Phytochemical profile, Adsorptive and Inhibitive behaviour of Costus afer extracts on aluminium corrosion in hydrochloric acid

Phytochemical screening and aluminium corrosion inhibitive property of aqueous stem and leaf extracts of Costus afer in hydrochloric acid was investigated using weight loss and hydrogen evolution techniques. Results indicate that the stem extract (SE) contains alkaloids, flavonoids, phenols, tannins, anthraquinones, glycosides, and terpenoids whereas saponins, flavonoids, tannins, glycosides and phlobatannins were detected in the leaf extract (LE). Values of corrosion inhibition efficiency obtained from hydrogen evolution method ranged from 58.93 % to 49.43 % and 65.43 % to 51.28 % at 303K to 333K for LE and SE respectively. From weight loss measurements, the values ranged from 56.21 % to 46.71 % and 61.14 % to 50.19 % for LE and SE respectively at 303K – 333K. The extracts of C. afer inhibited the corrosion process via physical adsorption mechanism and the adsorption process was best approximated by the Freundlich adsorption model. Arrhenius and transition state plot afforded kinetic and thermodynamic parameters like activation energy, enthalpy change, entropy change and change in free energy of adsorption. The higher corrosion inhibition efficiency of the stem is rationalised in terms of its many phytoconstituents which are rich sources of some heteroatoms like oxygen and nitrogen, usually implicated in corrosion inhibition

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