(367g) Effect of Cationic Species on the Activity and Inhibition Performance of NO2?/NO3? Corrosion Inhibitors

The effect of cationic species (Na⁺ and Ca²⁺) on the inhibition performance of NO₂^‒/NO₃^‒corrosion inhibitors were studied in 0.6 M Cl^‒ contaminated simulated concrete pore solution at different temperatures. The activity coefficients of ions in solution were calculated using the Pitzer virial coefficient approach utilizing a geochemical software called PHREEQC. From the modeling work, it was established that Ca²⁺ ions undergo more ionic interactions compared to Na⁺, which is due to its multivalent charge nature. Consequently, Ca²⁺ ions increase the stability in the electrolyte, hence decreasing the activity and activity coefficients of NO₂^‒/NO₃^‒ corrosion inhibitors, hindering their mobility to inhibit the carbon steel rebar. This modeling result was corroborated through an experimental study that included different electrochemical tests such as potentiodynamic polarization and electrochemical impedance spectroscopy at 25, 35, 45, and 55 ºC. It was concluded that at each temperature the inhibition performance of the tested corrosion inhibitors were as follows: Ca(NO₃)₂ < NaNO₃ < Ca(NO₂)₂ < NaNO₂. The results showed that all inhibitors performed well (up to 88% inhibition efficiency), however, performance decreased with increasing temperature due to accelerated electrochemical reactions and desorption of the corrosion inhibitor from the surface of the carbon steel rebar. Moreover, the activation energy, enthalpy of activation and entropy of activation of the corrosion process was calculated for each corrosion inhibitor. It was found that the activation energies, enthalpies, and entropies of the corrosion inhibitors were greater than the blank due to an adsorption mechanism, endothermic dissolution of the rebar, and increased energy dispersal from the displaced water molecules around the rebar from the adsorbed inhibitor molecules.