Saussurea obvallatta leaves extract as a potential eco-friendly corrosion inhibitor for mild steel in 1 M HCl

Abstract

The extract of saussurea obvallatta leaves (SOLE) has been examined for corrosion inhibition studies for mild steel (MS) in 1 M HCl solution by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and traditional mass change measurements. SOLE controlled maximum of 90 % corrosion rate of MS in 1 M HCl solution at 200 ppm of SOLE. SEM-EDX, AFM and Contact angle images revealed that, MS surface was least affected by the acid solution in presence of SOLE. FT-IR and UV–Visible absorption spectral values established the set of a corrosion defensive layer over the MS surface. Potentiodynamic measurement revealed that SOLE act as a both anodic and cathodic type of inhibitor. Quantum chemical calculations shows that, the EHOMO as an electron donor of SOLE donate electrons to appropriate acceptor molecules to the vacant d orbital of Fe atoms of MS. Un-filled 3d orbital of MS could bind with HOMO of the inhibitors. On the other hand filled 4s orbital could donate the electron to LUMO of the inhibitor as oftenly ELUMO indicates the ability of molecules to accept electrons. Variation of experimental temperature studies revealed that the stability of the protective layer decreased at higher temperature and corrosion activation energies increased in the addition of SOLE.