Significance of π–Electrons in the Design of Corrosion Inhibitors for Carbon Steel in Simulated Concrete Pore Solution

Chloride-induced corrosion of carbon steel reinforcements is one of the most important failure mechanisms of reinforced concrete structures. Organic corrosion inhibitors containing different functional groups were analyzed using cyclic potentiodynamic polarization to determine their effect on the pitting potential of carbon steel reinforcements in a 0.1 M Cl⁻ contaminated, simulated, concrete pore solution. It was found that organic compounds with π-electrons in a functional group had better performance. This is attributed to the high density of highest occupied molecular orbital energies found in carboxyl group π-bond. Accordingly, this increases the tendency of donating π-electrons to the appropriate vacant d-orbital of the carbon steel, forming an adsorption film. The best corrosion inhibition performance was achieved by poly-carboxylates followed by alkanolamines and amines. In addition, a novel approach to show the significance of corrosion inhibition phenomenon was applied by developing a quantitative structure-property relationship using the Signature molecular descriptor which correlates the occurrences of atomic Signatures in a data set to a property of interest using a forward stepping multilinear regression. The atomic Signature fragment capturing π-bond was the most influential of all of the fragments, which underscores the significance of π-bond electrons in the adsorption process. It was demonstrated that the [O](=[C]) atomic Signature plays a crucial role in the inhibition process at all heights, corroborating the experimental results.