Synergism between sodium molybdate and binary inhibitor (BHI + Zn2+) on corrosion inhibition of mild steel in aqueous medium containing 60 ppm Cl− ion

Abstract

The synergism between sodium molybdate and binary inhibitor (1-benzyl-3-hydroxy 1-H-indazole (BHI) +Zn2+) system on the corrosion inhibition efficacy of mild steel in an aqueous medium containing 60 ppm chloride ion was analyzed by means of gravimetric and electrochemical spectroscopic measurements. The effect of temperature, and immersion time on the corrosion behavior of mild steel has also been studied. The formed defensive layer on the mild steel surface was analysed in Fourier transforms infrared (FT-IR) spectroscopy and atomic force microscopy (AFM). The results show that ligands adsorbed on the metal surface. The experimental results of the adsorption study shows that the compound follows Langmuir, Temkin and Freundlich adsorption isotherms. The calculated ∆G°ads value (−20.264 kJ mol−1) supports the mechanism of physical adsorption. Using the temperature dependent inhibition efficiency experimental data, the activation energy and thermodynamic parameters were derived. The calculated Tafel constants suggest that the inhibitors are mixed type. The scanning electron microscopic (SEM) images showed that the roughness and the deep cracks of the metal surface are reduced significantly by the inhibitor system.