Corrosion inhibition of mild steel in hydrochloric acid by leaves extract of Tephrosia purpurea

Abstract

The poor corrosion resistance of mild steel makes serious issues (on both economical and safety aspects) in many industries and, the use of corrosion inhibitors is the opt solution to combat mild steel corrosion. The present study investigated the corrosion inhibition behavior of Tephrosia purpurea (T. purpurea) leaves extract on mild steel corrosion in 1 N HCl solution using gravimetric, electrochemical and surface morphological techniques such as Potentiodynamic polarization, Electrochemical Impedance technique (EIS), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The leaves extract of T. purpurea was characterized using UV-Visible (UV-Vis), Fourier-Transform Infrared Spectroscopy (FT-IR) and Gas Chromatography–Mass Spectrometry (GC-MS). The results derived from gravimetric and electrochemical studies showed the ability of T. purpurea as good corrosion inhibitor for mild steel in 1 N HCl, and it has been found that the inhibition efficiency (I.E in %) increases with increase in concentration of leaves extract molecules. The maximum inhibition efficiency of 95.4% was observed at 300 ppm extract concentration, above which there was no drastic change in inhibition efficiency. From Tafel graphs, it is noticed that the T. purpurea leaves extract exhibited mixed-type corrosion inhibition performance, Nyquist and Bode plots confirmed the single charge transfer mechanism of corrosion inhibition process. It was also obtained that, the adsorption of inhibitor molecules obeys Langmuir adsorption isotherm. The inhibition is mainly due to the adsorption of inhibitor molecules on the mild steel electrode surface, which was confirmed by FT-IR, SEM and AFM studies. From all the experimental results, it is concluded that the leaves extract of T. purpurea performed as a good corrosion inhibitor for mild steel in 1 N Hydrochloric acid medium.