KINETICS CONSIDERATION OF ETHANOL LEAVES EXTRACT OF COSTUS LUCANUSIANUS AS GREEN CORROSION INHIBITOR FOR MILD STEEL AND ALUMINIUM IN HCL SOLUTION

The chemical composition of ethanol leaves extract of Costus lucanusianus (ELECL) was evaluated by Gas Chromatography-Mass Spectroscopy (GC-MS) for corrosion inhibition of mild steel and aluminium in 1 M HCl using weight loss technique. A total of 18 compounds were identified. 11-Octadecenoic acid, methyl ester (30.01%); 9- Octadecenoic acid, 12-hydroxy-, methyl ester, [R-(Z)]- (25.53%); 9,12-Octadecadienoic acid, methyl ester (13.52 %); and Hexadecanoic acid, methyl ester (13.14%) were the major counpounds. The weight loss analysis showed ELECL as an effective corrosion inhibitor at low temperatures for mild steel and aluminium. At 1 g/l concentration, the inhibitory action of the extracts attained an inhibition efficiency of 94 % and 79 % in 1 g/l at 313 K and 303 K for mild steel and aluminium respectively. The extracts inhibitor compounds covered the metal surfaces following Freundlich adsorption isotherm. The enthalpy change showed an endothermic process while the entropy chnage showed an orderly adsorption of the inhibitor molecules on the metal surfaces.