Abstract

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The inhibitive effect of Spider Wisp / Cat's Whiskers (Cloeme gynandra) on the corrosion of mild steel in 0.1M HCl has been investigated by means of gravimetric analysis and Electrochemical (polarization) studies at 308,318 and 328K. A marked decrease of the corrosion rate (CR) was observed with increasing extracts concentration. An effective inhibition with 94.14% - 92.68% efficiency (I_E %) was reached at 100 mg inhibitor concentration as the temperature increased from 308 – 328K. The effect of temperature showed a decreasing I_E% with increasing temperature. The average value of activation energy, Ea is 27.40kJmol^-1which is lower than 40.00 kJmol^-1implying that the inhibitor is physically adsorbed on the mild steel surface. The value of heat of adsorption, Qads, having average of -13.95kJmol^-1, is an indication that inhibition efficiency and adsorption decrease with increase in temperature. Results clearly revealed that Spider Wisp / Cat's Whiskers inhibition activity proceeds via a physisorption. The adsorption of Spider Wisp / Cat's Whiskers onto the mild steel surface followed a Langmuir isotherm. Corrosion current (Icorr) density decreases in the presence of plant extract and the inhibition rate increases with increasing extract concentration which provides evidence for the inhibitive effect of the plants extract in HCl medium. The presence of Alkaloid, Flavonoid and Tannin is also an evidence of the inhibition potency of the extract. FT-IR results indicate that Spider Wisp / Cat's Whiskers (Cleome gynandra) contain heteroatom such as O, N, and multiple bonds in the molecule through which they adsorption takes place on the metal surface. Adsorption depends mainly on certain physicochemical properties of the inhibitor group, such as functional groups.

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