Unveiling Charge Compensation Effects in Na 2 O–Al 2 O 3 –SiO 2 Melts: Atomic-Scale Mechanisms and Implications for Fluidity from AIMD Simulations

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