The FT-IR spectra of the CaO-SiO 2 and CaO-SiO 2 -CaF 2 slags were measured to understand the structural aspects of (fluoro-) silicate systems. The relative intensity of Si-O rocking band is very strong at SiO 2 saturation condition and this band disappears in the composition greater than 44.1 (mol%) CaO in the CaO-SiO 2 binary system. The bands for [SiO 4 ]-tetrahedra at about 1 150-760 cm Ϫ1 split up with increasing content of CaO greater than 44.1 mol%. The IR bands in this wavenumber range are divided into four groups, that is about 1090, 990, 920, and 870 cm Ϫ1 , which have been assigned to NBO/Siϭ1, 2, 3, and 4, respectively. In the CaO-SiO 2 -CaF 2 (2CaO · SiO 2 -Satd.) system, the center of gravity of the bands at about 1 170-710 cm Ϫ1shifts from about 980 to 850 cm Ϫ1 by increasing the ratio X CaF 2 /X SiO 2 from 0.22 to 0.64. The bands for [SiO 4 ]-tetrahedra are observed from about 1 070 to 730 cm Ϫ1 in the CaO-17.6(mol%)SiO 2 -CaF 2 system, while these bands are observed from about 1 120 to 720 cm Ϫ1 in the CaO-40.0(mol%)SiO 2 -CaF 2 system. The effect of substitution of CaF 2 for CaO on the depolymerization of silicate network is observed to significantly depend on the SiO 2 content in the slags. The bands for [SiO 4 ]-tetrahedra are observed from about 1 110 to 720 cm Ϫ1 in the CaO-SiO 2 -14.1(mol%)CaF 2 system and the center of gravity of these bands shifts from about 990 to 850 cm Ϫ1 with increasing CaO/SiO 2 ratio. The fraction of the relatively depolymerized units continuously increases from about 0.5 to 0.8 as the composition of slags changes from 2CaO · SiO 2 to CaO saturation condition.

The viscosity of CaO-SiO 2 (-MgO)-Al 2 O 3 slags was measured to clarify the effects of Al 2 O 3 and MgO on the structure and viscous flow of molten slags at high temperatures. Furthermore, the infrared spectra of the quenched slags were analyzed to understand the structural role of Al 2 O 3 in the polymerization or depolymerization of silicate network. The Al 2 O 3 behaves as an amphoteric oxide with the composition of slags; that is, the alumina behaves as a network former up to about 10 mass pct Al 2 O 3 , while it acts as a network modifier, in parts, in the composition greater than 10 mass pct Al 2 O 3 . This amphoteric role of Al 2 O 3 in the viscous flow of molten slags at the Newtonian flow region was diminished by the coexistence of MgO. The effect of Al 2 O 3 on the viscosity increase can be understood based on an increase in the degree of polymerization (DOP) by the incorporation of the [AlO 4 ]-tetrahedra into the [SiO 4 ]-tetrahedral units, and this was confirmed by the infrared (IR) spectra of the quenched slags. The influence of alumina on the viscosity decrease can be explained on the basis of a decrease in the DOP by the increase in the relative fraction of the [AlO 6 ]-octahedral units. The relative intensity of the IR bands for the [SiO 4 ]-tetrahedra with low NBO/Si decreased, while that of the IR bands for [SiO 4 ]-tetrahedra with high NBO/Si increased with increasing Al 2 O 3 content greater than the critical point, i.e., about 10 mass pct in the present systems. The variations of the activity coefficient of slag components with composition indirectly supported those of viscosity and structure of the aluminosilicate melts.

The viscosities of CaO-SiO 2 (-MgO)-CaF 2 slags were 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 (IR) spectra of the quenched slags were analyzed to understand the structural role of CaF 2 in the modification of slag structure. The CaF 2 affects the critical temperature (T CR ) of the slags; that is, the higher the content of CaF 2 , the lower the T 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 (ϵ(mass pct CaO)/(mass pct SiO 2 )) ϭ 1.0, the T CR was decreased about 150 to 200 K by addition of 10 mass pct MgO, while the T CR was increased about 100 K by MgO addition at B ϭ 1.3. The effect of CaF 2 on the viscous flow of molten slags can be understood based on a decrease in the degree of polymerization by F Ϫ as well as by O 2Ϫ ions and this was confirmed by the IR spectra of the quenched slags. The relative intensity of the IR bands for [SiO 4 ]-tetrahedra with low NBO/Si decreased, while that of the IR bands for [SiO 4 ]-tetrahedra with high NBO/Si increased with increasing CaF 2 content. The decrease in viscosity of the CaO-SiO 2 -MgO-CaF 2 (B ϭ 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 ϭ 1.3).

The FT-IR spectra of the CaO-Al 2 O 3 and CaO-Al 2 O 3 -CaF 2 slags were measured to understand the structural aspects of (fluoro-) aluminate slags. The infrared spectra of the CaO-Al 2 O 3 slag was interpreted based on the relationship between bond length and force constant of Al-O bond. Thereafter, the role of F Ϫ ions in the depolymerization of aluminate network was discussed. The wavenumbers of [AlO 4 ]-tetrahedra higher than that of [AlO 6 ]-octahedra would be originated from the Al-O bond length in tetrahedra shorter than that in octahedra. In the

The sulfide capacity and the activity of MnO in the MnO-TiO 2 system were measured at 1 723 K. Also, the phase equilibria of the MnO-TiO 2 -MnS system were estimated by measuring the solubility of MnS in the melts. The thermodynamic behavior of MnO and TiO 2 in the MnO-TiO 2 system exhibits a negative deviation from ideality at 1 723 K. The sulfide capacity increases and the activity coefficient of MnS decreases with increasing MnO content in the MnO-TiO 2 system. The solubility of MnS in the MnO-TiO 2 system increases with increasing MnO content up to about 50 mol%, followed by nearly constant value of about 80 mass% MnS. The solubility of MnS equilibrated with MnO is in good correspondence with the value obtained from the phase diagram of the MnO-MnS binary system. Compared with the phase diagram of the MnO-SiO 2 -MnS system, a homogeneous liquid region in the MnO-TiO 2 -MnS system is found to be wider at the same temperature. The activity of MnS increases with increasing MnS content at a fixed MnO/TiO 2 ratio in the MnO-TiO 2 -MnS system. Also, the activity slightly decreases with increasing TiO 2 content at a fixed MnS/MnO ratio, whilst MnS activity rapidly decreases by increasing the content of MnO at a constant TiO 2 /MnS ratio.