Effect of Al₂O₃ Addition on the Precipitated Phase Transformation in Ti-Bearing Blast Furnace Slags

The present paper aims to provide a fundamental understanding on phase change of Ti-enriched crystalline phase induced by Al₂O₃ addition in Ti-bearing blast furnace slags with different basicities using Single Hot Thermocouple Technique and X-ray Diffraction. The results showed that an increase in the Al₂O₃ content led to phase change from rutile or perovskite to Mg₃Al₄Ti₈O₂₅ and prompted crystallization of the slags with basicity of 0.60 and 0.75, whereas only CaTiO₃ was precipitated at a basicity of 0.95. Both thermodynamic and kinetic analyses were conducted to study the slag crystallization, which would throw light on phase change and enhanced crystallization. To further reveal the relationship with Al₂O₃ addition on slag structure and crystallization, Fourier transform infrared spectroscopy and magic angle spinning-nuclear magnetic resonance were adopted, with AlO₄ tetrahedra and AlO₆ octahedra observed in the slag. For slags with the basicity of 0.60 and 0.75, AlO₆ octahedron, which was suggested to induce the phase change from TiO₂ or CaTiO₃ to Mg₃Al₄Ti₈O₂₅, was detected at high Al₂O₃ content. On the other hand, in slags with the basicity of 0.95, abundant Ca²⁺ may be connected to TiO₆ octahedra, resulting in CaTiO₃ formation.