Molecular Dynamics Simulations of Melt Structure Properties of CaO-Al2O3-Na2O Slag

Molecular dynamics (MD) simulations have been used to study the effect of Na ions on the structure properties of CaO-Al2O3-Na2O slag. The short- and medium-range structures of CaO-Al2O3-Na2O in this study are consistent with existing data. Through the replacement of Ca2+ ions with Na+ ions in CaO-Al2O3-Na2O slag, the structure of the AlO4 tetrahedron is stabilized as the proportion of AlO4 tetrahedron in the melt increases and the average values of the O-Al-O bond angle are closer to those of an ideal tetrahedron. The changes in the melt structure show that Ca2+ ions mainly play a role in modifying the network, while Na+ ions mainly play a role in the charge compensation of the AlO4 tetrahedron; thus, as more Na+ ions replace Ca2+ ions added to the melt, the charge compensation ability in the melt is enhanced, and the network modification ability is weakened. Part of the weak non-bridge oxygen (NBO) structures in the form of Al-NBO-Ca are transformed to strong bridge oxygen (BO) structures in the form of Al-BO-Al, and the microstructure of the melt gradually becomes complicated, which provides a reasonable explanation for the mechanism for the increase of macroscopic viscosity in CaO-Al2O3-Na2O slag with high Al content.

Automated summary

This study used molecular dynamics simulations to investigate the impact of Na ions on the structure properties of CaO-Al2O3-Na2O slag. The substitution of Ca2+ ions with Na+ ions stabilizes the structure of the AlO4 tetrahedron and enhances the charge compensation ability while weakening the network modification ability as more Na+ ions replace Ca2+ ions. The transformation of weak non-bridge oxygen (NBO) structures to strong bridge oxygen (BO) structures in the melt contributes to the increase in macroscopic viscosity in slag with high Al content.