Structure Analysis of CaO–SiO₂–Al₂O₃–TiO₂ Slag by Molecular Dynamics Simulation and FT-IR Spectroscopy

Abstract

The structure information in the CaO-SiO₂-14 mass% Al₂O₃–TiO₂ slag was investigated by the molecular dynamics simulation and the FT-IR spectroscopy at 1773 K. The influence of different additions of TiO₂ and varying CaO/TiO₂ ratios on the structure was studied to clarify the role of TiO₂ in the slag. The results show that there exist three stable units, [SiO₄] tetrahedron and [AlO₄] tetrahedron as well as [TiO₆] octahedron in the CaO-SiO₂-14 mass% Al₂O₃–TiO₂ slag. The average coordination numbers, CN_Si–Al and CN_Al–Al, are all approximately equal to 1 and are barely influenced by additions of TiO₂ and varying CaO/TiO₂ ratios, which indicates that both the [SiO₄] and [AlO₄] tetrahedrons are surrounded by only one [AlO₄] tetrahedron and some other units. Nevertheless, [AlO₄] can be linked by more than one [SiO₄] tetrahedron but [SiO₄] can only be surrounded by one [AlO₄] tetrahedron. The bridging oxygen, classified into Si–O–Si, Al–O–Al and Si–O–Al, is preferentially localized in Si–O–Al. However, it is found a little violation of the so-called Al avoidance principle which states that the Al–O–Al linkage is absent have been obtained with about (less than) 5% Al–O–Al, and the bond of Al–O–Al is hardly affected by TiO₂ additions. Replacement of CaO by TiO₂ can only result in a slight change of the degree of polymerization, indicating TiO₂ has the similar role as CaO to be a basic oxide.