Effect of CeO ₂ on viscosity, structure and crystallisation of CaO-Al ₂ O ₃ -SiO

The mould fluxes with appropriate viscosity and crystallisation are crucial materials in the continuous casting for rare earth alloyed steel. In this study, a novel mould fluxes, (36-0.5 x )CaO-(36-0.5 x )Al ₂ O ₃ -8SiO ₂ - x CeO ₂ -5Li ₂ O-5B ₂ O ₃ -10BaO (CASCLBB), was proposed. The effect of CeO ₂ content on viscosity, structure and crystallisation were systematically investigated. The viscosity value at 1400 °C was first increased from 0.62 Pa·s to 0.71 Pa·s with an increased CeO ₂ content from 0 wt.% to 4 wt.%. This was because the oxidation state of Ce ions shifted from Ce ⁴⁺ to Ce ³⁺ when CeO ₂ content was increased, accompanied by enhanced precipitation of crystalline phases such as Ca ₂ Al ₂ SiO ₇ , BaAl ₂ O ₄ , and BaCeO ₃ . The appearance of these crystalline phases induced phase separation, which became dominant from 0 wt.% to 4 wt.% CeO ₂ and consequently increased viscosity. However, the viscosity value decreased to 0.51 Pa·s when CeO ₂ content further increased 12 wt.%, which was attributed to decreased fractions of Q ² , Q ³ , BO, [BO ₃ ] and [AlO ₄ ] units. The increasing structural depolymerisation may have become dominant, resulting in a more depolymerised melt network and consequently reduced viscosity. Additionally, the mechanism of viscosity variation with temperature for a sample containing 8 wt.% CeO ₂ was discussed.