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 (mol%) 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 1 070 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.