Observation of Xe Hydrate Growth at Gas-Ice Interface by Microfocus X-ray Computed Tomography

The growth of Xe clathrate hydrate in a Xe-ice system was observed in situ by microfocus X-ray computed tomography (CT). In the initial stage of pressurization with Xe gas, quasi-two-dimensional hydrate growth on the ice surface was observed at the Xe-ice interface. With time, Xe hydrate grain grew not only along the ice surface (cover growth), but also toward the gas phase (outer growth), and inside the ice phase (inner growth). A lens-shaped Xe hydrate was formed at the initial interface between the gas phase and ice. Anisotropic hydrate growth resulted in a lens-shaped Xe hydrate. Xe hydrate growth at the gas-ice interface is strongly influenced by the supply of H2O molecules. The inner growth in the lens-shaped Xe hydrate changed in shape from spherical to elliptical. Variations in the contrast in cross-sectional CT images show that the inside of the Xe hydrate region became condensed as time elapsed. Inner growth would result from the formation of a condensed hydrate region, which may lead to a change in the Xe gas supply through the hydrate layer. Observations of Xe hydrate growth by microfocus X-ray CT can be applied to a discussion of the hydrate growth process in a gas-ice system.