Structural investigation of CaO-Al₂O₃ and CaO-Al₂O₃-CaF₂ slags via Fourier transform infrared spectra

The FT-IR spectra of the CaO-Al₂O₃ and CaO-Al₂O₃-CaF₂ slags were measured to understand the structural aspects of (fluoro-) aluminate slags. The infrared spectra of the CaO-Al₂O₃ slag was interpreted based on the relationship between bond length and force constant of Al-O bond. Thereafter, the role of F^- ions in the depolymerization of aluminate network was discussed. The wavenumbers of [AlO₄]-tetrahedra higher than that of [AlO₆]-octahedra would be originated from the Al-O bond length in tetrahedra shorter than that in octahedra. In the CaO_satd-Al₂O₃-CaF₂ system, the IR-transmitting bands of [AlO_nF_4-n]-complexes are observed through the entire composition of the fluoroaluminate system, while the bands of [AlO₄]-tetrahedra, [AlO₆]-and [AIF₆]-octahedra appear in the composition less than 24.0(mol%) CaF₂. In the 26.2 (mol%) Al₂O₃-containing system, the bands of interlinked [AlO₄]-tetrahedra are shown at only 2-liquids boundary, while these bands are shown in the whole composition region in the 41.5 (mol%) Al₂O₃-containing system. In the 41.7 and 51.0(mol%)CaO-Al₂O₃-CaF₂ systems, the transmitting bands of [AlO_nF_4-n]-complexes are observed through the entire composition, while those of [AlO₄]-tetrahedra are shown in the composition of X_CaF(2)/X_Al(2)O(3) ≤ 1.0. Also, the relative intensity of the bands indicating [AlO₄]-tetrahedra in the 51.0 (mol%) CaO-containing slag is much less than that in the 41.7 (mol%) CaO-containing system.