Experimental and quantum chemical studies on corrosion inhibition performance of pyrazolic derivatives for mild steel in hydrochloric acid medium, correlation between electronic structure and inhibition efficiency


ABSTRACT:

The inhibition of the corrosion of steel in 1 M HCl by pyrazole compounds 5-bromo-N-((3,5-dimethyl-1H-pyrazol-1- yl)pyridine-2-amine (AB8) and 3,5-dibromo-N-((3,5-dimethyl-1H-pyrazol-1-yl)pyridine-2-amine (AB9) has been studied by weight loss, electrochemical polarisation and electrochemical impedance spectroscopy measurements. The results obtained reveal that these compounds are efficient inhibitors. The inhibition efficiency increases with the increase of inhibitor concentration and reached 95 % for AB9 at 10-3 M. Potentiodynamic polarisation studies clearly reveal that the presence of all inhibitors does not change the mechanism of hydrogen evolution and that they act mixed inhibitors. The temperature effect on the corrosion behaviour of steel in 1 M HCl without and with the inhibitors at 10-3M was studied in the temperature range from 308-333K, it allows to determine the several thermodynamic parameters. The inhibitors were adsorbed on the steel surface according to the Langmuir adsorption isotherm model. From the adsorption isotherm some thermodynamic data for the adsorption process are calculated and discussed. Geometries optimization of all molecules considered in this study were fully optimized by using gradient corrected DFT with Becke’s three-parameter hybrid exchange functional and the Lee-Yang-Parr correlation functional (B3LYP) and with the 6-31G basis . The theoretical studies are to reduce the cost of research and the results obtained for corrosion inhibitors of mild-steel by this inhibitors demonstrated that correlation exists between inhibition efficiency and all parameters quantum chemicals. The directly calculated ionization potential (IP), electron affinity (A), dipole moment (µ), electronegativity (χ), electron affinity (A), global hardness (η), softness (σ), the global electrophilicity (ω), the fraction of electrons transferred (∆N), are all in good agreement with the available experimental data.

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