Microstructure characteristics during hydrate formation and dissociation revealed by X-ray tomographic microscopy
Microstructure characteristics during hydrate formation and dissociation revealed by X-ray tomographic microscopy
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DOI：
10.1007/s00367-012-0276-0
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发表时间：
2012-12-01
影响因子：
2.1
通讯作者：
Brewer, Peter G.
中科院分区：
文献类型：
--
作者：
Klapp, Stephan A.;Enzmann, Frieder;Brewer, Peter G.
尽管过去几年在基础天然气水合物研究方面取得了很大进展，但未知的前沿是天然气水合物在自然海底环境中的早期开始和早期分解：气泡与海水相遇并形成水合物，以及气体开始从水合物颗粒表面逸出。在本文中，我们报告了这两个主题，并展示了通过同步辐射 X 射线冷冻断层显微术 (SRXCTM) 获得的三维微观结构结果。当水合物形成分子（例如甲烷）超过溶解度时，水合物会沉淀，并在天然气水合物稳定区内与水结合。在这里，我们基于加利福尼亚州近海蒙特利峡谷深处的水下机器人原位实验，展示了不同气体混合物和海水的气泡表面形成水合物。气泡表面周围的水开始形成水合物，随后向气泡内生长，其边缘明显。随着时间的推移，气泡变得更小，同时气体被纳入新形成的水合物中。相比之下，目前的理解是水合物分解从水合物聚集体和颗粒的外表面开始。结果表明，在分解的早期阶段，新发现的管结构将保存完好的天然气水合物斑块连接到正在解离的区域，这表明水合物颗粒中的解离区域如何通过仍然完整且可能在后期分解的水合物连接起来。
Despite much progress over the past years in fundamental gas hydrate research, frontiers to the unknown are the early beginning and early decomposition of gas hydrates in their natural, submarine environment: gas bubbles meeting ocean water and forming hydrate, and gas starting to escape from the surface of a hydrate grain. In this paper we report on both of these topics, and present three-dimensional microstructure results obtained by synchrotron radiation X-ray cryo-tomographic microscopy (SRXCTM). Hydrates can precipitate when hydrate-forming molecules such as methane exceed solubility, and combine with water within the gas hydrate stability zone. Here we show hydrate formation on surfaces of bubbles from different gas mixtures and seawater, based on underwater robotic in situ experiments in the deep Monterey Canyon, offshore California. Hydrate begins to form from the surrounding water on the bubble surfaces, and subsequently grows inward into the bubble, evidenced by distinct edges. Over time, the bubbles become smaller while gas is being incorporated into newly formed hydrate. In contrast, current understanding has been that hydrate decomposition starts on the outer surface of hydrate aggregates and grains. It is shown that in an early stage of decomposition, newly found tube structures connect well-preserved gas hydrate patches to areas that are dissociating, demonstrating how dissociating areas in a hydrate grain are linked through hydrate that is still intact and will likely decompose at a later stage.