Quantum-Chemical Study of the Corrosion Inhibition of Mild Steel in 6% (wt/wt) HCl by means of Cyanoguanidine Derivatives

Abstract

Corrosion inhibitive efficiencies of Biguanide monohydrochloride, Dicyandiamide, Guanyl urea-o-hydrochloride and Biuret have been determined by the gravimetric method. It has been shown that the energy eigen values, and the π-electron distributions of the compounds, obtained using the Hückel method, can offer a very useful guide for the choice of inhibitors. The eigen value of the highest occupied molecular orbiials (HOMO), and those of the lowest unoccupied molecular orbitals (LUMO), which correspond to the ionisation energies and the electron affinities, respectively, bear a simple linear relationship with the logarithm of inhibitive efficiencies. It is seen that the inhibitive efficiency increases with the increase in the HOMO energy, while the inhibitive efficiency decreases with the increase in the electron accepting capacity of the inhibitor. Biguanide monohydrochloride is the most efficient inhibitor among the four cyanoguanidine derivatives studied, on account of its high electron donating capacity.