Effect of CeO 2 on viscosity, structure and crystallisation of CaO-Al 2 O 3 -SiO 2 -Li 2 O-B 2 O 3 -BaO mould fluxes

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.