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Abstract
Inhibition of copper corrosion in acidic medium by ethanolic extract of Momordica balsamina leaves was investigated. Findings reveal that the rate of copper corrosion increases with increasing temperature of the medium but decreases as the concentration of the Momordica balsamina extract added to the medium increases. Examination of the surface morphology of copper using Scanning Electron Microscopy (SEM) also reveals that while the surface of copper was seriously damaged in acidic solution in the absence of Momordica balsamina extract, addition of 0.8 mgL -1 of the extract significantly protected the copper surface from corrosion. Results obtained from adsorption and thermodynamic studies reveal that the adsorption of the inhibitor on the surface of the copper metal fitted well to both Freundlich ( R 2 ≥ 0.948) and Temkin ( R 2 ≥ 0.940) adsorption models and the low values of activation energies obtained ( Ea≤ 34.02 kjmol -1 ) indicate that the adsorption of the inhibitor on the copper surface favors the mechanism of physical adsorption. Negative signs of ΔG ads obtained in the study suggest that the adsorption of Momordica balsamina on the copper metal is thermodynamically favorable. The data obtained in this study demonstrate that extract of Momordica balsamina leaves probably contains one or more chemical species that protect copper against corrosion through the mechanism of physical adsorption. Keywords : Adsorption, Copper, Corrosion, Inhibitor, Momordica balsamina
Highlights
IntroductionCoefficients of determination; t = period of immersion (in hour); T = temperature (in Kelvin); = weight loss of copper in the presence of inhibitor (in g); = weight loss of copper in the absence of inhibitor (in g); x = a measure of adsorbed water molecules; θ = the degree of surface coverage of the inhibitor; ∆W = loss in weight of copper;
= equilibrium constant of adsorption; n = a constant for a given adsorbent at a particular temperature; R = universal gas constant; =
The pathway for oxidative destruction of copper in acidic medium in the presence of oxygen is shown in Scheme 1, and the value of Gibbs freeenergy change calculated for this redox reaction (∆G = -344.26 KJ) indicates that the corrosion process is spontaneous since the sign of ∆G obtained is negative
Summary
Coefficients of determination; t = period of immersion (in hour); T = temperature (in Kelvin); = weight loss of copper in the presence of inhibitor (in g); = weight loss of copper in the absence of inhibitor (in g); x = a measure of adsorbed water molecules; θ = the degree of surface coverage of the inhibitor; ∆W = loss in weight of copper; Due to their numerous desirable properties, metals and their alloys are widely used in applications ranging from bridge construction, sculpture molding, cutlery making, jewelry production, plumbing, ship building, and electrical power generation, transmission and distribution. The pathway for oxidative destruction of copper in acidic medium in the presence of oxygen is shown in Scheme 1, and the value of Gibbs freeenergy change calculated for this redox reaction (∆G = -344.26 KJ) indicates that the corrosion process is spontaneous since the sign of ∆G obtained is negative. Rate of Inhibitory Effect of African Pumpkin (Momordica balsamina Linn.)
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