Explicit study on the oxidation mechanism of nickel in molten Li2CO3-K2CO3

The oxidation behavior of nickel in Li + K carbonate melt is followed by me asuring the open-circuit potential and by electrochemical impedance spectro scopy under an O-2 + CO2 gas mixture in the ratio 90/10 at a total pressure of 1 atm at 650 degreesC. X-ray diffraction (XRD) and energy-dispersive sp ectroscopy are employed for qualitative and quantitative analyses of the di fferent compounds involved during the oxidation of nickel. Atomic force mic roscopy is used for both imaging the evolution of the oxide layer and deter mining its surface roughness. The in situ oxidation process of nickel demon strates three stages: rapid formation of a compact surface oxide (first sta ge), thicker oxide layer (second stage), and a porous oxide structure (thir d stage). The lithiation reaction has been identified to occur during the s econd stage. Formation of an intermediate and unstable compound, namely NiC O3, has been confirmed by XRD.