In aluminum electrolysis, sodium penetration into carbon cathodes is considered as the main cause of cell failure and efficiency loss, but the detailed mechanism is still not definitely clear. Since the macroscopic properties of material depend on the microscopic structures, a large-scale atomistic model of anthracite cathodes was constructed to represent several important structural characteristics. Combined with Monte Carlo and molecular dynamics simulations, the adsorption and diffusion behaviors of sodium were investigated, respectively. The results suggest that sodium adsorption mainly occurs in the larger micro-pores with the range of 10–19 Å, while it accords well with to type-I Langmuir adsorption model. The sodium is found to be preferentially adsorbed in arch-like structures with 5- or 7-membered rings or around heteroatom, especially oxygen. Moreover, the movements of sodium through carbon matrix mainly depend on the continuous diffusive motion while most sodium particles tend to be trapped in voids with small mobility. The calculated transport diffusion coefficient is equal to 6.132 × 10− 10 m2/ s, which is in outstanding agreement with experimental results. This fundamental research would contribute to the understanding of sodium penetration mechanism and the optimization of cathode industry in the future.

    Abstract
    1 Introduction
    2 Experimental
        2.1 Molecular model construction of the anthracite cathode
        2.2 Grand canonical Monte Carlo simulation
        2.3 Molecular dynamics simulation
    3 Results and discussions
        3.1 Large scale atomistic representation of the anthracite cathode model
        3.2 Structural characteristics analyses
        3.3 Interaction of sodium-carbon bulk
        3.4 Sodium adsorption mechanism
        3.5 Sodium migration mechanism
    4 Conclusions
    Acknowledgement 
    References

• Jie Li(School of Metallurgy and Environment, Central South University)
• Jiaqi Li(School of Metallurgy and Environment, Central South University)
• Hongliang Zhang(School of Metallurgy and Environment, Central South University)
• Tianshuang Li(School of Metallurgy and Environment, Central South University)
• Jin Xiao(School of Metallurgy and Environment, Central South University)