Abstract
Abstract The adsorption and the inhibitive properties of methanol extract of Euphorbia heterophylla on copper in 0.5 M HNO3 have been studied by weight loss method at different temperatures (30-50°C), potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and electrochemical frequency modulation (EFM) techniques. Also, the surface morphology was analyzed by scanning electron microscopy (SEM). It was found that the inhibition efficiency increases with increasing extract doses and decreased with increasing temperature. The polarization data revealed that this extract acts as mixed type inhibitor. The adsorption process was more favored at lower temperatures with larger negative standard free energy. The extract was adsorbed physically on the copper surface followed Frumkin isotherm.
Highlights
Metals are most commonly unstable in the atmosphere
The aggressive solutions used were made of AR grade HNO3 (7 M) and its concentration was checked using standardized NaOH. 0.5 M of acid was prepared by dilution using bidistilled water. 100 ml stock solutions (103 ppm) of investigated plant extracts were prepared by dissolving an accurately weighed quantity of plant extract (1 g) in an appropriate volume (1 L) of absolute methanol, and the required doses (5–25 ppm) were prepared by dilution with bidistilled water
The increase of Eff.% by increasing doses of the targeted extract showed that the inhibition process is affected by the adsorption of extract molecules onto the copper surface
Summary
Metals are most commonly unstable in the atmosphere. Corrosion is the process of a metal returning to the material’s stable thermodynamic state. Billions of dollars are spent annually for the replacement of corroded structures, machinery and components. The extracts of the plant contain mixtures of compounds having O, S and N element and are eco-friendly. These compounds having nitrogen and sulphur as constituent atoms were studied as the corrosion inhibitor in various acid media. The bioactive compounds present in the plant extract are as effective as synthetic inhibitors. These compounds act as inhibitors in the acid solution which interact with metals and affect the corrosion reaction in a number of ways. Some of them are well known to possess biological activities[15]
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