Study on the coupling effect of TiO2 and Al2O3 on the structure of CaO-SiO2-MgO-xAl2O3-yTiO2 slag systems

This study analyzes the influence both of TiO2 and Al2O3 content on the microstructure of CaO-SiO2-MgO-xAl2O3-yTiO2 (14mass%≤x≤22mass%，0≤y≤10mass%) blast furnace slag systems based on the change of slag viscosity, Raman spectroscopy and molecular dynamics. The Raman spectroscopy results indicate that an increase in TiO2 content leads to the gradual depolymerization of complex silicate structures (Q3 and Q2) into simpler structures (Q0 and Q1) in the slag. At the same time, the Al-O-Al bonds in the aluminate structures of the slag also depolymerize into simpler Al-O- forms, resulting in a decrease in the degree of polymerization of both silicates and aluminates. In contrast, an increase in Al2O3 content generally results in an increased degree of polymerization for the silicates and aluminates. Molecular dynamics simulations of the polymerization and depolymerization processes in the microstructure of the blast furnace slag reveal that Si and Al mainly exist in tetrahedral SiO4 and AlO4, while Ti primarily exists in pentavalent and hexavalent TiO5 and TiO6. TiO2 exhibits basic properties in this system, whereas Al2O3 demonstrates acidic behavior. The addition of TiO2 introduces free oxide ions into the system, causing the bridging oxygens to break into non-bridging oxygens, leading to the depolymerization of complex structures Q4 and Q3, which simplifies the slag structure. On the other hand, an increase in Al2O3 content tends to capture or share the oxide ions within the system to form AlO4, resulting in the polymerization of free oxygen into non-bridging oxygens, which further polymerize into bridging oxygens and lead to the consolidation of simple structures Q0 and Q1, resulting in a more complex slag structure. Both Raman spectroscopy analysis and molecular dynamics simulation results indicate that the degree of polymerization of SiO4 and AlO4 in the slag network structure is a crucial factor determining the fluidity of the slag.