Experimental and computational evaluation of illicium verum as a novel eco‐friendly corrosion inhibitor for aluminium

Abstract

Illicium verum extract is investigated as a corrosion inhibitor of aluminium in the presence of an acid medium using gravimetric and impedance techniques. The gravimetric results reveal that the adsorption of inhibitor on the metal surface is physisorption. The impedance measurements are used to interpret the electrochemical process occurring at the interface of aluminium and corrosive medium. The surface characteristics of aluminium are evaluated using scanning electron microscopy-energy dispersive X-ray spectroscopy. The percentage composition of chemical constituents present in the extract is obtained using gas chromatographymass spectrometry and E-anethole is found to be the main chemical component. The interaction between the chemical constituents or inhibitor molecules and the metal surface are evaluated using Monte Carlo simulation. The determination of electron density on the inhibitor molecules is performed using density functional theory. The results from this respective study demonstrate good inhibitive properties of the illicium verum extract towards the corrosion of aluminium in concentrated hydrochloric acid solution. K E Y W O R D Saluminium, corrosion inhibition, illicium verum extract, Monte Carlo simulation, electrochemical impedance spectroscopy 1 | INTRODUCTION Aluminium (Al) and its alloys are widely used, in the field of automotive, and aerospace engineering, packaging, and in other mechanical and engineering industries due to their lightweight, low cost, good mechanical strength and corrosion resistive properties. Al is resistant to corrosion due to the formation of stable aluminium oxide protective film over its surface in the presence of oxygen. However, the metal is corrosion resistant for engineering purposes only within the pH range of 4.5-8.5. [1] As the pH range is disturbed above or below this range, the metal undergoes rapid corrosion. During pickling and etching processes, Al comes into contact of acid solution having pH ranging between 1 and 3, which causes significant loss of the metal due to dissolution to form Al +3 . For pH, greater than 8.5, Al dissolves to form [Al(OH) 4 ] − . To reduce the corrosion rate of Al, appropriate inhibitors can be used in the pickling and etching solutions. [2][3][4][5] Inhibitors protect the metal by adsorbing onto the surface to form an adsorbed, dielectric barrier between the metal and the solution. As per the literature, the presence of hetero atoms and π-electrons in an inhibitor molecule is the basic criteria for determining good inhibitor behaviour. [6] There are various experimental findings to support this position, such as studies

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