Viscous Behavior and Structure Characteristic of CaF₂–CaO–Al₂O₃–MgO–(B₂O₃) Slag for Electroslag Remelting

The viscous behavior and microstructure of CaF₂–CaO–Al₂O₃–MgO slag with different B₂O₃ contents for electroslag remelting were investigated by employing the rotating cylinder method and molecular dynamics (MD) in conjunction with the Raman spectroscopy measurement. The results show that the viscosity of B₂O₃-containing ESR slag at 1823 K increased from 0.008 to 0.026 Pa s, the turning point temperature decreased from 1610 K to 1583 K, and the viscous flow activation energy of the slag decreased from 197.33 to 73.31 kJ mol⁻¹, when the increase of B₂O₃ content from 2 to 7mass pct. Increasing B₂O₃ promotes the formation of [BO₃]³⁻ structures and [AlO₃F]⁴⁻ structure unit and increases the degree of polymerization of the slag. It is preliminarily speculated that increasing B₂O₃ destroys [AlO₄]⁵⁻–[AlO₄]⁵⁻ structure to form [BO₃]³⁻–[AlO₄]⁵⁻ structure (or [BO₄]⁵⁻–[AlO₄]⁵⁻). Consistent with the results of molecular dynamics calculations, the Raman spectroscopy results also show that the aluminate structure network of ESR slag is depolymerized and more borate structures units are generated as B₂O₃ content increases. Therefore, B₂O₃ can complicate the melt structure and increase the viscosity of ESR slag.