Liquidus Phase Diagram of CaO-SiO₂-La₂O₃-Nb₂O₅ System with w(La₂O₃) = 15 to 25 Pct

The thermodynamic information of the CaO-SiO₂-Nb₂O₅-La₂O₃ system is of great significance for the utilization of Nb and RE resources from minerals. In this article, the phase equilibria of the CaO-SiO₂-Nb₂O₅-La₂O₃ system were investigated by equilibrium experiments. Twelve kinds of phase equilibria were determined, and then a spatial liquidus phase diagram was constructed. The primary phase fields of SiO₂, CaNb₂O₆, LaNbO₄, Ca₂Nb₂O₇ and CaSi₃La₄O₁₃ were determined, respectively. Meanwhile, the liquidus surfaces in the primary phase fields of SiO₂, Ca₂Nb₂O₇ and LaNbO₄ were determined. Finally, the CaO-SiO₂-Nb₂O₅-(17.5, 20, 22.5, 25 pct)La₂O₃ pseudo-ternary phase diagrams were also obtained. In addition to the experimental results, two theoretical rules applicable for the spatial quaternary phase diagram were also proposed to obtain indirect information on the bivariate interface between two adjacent primary phase fields. The first rule was the “tangent line rule” for judging related precipitation reaction types, and the second rule was the “highest temperature rule” for judging related temperature trends. The present work will be helpful for the utilization of Nb and RE resources and for the establishment of related thermodynamic databases.