Corrosion Inhibition Performance Of Alkaloid Extracts Of Calendula Officinalis ( Pot Marigold ) Plant On Aluminium , Carbon Steel And Zinc In 5 M Nitric Acid Solution

The use of plant extracts as inhibitors for the corrosion of metals/alloys, has gained very wide interest among researchers in recent times (Eddy et al., 2010; Ugi et al., 2016) Acid solutions are often used in industries for cleaning, discaling, and pickling of metallic structures. These are processes which are normally accompanied by considerable dissolution of the metal (Nnanna et al. 2010; Brinda et al., 2015). Introduction of inhibitors is one of the methods for protecting corrosion especially in acid solutions to prevent unexpected metal dissolution and acid consumption (Zhanga et al., 2009) The use of chemical as inhibitors has been minimized because of the environmental consequences. Plant extracts have become important because they are environmentally acceptable, inexpensive, readily available and renewable sources of materials. In very many cases the inhibitive effect of some plants extracts has been attributed to the presence of alkaloids in their chemical constituents (Loto et al. 2011; Oguzie et al., 2009; Ochoa et al., 2013). Calendula officinalis is a plant in the genus Calendula of the family Asteraceae. It is probably native to southern Europe, though its long history of cultivation makes its precise origin unknown, and it may possibly be of garden origin. Calendula officinalis is a shortlived aromatic herbaceousperennial, growing to 80 cm (31 in) tall, with sparsely branched lax or erect stems. The leaves are oblong-lanceolate, 5–17 cm (2–7 in) long, hairy on both sides, and with margins entire or occasionally waved or weakly toothed. The inflorescences are yellow, comprising a thick capitulum or flowerhead 4–7 cm diameter surrounded by two rows of hairy bracts. Pot marigold florets are edible. They are often used to add color to salads or added to dishes as a garnish and in lieu of saffron. The leaves are edible but are often not palatable. They have a history of use as a potherb and in salads. The present study is aimed at investigating the inhibiting effects of alkaloid extract of Pot Marigold Abstract: Alkaloid extract of Pot Marigold (Calendula officinalis) leaves was investigated as corrosion inhibitor of carbon steel, aluminium and zinc metals in 5 M HNO3 acid solutions using conventional weight loss, electrochemical polarization and electrochemical impedance spectroscopy studies. The weight loss results showed that the plant extract is an excellent corrosion inhibitor to all the metals tested, electrochemical polarization data revealed the mixed mode of inhibition and the results of electrochemical impedance spectroscopy have shown that the change in the impedance parameters, charge transfer resistance and double layer capacitance, with the change in concentration of the extract is due to the adsorption of active molecules leading to the formation of a protective layer on the surface of they metals. A physical adsorption mechanism was recorded by the inhibitor /metal interface and the Langmuir adsorption isotherm was well obeyed judging from the good correlation of the data to the isotherm. The inhibitor proved to be a stabled one on both metals and a spontaneous reaction process was recorded from the data of the Gibbs free energy.