Effect of MgO on viscosity and melt structure of mold flux for continuous casting

The viscosity and structure of mold flux with different MgO content were investigated in this study. Results show that the viscosity at 1583 K reduces from 0.39 to 0.35 Pa<middle dot>s, and the apparent activation energy decreases from 135.13 +/- 3.78 to 69.53 +/- 2.88 kJ/mol with the addition of MgO from 2 to 8 wt-%. Melt structure analyses suggest that the amount of more complex structural units, such as Q(3)(Si), Q(4)(Si), Si-O-Si and Al-O-Si decrease, meanwhile the simpler Q(0)(Si), Q(1)(Si) and Q(2)(Si) increase with increasing MgO content in the melt. However, [AlO4](5-) symmetric tetrahedral increases, while [AlO4](5-) asymmetric tetrahedral decreases with the addition of MgO due to the charge compensation effect. Finally, from the synthetic analyses of viscosity and melt structure, it can be concluded that the network breaker effect of O2- from MgO is much larger than the charge compensation effect of Mg2+ from MgO, which results in the reduction of viscosity and apparent activation energy of the mold flux melt.