Oxide melt solution calorimetry of rare earth oxides. Techniques, problems, cross-checks, successes

Key to the evaluation of the long-term durability and reactivity of REE-materials is the accurate determination of their thermodynamic properties. High-temperature oxide melt solution calorimetry offers an effective methodology for the determination of enthalpies of formation for REE-materials. Calorimetric techniques and crosschecks are summarized that demonstrate that consistent and correct thermodynamic data can be generated using lead borate and sodium molybdate solvents. A summary of recent calorimetric studies of REE-orthophosphates and REE-oxyapatites illustrates the successful application of our techniques in quantifying formation enthalpies and elucidating energetic trends.