FT-IR spectroscopic study on structure of CaO-SiO₂ and CaO-SiO₂-CaF₂ slags

The FT-IR spectra of the CaO-SiO₂ and CaO-SiO₂-CaF₂ slags were measured to understand the structural aspects of (fluoro-) silicate systems. The relative intensity of Si-O rocking band is very strong at SiO₂ saturation condition and this band disappears in the composition greater than 44.1 (mo1%) CaO in the CaO-SiO₂ binary system. The bands for [SiO₄]-tetrahedra at about 1150-760 cm^-1 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^-1, which have been assigned to NBO/Si-1, 2, 3, and 4, respectively. In the CaO-SiO₂-CaF₂ (2CaO·SiO₂-Satd.) system, the center of gravity of the bands at about 1170-710 cm^-1 shifts from about 980 to 850 cm^-1 by increasing the ratio X_CaF2/X_SiO2 from 0.22 to 0.64. The bands for [SiO₄]-tetrahedra are observed from about 1070 to 730 cm^-1 in the CaO-17.6(mol%)SiO₂-CaF₂ system, while these bands are observed from about 1120 to 720 cm^-1 in the CaO-40.0(mol%)SiO₂-CaF₂ system. The effect of substitution of CaF₂ for CaO on the depolymerization of silicate network is observed to significantly depend on the SiO₂ content in the slags. The bands for [SiO₄]-tetrahedra are observed from about 1110 to 720 cm^-1 in the CaO-SiO₂-14.1(mol%)CaF₂ system and the center of gravity of these bands shifts from about 990 to 850 cm^-1 with increasing CaO/SiO₂ 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·SiO₂ to CaO saturation condition.