Experimental, surface characterization and computational evaluation of the acid corrosion inhibition of mild steel by methoxycarbonylmethyltriphenylphosphonium bromide (MCMTPPB)

Abstract

The inhibition performance of the methoxycarbonylmethyltriphenylphosphonium bromide (MCMTPPB) on mild steel (MS) corrosion in 0.5 M H₂SO₄ has been evaluated using galvanostatic polarization (GP), potentiostatic polarization (PP), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and atomic force microscopy (AFM) techniques and complemented with the computational quantum calculations. GP study illustrates that the inhibition efficiency (%IE) increase with an increase in inhibitor concentration from 82.7% for 10^-5 M to achieve 99.8% for 10^-2 M. Polarization tafel curves clearly signify that MCMTPPB operates as a mixed type inhibitor. PP graph indicates that passivation was observed only for a lower concentration of MCMTPPB. Impedance results show that the double layer capacitance (C_dl) decrease and charge-transfer resistance (R_ct) increase with increase in the inhibitor concentration and hence increasing inhibition efficiency. Temperature influences the corrosion rate; inhibition efficiency and surface coverage decrease with increase in the temperature (298 K to 328 K). Surface characterization SEM with EDAX provide strong facts for the existence of inhibitor sheet over the MS surface. AFM studies are in good agreement with the results obtained by other techniques. Quantum chemical (QC) parameters obtained using AM1 Semi-empirical methods are found to be in good agreement with the experimentally measured inhibition efficiencies.