Fluidity and Structure of CaO–Al₂O₃–MgO–V₂O₃ Slag for Smelting Al–V Alloys: Influence of CaO/Al₂O₃ Ratio

This study explored the effect of CaO/Al₂O₃ ratio on the fluidity and structure of CaO–Al₂O₃–MgO–V₂O₃ slag used for smelting Al–V alloys. With increasing CaO/Al₂O₃ ratio, viscosity progressively decreased, while the free running temperature initially decreased and then increased, with a turning point at a ratio of 0.8. Introducing CaO disrupted the bridging oxygen by releasing free oxygen, leading to the formation of non-bridging oxygen. Consequently, bridging oxygen decreased while non-bridging oxygen and free oxygen increased with higher CaO/Al₂O₃ ratio, as demonstrated by XPS analysis. ²⁷Al MAS-NMR spectra revealed that AlO₄ tetrahedra consisting of Q²(Al), Q³(Al), and Q⁴(Al) units dominated the slag, accounting for more than 90 mol pct of the Al³⁺ species, with smaller amounts of AlO₅ and AlO₆ units. As the CaO/Al₂O₃ ratio increased, Q⁴(Al) and Q³(Al) units with highly coordinated bridging oxygens were continuously converted to Q²(Al) units, resulting in a lower degree of polymerization within the aluminate network.