TEM Studies of Weathering Reactions: The Importance of Mineral Structure, Microstructure and Composition

化学风化至关重要，因为它是高温高压下形成的硅酸盐矿物转化为沉积物和土壤成分的过程。尽管如此，对许多反应的转化机理和转化速率的结构和组成控制仍然知之甚少。这项建议描述了两个研究项目，旨在使用高分辨率透射电子显微镜来调查风化反应的微观特征，其中母质矿物和产物矿物之间存在显著的结构。第一种是角闪石族矿物的水化和氧化。第二个项目的重点是钙钛矿的风化，那里不会形成水合矿物，也不会发生氧化。本课程将考察一些具有接近端元组成的微观结构复杂的角闪石、相互生长和外露的角闪石，以及含有链宽缺陷的角闪石的风化反应。相互生长的角闪石提供了在相同的物理化学条件下比较风化速率和风化机理的机会，并评估了共格应变、缺陷和晶界对反应的聚焦程度。还将研究钙钛矿的风化情况。钙钛矿是核废料储存陶瓷的一种可能成分，其水热溶解已被广泛研究，但其自然风化反应在很大程度上被忽略了。向二氧化钛矿物的化学简单转化可能涉及相当大的结构遗传。这些项目的目的是阐明自然风化过程的晶体化学细节，从而加强我们对这些反应发生机制的了解。

Chemical weathering is of fundamental importance because it is the process by which silicate minerals formed at high-temperatures and pressures are converted to the constituents of sediments and soils. Despite this, the structural and compositional controls on the mechanisms and rates of transformations of many reactions are still poorly understood. This proposal describes two research projects designed to use high-resolution transmission electron microscopy to investigate the microscopic characteristics of weathering reactions where significant structural exists between the parent and product minerals. The first of these involves hydration and oxidation of amphibole-group minerals. The second project focuses on perovskite weathering, where hydrous minerals are not formed and oxidation does not occur. The weathering reactions of a selection of microstructurally complex amphiboles with close to end-member compositions, intergrown and exsolved amphiboles, and amphiboles containing chain-width defects will be examined. Intergrown amphiboles offer the opportunity to compare weathering rates and mechanisms under the same physiochemical conditions and to evaluate the degree to which reactions are focused by coherency strain, defects, and grain boundaries. The Weathering of perovskite will also be examined. Hydrothermal dissolution of perovskite, a possible component of nuclear waste storage ceramics, has been studied extensively, but the natural weathering reactions have been largely ignored. The chemically simple transformation to TiO2 minerals may involve considerable structural inheritance. The aims these projects are to clarify the crystal chemical details of the natural weathering processes, thus enhancing our understanding of the mechanisms by which these reactions occur.