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

Abstract

The lack of thermodynamic information, such as primary phase fields and liquidus temperatures, in the CaO-SiO2-Nb2O5-La2O3 quaternary system phase diagram has restricted the comprehensive utilization of the niobium (Nb) and rare earth (RE) resources. In this work, the phase equilibria in low basicity region (w(CaO)/w(SiO2)<1) of CaO-SiO2-Nb2O5-(0–15 wt%)La2O3 system at 1373–1873 K were experimentally studied by thermodynamic equilibrium experiment, and then, the results were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectrometry (EDS). Additionally, an optimized method was proposed to process the compositions of equilibrium liquid phases at different temperatures. According to the experimental results, the univariate line between CaNb2O6, SiO2 and LaNbO4 primary phase fields, interface between CaNb2O6 and SiO2 primary phase fields and isothermal liquidus surfaces in SiO2 primary phase field were determined. Finally, the spatial phase diagram of CaO-SiO2-Nb2O5-La2O3 within specific region was constructed, and furthermore, the phase diagram was also presented in CaO-SiO2-Nb2O5 pseudo-ternary system with w(La2O3) = 5 wt%, 10 wt% and 15 wt%. The research results have guiding significance for the improvement of related phase diagram and the comprehensive utilization of Nb and RE resources.