Bromide as Corrosion Inhibitor for Mild Steel in Sulphuric Acid

The inhibition effect of the (2-Hydroxyethyl) triphenyl phosphonium bromide (HETPB) on mild steel corrosion in 0.5 M H2SO4 have been determined by electrochemical techniques like potentiodynamic polarization (PDP), potentiostatic polarization (PSP) and electrochemical impedance spectroscopy studies (EIS). Potentiodynamic polarization study reveal that HETPB is an anodic type inhibitor with 98% efficiency at the concentration range of (1×10-2 to 4×10-3) M for mild steel in 0.5 M sulfuric acid. Potentiostatic polarization study shows that HETPB is a non-passivating type of inhibitor at higher concentrations and act as passivating type of inhibitor at lower concentrations. The corrosion behavior of steel in 0.5 M H2SO4 without and with the inhibitor at various concentrations was studied at the temperature range of (298 to 328) K. The adsorption of HETPB accords to Langmuir adsorption isotherm. Kinetic parameter such as effective activation energy (Ea) has been evaluated from the effect of temperature on corrosion and inhibition processes. The negative values of thermodynamic parameter like Gibbs free energy of adsorption (AG°ads) indicate the spontaneity of adsorption process. The surface morphology of the tested mild steel specimens in the presence and absence of inhibitors have been studied by using the respective images of SEM and AFM. Quantum chemical calculations have been performed and several quantum chemical indices were calculated and correlated with the corresponding inhibition efficiencies.