We present a review of a unique non-destructive method for the real-time monitoring of phase transformations and nano-pore evolution in dehydrating rocks: transmission small- and wide-angle synchrotron X-ray scattering (SAXS/WAXS). It is shown how SAXS/WAXS can be applied to investigating rock samples dehydrated in a purpose-built loading cell that allows the coeval application of high temperature, axial confinement, and fluid pressure or flow to the specimen. Because synchrotron sources deliver extremely bright monochromatic X-rays across a wide energy spectrum, they enable the in-situ examination of confined rock samples with thicknesses of ≤ 1 mm at a time resolution of order seconds. Hence, fast kinetics with reaction completion times of about hundreds of seconds can be tracked. With beam sizes of order tens to hundreds of micrometres, it is possible to monitor multiple interrogation points in a sample with a lateral extent of a few centimetres, thus resolving potential lateral spatial effects during dehydration and enlarging sample statistics significantly. Therefore, the SAXS/WAXS method offers the opportunity to acquire data on a striking range of length scales: for rock samples with thicknesses of ≤ 10-3 m and widths of 10-2 m, lateral interrogation-point spacing of ≥ 10-5 m can be achieved. Within each irradiated interrogation-point volume, information concerning pores with sizes between 10-9 to 10-7 m and the crystal lattice on the scale of 10-10 m is acquired in real-time. This article presents a summary of the physical principles underpinning transmission X-ray scattering with the aim to provide a guide for the design and interpretation of time-resolved SAXS/WAXS experiments. It is elucidated [a] when and how SAXS data can be used to analyse total porosity, internal surface area, and pore-size distributions in rocks on length scales from ca. 1 to 300 nm; [b] how WAXS can be employed to track lattice transformations in situ; and [c] which limitations and complicating factors should be considered during experimental design, data analysis, and interpretation. To illustrate the key capabilities of the SAXS/WAXS method, we present a series of dehydration experiments on a well-studied natural gypsum rock: Volterra alabaster. Our results demonstrate that SAXS/WAXS is suited excellently for the in-situ tracking of dehydration kinetics and the associated evolution of nano-pores. The phase transformation from gypsum to bassanite is correlated directly with nano-void growth on length scales between 1 and 11 nm for the first time. A comparison of the SAXS/WAXS kinetic results with literature data emphasises the need for future dehydration experiments on rock specimens because of the impact of rock fabric and the generally heterogeneous and transient nature of dehydration reactions in nature. It is anticipated that the SAXS/WAXS method combined with in-situ loading cells will constitute an invaluable tool on the ongoing quest for understanding dehydration and other mineral replacement reactions in rocks quantitatively.

中文翻译：

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用透射小角和广角同步加速器 X 射线散射实时跟踪变质脱水反应：石膏脱水案例

我们回顾了一种独特的非破坏性方法，用于实时监测脱水岩石中的相变和纳米孔演化：透射小角和广角同步加速器 X 射线散射 (SAXS/WAXS)。展示了如何将 SAXS/WAXS 应用于研究在专用加载单元中脱水的岩石样本，该加载单元允许同时应用高温、轴向限制和流体压力或流向样本。由于同步加速器源可在很宽的能谱范围内提供极其明亮的单色 X 射线，因此它们能够以秒级的时间分辨率对厚度≤ 1 毫米的受限岩石样品进行原位检查。因此，可以跟踪反应完成时间约为数百秒的快速动力学。光束尺寸为数十至数百微米，可以监测横向范围为几厘米的样本中的多个询问点，从而解决脱水过程中潜在的横向空间效应并显着扩大样本统计数据。因此，SAXS/WAXS 方法提供了在惊人的长度范围内获取数据的机会：对于厚度 ≤ 10-3 m、宽度为 10-2 m、横向询问点间距 ≥ 10-5 的岩石样品m 可以实现。在每个受照射的询问点体积内，实时获取有关尺寸在 10-9 至 10-7 m 之间的孔隙和 10-10 m 尺度上的晶格的信息。本文概述了支持透射 X 射线散射的物理原理，旨在为时间分辨 SAXS/WAXS 实验的设计和解释提供指导。阐明了 [a] 何时以及如何使用 SAXS 数据来分析岩石的总孔隙度、内表面积和孔径分布，长度尺度从大约 1至300纳米；[b] 如何使用 WAXS 来原位跟踪晶格变换；[c] 在实验设计、数据分析和解释过程中应考虑哪些限制和复杂因素。为了说明 SAXS/WAXS 方法的关键功能，我们在经过充分研究的天然石膏岩：Volterra alabaster 上进行了一系列脱水实验。我们的结果表明，SAXS/WAXS 非常适合原位跟踪脱水动力学和相关的纳米孔演化。从石膏到贝桑石的相变首次与 1 到 11 nm 之间的长度尺度上的纳米空隙生长直接相关。SAXS/WAXS 动力学结果与文献数据的比较强调了未来对岩石标本进行脱水实验的必要性，因为岩石结构的影响以及自然界中脱水反应的普遍异质性和瞬态性质。预计 SAXS/WAXS 方法与原位加载单元相结合，将成为持续寻求定量了解岩石中的脱水和其他矿物置换反应的宝贵工具。从石膏到贝桑石的相变首次与 1 到 11 nm 长度尺度上的纳米空隙生长直接相关。SAXS/WAXS 动力学结果与文献数据的比较强调了未来对岩石标本进行脱水实验的必要性，因为岩石结构的影响以及自然界中脱水反应的普遍异质性和瞬态性质。预计 SAXS/WAXS 方法与原位加载单元相结合，将成为持续寻求定量了解岩石中的脱水和其他矿物置换反应的宝贵工具。从石膏到贝桑石的相变首次与 1 到 11 nm 长度尺度上的纳米空隙生长直接相关。SAXS/WAXS 动力学结果与文献数据的比较强调了未来对岩石标本进行脱水实验的必要性，因为岩石结构的影响以及自然界中脱水反应的普遍异质性和瞬态性质。预计 SAXS/WAXS 方法与原位加载单元相结合，将成为持续寻求定量了解岩石中的脱水和其他矿物置换反应的宝贵工具。SAXS/WAXS 动力学结果与文献数据的比较强调了未来对岩石标本进行脱水实验的必要性，因为岩石结构的影响以及自然界中脱水反应的普遍异质性和瞬态性质。预计 SAXS/WAXS 方法与原位加载单元相结合，将成为持续寻求定量了解岩石中的脱水和其他矿物置换反应的宝贵工具。SAXS/WAXS 动力学结果与文献数据的比较强调了未来对岩石标本进行脱水实验的必要性，因为岩石结构的影响以及自然界中脱水反应的普遍异质性和瞬态性质。预计 SAXS/WAXS 方法与原位加载单元相结合，将成为持续寻求定量了解岩石中的脱水和其他矿物置换反应的宝贵工具。