Calorimetry Under Extreme Conditions

地球内部处于高温和高压状态，导致存在的矿物发生结构变化。必须测量所涉及材料的热力学性质，以适当地约束和模拟导致板块构造、火山活动和地震的化学过程。该项目开发并应用了新的方法来测量与矿物反应有关的热效应，重点放在三个领域：对在数十万个大气压下制备的非常小的样品的研究，直接测量岩石在熔化温度(1000-2500摄氏度)下的反应热，以及测量硫化物的能量，硫化物对金属矿石、地球深处和陨石都很重要。实验依赖于专门和独特的量热(热量测量)设备，这些设备可在加州大学戴维斯分校的纳夫洛茨基热学设施和加州大学伯克利分校的合作者弗朗西斯·赫尔曼的实验室中获得。伯克利分校的硅芯片上的微机械热量计将测量微克尺寸的高压相样品的热容，这种量热仪已用于固体物理界的薄膜和小晶体。它们在高压矿物相中的应用需要一些技术的改进和发展。高温下的工作将依赖于戴维斯的一套定制和商用热量计。高压硅酸盐相(尖晶石、钙钛矿、钙钛矿、石榴石等)的热容和磁性转变将用芯片上的量热法测量。从这些测量得出的熵将与其他热力学数据结合起来，对地幔的相化学提供严格的约束。将测量铁-硫系和铁-镍-硫系的相形成热。一些氧化物和硅酸盐的高温相变和熔化将被表征。总之，这些不同的数据将被用来了解地球上发生的高温过程。这些数据还应用于高温材料加工、陶瓷、冶炼和精炼。对热力学参数的基本理解将分子水平上的结构与宏观性质联系起来，并为理论计算提供基准。

The interior of the Earth is at high temperature and high pressure, leading to structural transformations in the minerals present. The thermodynamic properties of the materials involved must be measured to properly constrain and model the chemical processes leading to plate tectonics, volcanism, and earthquakes. This project develops and applies new methodology for measuring the heat effects associated with mineral reactions, with emphasis in three areas: the study of very small samples prepared at pressures of several hundred thousand atmospheres, the direct measurement of heats of reactions at temperatures where rocks melt (1000 - 2500 degrees Centigrade), and the measurement of energetics of sulfides, important to metal ores and to the deep Earth and meteorites.The experiments rely on specialized and unique calorimetric (heat measuring) equipment, available in Navrotsky's Thermochmistry Facility at UC Davis and in the laboratories of Frances Hellman, a collaborator at UC Berkeley. The heat capacities of microgram sized samples of high pressure phases will be measured using micromachined calorimeters on a silicon chip at Berkeley, which have been used in the solid state physics community for thin films and small crystals. Their application to high pressure mineral phases requires some modification and development of techniques. The work at high temperature will rely on a suite of custom built and commercial calorimeters at Davis. The heat capacities and magnetic transitions in high pressure silicate phases (spinel, wadsleyite, perovskite, garnet, and others) will be measured by calorimetry on a chip. The entropies derived from these measurements will be combined with other thermodynamic data to provide tight constraints on the phase chemistry of the Earth's mantle. The heats of formation of phases in the iron-sulfur and iron-nickel sulfur system will be measured. High temperature phase transitions and melting in a number of oxides and silicates will be characterized. Together, these various data will be used to understand high temperature processes occurring in the Earth. The data also have applications in high temperature materials processing, ceramics, smelting and refining. A fundamental understanding of thermodynamic parameters links structure on the molecular level with macroscopic properties and provides benchmarking for theoretical calculations.