The assessment of thermodynamic parameters in the Al2 O3 -Y2 O3 system and phase relations in the Y-Al-O system

Thermodynamic parameters for solid and liquid phases in the Al2O3-Y2O3 system are assessed using new calorimetric measurement for the YAG (Y3Al5O12), YAP (YAlO3) and YAM (Y4Al2O9) phases. The calculated phase diagram of the Al2O3-Y2O3 system is in reasonable agreement with experimental data. According to the calculations, the YAP phase melts congruently and is stable down to the low temperatures, while the YAM phase disproportionates to a mixture of YAP and Y2O3 phases at temperatures below 1385 K. The calculated entropy of the YAG phase 300.1 J/(mol · K) is between 2 experimentally determined values 284.8 and 349.1 J/(mol · K). However, the difference between calculated and experimental values exceeds uncertainty limits of adiabatic calorimetry data. The enthalpies of melting for the YAG and YAP phases calculated in this study are in reasonable agreement with DTA measurements. The calculated enthalpy of melting for the YAG phase is not consistent with estimates based on solution calorimetric data. New independent measurement of the standard entropy and enthalpy of melting are desirable for the YAG, YAM and YAP phases. The liquidus surface and isothermal section at 2000 K for ternary Al-Y-O system are calculated in this study.