Grain and Phase Boundaries in Mantle Assemblages: Atom Probe and Electron Microscopy/Diffraction Approaches

地幔组合中的晶粒和相边界：原子探针和电子显微镜/衍射方法

• 批准号: 1947439
• 负责人: Reid Cooper
• 金额: $ 51.45万
• 依托单位: Brown University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-04-01 至 2025-03-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1947439&HistoricalAwards=false
• 关键词: Grain; Phase; Boundaries; Mantle; Assemblages

The research pursued under this grant seeks to enhance understanding of the chemistry and physics of grain boundaries in crystalline solids, with particular emphasis on boundaries in silicate materials representative of the upper mantle of the Earth. Typical crystalline solids consist of myriad crystals (grains), frequently having random spatial orientation, bonded together across ribbon-like, two-dimensional boundaries. These boundaries have specific structure and chemistry, different in fundamental ways from the grains on either side; the boundaries frequently control the physical properties of the solid overall, e.g., strength, viscosity, electrical and ionic conductivity, optical transmittance, etc. In Earth and planetary science, the community’s interests reflect the breadth of these properties, although particularly the mechanical and electrochemical ones: boundaries between grains of the same mineral, boundaries between grains of different minerals (phase boundaries) and boundaries between minerals and melts affect directly phenomena such as (i) the rate of mantle deformation (which effects plate tectonics), (ii) the attenuation of seismic wave energy, and (iii) the chemical composition of magmas (particularly of trace elements, which facilitates understanding of melting and magma-migration processes in the Earth). Prominent in this specific research is the application of a new and exciting analytical technique to the study of grain- and phase-boundary structure and chemistry: atom probe tomography (APT). With appropriate care in specimen preparation and data analysis, APT can characterize boundary chemistry at the very atomic scale, allowing precise questions concerning materials dynamics to be posed and scrutinized. A beauty of the approach is that one can so learn the physics of scaling of mechanical and chemical responses from the sub-nanometer to the kilometer-plus dimensions. The research has implications both economic and in workforce development. Grain- and phase-boundary structure and chemistry in ionic and covalent-bonded solids (as are minerals) is a primary concern in the development of advanced ceramics for battery/fuel cell, photovoltaic, and structural applications. Employing APT in an effective way for the chemical design of grain/phase boundaries is a direct extension of the research supported here. The “effective way” caveat has everything to do with advances in APT approach (specimen preparation, imaging conditions, data analysis): these necessary advances will constitute no small part of the education accumulated—and promulgated—by the program participants. The research specifically focuses on grain and phase boundary structure and chemistry in (a) deformed rock of upper-mantle chemistry/mineralogy (olivine plus pyroxenes) and (b) olivine grain boundary interface(s) with a host magma. The former focus examines mantle aggregates deformed (experimentally) in diffusion creep–grain/phase boundary sliding. Characterizing the impact of the spatial orientation of deviatoric stress on boundary structure and chemistry can elucidate aspects of the physics of plastic instability in the mantle—a crucial issue in creating and sustaining plate tectonics. The latter focus addresses issues in the crystallization of basaltic magma and the role grain boundaries might play in (i) storing incompatible trace elements as well as (ii) affecting/effecting the mobilization of large magma bodies that are partially crystallized.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

该赠款下的研究旨在增强对晶体固体中晶界的化学和物理的理解，特别强调代表地球上层地幔的有机硅材料的边界。典型的晶体固体由众多晶体（晶粒）组成，通常具有随机的空间取向，并在带状的二维边界上粘合在一起。这些边界具有特定的结构和化学反应，其基本方式不同于两侧的谷物。边界经常控制固体总体的物理特性，例如强度，粘度，电气和离子电导率，光传递性，光学传播等，在地球和行星科学中，社区的兴趣反映了这些特性的宽度，尽管机械和电化学的范围：尤其是机械和电化学的界限：在同一矿物质之间的边界以及不同矿物质之间的边界之间的界限（阶段），而不是在不同的矿物质之间（相同矿物）之间的边界（阶段）之间的粒度（阶段）之间的边界（ （i）地幔变形速率（影响板块构造），（ii）地震波能的衰减以及（iii）岩浆的化学组成（部分意义上的痕量元素，设施理解融化和地球上的岩浆移动过程）等现象。在这项特定研究中，重要的是将一种新的令人兴奋的分析技术应用于晶粒和相结合结构和化学研究：原子探针断层扫描（APT）。通过在标本制备和数据分析中进行适当的护理，APT可以在非常原子的尺度上表征边界化学，从而可以将有关材料动力学的精确问题定位和审查。该方法的一种美是，可以学习从亚纳米到千分尺度的机械和化学反应的缩放物理学物理学。这项研究在经济和劳动力发展方面都具有含义。离子和共价固体固体（以及矿物质）中的晶粒和相结合结构以及化学是在开发用于电池/燃料电池，光伏和结构应用的晚期陶瓷的主要关注点。以有效的方式采用APT进行谷物/相边界的化学设计是此处支持的研究的直接扩展。 “有效的方法”警告与APT方法的进步有关（标本准备，成像条件，数据分析）：这些必要的进步将不大的构成计划参与者所获得的教育和颁布的教育。该研究专门针对（a）上层化学/矿物学（橄榄石加辉石）和（b）带有宿主岩浆的（b）橄榄石晶界边界界面的（olivine Plus pyroxenes）和（b）橄榄石晶界的变形岩石中的晶粒和相边界结构和化学。前焦点检查地幔聚集体在扩散蠕变/相边界滑动中变形（实验性）。表征偏压应力对边界结构和化学的空间取向的影响可以阐明地幔中塑性不稳定性物理的各个方面，这是创建和维持板块构造的关键问题。后来的重点解决了基底岩浆结晶中的问题以及晶粒边界可能在（i）存储不兼容的微量元素以及（ii）影响/影响动员大型岩浆体的（部分结晶的大型岩浆体）中所扮演的问题。该奖项反映了NSF的法定任务，并通过评估范围来诚实地对其进行评估，并通过评估范围进行了评估。