Corrosion inhibition of tin, indium and tin–indium alloys by adenine or adenosine in hydrochloric acid solution

The influence of the concentration of adenine (AD), adenosine (ADS) on the electrochemical corrosion behavior of tin, indium and tin–indium alloys in 0.5 M HCl solution at different temperatures was studied. The investigation involved potentiodynamic cathodic polarization and extrapolation of cathodic and anodic Tafel lines techniques. The inhibition efficiency (IE%) increases with an increase in the concentration of adenine or adenosine of all investigated electrodes. The inhibition process was attributed to the formation of adsorbed film on the surfaces of the electrodes that protects the surface against corrosive agent. The data exhibited that the inhibition efficiency slightly decreases with increasing temperature.Frumkin adsorption isotherm fits well the experimental data. The plots of ln K vs. 1/T   in the presence of the two studied inhibitors showed linear behavior. The standard enthalpy, ΔHads∘, entropy, ΔSads∘ and free energy changes of adsorption ΔGads∘ were evaluated; the calculated values of ΔHads∘ and ΔGads∘ were negative while those for ΔSads∘ were positive. Mainly, all the above results are suggestive of physisorption of the inhibitor molecules on the surfaces of the investigated electrodes.