The Synergistic Effects of Iodide Ion on the Corrosion Inhibition of Mild Steel in H2SO4 Using Benzoyl Phenylthiourea Inhibitor

Abstract

The synergistic action caused by iodide ions on the corrosion inhibition of mild steel in 0.5 M H2SO4 in the presence of Benzoyl phenylthiourea BPT has been investigated using gravimetric technique. It is found that the BPT inhibits the corrosion of mild steel in the acidic medium. The addition of iodide ions enhances its inhibition efficiency to a considerable extent. At fixed concentration of PBT, the inhibition efficiency increases with the increase in KI concentration, until 0.005M, then Inh% is decreased with further increase in KI concentration. The increase in Inh% values in presence of fixed BPT concentration at different iodide concentrations indicates that BPT forms an insoluble complex at lower KI concentrations by undergoing a joint adsorption. While at higher concentrations of KI, competitive adsorption is found between iodide ions and the formed complex leading to less Inh%. The adsorption of BPT in the studied concentration is found to obey Langmuir and Temkin adsorption isotherms. The results show that corrosion rate increased with increasing temperature. Activation energies of 51.50 and 52.286 kJ mol−1 for the corrosion processes were observed in absence and presence of iodide ion, respectively. The adsorption of the inhibitor on surface of mild steel was found to be exothermic and spontaneous.