Structural Investigation of CaO-Al2O3 and CaO-Al2O3-CaF2 Slags via Fourier Transform Infrared Spectra.

Abstract

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 - 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 CaO satd -Al 2 O 3 -CaF 2 system, the IR-transmitting bands of [AlO n F 4-n ]-complexes are observed through the entire composition of the fluoroaluminate system, while the bands of [AlO 4 ]-tetrahedra, [AlO 6 ]- and [AlF 6 ]-octahedra appear in the composition less than 24.0 (mol%) CaF 2 . In the 26.2 (mol%) Al 2 O 3 -containing system, the bands of interlinked [AlO 4 ]-tetrahedra are shown at only 2-liquids boundary, while these bands are shown in the whole composition region in the 41.5 (mol%) Al 2 O 3 -containing system. In the 41.7 and 51.0(mol%)CaO-Al 2 O 3 -CaF 2 systems, the transmitting bands of [AlO n F 4-n ]-complexes are observed through the entire composition, while those of [AlO 4 ]-tetrahedra are shown in the composition of X CaF2 /X Al2O3 ≤1.0. Also, the relative intensity of the bands indicating [AlO 4 ]-tetrahedra in the 51.0 (mol%) CaO-containing slag is much less than that in the 41.7 (mol%) CaO-containing system.