Corrosion Inhibition and Adsorption Properties of Ethanolic Extract of Calotropis for Corrosion of Aluminium in Acidic Media

The corrosion inhibition of aluminium in sulfuric acid solution in the presence of different plant parts, namely, leaves, latex, and fruit was studied using weight loss method and thermometric method. The ethanolic extracts of Calotropis procera and Calotropis gigantea act as an inhibitor in the acid environment. The inhibition efficiency increases with increase in inhibitor concentration. The plant parts inhibit aluminium, and inhibition is attributed, due to the adsorption of the plant part on the surface of aluminium. 1. Introduction Aluminium is widely used in chemical industries due to its low cost and easy availability for fabrication reaction of vessel, tanks, pipeline, and boiler. Alumninium suffers from severe corrosion in aggressive environments, and it has to be protected. The corrosion of metal in aqueous solution occurs in two steps oxidation and reduction. Oxidation reaction takes place at anode, whereas reduction takes place at cathode. The cathodic reaction may be either by evolution of hydrogen or absorption of oxygen. The use of inhibitors is one of the best methods of protecting metals against corrosion [1, 2]. Most corrosion inhibitors are organic compounds having hetero atoms in their aromatic or long carbon chain. However, there is increasing concern about the toxicity of most corrosion inhibitors. The toxic effect does not only affect living organisms but also poison the environment. Due to toxicity of some corrosion inhibitors, there has been increasing search for green corrosion inhibitors [3]. Natural products of plant origin containing different organic compounds (e.g., alkaloids, tannins, pigments, organic, and amino acids) are known to have inhibitive action [4, 5]. Inhibitors in this class are those that are environment friendly, less polluting, cheap, and easily available and are obtained from natural products such as plant extracts [6]. Several studies have been carried out on the inhibition of corrosion of metals by plant extract [7–13]. Aluminium is a reactive metal to reduce the corrosion problem in these environment inhibitive effects of various naturally occurring substances like Datura stramonium [14], Tannin beet root, Tamarind, Pomegranate juice, Saponin [15], Embellica officinalis, Terminalia bellerica, Mahasudarshana churna, Prosopis juliflora [16], Caparis decidu [17], Adhatoda vasica, Vinca rosea, Heena [18], Eugenia jambolana, pomegranate and Peels [19, 20], Tannins, Caffeine, Prosopis cineraria [21], and Ficus religiosa [22] that have been evaluated as effective corrosion inhibitors. Calotropis is used as a