Allyl thiourea as a corrosion inhibitor for cold rolled steel in H3PO4 solution

The inhibition effect of allyl thiourea (ATU) on the corrosion of cold rolled steel (CRS) in 1.0 M H3PO4 solution at 20–50 °C was studied by weight loss, potentiodynamic polarisation, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) methods. The results show that ATU is a good inhibitor, and the maximum inhibition efficiency of 0.5 mM inhibitor is higher than 95% at all studied temperatures. The adsorption of ATU obeys Langmuir adsorption isotherm. Polarisation curves show that ATU behaves as a mixed-type inhibitor. EIS spectra exhibit one capacitive loop. The inhibition action is also evidenced by SEM.

► Allyl thiourea (ATU) acts as a good inhibitor for steel in 1.0 M H3PO4.
► Inhibition efficiency increases slightly with the temperature at 0.2–0.5 mM.
► The adsorption of ATU on steel surface obeys Langmuir adsorption isotherm.
► ATU behaves as a mixed-type inhibitor.