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

Abstract

• [AlF 5 ] 2− , [AlF 4 ] − , [AlF 6 ] 3− and [Al 2 F x ] (x−6)− always coexist in molten salt system. • The action intensity of Ca 2+ on [AlF x ] (x−3)− is [AlF 4 ] − < [AlF 6 ] 3− < [AlF 5 ] 2− . • The self-diffusion property of Al 3+ is [AlF 5 ] 2− > [AlF 6 ] 3− > [AlF 4 ] − . The lack of micro-mechanism research on the influence of Ca 2+ 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 [AlF 5 ] 2− , [AlF 6 ] 3− , [AlF 4 ] − , [Al 2 F 9 ] 3− and [Al 2 F 10 ] 4− coexist in molten salt system. With the increase of Ca 2+ , [AlF 5 ] 2− is more easily attracted by Ca 2+ but has better self-diffusion performance, and [AlF 6 ] 3− is more easily crosslinked with other [AlF x ] (x−3)− .