Experimental and theoretical investigation of spiro heterocyclic compound as potential inhibitor for mild steel in acid media

Abstract

The corrosion inhibition performance of spiropyrazoline was explored for mild steel corrosion in 1M HCl and 0.5M H2SO4 using weight loss, potentiodynamic polarization and electrochemical impedance studies. Inhibition efficiency of the inhibitor increased with increase in concentration within the range of 1–9 ppm. Spiropyrazoline inhibitor showed better inhibition performance of 92.6 %, 97.7 % in 1 M HCl and 0.5 M H2SO4, respectively at 9 ppm concentration by forming protective film on the metallic surface. Electrochemical impedance spectroscopy analysis (EIS) revealed an increase in polarization resistance due to the adsorbed inhibitor molecules. Potentiodynamic polarization analysis reveals that spiropyrazoline behaved as a mixed type inhibitor. The adsorption of the inhibitor on the metal surface found to obeying Langmuir and Temkin adsorption isotherm at room temperature. Surface morphology of the protective layer was examined by FTIR, scanning electron microscopy and atomic force microscopy. The inhibition mechanism of the inhibitor molecule was proposed in the light of the quantum chemical calculations using DFT.