Corrosion inhibition performance of pyranopyrazole derivatives for mild steel in HCl solution: Gravimetric, electrochemical and DFT studies

Two pyranopyrazole derivatives namely, 6-amino-4-(4-methoxyphenyl)-3-methyl-2,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile (AMPC) and 6-amino-4-(4-chlorophenyl)-3-methyl-2,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile (ACPC) were synthesized and investigated as an inhibitor for mild steel corrosion in 15% HCl solution by using weight loss measurement and electrochemical techniques. The experimental results showed that the inhibition efficiency of studied inhibitors increased with increasing inhibitor concentration whereas decreased with an increase in temperature. Corrosion inhibition efficiency of 96.1 and 94.6 was obtained with 300 ppm of AMPC and ACPC, respectively, at 303 K. Potentiodynamic polarization studies showed that both studied inhibitors were mixed type in nature. The potential of zero charge (E-pzc) for the mild steel was determined by electrochemical impedance spectroscopy method. The adsorption of both inhibitors on mild steel surface obeyed Langmuir adsorption isotherm. The surface morphology of the uninhibited and inhibited mild steel specimens was studied by using scanning electron microscopy (SEM), energy dispersion X-ray spectroscopy (EDX) and atomic force microscopy (AFM). The Density Functional Theory (DFT) was applied for theoretical studies of the inhibitors. (C) 2016 Elsevier B.V. All rights reserved.