Effect of B2O3 on the viscosity, structure and crystalline phase of CaO-MgO-Al2O3-SiO2-MnO-based high alumina slags

The effects of B₂O₃ on viscosities, structures and phase transitions of CaO-MgO-Al₂O₃-SiO₂-MnO-(0-8.0wt%)B₂O₃ slags were investigated in this work. From the viscosity experimental results, the slag viscosities declined and the E_η decreased from 205.19 to 175.95 kJ/mol with the addition of B₂O₃ in slags from 0 to 8.0 wt%. From the structure analysis by using FTIR and XPS, B₂O₃ entered into the silicate network to increase the slag polymerization degree, while the formation of simple two-dimensional BO₃ trihedral units could significantly decline the symmetry and stability of the structure. The effects of decreasing the network stability and forming low-melting eutectics were more dominated than the effects of increasing the structure polymerization degree, which could reduce the slag viscosity. Furthermore, adding B₂O₃ could decrease the slag initial precipitation temperature and change the primary crystal phase of the slag from melilite to spinel. The comprehensive effects of reducing the slag structure stability and decreasing the influence of solid phase on viscosity eventually resulted in the improvement of the slag fluidity.