Phase equilibria in medium basicity region of CaO-SiO2-Nb2O5-(5%,10%,15%) La2O3 system

The thermodynamic information, such as primary phase fields and liquidus temperatures, in the CaO-SiO2-Nb2O5-La2O3 quaternary system phase diagram is important for the comprehensive utilization of niobium and rare earth resources. In the current work, the phase equilibria of CaO-SiO2-Nb2O5-(0-15%)La2O3 system within medium basicity region at 1373-1673 K were experimentally studied. X-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersive spectrometer (EDS) were used to identify the type and composition of equilibrium phases in the quenched samples after thermodynamic equilibrium experiment. According to the experimental results, the univariate line between CaNb2O6-Ca2Nb2O7-LaNbO4 primary phase fields, the bivariate interface between CaNb2O6-Ca2Nb2O7 primary phase fields, the bivariate interface between CaNb2O6-LaNbO4 primary phase fields, and isothermal liquidus surfaces in CaNb2O6 and Ca2Nb2O7 primary phase fields were determined, respectively. Finally, CaO-SiO2-Nb2O5-La2O3 phase diagram within specific region was spatially constructed, and the results were also presented in the form of CaO-SiO2-Nb2O5 pseudo-ternary system phase diagram with w(La2O3) = 5%, 10% and 15%. The research results are important for the comprehensive utilization of Nb and RE resources, meanwhile, they are also important for the improvement of related phase diagrams.