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

Abstract

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, increasing 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 dataset to a property of interest using a forward stepping multilinear regression. The atomic Signature fragment capturing π–bond was the most influential of all 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.

Adsorption and Surface Analysis of Sodium Phosphate Corrosion Inhibitor on Carbon Steel in Simulated Concrete Pore Solution

“…E HOMO (−2.88 eV) provides insight of the ability of a molecule to donate an electron to vacant cation orbital, while E LUMO (5.76 eV) indicates the ability of a structure to accept an electron creating a feedback bond [ 12 , 51 ]. A high E HOMO along with a low E LUMO are often associated with enhanced ability of the corrosion inhibitor to adsorb onto the metal surface, thus imparting superior corrosion inhibition.…”

“…A high E HOMO along with a low E LUMO are often associated with enhanced ability of the corrosion inhibitor to adsorb onto the metal surface, thus imparting superior corrosion inhibition. The difference between E HOMO and E LUMO would be the Δ E gap ( E LUMO − E HOMO = 8.64 eV), which gives an indication of the reactivity of a molecule [ 12 , 52 ]. A low Δ E gap is favorable since low energy will be required to put the molecule in an excited stage, thus affecting the chemical reactivity, kinetic stability, and polarizability of a molecule [ 53 ].…”

“…Electrochemical tests were carried out in an SCPS prepared by filtering a saturated calcium hydroxide (Ca(OH) 2 ) solution. Accordingly, 0.6 M Cl − were added by means of NaCl to mimic concrete structures exposed to harsh marine environments [ 12 ]. The pH of the solution was measured at room temperature and found to be 12.6.…”

“…The use of quantum computational chemistry by applying density functional theory (DFT) can help to understand and articulate the inhibition mechanism of different corrosion inhibitors [ 11 ]. DFT analysis provides correlation between the effect of molecular structure on the inhibition and the adsorption process, which include the effect of electronic configuration, π-bonds, heteroatoms, and heterocycles [ 12 ]. Usually, the frontier molecular orbitals, dipole moments, Mulliken population analysis, and other quantum chemical properties contribute towards identifying the active reaction sites of a corrosion inhibitor [ 11 ].…”

Electrochemical and DFT Study of NaNO2/NaNO3 Corrosion Inhibitor Blends for Rebar in Simulated Concrete Pore Solution

“…It was observed that the electron density did not vary greatly over the molecules, leading to flat adsorption on the metal surface with contact of each atom. However, for the NO 3 − , the charge difference was greater, with a positive MAC located on the central N atom due to the resonance of the π-bonding between the N and the O atoms which have a higher electron affinity [42]. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) surfaces are shown in Figure 11.…”