Molecular dynamics analysis of the effect of F on the structure of molten Na2O-NaF-Al2O3-SiO2 system

For the molten quaternary Na2O-NaF-SiO2-Al2O3 system at 1 673 K, the effect of F ion on the distribution of Si and Al tetrahedral complex anions, and the relationship between the Si and Al tetrahedra has been investigated by applying molecular dynamics simulation. In the calculation, SiO2 and Al2O3 contents in the melts were all fixed to 50.0 and 16.6 mol% respectively and only the ratio of Na2O/Na2F2 was changed. It was found that NaF in the aluminosilicate melts was able to work as a network modifier for Al tetrahedra linkages but not for Si ones. Namely, F can break the linkage between Al tetrahedra and coordinate to Al tetrahedra. The replacement of nonbridging oxygen in Si tetrahedra by F ions was possible since the calculated results showed the existence of a small amount of F coordinated to Si tetrahedra.