Electrochemical measurements and theoretical calculations on the inhibitive interaction of Plectranthus amboinicus leaf extract with mild steel in hydrochloric acid

The corrosion inhibition property of Plectranthus amboinicus leaves extracts for mild steel in HCl has been studied using EIS and potentiodynamic polarization techniques. Two main constituents of the leaf thymol and 1,8-cineole were also monitored for their inhibition behaviour, both in the individual form and in combination with each other. EIS studies revealed that the dried and fresh leaf extracts of PA (PADE and PAFE) show fairly good inhibition efficiencies (upto 98% for PADE and 93% for PAFE) in the studied system. Potentiodynamic polarization studies revealed the mixed type inhibition behaviour of the extracts. The synergism studies and theoretical calculations done using Gaussian 03 program revealed that the combination of thymol and cineole exhibited enhanced inhibition efficiency compared to the individual forms. The weight loss measurements also revealed the inhibition potential of the extracts. The mode of adsorption of the extracts was found obeying Langmuir isotherm.