Abstract

<p class="PaperTitle"><span lang="EN-GB">This study investigates the inhibition potential of Vernonia amygdalina stem extract (VAE) on the corrosion of mild carbon steel immersed in 1 M HCl solution containing various concentrations of the inhibitor. The corrosion rate and inhibition efficiency were evaluated using mass loss and adsorption techniques. The results revealed that VAE efficiently inhibits the corrosion rate of mild carbon steel immersed in the acidic medium. The concentration of 0.6 g/L provides the highest inhibition efficiency of 78.1 %. The adsorption process was consistent with the physisorption mechanism and obeyed the Langmuir isotherm. The functional groups responsible for inhibition were identified using Fourier Transform Infrared (FTIR) spectra. The surface morphology of the corroded samples examined with Scanning Electron Microscope (SEM) revealed the presence of protective oxide layer. Inhibition efficiency was found depended on the presence of oxalate, phytate, tannins, saponins and flavonoids in the VAE. It has been concluded that VAE is safe, cheap and efficient corrosion inhibitor for mild carbon steel.</span></p>

Highlights

Corrosion is gradual deterioration of materials generated by their chemical interaction with the environment [1]
The corrosion rate was found to decrease with increasing concentration of Vernonia amygdalina stem extract (VAE) in the corrosion medium
A significant retardation in the rate of corrosion can be observed after 288 h (12 days) and the effect is more pronounced with the addition 0.8 g/L of VAE

Summary

Introduction

Corrosion is gradual deterioration of materials generated by their chemical interaction with the environment [1]. Inhibitors protect the metals by effectively adsorbing on their surfaces and blocking the active sites for metal dissolution and hydrogen evolution, respectively In such a way, metal corrosion in aggressive environments becomes hindered [2]. The present work reports the inhibitory action of VAE (extract from VA stem) on the mild steel corrosion in 1 M hydrochloric acid. It is noteworthy, that chloride ions present in the media under investigation have the tendency to be adsorbed on metal surfaces. The mild steel coupons were totally immersed in 250 ml capacity beakers containing 100 ml of 1M HCl solution. The surface features of the mild steel coupons were examined with SEM before and after exposure to HCl solution for 360 h (15 days) in the presence and absence of inhibitor, respectively

Results and discussion

Methods

Conclusion