Electrochemical impedance studies of the initial-stage corrosion of 310S stainless steel beneath thin film of molten (0.62Li, 0.38K)2CO3 at 650 °C

Electrochemical impedance spectroscopy (EIS) has been used to study the initial-stage corrosion of 310S stainless steel beneath thin film of molten (0.62Li, 0.38 K)2CO3 at 650 °C in air. Two-electrode system is used to fabricate molten-salt film. The thickness of molten salt approximated from electrolyte resistance decreases rapidly until it is smaller than 6 mg/cm2. The appearance of diffusion-related impedance at the end of the test is linked to the severe loss of molten salt which causes twisted diffusion paths. More molten salt on the surface of 310S causes a longer lithiation process and more profound degradation of the oxide film.

Research highlights
► Thickness of molten salt on the electrode decreases rapidly due to its volatility.
► Corrosion rate of stainless steel fluctuates and three stages are identified.
► Impedance in middle stage shows two loops owing to outgrowth of oxide film.
► Loss of molten salt makes diffusion process and charge transfer more difficult.