Effect of Fluorine on the Structure of High Al2O3-Bearing System by Molecular Dynamics Simulation

Calcium aluminosilicate is the most important slag system in continuous casting, while CaF2 is commonly used as a fluxing agent in mold fluxes. In this study, the structural properties of the CaO-Al2O3-SiO2-CaF2 system with varying fluorine content have been investigated by molecular dynamics simulation using the pairwise potential model. The results showed that with the substitution of oxygen ions by fluorine ions, the average bond length of Si-O remained unchanged, while the average bond length of Al-O increased from 1.74 to 1.75 angstrom. The addition of fluorine contributed to the increase in the bridging oxygen proportion and the network connectivity (Q(n)) degree, suggesting that the polymerization of melts was enhanced. Meanwhile, the threefold-coordinated Al was found when mass fraction of fluorine was increased, and it was due to that the fluorine ions substituted the oxygen ions and formed the [AlO3F] tetrahedron. The Al avoidance principle is not applicable in the CaO-Al2O3-SiO2-CaF2 system with a high content of Al2O3. (C) The Minerals, Metals & Materials Society and ASM International 2015