The structure information in the CaO-SiO
2-14 mass% Al
2O
3–TiO
2 slag was investigated by the molecular dynamics simulation and the FT-IR spectroscopy at 1773 K. The influence of different additions of TiO
2 and varying CaO/TiO
2 ratios on the structure was studied to clarify the role of TiO
2 in the slag. The results show that there exist three stable units, [SiO
4] tetrahedron and [AlO
4] tetrahedron as well as [TiO
6] octahedron in the CaO-SiO
2-14 mass% Al
2O
3–TiO
2 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 TiO
2 and varying CaO/TiO
2 ratios, which indicates that both the [SiO
4] and [AlO
4] tetrahedrons are surrounded by only one [AlO
4] tetrahedron and some other units. Nevertheless, [AlO
4] can be linked by more than one [SiO
4] tetrahedron but [SiO
4] can only be surrounded by one [AlO
4] 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 TiO
2 additions. Replacement of CaO by TiO
2 can only result in a slight change of the degree of polymerization, indicating TiO
2 has the similar role as CaO to be a basic oxide.
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