Structure and flow properties of coal ash slag using ring statistics and molecular dynamics simulation: Role of CaO/Na2O in SiO2–Al2O3–CaO–Na2O

Abstract

Molecular dynamics simulation was applied to investigate the microstructure of slag in SiO2-Al2O3-CaO-Na2O system. A new structure model for slag was established through ring-statistics by MD simulation. The network structure was simplified into crosslinked rings divided into three types based on the ring size. The change of amorphous structure was well described by ring distribution. The destruction of slag structure by Ca2+ is more significant than Na+, and high CaO/Na2O resulted in low content of medium and large rings and low viscosity. The ring distribution coefficient (Rdc) was defined to establish the relationship between structure and viscosity: ŋ=26.7Rdc-10.2. When CaO/Na2O ratio increases, the ring distribution transforms from medium or high-order to low-order, leading to the decreasing of Rdc and slag viscosity. Moreover, CaO/Na2O ratio also changes the diffusivity of slag and thus the melting behavior. Finally, a linear relationship between the empirical liquidus temperature (Tliq) and atomic diffusivity from the MD simulations was obtained.