Experimental Study on the Phase Relations of the SiO2-MgO-TiO2 System in Air at 1500°C

We investigated the phase relations of the SiO2-MgO-TiO2 system in air at 1500°C using the high-temperature isothermal equilibration/quenching technique, followed by x-ray diffraction measurements and direct phase analysis using scanning electron microscopy coupled with x-ray energy dispersive spectrometry. One single liquid phase domain, five two-phase domains (liquid-TiO2, liquid-cristobalite, liquid-MgO·SiO2, liquid-2MgO·SiO2, and liquid-MgO·2TiO2), and five three-phase regions (liquid-TiO2-MgO·2TiO2, liquid-MgO·SiO2-cristobalite, liquid-TiO2-cristobalite, liquid-MgO·SiO2-2MgO·SiO2 and liquid-2MgO·SiO2-MgO·2TiO2) were observed. We constructed a 1500°C isothermal phase diagram based on the experimentally measured liquid compositions. We compared simulations using MTDATA and FactSage thermodynamic software and their databases with the experimental results obtained in this study. These results can be used to provide guidelines for updating the MTDATA and FactSage titania-bearing thermodynamic databases by reassessing the thermodynamic properties of the phase with new experimental data.

A study on phase equilibria in the CaO-Al2O3-SiO2-“Nb2O5”(5 mass pct) system in reducing atmosphere

Phase equilibria in 5 mass% ?Nb2O5? plane of CaO-Al2O3-SiO2-?Nb2O5? system at 1873 K in an oxygen partial pressure of 1.78?10-6 Pa have been investigated through isothermal equilibration and quenching followed by EPMA examinations. In order to characterize the effect of niobium oxide on the phase relationship of the CaO-Al2O3-SiO2 system, Nb2O5-containing and Nb2O5-free samples with the same CaO/Al2O3/SiO2 weight ratio were investigated simultaneously. The ratios of CaO/Al2O3/SiO2 were selected from the CaO?2Al2O3-liquid two-phase equilibrium region in the CaO-Al2O3- SiO2 system at1873 K. It was found that the adding of 5 mass% Nb2O5 to the CaO-Al2O3-SiO2 system caused the original CaO?2Al2O3-liquid equilibrium to become three different new equilibria. The three equilibria were single liquid phase, CaO?6Al2O3-liquid and gehlenite-CaO?2Al2O3-liquid equilibrium respectively. The gehlenite phase may be a new solid solution of 2CaO?Al2O3?SiO2 and NbOx with melting point higher than 1873 K.