Abstract: In CaO-Al₂O₃-CaF₂ ternary slag system， the variations of the melt structures including the short-range and medium-range structure， and bond-angle change of the slag with different CaF₂ content were studied using molecular dynamics(MD)method. The results showed that the average bond lengths of Ca—F， Al—F， Ca—O and Al—O are 0.2345， 0.1895， 0.2325 and 0.1745nm，respectively. With the addition of CaF₂， there is a dynamic equilibrium between Ca²⁺and the coordination anions(O^2- and F^-)， and the total coordination number(CN)is maintained between 6 and 7. The Al—O tetrahedral structure in the system can be transformed from the complex(Q⁴ and Q³)to simple(Q² and Q¹)structure and from the Al—O tetrahedral［AlO₄］^5- to［AlO₃F］^4- structure， resulted to depolymerize the network structure of the melt. These observations from atomic scale well explain that the addition of CaF₂ can improve the fluidity of CaO-Al₂O₃-CaF₂ slag. The bond angle analysis indicates that the F^- in the system is more likely to replace the original O^2- position and the network structure with the Al³⁺ core has still be a tetrahedral structure， which does not cause a large-scale atomic rearrangement.

Key words: CaO-Al₂O₃-CaF₂, melt structure, molecular dynamics, bond length, bond angle