Mathematical and Electrochemical Investigation of Lamium flexuosum Extract as Effective Corrosion Inhibitor for CS in Acidic Solution Using Multidimensional Minimization Program System

Methylene dichloride extract of Lamium flexuosum was investigated as a corrosion inhibitor for carbon steel (CS) in a 1.0 M hydrochloric acid (HCl) solution at different temperatures. Weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy techniques were employed for this investigation. A multidimensional minimization program system (Levenberg Methods) was used in order to optimize the electrical equivalent circuit for experimental data. The obtained results show a good inhibition efficiency of the tested extract, which increased by increasing concentration and decreased while temperature rises. This extract acted as a mixed-type corrosion inhibitor reaching an efficiency value of 83.50% at 900 ppm. The adsorption of the extract on the CS surface was found to follow the Freundlich isotherm with a physisorption mode. The analysis of the surface morphology of the steel via atomic force microscope shows that in the absence of the extract, the obtained standard deviation was 40.42 nm, while in acidic solution large valleys and peaks with an average roughness of 451.11 nm were observed. However, in the presence of the investigated extract (LFMDE), much fewer corrosion damages with small peaks were noticed at 90.91 nm, indicating that the adsorption of microscopically thin film on the CS surface prevented the hydrochloric acid solution attack.