Synergistic corrosion inhibitor of carbon steel by dihydroxy benzyl phosphonic acid -Zn2+ system in O.5 M H2SO4: Experimental and theoretical studies

Abstract

The synergistic effect of dihydroxy benzyl phosphonic acid (DAP) and zinc sulfate ZnSO4 (Zn2+) system in 0.5 M H2SO4 solution on carbon steel X48 has been evaluated using potentiodynamic polarization measurements, electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM), and quantum methods (DFT). The combination of DPA and Zn2+ has been demonstrated to have remarkable inhibitory efficiency (96%). DPA/Zn2+ formulation operate as a mixed inhibitor, inhibiting both the anodic and cathodic reactions to the same amount, according to polarization studies. The diameter of the semicircles increases with the addition of DPA/Zn2+ formulation. Furthermore, the double layer capacitance Cdl decreases and Rt values increase with this combination of DPA and Zn2+, confirming the significant adsorption on the surface steel. The adsorption isotherm of Langmuir is approached by the adsorption on the metal surface. The nature of the protective coating is also determined using surface characterization techniques (FTIR and SEM). The molecular orbital (HOMO and LUMO) energies, energy gap (ΔEgap), dipole moment (μ), global hardness (η), global softness (σ), electrophilicity index (ω), absolute electronegativity (χ) and the fraction of transferred electrons (ΔN) have been determined as supporting evidence.