Inhibition Action of Allyl Thiourea for Steel in H₂SO₄ Solution

The inhibition action of allyl thiourea (ATU) on cold rolled steel (CRS) in 1.0 mol/L H2SO4 solution at 20 ℃~50 ℃ was investigated by weight loss, potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS). The results showed that ATU is a good inhibitor for CRS in H2SO4 solution, and inhibition efficiency was higher than 94% with the inhibitor concentration of 0.2 mmol/L. Three adsorption thermodynamic parameters including adsorption free energy ΔG0, adsorption enthalpy ΔH0 and adsorption entropy ΔS0 were also calculated. The inhibition mechanism was discussed in detail according to the parameters. The adsorption of ATU on CRS surface obeys Langmuir adsorption isotherm equation. Polarization curves showed that ATU acts as a mixed-type inhibitor. All EIS spectra exhibit one capacitive loop at high frequency followed by a small inductive loop at low frequency, and the charge transfer resistance increases remarkably after adding ATU inhibitor.