Thermodynamic and Adsorption Evaluation of Codiaeum Variegatum Brilliantissima – Zanzibar as Inhibitor of Mild Steel Corrosion in 1 M HCl

This study evaluated the thermodynamic and adsorption properties of aqueous extract of Codiaeum Variegatum Brilliantissima – Zanzibar (Wire Croton) as an inhibitor of mild steel corrosion in 1 M HCl base stock solution using gravimetric measurement focused on the effect of immersion time, inhibitor concentration and temperature. The result showed that the adsorption of the cold aqueous extracts of Wire Croton on mild steel surface favored Langmuir adsorption isotherm as supported by an overall correlation coefficient (R2) close to unity. The equilibrium constant of adsorption process (Kads) for Wire Croton inhibitor evaluated mathematically is 0.0106, 0.0131, 0.1276, 0.1171 and 0.0269 (mg/L) with free energy of adsorption (ΔGo ads) values of 1.345, 0.821, -5.256, -5.182 and -1.445 kJ/mol for concentrations of 73.6, 147.2, 220.8, 294.4 and 368 mg/L exposed to 303, 313, 323, 333 and 343 K respectively. The small values of Kads suggest weak adsorption which is corroborated by the low negative values of the free energy of adsorption, ΔGo ads, values obtained from thermodynamic measurements. The adsorption of Wire Croton inhibiting particles on the mild steel surface was favorable from thermodynamic point of view since values of ΔGo ads for more concentrations of the inhibitor were negative and provided proof that aqueous extract of the inhibitor is an efficient inhibitor.