Corrosion behaviour of sensitized AISI-type 316L stainless steel in molten carbonate fuel cell in cathode-gas environment

Corrosion of the cell components is a major problem in the development of the molten carbonate fuel cell (MCFC). This study describes the effect of sensitization on the corrosion characteristics of AISI-type 316L stainless steel in a 62/38 lithium-potassium carbonate eutectic melt in the cathode-gas environment. After solution treatment at 1200 degrees C for 4 h followed by sensitization treatment at 650 degrees C for predetermined time, the corrosion behaviour of the sensitized sample is analyzed electrochemically by a potentiodynamic method. The sensitized sample displays behaviour which is typical of active-passive transition. Increasing the time of the sensitization treatment causes the corrosion potential to shift in the cathodic direction. In addition, the passive film becomes more unstable and supports a high passive current, i.e., the substrate is more susceptible to intergranular corrosion (IGC). Morphological observation of samples immersed in a carbonate melt reveal a change in corrosion mechanism from initial IGC to localized corrosion. Huge cavities develop from grooves after 200 h of immersion in a carbonate melt. A combination of a Cr-depleted region due to sensitization and decreasing oxygen concentration from top to bottom of the oxide layer, is considered to be the main reason for the change in corrosion morphology. (C) 1999 Elsevier Science S.A. All rights reserved.