Correlation study between network structure and fluidity of high-BaO aluminosilicate melt: MD simulation and Raman spectroscopy

Abstract

The BaO-bearing aluminosilicate melt plays a remarkable role in the preparation of glass-ceramics and molten iron production from blast furnace (BF). In this paper, the correlation study between network structure and fluidity of high-BaO aluminosilicate melt was investigated by molecular dynamics (MD) simulation and Raman spectroscopy, aiming to clarify the influence of high BaO content in the low-basicity slag melt. The results indicated that the viscosity decreased with an increase in BaO content from 0 to 20wt%, indicating that the depolymerization effect of O²⁻ provided by BaO was larger than the polymerization effect of Ba²⁺ caused by its charge compensation on [AlO₄]. Moreover, considering the mole concentration of BaO and Al₂O₃, a continuous increase of BaO would cause some excess Ba²⁺ ions to behave as network modifier instead of charge compensator, further reducing the degree of polymerization. MD simulation revealed that Si⁴⁺ formed four coordinated [SiO₄], and Al³⁺ could form four coordinated [AlO₄] and higher coordinated [AlO₅] and [AlO₆]. The content of free oxygen (O²⁻) and tri-clusters oxygen (O^t) was very low. The concentration of non-bridging oxygen (O⁻) increased significantly, whereas that of bridging oxygen decreased. Moreover, the macromolecular Si-based ($Q_{Si}^n$) and Al-based ($Q_{Al}^n$) units were broken down to generate more small molecular structure. Raman spectroscopy analysis also showed the similar depolymerization impact on Si-based structure, which indicated that the increase of BaO cut off the bridging oxygen connection between structural units and depolymerized the complex network structure of the melt.