Viscosity and structure of CaO–BaO–SiO₂–Al₂O₃-based mold slags for continuous casting of high titanium steel with different TiO₂ absorption

The effect of TiO₂ absorption into two different CaO–BaO–SiO₂–Al₂O₃-based mold slags from the steel plant on the viscosity, melting performance and microstructure of slags was investigated through the measurement of the viscosity–temperature relationship, melting temperature and Raman spectroscopy. The parameter of the number of non-bridging oxygen per tetrahedrally-coordinated atom (NBO/T) was also calculated to explain the microstructure variation of molten slags with different TiO₂ absorption. The variation of the actual slag consumption and the depth of the liquid slag in mold was explained through the comparison of the viscosity and the melting temperature of two different slags. The viscosity of mold slags (basicity = 0.6) decreased from 1.1 to 0.68 Pa s with the increase in the TiO₂ absorption from 0 to 10%, while that of slags (basicity = 0.7) decreased from 0.76 to 0.56 Pa s with the TiO₂ absorption from 0 to 6%. The activation energy of both two groups of slags had the tendency to decrease with the increasing TiO₂ absorption. The network structure of both two groups of slags measured by the Raman spectra showed that the fraction of complex structure units (Q¹, Q², Q³ and Al–O–Al) decreased and simple structure units (Al–O⁻ and Q⁰) increased with the increase in TiO₂ absorption. NBO/T also increased with the increase in the TiO₂ absorption, indicating that the absorption of TiO₂ into slags resulted in the destruction of silicate/aluminate structure. Hence, the absorption of TiO₂ into the current CaO–BaO–SiO₂–Al₂O₃ mold slags decreased the degree of polymerization of these slags and then led to the decrease of viscosity.