Influence of CaF_2 on Viscosity and Structure of Molten Slags

摘要

The viscosity of the CaO-SiO_2 (-MgO)-CaF_2 slags was measured to clarify the effect of CaF_2 on the viscous flow of molten slags at high temperatures and the solidification behavior of slags. Furthermore, the infrared spectra of the quenched slags were analyzed to understand the structural role of CaF_2 in the modification of slag structure. The CaF_2 would significantly affect the critical temperature of the slags; that is, the higher the content of CaF_2, the lower the TCR of the slags. It was suggested that some extent of undercooling as a driving force would be needed for the precipitation of solid particles in the melt. In the composition of (%CaO)/(%SiO_2) = 1.0, the T_(CR) was significantly decreased about 150-200 K by addition of 10 mass% MgO, while the T_(CR) was increased about 100 K by MgO addition at (%CaO)/(%SiO_2) = 1.3 The effect of CaF_2 on the viscous flow of molten slags could be understood based on a decrease in the degree of polymerization by F as well as O~(2-) ions and could be confirmed by the infrared spectra of the quenched slags. The relative intensity of the IR bands for [SiO_4]-tetrahedra with low NBO/Si decreased, whilst that of the IR bands for [SiO_4]-tetrahedra with high NBO/Si increased with increasing CaF_2 content, A decrease in viscosity of the CaO-SiO_2-MgO-CaF_2 (B = 1.0) system by CaF_2 addition was negligible, while the effect of CaF_2 on the viscosity was significant in the more basic system (B = 1.3).