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Amphoteric oxides (Al 2 O 3 and B 2 O 3) represent opposite effects on the structure and properties of silicate melts in different conditions, while the understanding about the transition from acidity to basicity is far from complete. Molecular dynamics simulation was adopted in the present study to investigate the performance and acidity-basicity transformation of Al 2 O 3 and B 2 O 3 in the SiO 2 –CaO–Al 2 O 3 –B 2 O 3 system. The results showed that, different from Ca2+ ions, excessive Al3+ or B3+ ions tend to destroy the bridge oxygen structures, showing the function of basic oxide. This is similar to the behavior of Ca2+ ions and other basicity ions. It was found that, on the one hand, B3+ ions tend to form [BO 3 ]3- planar triangular structures with the increase of B3+ ions contents, on the other hand, B3+ ions could reduce the stability of Si–O bonds. Therefore, B3+ ions could make the system structure less stable, which is the reason why the B 2 O 3 is a kind of active agent. In addition, because of the significant differences in lattice energy and atomic structure between Al 2 O 3 and B 2 O 3 , the effects of Al 2 O 3 and B 2 O 3 on the thermodynamic properties of silicate melts are quite different. [ABSTRACT FROM AUTHOR]

• The influence of MnO content more than or less than 4 wt% on the structure and properties of slag is different. • High bacisity and the MnO content exceeds 4 wt% enhanced depolymerization of aluminosilicate structure by MnO. • The micro complexity of slag system is positively correlated with the macro viscosity. • Low basicity and high MnO promote lower liquidus temperature of slag. In this paper, molecular dynamics (MD) is used to simulate the local structural order, oxygen bond network and transportation characteristics of the slag system under different basicity, and the influence of MnO on the properties such as viscosity, liquidus temperature and enthalpy was studied. MnO or basicity will not affect the bond length and the coordination number of Si-O, but the coordination number of Al-O is slightly reduced. The conversion rate of BO and TOs to NBO or FO is accelerated when CaO/SiO 2 ratio is 1.2 and MnO exceeds 4 wt%. It indicates that an increase in MnO content at high basicity will make the depolymerization of the slag structure more obvious. The total self-diffusion coefficient of each atoms increases with the increase of basicity and MnO, while the viscosity of slag showed an opposite trend. The enthalpy of the slag increases linearly and the conditions of low basicity and high MnO are beneficial for keeping a low liquidus temperature and realizing the stable and smooth of the blast furnace. [ABSTRACT FROM AUTHOR]