Determination of the corrosion inhibiting properties of ethanol extract of Pennisetum purpureum in acidic solutions

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Determination of the corrosion inhibiting properties of ethanol extract of Pennisetum purpureum in acidic solutions

Chinonso Blessing Adindu
Department of Chemistry, Imo State University, Owerri, Nigeria
Received: 01 July 2023; Revised: 26 July 2023; Accepted: 29 July 2023; Published: 28 August 2023

Abstract: – The corrosion inhibition of mild steel by leave extract of Pennisetum purpureum (PP) in 1 M HCl and H_2 SO_4 was studied using gravimetric, electrochemical and computer simulation methods of corrosion monitoring. The results obtained showed that the PP extract retarded the mild steel corrosion in both acidic solutions and that inhibition efficiency improved with concentration increase but decreased gradually with prolonged exposure time. Electrochemical results revealed that the extract reduced both the anodic and cathodic corrosion reactions by the adsorption of some of its chemical constituents on the metal surface. To further confirm the adsorption characteristics of the extract, some of its constituents were simulated using density functional theory simulation method.

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Keywords: Corrosion, inhibitor, Pennisetum purpureum, polarization, simulation

I. Introduction

Corrosion is the gradual and continuous deterioration of metals exposed to the environment, corrosion is as old as age itself [1-3]. Scientists have employed many methods to control this environmental menace. One of the most effective ways of corrosion control is the use of corrosion inhibitors [4-5], these are compounds known to effectively retard the undesirable destructive effects of aggressive solutions and prevent the dissolution of metals and their alloys [6-7]. Acidic media which are always employed in industrial acid cleaning, acid pickling as well as acid descaling, need the use of corrosion inhibitors to reduce corrosion on metallic materials. Lately, many corrosion inhibitors used in corrosion control are sourced from either organic or synthetic background with little or no modification. Some of these inhibitors are imidazole based inhibitors and Chromates. The applications of these materials are currently restricted due to their toxicity and other environmental issues. Many plant materials have been in use as corrosion inhibitors for metals in acidic and alkaline environments, [8-12]. Their main advantages include low cost, environmentally friendly and readily available [13-15]. The inhibitive performance of plant materials are usually due to the presence in their composition of the species of complex organics which includes alkaloids, tannins and nitrogenous bases as well as proteins, carbohydrates and degradation products [16-17]. These inhibitors function in many ways to control corrosion: by adsorption as a thin film onto the metal surface. Inhibitors reduce corrosion reactions by reducing both the anodic or cathodic corrosion current density in an electrochemical environment, reducing the movement or diffusion of electrons to the surface of the metal and increasing the electrical resistances of the surface [18]. This work reports the corrosion inhibition behavior of Pennisetum purpureum in 1 M HCl and 0.5 M H_2 SO_4 respectively.

II. Materials and method

2.1 Materials

The mild steel specimen used for the experiments has the composition (weight %) C -0.30, Si – 0.30, Mn – 0.30, P – 0.045, S – 0.050, Cr – 0.064, Cu – 0.040, Ti – 0.04 and the balance Fe [19]. Analytical grade reagents (distilled water, acetone, absolute ethanol, HCl and H_2 SO_4) were used in the preparation of materials. The plant material used for the experiment was collected from the botanical garden of the Imo State University Owerri, dried at 25℃ (room temperature) ground with a mechanical grinder and kept for further use. 25 g of the plant material was dipped 1000 ml of absolute ethanol and kept for 72-h, and then triple filtered. Quantification of the amount of the plant material that was extracted into the solution was done by subtracting the weight of the dried residue from the weight of the plant material before extraction. The test solutions were then prepared from the stock solution by diluting in the concentrations of 200, 400, 600, 800 and 1000 mg/L.