THE ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY (EIS)OF CORROSION OF PURE Fe AND Cr AT 600°C UNDER SOLID NaCl DEPOSIT IN WATER VAPOR

摘要

The corrosion behavior of pure Fe and pure Cr at 600 °C under a deposit of solid NaCl with and without the presence of water vapor was studied by using electrochemical impedance spectroscopy (EIS) and mass gain measurements. The mass gain of all materials sharply increased when the water vapor was introduced into the system. The EIS measurements showed that only one capacitive loop appeared in EIS for both metals in different corrosion environments. The ionic transfer resistance and capacitance of the oxide films, which can be obtained after EIS fitting, here represent the characters of the oxide film. Therefore, the properties of the oxides film on the surface of specimens were analyzed based on those parameters. The ionic transfer resistance for both materials coated with solid NaCl decreased obviously when the water vapor presented. The capacitance for both materials decreased with time as solid NaCl presented only and increased when the water vapor was added. The values of ionic transfer resistance and capacitance of Fe is different from those of Cr. To some degree, the corrosion rates and the porosity of the corrosion products have some relationship with the ionic transfer resistance and the capacitance. The corrosion performances of two metals were analyzed basing on the EIS as compared with the result of pure solid NaCl.