CORROSION INHIBITION CHARACTERISTICS OF Vernonia Amygdalina STEM EXTRACTS ON MILD STEEL IN ACIDIC MEDIUM

Abstract

The corrosion inhibition characteristics of Vernonia Amygdalina stem extracts was carried out using gravimetric technique on mild steel in 1.0 M HCl acid solution at temperature ranges of 303 to 333 K. While the mechanism of corrosion inhibition through suspected adsorption was determined by fitting the corrosion inhibition data into the Langmuir and Temkins isotherms. The thermodynamic parameters were also mathematically determined. The results obtained exhibited good corrosion inhibition properties. The weight loss and corrosion rate of mild steel in the presence of the extract inhibitor decreased with increased extract concentration. Temperature increase, increased weight loss and consequent corrosion rate. Comparatively, the extract directly improved corrosion inhibition efficiency with extract concentration and time. The recorded low corrosion inhibition efficiency values of 52.55 percent of 5.0 g/L extract at 303 K was attributed to short measurement time interval. The isotherms data attributed the corrosion inhibition mechanism to adsorption. Furthermore, the Langmuir isotherm reveals that the surface of the mild steel was not uniform, whereas the Temkins isotherm reveals that repulsion on the adsorbent surface. Thermodynamically, the negative ∆Gads signifies that the Vernonia amygdalina stem extract adsorption on mild steel was a spontaneous process while lower negative ∆Gads values indicates physiosorptive process. Interestingly, the Vernonia amygdalina stem extract increased the activation energy Ea confirming its ability slow down corrosion.