Evaluation of thiocarbohydrazide derivative as corrosion inhibitor for C1018 carbon steel in 3.5% NaCl + 500ppm HAc solution: Electrochemical, SEM, FTIR and computational studies

N'-((E)-3-phenylallylidene)hydrazinethiocarbohydrazide (PHCT) was synthesized, purified, characterized and assessed for its inhibitive property against the sweet corrosion of C1018 carbon steel in CO₂-saturated 3.5 % NaCl + 500 ppm HAc solution at 25 and 60 °C. At 50 ppm and 25 °C, electrochemical impedance spectroscopy (EIS) confirmed that the presence of PHCT in the electric double layer fortified the hydrophobicity of the region and mitigated rate of charge transfer. Potentiodynamic polarization (PP) measurements at 25 °C showed that PHCT is a mixed-type inhibitor, which could reduce corrosion rate from 24.32 mpy in blank to 0.67 mpy at 50 ppm dosage and deliver 97.24 % inhibition efficiency. PHCT adsorbs, principally, using its NH₂, C = S and C = C functional groups, based on FTIR characterization. Computational modeling using the FMO and MEP analyses confirmed that PHCT exhibits higher electron donating than electron accepting power and interacts with the metal surface through nitrogen and sulfur atoms. Scanning electron microscopy (SEM) confirmed the ability of PHCT to protect the steel surface from localized pitting corrosion. Although increasing the temperature up to 60 °C diminished the efficiency of PHCT, the inhibitor was able to provide up to 92 % efficiency.