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

Abstract

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.