Thermodynamic characterization of metal dissolution and inhibitor adsorption processes in mild steel/2,5-bis(n-thienyl)-1,3,4-thiadiazoles/hydrochloric acid system

The corrosion inhibition of mild steel in 1 M hydrochloric acid solution by some 2,5-bis(n-thienyl)-1,3,4-thiadiazoles (n-TTH) has been studied in relation to the concentration of the inhibitors as well as the temperature using chemical (weight loss) and electrochemical (ac impedance and dc polarisation) techniques. All the methods employed are in reasonable agreement. The protection efficiency increases with increasing inhibitors concentration and with increasing temperature. The thermodynamic functions of dissolution and adsorption processes were calculated from experimental polarisation data and the interpretation of the results are given. Adsorption of n-TTH was found to follow the Langmuir’s adsorption isotherm and the ability of the molecule to chemisorb on the steel surface was dependent on the position of the sulphur atom on the thienyl substituent.