The corrosion inhibition of Al-Si alloy in 1 M HCl solution using some carbamidic thioanhydride derivatives at various concentrations has been studied using potentiodynamic polarization, electrochemical impedance spectroscopy, electrochemical frequency modulation, and hydrogen evolution techniques. Results obtained indicate that the inhibition efficiency (% g) reached 94 % at 2 9 10-5 M concentration and was found to increase with increasing the inhibitor concentrations. % g decreased with increasing the temperature. Potentiodynamic polarization curves showed that the investigated derivatives were mixed-type inhibitors. Some activation and adsorption thermodynamic parameters (DH, DG, and DS) were calculated and discussed. The adsorption of these derivatives on the alloy surface was found to obey Langmuir adsorption isotherm. The electrochemical results are in good agreement with the calculated quantum chemical HOMO and LUMO energies of the tested molecules.

:Inhibition performance of Lornoxicam & Tenoxicam against corrosion of carbon steel in 1 M H 2 SO 4 solutions was investigated by weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements. The inhibition efficiency increased with increasing inhibitor's concentration, but decreased with increase in temperature. Potentiodynamic polarization curves showed that, the inhibitors were of mixed type. The apparent activation energy ( ) and other thermodynamic parameters for the corrosion process have also been calculated and discussed. The inhibition of carbon steel corrosion is due to the adsorption of the inhibitor molecules on the surface, which follows Temkin adsorption isotherm. The mechanism of inhibition was discussed in the light of the chemical structure of the undertaken inhibitors.