Anti-corrosive properties of Urena lobata leaves extract for mild steel in 0.5 M H2SO4: Electrochemical and Spectroscopic studies

Corrosion inhibition potential of Urena lobata leaves extracts (ULLE) were carried out using electrochemical and spectroscopic methods. Electrochemical Impedance Spectroscopy (EIS) revealed that charge transfer resistance (Rct) increased from 386.4 – 984.5 W cm2 while the capacitance of double-layer (Cdl) decreased from 4.8 – 3.2 μF cm-2 with increasing ULLE concentration from 0.2 – 1.0 g/L. The decreased in Cdl values with increase in concentration was due to the increase in the surface coverage by the inhibitor which resulted in an increase in the inhibition efficiency. Potentiodynamic polarization (PDP) showed the maximum range of shift in corrosion potential (Ecorr) values is 52.1 mV which suggested that ULLE acts as mixed type inhibitor that is predominantly cathodic due to the higher the values of Tafel cathodic slopes (βc) over those of the anode (βa). UV-Visible spectroscopy (UV-Vis) and GC-MS results revealed the presence of organic compounds in the inhibitor which were responsible for the extracts’ ability to inhibit corrosion of mild steel. The inhibition process followed physisorption with Langmuir R-squared values (R2) of 0.9983 and 1.0000 for PDP and EIS respectively. Thermodynamic parameters showed that the adsorption of inhibitor on the mild steel surface was feasible, spontaneous and exothermic.