Abstract
Clathrate hydrates are inclusion compounds in which guest molecules are trapped in a host lattice formed by water molecules. They are considered an interesting option for future energy supply and storage technologies. In the current paper, time lapse 3D micro computed tomographic (µCT) imaging with ice and tetrahydrofuran (THF) clathrate hydrate particles is carried out in conjunction with an accurate temperature control and pressure monitoring. µCT imaging reveals similar behavior of the ice and the THF clathrate hydrate at low temperatures while at higher temperatures (3 K below the melting point), significant differences can be observed. Strong indications for micropores are found in the ice as well as the THF clathrate hydrate. They are stable in the ice while unstable in the clathrate hydrate at temperatures slightly below the melting point. Significant transformations in surface and bulk structure can be observed within the full temperature range investigated in both the ice and the THF clathrate hydrate. Additionally, our results point towards an uptake of molecular nitrogen in the THF clathrate hydrate at ambient pressures and temperatures from 230 K to 271 K.
Highlights
Ice has been ubiquitous in colder climates worldwide and, since the advent of refrigeration, even in warmer regions [1,2]
The performance of a custom-built pressure monitored cooling stage is assessed in four experiments using nitrogen, water-ice, THF clathrate, and 1,3-dioxolane clathrate, respectively
In the first set of experiments we demonstrate that pressure and voltage signals provide critical information about the state of the sample and phase-change events
Summary
Ice has been ubiquitous in colder climates worldwide and, since the advent of refrigeration, even in warmer regions [1,2]. Apart from ices made of pure H2 O, ice-like solids containing guest molecules are seen in astrophysical environments, e.g., in cometary ice upon warming [9,10], in the mantle of icy moons [11,12,13] or on the Mars pole caps [14,15,16]. These ice-like solids are clathrate hydrates (CHs), sometimes called gas hydrates or clathrates in short.
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