The assessment of thermodynamic parameters in the Al2O3-Y2O3 system and phase relations in the Y-Al-O system

Thermodynamic parameters for solid and liquid phases in the Al2O3-Y2O3 syst em are assessed using new calorimetric measurement for the YAG (Y3Al5O12), YAP (YAlO3) and YAM (Y4Al2O9) phases. The calculated phase diagram of the A l2O3-Y2O3 system is in reasonable agreement with experimental data. Accordi ng 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 entrop y of the YAG phase 300.1 J/(mol.K) is between 2 experimentally determined v alues 284.8 and 349.1 J/(mol.K). However, the difference between calculated and experimental values exceeds uncertainty limits of adiabatic calorimetr y data. The enthalpies of melting for the YAG and YAP phases calculated in this study are in reasonable agreement with DTA measurements. The calculate d enthalpy of melting for the YAG phase is not consistent with estimates ba sed on solution calorimetric data. New independent measurement of the stand ard 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 A l-Y-O system are calculated in this study.