Adsorption and Thermodynamic Characteristics of Phenylpropanoids of Alpinia galanga as Corrosion Inhibitors on Mild Steel

The problem of corrosion in the industry has been a major concern. Natural products obtained from plant sources have been employed as substitutes to the common organic corrosion inhibitors. Three phenylpropanoids from Alpinia galanga namely, 1′-acetoxychavicol acetate, methyl eugenol and eugenol acetate have been appraised as ecologically sustainable corrosion inhibitors on mild steel in an acid medium utilizing weight loss and electrochemical methods. Corrosion rates were assessed at temperatures ranging from 300 K to 333 K. The inhibition efficiencies of the phenylpropanoids increase with increasing inhibitor concentrations but decrease with rise in temperature and immersion time. Potentiodynamic polarization measurements reveal all the inhibitors behaving as mixed kind of inhibitors. Adsorption of the constituents on mild steel surface complies with the Langmuir adsorption isotherm model. Thermodynamics of the inhibition process were appraised. The negative values of ΔG _ads designates spontaneity of the adsorption process and the steadiness of the adsorbed inhibitor molecules on the mild steel surface. The film created was further characterized by SEM to show the effectiveness of the constituents as good corrosion inhibitors in acidic medium. These constituents of Alpinia galanga can find applications as environmentally friendly corrosion inhibitors on mild steel in acidic medium.