Chloride (Cl^-) corrosion of metal alloys in presence of sulfur species is a well-recognized problem in industries. Especially, thiosulfates (S₂O₃^2-), which is one of the most dangerous corrosion promoters contributes significantly towards rapid and severe failures of these alloys. In this research study, corrosion of mild steel in presence of S₂O₃^2- and ammonium chloride (NH₄Cl) was investigated using linear polarization and electrochemical impedance spectroscopy (EIS) techniques. Current density was measured as a function of time and corrosion rates were assessed for varied concentrations of S₂O₃^2- and NH₄Cl acid salt. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-Ray fluorescence (XRF) spectroscopy and X-ray diffraction (XRD) were employed to probe the surface morphology and the scales formed on the steel surface. Impedance measurements coupled with equivalent circuit analysis were utilized to interpretate the corrosion reaction mechanism at the electrode-solution interface. The surface analyses provided valuable insights into the nature and severity of mild steel corrosion in integration with the corrosivity of the S₂O₃^2- and Cl^- species.

Keywords: Carbon steel corrosion, Chloride corrosion, Thiosulfate, Polarization, Impedance, SEM