Monitoring of Hot Corrosion Behaviors for Alloys and Aluminide Coatings under Molten Sulfate Film with Thermal Cycles

In this study, a thin molten sulfate film was formed on the metallic samples and their corrosion processes have been monitored by electrochemical impedance technique under thermal cyclic condition. Inconel 600, nickel and aluminide diffusion coatings were used as samples. 50 mol%Na2SO4- 50 mol%Li2SO4 was used for preparing the molten sulfate film. Two kinds of specially designed electrochemical cells have been used in this study. One is three-electrode configuration and another is two-electrode configuration. Electrochemical impedance measurements were used for monitoring the degradation processes for all samples tested. It was found that both corrosion resistance and the change of molten sulfate film has been monitored successfully during 6 thermal cycles. In every thermal cycle, the corrosion resistance increased when the temperature shifted to lower values and decreased with the rising of temperature. Also, A drastic increase in corrosion resistance and the resistance of the molten salt film was observed when the temperature decreased below the melting point of the mixed molten sulfate film. Although both three-electrode and two-electrode configurations were usable for electrochemical measurements under molten sulfate film, it was concluded that the newly designed two-electrode configuration is more suitable under thermal cyclic condition