Summary: | In view of the fact that Ti−bearing blast furnace primary slag has been explored limitedly and its viscosity−structural property is not fully understood, the phase compositions, viscosity and structure of CaO−8%MgO−Al<sub>2</sub>O<sub>3</sub>−SiO<sub>2</sub>−TiO<sub>2</sub>−5%FeO slag are investigated by X-ray diffractometer, rotating cylinder method, Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy respectively, considering the effect of Al<sub>2</sub>O<sub>3</sub> and TiO<sub>2</sub>. The critical temperature that is defined as the temperature below which the viscosity of slag increases quickly, could be explained by the relative amount of perovskite to melilite from phase compositions analysis. The slag viscosity first increases with increasing Al<sub>2</sub>O<sub>3</sub> content from 10 to 15 mass%, and then decreases with the further increase of Al<sub>2</sub>O<sub>3</sub> to 18 mass%. Increasing TiO<sub>2</sub> content continuously lowers the viscosity. FTIR and Raman spectra results show that increasing Al<sub>2</sub>O<sub>3</sub> or decreasing TiO<sub>2</sub> content leads to complex Si−O and Ti−O networks structure, corresponding to the slag viscosity variation. The effect of weak linkages of Si−O−Al is more dominant when Al<sub>2</sub>O<sub>3</sub>exceeds 15 mass%, which results in the decrease of viscosity.
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