The influence of 2,4,6-tris (2-pyridyl)-1,3,5-triazine (TPTZ) on the corrosion of tin, indium and tin–indium alloys in 0.5 M HCl solution at different temperatures was studied. Potentiodynamic cathodic polarization and extrapolation of cathodic and anodic Tafel lines techniques were used to obtained experimental data. In the case of tin, the percent inhibition efficiency (IE%) increases as both concentration of TPTZ and temperature are increased. The value of activation energy (Ea) is smaller in the presence of TPTZ than that in uninhibited solution, and decreases with increasing the concentration. However, the effect of TPTZ on indium and the investigated alloys exhibited similar behavior; so, the maximum inhibition efficiency is observed at lowest concentration (10−6 M) of TPTZ. Then, the value of inhibition efficiency starts to decrease gradually with increasing TPTZ concentration than that of 10−6 M. But at higher concentration (10−3 M) the corrosion current density (Icorr) is still lower than that in uninhibited solution. SEM photographs support that the higher inhibition efficiency is observed at 10−6 M of TPTZ.
The plots of ln K versus 1/T in the presence of the TPTZ in the case of tin, the inhibitor showed linear behavior. The standard enthalpy, ΔH°ads., entropy, ΔS°ads. and free energy changes of adsorption ΔG°ads. were evaluated using Frumkin adsorption isotherm.