Thermochemistry of rare-earth aluminate and aluminosilicate glasses

A series of REAlO₃-composition glasses (RE=La, Pr, Nd, Sm, Gd) were synthesized using containerless processing techniques. DSC shows no evidence of a glass transition prior to crystallization. Onset crystallization temperature increases with decreasing ionic radius of the rare-earth. Transposed temperature drop calorimetry (from room temperature to 1078 K) determined the enthalpies of vitrification at 298 K. Their large values confirm that REAlO ₃ compositions are reluctant glass formers. For glasses along the 2REAlO₃-3SiO₂ join, strongly negative heats of mixing support the absence of miscibility gaps except possibly for very high silica content. Enthalpies of mixing become more exothermic with increasing basicity (larger size) of substituting RE³⁺.