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.

根据这项赠款开展的研究旨在加强对晶体固体中晶界的化学和物理的了解，特别是对代表地球上地幔的硅酸盐材料中的晶界的了解。典型的晶体固体由无数的晶体(颗粒)组成，通常具有随机的空间取向，跨越带状的二维边界粘合在一起。这些边界具有特定的结构和化学成分，与两侧的颗粒在根本上不同；边界经常控制固体的整体物理性质，例如强度、粘度、电性和离子传导性、光学透过率等。在地球和行星科学中，社区的兴趣反映了这些性质的广度，尽管特别是机械和电化学的：同一矿物的颗粒之间的边界，不同矿物的颗粒之间的边界(相界)以及矿物和熔体之间的边界直接影响以下现象：(I)地幔变形的速度(影响板块构造)，(Ii)地震波能量的衰减，以及(Iii)岩浆的化学成分(特别是微量元素，这有助于了解地球上的熔融和岩浆迁移过程)。在这一具体研究中，突出的是一种新的和令人兴奋的分析技术在研究晶界和相界结构和化学方面的应用：原子探针层析成像(APT)。如果在样品准备和数据分析方面给予适当的注意，APT可以在非常原子的尺度上表征边界化学，从而能够提出和仔细研究关于材料动力学的精确问题。这种方法的一个好处是，人们可以这样学习机械和化学反应的物理尺度，从亚纳米到千米以上的维度。这项研究对经济和劳动力发展都有影响。离子和共价键合固体(如矿物)中的晶界和相界结构和化学是电池/燃料电池、光伏和结构应用的先进陶瓷开发中的主要问题。将APT用于颗粒/相界的化学设计是本文所支持的研究的直接延伸。“有效方式”的警告与APT方法的进步(标本准备、成像条件、数据分析)密切相关：这些必要的进步将构成项目参与者积累和公布的教育的不小部分。重点研究了(A)上地幔化学/矿物学变形岩石(橄榄石+辉石)和(B)橄榄石晶界界面(S)与寄主岩浆的颗粒和相界结构与化学。前者的重点是考察在扩散蠕变-颗粒/相界滑动中(实验上)变形的地幔集合体。表征偏应力的空间取向对边界结构和化学的影响可以解释地幔塑性不稳定的物理方面--这是建立和维持板块构造的关键问题。后者的重点是解决玄武岩岩浆结晶中的问题，以及晶界在(I)储存不相容的微量元素以及(Ii)影响/影响部分结晶的大型岩浆体的动员中可能发挥的作用。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。