Apatite: The Effect of Volatiles on its Structure, Stability and Thermodynamic Properties

为了加深我们对磷灰石的结构、稳定性和热力学性质随其羟基、氟和氯含量的函数的理解，人们设计了一系列的实验、分析研究和模拟工作。拟议的工作将具体集中在(1)合成端元、二元和三元磷灰石的组成和结构表征；(2)结晶实验，以评估在岩浆温度下系统的低OH部分是否存在溶液；以及(3)贫OH磷灰石和熔盐之间的交换实验，以研究沿氟磷灰石-氯磷灰石连接的热力学混合特性，并建立氟磷灰石(FAP)-氯磷灰石(ClAP)-羟基磷灰石(OHAp)固溶体的二元和三元混合模型。这些成果将适用于地球和行星地球科学、材料科学和技术开发的各个领域。磷灰石是地球上地质系统中几乎无处不在的矿物，存在于各种行星材料中。其隔离微量元素的能力使其对火成岩、变质岩和沉积岩的岩石成因和年代学研究具有重要意义。然而，由于它的稳定性依赖于含有F、Cl和OH的阴离子固溶体的事实，它的稳定性仍然很差。由于分析这些阴离子组分的困难，缺乏体系中贫OH部分的稳定性信息，以及缺乏三元体系中的系统结构数据，阻碍了对这种固溶体的建模。在这个项目中，实验室合成实验、详细的X射线和核磁共振表征、密集的成分分析和结晶学模型将结合在一起来填补这一空白。最后，使用KCl-KF熔盐的阴离子交换实验将提供关于建立体系中三元固溶体热力学模型所需的混合过剩能量的定量信息。这个项目将资助石溪大学的一名研究生。磷灰石的热力学溶液模型可能在许多研究领域具有广泛的适用性，因为这种矿物是各种经济、工程和医学应用的基础。

A series of experiments, analytical studies, and modeling efforts have been designed to further our understanding of the structure, stability, and thermodynamic properties of apatite as a function of its OH, F, and Cl contents. The proposed work will focus specifically on (1) compositional and structural characterization of synthesized endmember, binary, and ternary apatites; (2) crystallization experiments to assess the presence or absence of a solvus within the low OH portion of the system at magmatic temperatures; and (3) exchange experiments between OH-poor apatite and molten salt to investigate thermodynamic mixing properties along the fluorapatite-chlorapatite join and to develop binary and ternary mixing models for fluorapatite (FAp) - chlorapatite (ClAp) - hydroxylapatite (OHAp) solid solutions. These results will be applicable to a variety of fields of terrestrial and planetary geoscience, materials science, and technology development.Intellectual merit. Apatite is an almost ubiquitous mineral in geological systems on Earth and is found in a variety of planetary materials. Its ability to sequester trace elements makes it important to petrogenetic and geochronological studies of igneous, metamorphic, and sedimentary rocks. However, its stability remains poorly constrained due to the fact that its stability depends on an anionic solid solution with F, Cl, and OH. Modeling of this solid solution has been hindered by difficulties in analyzing these anionic constituents, lack of stability information in the OH-poor part of the system, and lack of systematic structural data within the ternary system. In this project, laboratory synthesis experiments, detailed X-ray and NMR characterization, and intensive compositional analysis, and crystallographic models will be linked to fill this gap. Finally, anion exchange experiments using KCl- KF molten salts will provide quantitative information on the excess energies of mixing needed for development of a thermodynamic model for ternary solid solutions in the system.Broader impacts. This project will support a graduate student at Stony Brook. The thermodynamic solution model for apatite is likely to have wide applicability in many fields of research as this mineral is the basis for diverse economic, engineering, and medical applications.