Unveiling Charge\nCompensation Effects in Na<sub>2</sub>O–Al<sub>2</sub>O<sub>3</sub>–SiO<sub>2</sub> Melts:\nAtomic-Scale Mechanisms and Implications for Fluidity from AIMD Simulations

The charge compensation effect of alkaline leads to the\nunexpected\nrise in slag viscosity and the shutdown of industrial processes such\nas coal gasification and other processes related to solid fuel utilization.\nIt is a challenge for the traditional polymerization theory to explain\nthe chemical nature of the charge compensation effect. Ab initio molecular\ndynamics simulations were conducted to explore the mechanism of the\ncharge compensation effect in the Na<sub>2</sub>O–Al<sub>2</sub>O<sub>3</sub>–SiO<sub>2</sub> system. By analyzing the atomic\ndiffusion trajectories and transient coordination, we obtained a crucial\nunderstanding of the charge compensation effect. The transition balance\nbetween the bridging- and tricluster-oxygen structures is altered\nby Na<sub>2</sub>O. Na coordinates with the bridging-oxygen to form\nSiOAlNa and Al<sub>2</sub>ONa, and these structures have lower structural\nenergy than the original tricluster-oxygen. This structural rearrangement\nleads to a decrease in the structural energy of the melt, hindering\nthe exchange and diffusion of atoms in the melt and causing an increase\nin viscosity. A theoretical model relating structural energy and viscosity\nwas derived as η = (<i>A</i>/<i>T</i>)<i>e</i><sup>8.314</sup><i><sub>E<sub>k</sub></sub></i><sup><i><sub>k</sub></i></sup>– <i>B</i>. Our results offer illuminating insights into the relationship between\nthe structure and fluidity of high-temperature silicate fluids.