Effect of fluorine on melt structure for CaO-SiO2-CaF2 and CaO-Al2O3-CaF2 by molecular dynamics simulations

Abstract

The melt structure with fluorine addition has been investigated using molecular dynamics (MD) simulation for the CaO-SiO2-CaF2 and CaO-Al2O3-CaF2 ternary slag system. By analyzing the coordination number of the network framework, the results indicate that the structure of Si-O tetrahedron is more stable than the structure of Al-O tetrahedron. F- ions are dominantly coordinated with Ca2+, there is a dynamic equilibrium between Ca2+ and the coordination anions (O2- and F-) in both systems, and the total coordination number (CN) is maintained between 6 and 7. The analysis of the distribution of oxygen types demonstrates the degree of polymerization (DOP) of network structure in CaO-SiO2-CaF2 system is lower than that in CaO-Al2O3-CaF2 system. Although the addition of CaF2 can lower the viscosity of both slag systems, the microscopic reasons for that are completely different: in CaO-SiO2-CaF2 system, CaF2 actually acts as network diluent, and creates the space where particles can move longer. But in CaO-Al2O3-CaF2 system, CaF2 can depolymerize the network structure of the melt.