Effects of the Different Solid Deposits on the Corrosion Behavior of Pure Fe in Water Vapor at 500°C

A comprehensive corrosion investigation of pure Fe in an environment of solid sodium salt deposit (i.e., NaCl or Na(2)SO(4)) with mixtures of H(2)O and O(2) at 500°C was conducted by mass gain measurement, X-ray diffraction (XRD), scanning electron microscope (SEM), potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). The results showed that corrosion rates were accelerated with solid NaCl or Na(2)SO(4) deposit due to their reaction with the formed protective scale of Fe(2)O(3) and subsequently resulted in its breakdown. The corrosion rate of pure Fe with solid NaCl is higher than that with solid Na(2)SO(4) because of the lower activation energy (E(a)) for chemical reaction of Fe in solid NaCl+H(2)O+O(2) (i.e., 140.5 kJ/mol) than that in solid Na(2)SO(4)+H(2)O+O(2) (i.e., 200.9 kJ/mol). Notably, the electrochemical corrosion rate of pure Fe with solid NaCl deposit, 1.16 × 10(−4) A/cm(2), was a little lower than that with solid Na(2)SO(4) deposit.