Thiourea and its derivatives have been studied for several decades, for their corrosion inhibition characteristics with steels. However, their interaction mechanisms with steel are not well understood. Such an understanding may be vital for design of novel thiourea derivatives as corrosion inhibitors for steels. We have carried out state of the art density functional theory (DFT) computations and experiments (weightloss, polarization and electrochemical impedance) to understand the effect of thioureas on corrosion of steel. The interactions of thiourea and dibutyl thiourea separately on an iron surface have been investigated using DFT. DFT indicates strong interactions between Fe atoms of the surface and C, S - atoms of the molecule while the N-atoms do not show any significant proclivity towards interactions with the Fe-surface. Among the hollow and bridge sites on the Fe-surface, S-atom was found to preferentially occupy the hollow site which facilitates formation of four strong Fe-S bonds which possibly explains the strong corrosion inhibition by thioureas on steels. Besides, DFT computations provided insights for design of much more promising molecules for corrosion inhibition. Experimentally, dibutyl thiourea was found to have an extraordinary inhibition effect for steel in 1N HCl in accordance with DFT computations.

Subject
Circuits, Electrochemical impedance spectroscopy, Materials, Geometry, Derivatives, Metals, Inhibition efficiency, Corrosion inhibitors, Steel, Dry film thickness, Polarization, Potentiodynamic polarization, Electrolytes
Keywords:
Corrosion inhibitors, thiourea derivatives, DFT, experiments
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2019
Association for Materials Protection and Performance (AMPP)
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