Thiourea and N-Methylthiourea as Corrosion Inhibitors for Steel in Phosphoric Acid

摘要

The effect of thiourea (TU) and N -methylthiourea (MTU) on the corrosion of mild steel in 0.5?M H~(3)PO~(4)was examined using potentiodynamic polarization curve measurements, electrochemical impedance spectroscopy techniques and quantum chemical calculations. Results obtained revealed that MTU is more effective than TU in 0.5?M H~(3)PO~(4). Theoretical fitting of different adsorption isotherms such as Langmuir, Flory–Huggins, Temkin, and the kinetic-thermodynamic models was tested. The thermodynamic activation parameters were calculated. Quantum chemical parameters were calculated and explained. The data explained that the inhibition of mild steel by TU in 0.5?M H~(3)PO~(4)take place through chemical adsorption mechanism, while physicochemical adsorption mechanism is suggested for MTU.