Effect of structure on the anti-corrosive properties of starting organic compounds and the produced amine epoxy adducts on mild steel in 0.1M HCl: An experimental and theoretical study

Studies were carried out to evaluate the structural effects of four inhibitors (Mono ethanolamine (MEA), phenyl glycidyl ether (PGE), N - (2- hydroxy - 3- phenoxy propyl) ethanolamine (NHPE) and N, N' - (-2 hydroxy - 3 - phenoxy propyl) ethanolamine (N N' HPE) in inhibiting the corrosion of mild steel in 0.1M HCl. Appropriate analytical procedures and instrumentation such as the use of Fourier transform infrared (FTIR) spectrophotometer were employed in the analysis of the structures of the inhibitors. Quantum chemical modeling calculation was employed to better understand the variation in the inhibition efficiencies of the studied inhibitors. After eight weeks of immersing the mild steel sheets in 0.1M HCl with each of the four studied inhibitors, the mean percentage weight loss of the mild steel were 17.74, 30.13, 5.39 and 1.08% for MEA, PGE, NHPE and NN1HPE respectively. The FTIR analysis of the structure of the inhibitors shows that the presence of functional groups such as -OH, -NH, Ar-C = C - and -OCH3 significantly helped to increase the inhibition efficiencies of NHPE and NN' HPE respectively. From the weight loss experiment, it was observed that the inhibition efficiencies of the four studied inhibitors on the mild steel in the acidic media decreased in the following order: N N1HPE > NHPE > MEA > PGE which was further confirmed by the FTIR analysis. The lower values of parameters such as ELUMO, energy gap, ionization potential, global hardness and total energy and as well as the higher valves of parameters such as EHOMO, dipole moment, electro affinity, electro negativity, chemical softness, total surface area and polarizability, obtained for NHPE and NN1HPE respectively greatly increased the adsorption and donation of their electrons to the metal substrate surface thus were able to more efficiently inhibit the rapid corrosion of the mild steel in the acidic media than the two other studied inhibitors (MEA and PGE).