effect of CaF(2) on the viscosities and structures of CaO-SiO(2)(-MgO)-CaF(2) slags, The

Metallurgical and Materials Transactions, Oct 2002 by Park, Joo Hyun, Min, Dong Joon, Song, Hyo Seok

The viscosities of CaO-SiO^sub 2^(-MgO)-CaF^sub 2^ slags were measured to clarify the effect of CaF^sub 2^ on the viscous flow of molten slags at high temperatures and the solidification behavior of slags. Furthermore, the infrared (IR) spectra of the quenched slags were analyzed to understand the structural role of CaF^sub 2^ in the modification of slag structure. The CaF^sub 2^ affects the critical temperature (T^sub CR^) of the slags; that is, the higher the content of CaF^sub 2^, the lower the T^sub CR^ of the slags. It is suggested that some extent of undercooling as a driving force is needed for the precipitation of solid particles in the melt. In the composition of B (=(mass pct CaO)/(mass pct CaO)/(mass pct SiO^sub 2^)) = 1.0, the T^sub CR^ was decreased about 150 to 200 K by addition of 10 mass pct MgO, while the T^sub CR^ was increased about 100 K by MgO addition at B = 1.3. The effect of CaF^sub 2^ on the viscous flow of molten slags can be understood based on a decrease in the degree of polymerization by F^sup -^ as well as by O^sup 2-^ ions and this was confirmed by the IR spectra of the quenched slags. The relative intensity of the IR bands for [SiO^sub 4^]-tetrahedra with low NBO/Si decreased, while that of the IR bands for [SiO^sub 4^]-tetrahedra with high NBO/Si increased with increasing CaF^sub 2^ content. The decrease in viscosity of the CaO-SiO^sub 2^-MgO-CaF^sub 2^ (B = 1.0) system by CaF^sub 2^ addition was negligible, while the effect of CaF^sub 2^ on the viscosity was significant in the more basic system (B = 1.3).

ACKNOWLEDGMENTS

This work was financially supported by POSCO (Grant No. 2000-X-060). Also, one of the authors (JHP) was supported by the Brain Korea 21 Project.

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JOO HYUN PARK, DONG JOON MIN, and HYO SEOK SONG

JOO HYUN PARK, Researcher, formerly Doctoral Student, Department of Metallurgical Engineering, Yonsei University, is with the STS Research Group, Technical Research Laboratory, POSCO, Pohang 790-785, Korea. Contact e-mail: basicity@posco.co.kr DONG JOON MIN, POSCO Professor and Assistant Dean of Engineering College, is with the Department of Metallurgical Engineering, Yonsei University, Seoul 120-749, Korea. HYO SEOK SONG, Senior Researcher, is with the STS Research Group, Technical Research Laboratory, POSCO.

Manuscript submitted January 22, 2002.