Understanding the Role of Clay Mineral Surface Interactions in Pressure Solution

这项建议结合了地质学、材料学和胶体科学三个学科，在露头、显微、亚显微和分子水平上研究微米矿物表面的相互作用。这项工作的动机是地质学和最近对石英-粘土矿物界面上的石英溶解和云母解理上碳酸盐晶体生长的实验室观察(在这里描述)。使用先进的表面力测量仪器进行的初步实验研究使我们能够测量埃级云母表面之间的短程静电、水合作用和其他力，以及离子进入云母-流体-云母界面的扩散速率，以获得与自然地质条件相当的流体成分和压力。结果表明，扩散速率对流体成分(钠和钙)很敏感。它们还暗示，离子的扩散可能不是薄层流体内传质的速率限制步骤，这是为了解释与粘土矿物有关的增强石英压力溶液的原因。相反，限速步骤似乎是离子与矿物表面的反应(结合和交换)。初步结果表明，云母对压在其上的石英表面在含有电解液的水中的溶解有很强的影响，这在对称的云母-云母或二氧化硅-二氧化硅系统中是观察不到的。我们测量了石英表面的退缩(溶解)速率高达1,500A/天(1A/分钟)。该项目的智能优点很大程度上归功于使用表面力仪器(SFA)直接测量表面相互作用、表面溶解、离子传输、结合和交换速率以及在各种水盐溶液中的晶体生长。SFA已被证明是量化动态和动力学过程的一种新颖而准确的方法。这是第一次进行模拟地质现象的实验，为地球科学中的各种关键问题提供答案。事实上，可以直接观察到碳酸盐晶体在云母解理之间的优先生长，并类似于自然发生的情况，这是令人惊讶的，反映了未来工作的重要性。关于黑云母-黑云母和石英-云母系统的实验将继续进行，并阐明与压力溶解有关的过程。天然材料和实验材料的表面将通过扫描电子显微镜、原子力显微镜、微探针、X射线光电子能谱(XPS)和二次离子质谱仪(SIMS)进行分析。我们的实验条件将以代表广泛地质时代、流体成分和温度-压力条件的地质样品为指导，并将结果与之进行比较。预测这些和其他类型的相互作用的理论基础目前尚不清楚。然而，这项工作将包括由尤兹·兰德曼教授(佐治亚理工学院)和西德尼·叶教授(麻省理工学院)对我们的发现进行理论分析，他们是电化学反应和表面腐蚀的计算机模拟(建模)领域的专家。这项研究的更广泛影响包括对不同矿物密切接触时矿物-流体-矿物相互作用的基本理解。在地质科学中的应用包括解释粘土矿物和电解质离子在石英加压溶解/沉淀中的作用。在材料科学等其他领域，这项工作与腐蚀、复合材料和水基陶瓷材料的“胶体加工”、生物矿化和混合胶体颗粒分散有关。拟议的研究计划为进入不同领域的学生提供了一个理想的教育平台，例如提高地质学学生对材料和表面科学的兴趣，以及提高材料和工程专业学生对地球科学在实验室、实地考察和理论层面的兴趣。此外，一名西班牙裔女性将直接参与这一项目，因为她已经接受了使用SFA、XPS、AFM和SEM对矿物表面进行详细表征的培训。由于这项提案的广泛兴趣，该项目将支持学生参加地球化学和材料方面的会议。该项目将包括与华盛顿史密森博物馆的直接交流，因为我们的结果与展出的样本有关；他们还为这里提出的研究提供了黑云母样本。

ABSTRACTThis proposal combines three disciplines - geology, materials and colloidal science - to study micamineral surface interactions at the outcrop, microscopic, submicroscopic, and molecular levels. This work is motivated by geologic and very recent laboratory observations (described here) on quartz dissolution at quartz-clay minerals interfaces and on growth of carbonate crystals on mica cleavages. Initial experimental investigations using advanced surface force-measuring instruments have allowed us to measure the short-range electrostatic, 'hydration' and other forces between mica surfaces at the angstrom level, and the diffusion rates of ions into the mica-fluid-mica interfaces for fluid compositions and pressures comparable to natural geological conditions. The results show that the diffusion rate is sensitive to fluid composition (for sodium and calcium). They also imply that diffusion of ions is probably not the rate limiting step in mass transfer within thin fluid films, as has been proposed to explain enhanced quartz pressure solution when associated with clay minerals. Rather, the rate-limiting step appears to be the reaction (binding and exchange) of ions with the mineral surface. Preliminary results show a strong effect of mica on the dissolution of a quartz surface pressured against it in water containing electrolyte, which is not observed in symmetrical mica-mica or silica-silica systems. We have measured retreat (dissolution) of the quartz surface at rates up to 1,500A per day (1A/min).The intellectual merit of this project is largely due to the use of the Surface Forces Apparatus (SFA) to directly measure surface interactions, surface dissolution, ionic transport, binding and exchange rates, and crystal growth in various aqueous salt solutions. The SFA has proved to be a novel and accurate way to quantify dynamic and kinetic processes. This is the first time that experiments have been performed to mimic geologic phenomena providing answers for various crucial questions in earth sciences. The fact that the preferential growth of carbonate crystals between the mica cleavages could be directly observed, and to be analogous to natural occurrences, is amazing and reflects the importance for future work. Experiments involving biotite-biotite and quartz-mica systems will continue and elucidate the processes related to pressure solution. Surfaces of natural and experimental materials will be analyzed by SEM, AFM, microprobe, X-ray photoelectron spectroscopy (XPS) and Secondary Ion Mass Spectroscopy (SIMS). Our experimental conditions will be guided by and the results compared with geologic samples representing a wide range of geologic age, fluid composition and temperature-pressure conditions. The theoretical basis for predicting these and other type of interactions are at present unknown. However, this work will include theoretical analysis of our findings by Prof. Uzi Landman (Georgia Tech) and Prof. Sidney Yip (MIT), who are experts in the area of computer simulations (modeling) of electrochemical reactions and corrosion of surfaces.The broader impact of this research comprises basic understanding of mineral-fluid-mineral interactions when dissimilar minerals are in close contact. Applications in geological sciences include explaining the role of clay minerals and electrolyte ions in pressure solution/precipitation of quartz. In other fields such as material science the work is relevant to corrosion, the 'colloidal processing' of composites and water-based ceramic materials, biomineralization and mixed colloidal particle dispersions. The proposed research plan provides an ideal educational platform for students entering diverse fields, for instance, increasing the interest of geology students in the material and surface sciences, and of materials and engineering students in earth sciences at the laboratory, fieldwork and theoretical levels. Additionally, a female Hispanic will be directly involved in this project since she has been trained to perform detail characterization of mineral surfaces using the SFA, XPS, AFM and SEM. This project will support student participation at meetings both in geochemistry and materials owing to the broad interest of this proposal. This project will include direct communication with the Smithsonian museum in Washington since our results are related to samples on display; they have also provided biotite samples for the studies proposed here.