Effect of Fluorine on Melt Structure for CaO–SiO<sub>2</sub>–CaF<sub>2</sub> and CaO–Al<sub>2</sub>O<sub>3</sub>–CaF<sub>2</sub> by Molecular Dynamics Simulations
Xiaobo Zhang, Chengjun Liu, Maofa Jiang
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.