In situ monitoring of phase transformation microstructures at Earth's mantle pressure and temperature using multi-grain XRD
In situ monitoring of phase transformation microstructures at Earth's mantle pressure and temperature using multi-grain XRD
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DOI：
10.1107/s1600576715012765
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发表时间：
2015-10-01
影响因子：
6.1
通讯作者：
Merkel, Sebastien
中科院分区：
文献类型：
--
作者：
Rosa, Angelika Dorothea;Hilairet, Nadege;Merkel, Sebastien
显微组织控制着材料的力学性能，并在相变过程中发生剧烈变化。对转变不同阶段的微观结构的详细了解对于新材料的设计和限制地球物理过程很重要。然而，在晶界对相变组织的实验研究大多基于对淬火产物的非原位观察，这很难与块体样品的性质和相变动力学相关联。在这里，展示了多晶样品的多晶结晶学，结合电阻加热的金刚石压腔，可以用来研究在高压和高温下经历原位相变的材料的微结构特性。这种方法允许提取转化样品中数百个颗粒的结晶学参数和取向。在转变的不同阶段，可以监测关于母相和新形成相之间的晶粒度分布和取向关系的重要整体信息。这些数据可以用来解释转变机制(例如，共格生长和非共格生长)、生长速度和单个颗粒的取向相关生长。这一方法在22 GPa940K的含水镁硅酸中心点水中的α-伽马相变上得到了验证。这种相变很可能发生在深部冷俯冲板块中地球上地幔中最丰富的矿物(镁0.8Fe0.2SiO4)中，并对它们的俯冲行为起着重要作用。
Microstructures govern the mechanical properties of materials and change dramatically during phase transformations. A detailed understanding of microstructures at different stages of a transformation is important for the design of new materials and for constraining geophysical processes. However, experimental studies of transformation microstructures at the grain scale have been mostly based on ex situ observations of quenched products, which are difficult to correlate with bulk sample properties and transformation kinetics. Here, it is shown how multi-grain crystallography on polycrystalline samples, combined with a resistively heated diamond anvil cell, can be applied to investigate the microstructural properties of a material undergoing a phase transition in situ at high pressure and high temperature. This approach allows the extraction of the crystallographic parameters and orientations of several hundreds of grains inside a transforming sample. Important bulk information on grain size distributions and orientation relations between the parent and the newly formed phase at the different stages of the transformation can be monitored. These data can be used to elucidate transformation mechanisms (e.g. coherent versus incoherent growth), growth rates and orientation-dependent growth of individual grains. The methodology is demonstrated on the alpha-gamma phase transitions in hydrous Mg2SiO4 center dot H2O up to 22 GPa and 940 K. This transformation most likely occurs in the most abundant mineral of the Earth's upper mantle (Mg0.8Fe0.2SiO4) in deep cold subducted slabs and plays an important role in their subduction behaviour.