Phase equilibria in the TiO2–Nb2O5 system: New experiments and thermodynamic modeling

Abstract

Phase equilibria in the TiO2–Nb2O5 system has been investigated by using the high-speed pyrometer, scanning electron microscopy and X-ray powder diffraction. The liquidus temperatures in the whole composition region are determined by cooling trace tests. Combining with the observation of solidification structure, liquidus at the TiO2-rich corner are clarified and the eutectic composition of Liquid→TiO2+TiNb2O7 is revised to be 62.3 mol % TiO2. TiNb2O7 has been measured to have some solid solubility, and the existence of Ti2Nb6O19 at high temperature is confirmed. It would probably form through the peritectic reaction of Liquid + TiNb2O7→Ti2Nb6O19. Moreover, congruent reactions of Liquid→TiNb2O7 and Liquid→TiNb5O14.5 are measured as 1491 °C and ∼1478 °C, respectively. Subsequently, thermodynamic assessment of TiO2–Nb2O5 system has been carried out by means of the CALPHAD method, and a set of self-consistent thermodynamic parameters is obtained. Calculated TiO2–Nb2O5 phase diagram can reasonably reproduce the available experimental data. The provided TiO2–Nb2O5 phase diagram and thermodynamic parameters may be useful to the development of titanium niobates and further multicomponent thermodynamic database.