Experimental and theoretical studies for corrosion inhibition of carbon steel by imidazoline derivative in 5% NaCl saturated Ca(OH)2 solution

The inhibition activity of an imidazoline derivative, namely 1-[N,N′-bis(hydroxylethylether)-aminoethyl]-2-stearicimidazoline (HASI) for carbon steel in 5% NaCl saturated Ca(OH)2 solution was investigated using electrochemical measurements in conjunction with Raman and Fourier transform infrared (FTIR) spectroscopy techniques. Quantum chemical calculations and molecular dynamic (MD) simulations were applied to analyze the experimental data and elucidate the adsorption behavior and inhibition mechanism of inhibitor. The results indicate that HASI is an effective inhibitor in protecting carbon steel from corrosion in alkaline chloride solution and acts as a cathodic type inhibitor with the dominant suppression of cathodic reduction of oxygen. The inhibition behavior of HASI is strongly related to its adsorption activity on carbon steel surface, which leads to an enhancing in the corrosion resistance of carbon steel and a reduction in the corrosion rate. Density functional theory (DFT) calculations suggest that the NC–N region in imidazoline ring is the most active reaction site for the inhibitor adsorption on metal surface via the donor–acceptor interactions between the lone electron pairs on nitrogen atoms together with the π-electrons of heterocyclic and the vacant d orbital of iron atoms. The adsorption of inhibitor on three typical surfaces (Fe (1 0 0), F2O3 (1 1 0) and F3O4 (1 0 0)) takes nearly parallel to the surface so as to maximize its contact with the surface, as shown as the MD simulations. The experiments incorporating the theoretical calculation and MD simulation can provide an insight into the understanding of interactions between the inhibitor molecules and the carbon steel surfaces.

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► An imidazoline derivative can effectively inhibit carbon steel corrosion in alkaline solution.
► The compound acts as a cathodic type inhibitor by retarding the reduction of oxygen.
► The NC–N region in imidazoline ring is the most active adsorption site.
► Adsorption of inhibitor takes parallel to metal surface with high interaction energy.
► Theory calculation and MD simulation can give an insight into the inhibition mechanism.