Evaluation of newly synthesized hydrazones as mild steel corrosion inhibitors by adsorption, electrochemical, quantum chemical and morphological studies

Abstract

Inhibition effect of newly synthesized heterocyclic aromatic compounds, 3-(cyano-dimethyl-methyl)-benzoic acid thiophen-2-ylmethylene-hydrazide (CBTH) and 3-(cyano-dimethyl-methyl)-benzoic acid furan-2-ylmethylene-hydrazide (CBFH) was studied on mild steel corrosion in hydrochloric acid medium by gravimetric, electrochemical and morphological techniques and correlated with quantum chemical indices of the respective molecules. At optimized concentration (2 mM), CBTH and CBFH showed the highest inhibition efficiency of 87.1% and 85.3%, respectively. Impedance study revealed that simultaneous increase in polarization resistance and decrease in double layer capacitance with increasing inhibitor concentration is due to adsorption phenomenon of hydrazones. Inhibitors shift the corrosion potential to less negative value which hinders dissolution of mild steel and evolution of hydrogen and it is more pronounced in anodic reaction. Corrosion current density decreased from 0.2 mA cm−2 (blank) to 0.0177 and 0.026 mA cm−2 and polarization resistance increased from 199 Ω cm2 to 1590 and 1552 Ω cm2 for CBTH and CBFH, respectively. Quantitative structure activity relationship (QSAR) results showed good correlations between a number of quantum chemical parameters and the experimentally determined inhibition efficiency. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) analyses confirmed the formation of protective inhibitory film.

Keywords

• Mild steel
• corrosion
• hydrazone
• adsorption
• electrochemical techniques