Molecular Dynamics Analysis of the Mg2+ Structure Behavior in SiO2–CaO–Al2O3–MgO Slag System

Abstract

In order to analyze the structural behavior of Mg2+ in the slag and the difference of structural behavior with Ca2+, this paper examines the variation rule of microstructure of SiO2–CaO–Al2O3–MgO slag system with the increase of MgO/CaO ratio by molecular dynamics simulation. The results indicate that in the system, Mg2+ can exist in three coordination forms when combined with oxygen: 4, 5, and 6. It can form ionic bonds with anions to exist as a network modifier, and it can also participate in network formation by forming [MgO4] tetrahedra through Mg–O covalent bonds. Under the condition of constant SiO2 and Al2O3 content, as the MgO/CaO ratio increases, the proportion of MgIV in the slag first increases and then decreases, with a turning point at 30.25%. In contrast, the MgVI ratio shows a decrease followed by an increase, with a minimum value of 17.33%. Ca2+ in the system mainly exists as a network modifier, and its modifying effect first decreases and then increases with the increase of MgO/CaO ratio. The stability of the Si–O and Mg–O tetrahedral structures changes little with the increase in Mg2+ content, while the stability of the Al–O tetrahedral structure decreases, and AlIV gradually transforms into higher coordinated Al. The content of bridge oxygen and the high polymerization degree structural units increase with the addition of Mg2+, leading to an increase in the melt polymerization degree.