Evaluation of Benzyl Triphenyl Phosphonium Chloride as Corrosion Inhibitor for Mild Steel in Phosphoric Acid

The effect of Benzyl triphenyl phosphonium chloride (BTPPC) on the corrosion of mild steel in a solution of 0.3 M phosphoric acid has been investigated at various inhibitor concentrations and temperatures by Potentiodynamic Polarization Studies, Potentiostatic Polarization Studies, Electrochemical Impedance Spectroscopy Studies (EIS), Temperature Kinetic Studies and Scanning Electron Microscopy (SEM). Results obtained from Potentiodynamic polarization studies reveal that BTPPC is a mixed type inhibitor for mild steel in 0.3 M phosphoric acid. Potentiostatic polarization studies show that BTPPC is a non-passivating type of inhibitor. The corrosion behavior of steel in 0.3 M H3PO4 with and without the inhibitor at various concentrations was studied in the temperature range from (298.15 to 338.15) K. The inhibition efficiency increases with an increase in concentration at all temperatures. The inhibition efficiencies decrease with an increase in temperature for lower concentrations of BTPPC, but for the higher concentration such as 1×10-3M, inhibition efficiencies decrease with an increase in temperature up to 318.15 K and then increase with a further increase in temperature up to 338.15 K. The adsorption of BTPPC accords to the El-Awady adsorption isotherm. Kinetic and thermodynamic parameters such as effective activation energy (Ea), Gibbs free energy of adsorption (AG°ads) and heat of adsorption (AH°ads) indicate that adsorption of BTPPC on the mild steel surface is primarily physical in nature. The results of scanning electron microscopy are in agreement with the electrochemical analysis results.