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• Nb is mainly in the +5 valence state and exists in the form of [NbO 6 ]7− octahedron. • The melt conductivity increases with the increase of Nb 2 O 5 content. • Ti in the melt is dominated by Ti4+ and exists in the [TiO 6 ]8− octahedron structure. Electrical conductivity is a very important physical parameter in the process of electrolytic extraction of niobium from molten niobium-enriched slag or preparation of ferroniobium alloy by reduction melting separation in electric arc furnace. The effects of Nb 2 O 5 , CaO/SiO 2 ratio and TiO 2 on the electrical conductivity of CaO-SiO 2 -Nb 2 O 5 -TiO 2 -CeO 2 -CaF 2 melt were studied by AC four-electrode method. The melt structure was studied by XPS to reveal the change rules of melt conductivity. The results show that the addition of Nb 2 O 5 or increasing the CaO/SiO 2 ratio in the melt can depolymerize the melt network structure and effectively improve the melt conductivity, and the activation energy of the conductivity is negatively correlated with the Nb 2 O 5 content and the CaO/SiO 2 ratio. With the increase of TiO 2 content in the melt, the melt network structure polymerizes, the melt conductivity decreases, and the activation energy of conductivity also showed a decreasing trend. [ABSTRACT FROM AUTHOR]

• The viscosity was proportional to the CeO 2 content and the CeO 2 /Al 2 O 3 ratio. • CeO 2 made the structure of the silicon oxide ionic group to be simple. • The viscosity of the melt was influenced by the combination of Ce4+ and Ce3+. The effect of the CeO 2 content and CeO 2 /Al 2 O 3 ratio on the melt viscosity of CaO-SiO 2 (-Al 2 O 3)-CeO 2 was determined using the rotating cylinder method. The structural characteristics of the quenched vitreous samples were investigated with a Raman spectrometer. The results showed that the melt viscosity of CaO-SiO 2 (-Al 2 O 3)-CeO 2 decreased significantly with increases in the CeO 2 content and the CeO 2 /Al 2 O 3 ratio. Q 3/ Q 2, which represents the degree of polymerization of the melt, decreased with an increase in the CeO 2 content and the CeO 2 /Al 2 O 3 ratio. Ce in the CaO-SiO 2 (-Al 2 O 3)-CeO 2 system was present as a mixture of Ce4+ and Ce3+ in high-purity Ar atmosphere at a temperature of 1540 °C. In the CaO-SiO 2 (-6%Al 2 O 3)-6%CeO 2 system, the melt viscosity was higher in the presence of Ce4+ and Ce3+ than in the presence of Ce3+, indicating that the melt viscosity of CaO-SiO 2 (-Al 2 O 3)-CeO 2 was determined by the combination of Ce4+ and Ce3+. CeO 2 acted as a network modifier in the melt. [ABSTRACT FROM AUTHOR]