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 CaOsetd-Al2O3-CaF2 system, the IR-transmitting bands of [AIO(n)F(4-n)]-complexes are observed through the entire composition of the fluoroaluminate system, while the bands of [AIO(4)]-tetrahedra, [AIO(6)]- and [AIF(6)]-octahedra appear in the composition less than 24.0 (mol%) CaF2. In the 26.2 (mol%) Al2O3-containing system, the bands of interlinked [AIO(4)]-tetralhedra 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 [AlOnF4-n]-complexes are observed through the entire composition, while those of [AIO(4)]-tetrahedra are shown in the composition of X-CaF2/X(Al2O3)less than or equal to1.0. Also, the relative intensity of the bands indicating [AIO(4)]-tetrahedra in the 51.0 (mol%) CaO-containing slag is much less than that in the 41.7 (mol%) CaO-containing system.