Effects of amphoteric oxide (Al2O3 and B2O3) on the structure and properties of SiO2-CaO melts by molecular dynamics simulation

ABSTRACT Al2O3 and B2O3 possess properties of amphoteric oxide, so Al2O3 and B2O3 have many different influences on the structure and properties of silicate melts, while its influence mechanism in atomic scale has not yet been fully understood. Molecular dynamics (MD) simulation was conducted to gain a clear understanding about the influences of Al2O3 and B2O3 on the structure and properties of SiO2-CaO-Al2O3 (SiO2-CaO-B2O3) silicate melts at 1773 K. The results show that when the Al2O3 content is less than 25 wt.%, the Al2O3 in the system is almost acidic in the studied system, and the bridging oxygen content and polymerization degree of the system increase with the increase of Al2O3 content. When the content of Al2O3 exceeds 25 wt.%, part of Al2O3 in the system becomes basic, which makes the bridging oxygen content of the system decrease and the growth rate of polymerization degree decrease. The effect of B2O3 on the network structure of SiO2-CaO-B2O3 (SCB) system is similar to that of Al2O3 in SiO2-CaO-Al2O3 (SCA) system, but the inflection point from acid to basic is lower (21 wt.%) and the basicity is stronger. Moreover, through two suitable viscosity calculation models, combined with experimental data, it shows that the viscosity of SCA system increases with the increase of Al2O3 content, while that of SCB system is just the opposite.