Electrochemical and theoretical studies of some monoterpenic thiazolidinones as corrosion inhibitors for steel in acidic media.

This work deals with the study of the inhibition activity of three thiazolidinones (prepared from monoterpenic ketones) on the deterioration of S300 steel in hydrochloric acid solution. The potentiodynamic polarization was used to investigate the electrochemical behavior of the studied inhibitors which were revealed to be mixed type ones. It was established that the studied compounds have significantly inhibited the dissolution of steel with the highest inhibition efficiency of 84% at 293 K. This inhibition efficiency increases with an increase in the inhibitor's concentrations ranging between 1 × 10⁻⁴ and 5 × 10⁻³mol/L, proving the mixed type character. Moreover, the corrosion behavior of steel in 1 M HCl in the absence and presence of the inhibitors at 5 × 10⁻³mol/L was studied at the temperature range of 293 − 323 K. The obtained results also revealed that the adsorption of inhibitors on steel surface might take place at specific homogeneous sites, obeying to the Langmuir adsorption isotherm. Thermodynamic parameters such as enthalpy, entropy and activation energy were determined. The scanning electron microscopy combined with dispersive X-ray spectroscopy examinations and Raman technique was used to explore the surface morphology and the elemental composition. Scanning electron microscope (SEM) images show that the surface damage is reduced in the presence of the three studied inhibitors. The quantum chemical calculations using density functional theory (DFT) were performed to provide some insights into the electronic density distribution as well as the nature of inhibitor-steel interaction. The corresponding results show that the three thiazolidinones act as inhibitors by improving a good barrier for corrosion protection. Also, the rearrangement in the compound's structure affects their inhibitory activity. [ABSTRACT FROM AUTHOR]