Abstract
A comprehensive corrosion investigation of pure Fe in an environment of solid sodium salt deposit (i.e., NaCl or Na2SO4) with mixtures of H2O and O2 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 Na2SO4 deposit due to their reaction with the formed protective scale of Fe2O3 and subsequently resulted in its breakdown. The corrosion rate of pure Fe with solid NaCl is higher than that with solid Na2SO4 because of the lower activation energy (Ea) for chemical reaction of Fe in solid NaCl+H2O+O2 (i.e., 140.5 kJ/mol) than that in solid Na2SO4+H2O+O2 (i.e., 200.9 kJ/mol). Notably, the electrochemical corrosion rate of pure Fe with solid NaCl deposit, 1.16 × 10−4 A/cm2, was a little lower than that with solid Na2SO4 deposit.
Highlights
IntroductionCorrosion of metal materials is severe in the environment with solid salt deposit and dry or wet O2 at medium and high temperatures [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18], especially for turbine blades in planes or ships and power boilers
In our previous studies [1, 13], it is found that the corrosion of pure Fe in both corrosion environments includes a chemical corrosion process and an electrochemical corrosion process, while the overall corrosion is dominated by the chemical corrosion process with a percentage of over 90%
It suggests that the corrosion mechanism of pure Fe in the two corrosion environments involves the interaction of the chemical and the electrochemical reactions, which is similar with pure Fe in solid Na2SO4 + H2O + O2 [26]
Summary
Corrosion of metal materials is severe in the environment with solid salt deposit and dry or wet O2 at medium and high temperatures [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18], especially for turbine blades in planes or ships and power boilers. Scanning reactions follow “ce mechanism,” in which Fe and Fe2O3 first react chemically with NaCl, water vapor, and oxygen to generate HCl (g). The corrosion differences of pure Fe with solid NaCl and solid Na2SO4 deposit in water vapor were comparatively studied to cognize the corrosion behaviors of materials in the corrosion profoundly
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