In-depth investigation of cefalexin's action mechanism as Al-Cu alloy corrosion inhibitor in 0.5 M HCl medium

This research work aims at evaluating the inhibiting properties of the antibiotic drug cefalexin on Al-Cu alloy corrosion in 0.5 M HCl. Electrochemical characterizations (polarization curve, polarization resistance and electrochemical impedance spectroscopy), and surface analysis (scanning electronic microscopy) are performed in order to investigate the inhibition mechanism and to optimize the cefalexin's concentration. The obtained results highlight the excellent corrosion protection of cefalexin especially for the optimal concentration 800 ppm where the polarization resistance increases significantly from 6.04 Omega.cm(2) (in absence of inhibitor) to 49.15 Omega.cm(2 )(in presence of inhibitor). Also, the current density value drops abruptly from 110.00 mu A cm(-2)(in absence of inhibitor) to 5.51 mu A cm(-2) (in presence of inhibitor). In this case, 800 ppm represents the best inhibition efficiency reaching up 94%. The proposed mechanism suggests that the adsorption of cefalexin inhibitor onto the alloy surface followed by simple blocking of its active sites which yields an anodic character to the studied inhibitor. It is observed that the cefalexin adsorption on Al-Cu alloy's surface in 0.5 M HCl medium obeys to Langmuir isotherm's adsorption. Consequently, the corrosion inhibition is due to the formation of a mono-layer onto metal surface, thereby limiting the electrolyte's interaction. Quantum chemical calculations using DFT technique has been used to calculate some electronic properties of the molecule in order to determine the correlation between the inhibitive effect and the molecular structure of cefalexin.