Ab initio molecular dynamics study on microstructure and diffusion properties of CaF2-2.2NaF-AlF3 system

Highlights: • [AlF₅]²⁻, [AlF₄]⁻, [AlF₆]³⁻ and [Al₂F_x]^(x−6)− always coexist in molten salt system. • The action intensity of Ca²⁺ on [AlF_x]^(x−3)− is [AlF₄]⁻ < [AlF₆]³⁻ < [AlF₅]²⁻. • The self-diffusion property of Al³⁺ is [AlF₅]²⁻ > [AlF₆]³⁻ > [AlF₄]⁻. The lack of micro-mechanism research on the influence of Ca²⁺ in cryolite molten salt has brought great difficulties to the improvement of current efficiency in actual production. The microstructure and diffusion characteristics of molten salt were studied by using ab initio molecular dynamics method, combined with the bridge fluorine distribution and diffusion coefficient of different complex ions. It is found that [AlF₅]²⁻, [AlF₆]³⁻, [AlF₄]⁻, [Al₂F₉]³⁻and [Al₂F₁₀]⁴⁻ coexist in molten salt system. With the increase of Ca²⁺, [AlF₅]²⁻ is more easily attracted by Ca²⁺ but has better self-diffusion performance, and [AlF₆]³⁻ is more easily crosslinked with other [AlF_x]^(x−3)−.