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Electrochemical measurements employing ac and dc techniques as well as atomic force microscopy were used to study the electrochemical corrosion behavior of ingot iron with two different microstructures: conventional polycrystalline ingot iron (CPII) and bulk nanocrystalline ingot iron (BNII) fabricated from CPII by severe rolling, without and with inhibitors. The corrosive media was 0.1 M H(2)SO(4) solution, while thiourea (TU) was employed as inhibitor, with a concentration of 5.0 mM, as well as a 1:1 combination of TU and KI. Impedance and polarization results show that BNII was more susceptible to corrosion in the uninhibited acid. The presence of TU improved the corrosion resistance of both specimens comparably, while KI reduced the inhibition efficiency of TU. Infrared spectrophotometry revealed that the interfacial species for CPII and BNII in the presence of TU were quite identical and markedly different from that in TU + KI. Molecular dynamics (MD) simulations were performed to illustrate the adsorption process of TU at a molecular level, and the theoretical predictions showed good agreement with the electrochemical results.