Structural Evolution Mechanism of Na₂O in Regulating the Viscosity-Temperature Characteristics of Silicate Slag

The flow behavior of molten slag directly impacts the stability of slag removal processes in high-temperature furnaces, with alkali metal oxides exerting a significant influence on slag flow characteristics. To elucidate the structural evolution mechanism by which Na₂O modulates the viscosity-temperature properties of silicate slag, molecular dynamics simulations, FactSage thermodynamic calculations, and Raman spectroscopy analysis are employed to investigate the effects of NaO content on slag structure and viscosity under fixed SiO₂/Al₂O₃ conditions. Results indicate that as Na₂O content increases within the 0 wt%-8.91 wt% range, the complex structural unit [Si₂O₅]²⁻(Q³) continuously depolymerizes into [SiO₄]⁴⁻(Q⁰) and [Si₂O₇]⁶⁻(Q¹), leading to increased non-bridging oxygen (NBO) proportion and decreased polymerization degree (DOP). Concurrently, Na⁺ compensates for Al³⁺ charges, promoting the transformation of unstable [AlO₆] octahedra into more stable [AlO₄] tetrahedra. The network depolymerization effect of Na₂O dominates its macroscopic viscosity-temperature behavior, resulting in a significant viscosity decrease with a good linear correlation between viscosity and degree of polymerization. Below the liquidus temperature range, when Na₂O<8.91 wt%, its addition suppresses slag crystallization tendencies. This promotes the transformation of high-melting-point minerals like wollastonite and calcium feldspar into low-melting-point feldspars, thereby enhancing slag fluidity and reducing viscosity. This study reveals the microscopic mechanism by which Na₂O regulates the viscosity-temperature characteristics of silicate slag, providing a theoretical basis for safe slag disposal.