Thermodynamic Properties of Spinels and Garnets

该项目将使用固体电解质、相平衡和电学测量相结合的方法来确定MgAl2O4-FeCr2O4-Fe3O4尖晶石中的活性-组成关系和阳离子位置分布。量热法测得的金铝榴石的热值与由精确的相平衡测量得到的值相矛盾。测量的铁铝尖晶石和尖晶石的稳定场之间也存在差异。铁铝榴石和铁铝尖晶石的自由能将用氧化锆电解液技术作为温度的函数来测定。将热力学数据集成到内部一致的数据库中，提供了在非常高的压力下计算相图和将岩石学输入到地球结构问题中的手段。这种方法将被用来研究在俯冲板块和上地幔之间的界面上观测到的地震波反射和转换的原因。

The project will determine activity-composition relations and cation site distributions in MgAl2O4-FeCr2O4-Fe3O4 spinels using a combination of solid electrolyte, phase equilibrium and electrical measurements. The enthalpy of almandine garnet obtained calorimetrically conflicts with values derived from precise phase equilibrium measurements. There are also discrepancies between the measured stability fields of almandine and hercynite spinel. The free energies of almandine and hercynite will be determined as a function of temperature using the ZrO2 electrolyte technique. Integration of thermodynamic data into an internally-consistent data base provides the means to calculate phase diagrams at very high pressures and to make petrologic input into problems of earth structure. This method will be used to investigate the reasons for observed reflections and conversions of seismic waves at the interfaces between subducting slabs and overlying mantle.