Drop solution calorimetry was used to determine the enthalpy of solution in lead borate for three different materials with the chemical composition Y3Al5O12. Crystalline yttrium aluminum garnet (YAG), a crystalline mixture of 3 YAlO3 (perovskite) plus Al2O3 (α-alumina), and a glass, were all synthesized by containerless melting and cooling. The enthalpies of drop-dissolution per mole of Y3Al5O12 were 472.49 ± 4.19, 440.35 ± 3.59, and 196.02 ± 3.39 kJ/mol, respectively, for the garnet, the crystalline mixture, and the glass. The garnet phase is thermodynamically stable with respect to the corresponding mixture of α-alumina and perovskite confirming that the two phase mixture is metastable. The enthalpy of vitrification of YAG is 276.47 ± 5.40 kJ/mol (13.82 ± 0.27 kJ/g atom). This high value for the enthalpy of vitrification is related to the reluctant glass forming ability of the YAG composition. The heat of fusion of Y3Al2O12 is estimated to be 25.8 kJ/g atom or 516 kJ/mol at its melting point, 2240 K.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Ceramics and Composites
- Condensed Matter Physics
- Materials Chemistry