Structure and properties of grain and phase boundaries in rocks

晶界和相界是岩石中重要的结构缺陷。在多晶材料中，颗粒界面以许多不同的构型存在，形成扩展的三维网络，非常像构成泡沫的液体薄膜网络。尽管晶界结构是在纳米尺度上测量的，但岩石的宏观性质，如弹性、强度、导电性和扩散质量传输的效率，取决于晶界的物理和化学性质。例如，在不同的热力学条件和流体化学条件下，颗粒和相界的界面能和润湿性的变化对于广泛的地球科学问题具有基本的重要性，这些问题包括大洋脊处的熔体输送、地震间强度恢复、地热和碳氢化合物储藏中的流体输送以及核废料处置场所。我们对晶界结构的概念观点很大程度上源于对金属和陶瓷的观察，但我们根本不知道现有的晶界模型在多大程度上代表了岩石。特别是，岩石中颗粒和相界的结构特性作为取向和能量的函数，以及它们与传输特性的关系在很大程度上仍然难以捉摸。实验和分析技术的最新进展(双晶合成、高分辨率电子显微镜(HREM)、分析电子显微镜、聚焦离子束(FIB)、原子力显微镜(AFM)、二次离子质谱仪(SIMS)深度剖析等)以及计算方法(从头算电子结构计算(DFT)、分子动力学(MD)模拟)允许以前所未有的空间分辨率和分析精度研究晶界结构。在这个项目中，我们建议研究一种重要的造岩矿物，如橄榄石的颗粒和相界的结构特性。我们计划使用合成的双晶样品来研究晶界结构。这为在完整的、未改变的样品上系统地改变晶界结构参数提供了独特的可能性。为了在原子尺度上解析晶界结构，我们将把电子显微镜的观测结果与晶界原子模型的预测结果进行比较。这种方法将为实验观察到的晶界所需的图像模拟提供关键的输入参数。

Grain boundaries and phase boundaries are important structural defects in rocks. In polycrystalline materials grain interfaces are present in many different configurations forming extended three-dimensional networks very much like the networks of liquid films that constitute foams. Even though grain boundary structures are measured on the nanometer scale, the macroscopic properties of rocks such as elasticity, strength, electrical conductivity, and the efficiency of diffusive mass transport depend on the physical and chemical properties of grain boundaries. For example, variation of interfacial energy and wettability of grain and phase boundaries at different thermodynamic conditions and fluid chemistry are of basic importance for a broad range of geosciences problems that encompass melt transport at ocean ridges, interseismic strength recovery, fluid transport in geothermal and hydrocarbon reservoirs and nuclear waste disposal sites. Our conceptual view of the grain boundary structure stems largely from observations on metals and ceramics, but we simply do not know to what extent existing grain boundary models are representative for rocks. In particular, structural properties of grain and phase boundaries in rocks as a function of orientation and energy and their relation to transport properties remain largely elusive. Recent advances in experimental and analytic techniques (bicrystal synthesis, High- Resolution Transmission Electron Microscope (HREM), analytical TEM, Focussed Ion Beam (FIB), Atomic Force Microscopy (AFM), Secondary Ion Mass Spectrometer (SIMS) depth profiling etc.) as well as computational methods (ab initio electronic structure calculations (DFT), molecular dynamics (MD) simulations) allow investigating the grain boundary structure with unprecedented spatial resolution and analytical precision. In this project we propose studying the structural properties of grain and phase boundaries of an important rock-forming mineral, such as olivine. We plan to investigate the grain boundary structure using synthetic bicrystal samples. This gives the unique possibility to vary grain boundary structural parameters systematically on intact, unaltered specimens. To resolve the grain boundary structure on the atomic scale we will compare the TEM observations with predictions from atomistic models of the boundary. This approach will provide crucial input parameters for the required image simulation of the experimentally observed grain boundary.