Structure and transport properties of Ca$_2$SiO$_4$–MnO$_x$ melts: A molecular dynamics simulation study

Abstract

The structural and transport properties of Mn-bearing silicate melts are strongly influenced by the oxidation state of manganese, which plays an important role in many metallurgical slag systems. In this study, classical molecular dynamics simulations were performed to investigate the effect of the manganese valence state on the atomic structure, diffusion behavior, and viscosity of Ca$_2$SiO$_4$–MnO$_x$ melts containing Mn$^{2+}$, Mn$^{3+}$, and Mn$^{4+}$ over a wide range of Mn concentrations. Structural analysis based on radial distribution functions and coordination statistics reveals that increasing Mn oxidation state enhances short-range structural ordering and promotes greater Si–Si connectivity within the silicate network. The degree of polymerization decreases with increasing Mn content for all oxidation states, indicating progressive depolymerization of the silicate framework. However, distinct differences between Mn valence states are observed, with Mn$^{4+}$-containing melts exhibiting the highest polymerization degree at moderate Mn concentrations. Diffusion coefficients of the constituent species show a strong dependence on both Mn concentration and oxidation state, with higher atomic mobility observed in the more depolymerized systems. Correspondingly, the calculated viscosities decrease with increasing Mn content for Mn$^{2+}$ and Mn$^{3+}$ melts, whereas Mn$^{4+}$-containing melts exhibit an increase in viscosity at higher Mn concentrations. These results demonstrate that the oxidation state of manganese plays a key role in controlling silicate network connectivity and melt transport properties, providing atomistic insight into the structure–property relationships governing Mn-bearing metallurgical slag systems.

The authors' abstract, as published at the source. Chemical Engineering Science, 2027 · DOI ↗