Structures of Canonical Clathrate Hydrates

Ripmeester, John A.; Takeya, Satoshi; Alavi, Saman

doi:10.1002/9783527695058.ch5

Cited by 5 publications

(11 citation statements)

References 86 publications

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“…3 shows the symmetries of the T and P cages in the ideally ordered forms. They are 6mm and 6 � m2, respectively, and identical with the predicted true forms (16,17). The whole cage combination of the unit cell is 6D•2T 4 •2T 2 P 2 .…”

Section: Resultssupporting

confidence: 63%

“…1). The major three structures of clathrate hydrates are the cubic structure-I (CS-I), the cubic structure-II (CS-II) and the hexagonal structure-III (HS-III), which only consist of water (13, [16][17]. The CS-I and the CS-II correspond to A15 and C14 of the FK phase, respectively (18), however, the final primitive FK phase, Z, is still absent in the clathrate hydrates while it is predicted as HS-I (see Fig.…”

Section: Introductionmentioning

confidence: 99%

“…The HS-III ( 19) is a truncated form of HS-I of the FK phase. While a total of 27 FK phases have been found in alloys, only five have been found in the clathrate hydrates, i.e., CS-I, CS-II, HS-III, TS-I and TrS-I (17). This means that the art of periodically arranging only tens to hundreds of water has not yet been established.…”

Section: Introductionmentioning

confidence: 99%

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Discovery of the final primitive Frank-Kasper phase of clathrate hydrates

Muromachi,

Takeya

2024

Preprint

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In weakly bound materials such as water, one of the three primitive Frank-Kasper (FK) phases, the Z phase, is long absent due to the relatively unstable framework. The Z phase in clathrate hydrate, which is known as the HS-I structure, has now been discovered by precise tuning of the molecular guest structure. In the crystal structure, the never stabilized combination water cage of two 15-hedra and two 14-hedra formed with its original symmetries, providing sufficient gas capacity to the 12-hedral cages. With the discovery of the final FK clathrate hydrate, guest design now enables engineering of weak interactions in any mix of the three, illuminating how to leverage properties of clathrates in the broadest sense.

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Section: Resultssupporting

confidence: 63%

Section: Introductionmentioning

confidence: 99%

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Discovery of the final primitive Frank-Kasper phase of clathrate hydrates

Muromachi,

Takeya

2024

Preprint

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“…Gas hydrates are ice-like inclusion compounds, in which guest molecules are encapsulated inside hydrogen-bonded water cages. 1 Specifically, naturally occurring gas hydrates primarily composed of methane (CH 4 ) are called CH 4 hydrates, and they could represent a substantial global natural gas resource. 2,3 Preliminary estimates are underway to determine the total global recoverable resource volume of CH 4 hydrates from sea-bottom sediments, and field tests have been conducted for natural gas production from CH 4 hydrates.…”

Section: Introductionmentioning

confidence: 99%

Multi-phase retrieval of methane hydrate in natural sediments by cryogenic x-ray computed tomography

Takeya,

Hachikubo,

Sakagami

et al. 2024

The Journal of Chemical Physics

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In this study, we observed natural methane (CH4) hydrate sediments, which are a type of unconventional natural gas resources, using x-ray computed tomography (CT). Because CH4 hydrates are formed by hydrogen bonding of water molecules with CH4, material decomposition becomes challenging when CH4 hydrates coexist with liquid or solid water in natural sediments. Tri-contrast (absorption, refraction, and scattering) imaging was performed via diffraction enhanced x-ray CT optics using monochromatic synchrotron x rays. The quantitative characterization of the contrast changes successfully enabled the decomposition of CH4 hydrates coexisting with frozen seawater (ice) in natural sediments obtained from the Okhotsk Sea. This study reveals complementary structural information about the microtexture and spatial relation among CH4 hydrates, ice, and pores by utilizing the distinct physical properties of x rays when passing through the materials. These results highlight the exceptional capabilities of high-resolution multicontrast x-ray tomography in materials science and geoscience applications.

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“…For gas hydrates, there are three types of crystal structures mainly depending on the van der Waals radius of the guest species . For the CO hydrate, the cubic structure I (sI), which belongs to space group Pm 3̅ n comprising 46 water molecules, kinetically forms two small 5 12 cages and six large 5 12 6 2 cages.…”

Section: Introductionmentioning

confidence: 99%

Dissociation Kinetics and Metastability of Carbon Monoxide Hydrates Correlating with Phase Change in Water Ice

2022

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The crystallographic structure of the thermodynamically unstable structure I carbon monoxide (CO) hydrate and its dissociation kinetics were investigated by powder X-ray diffraction and calorimetry. The dissociation of the binary gas hydrates of CO and CH4, CO2, N2, or Ar as secondary guests was also investigated. Here, we observed that the phase transition of ice (amorphous, cubic, and hexagonal ice) formed by CO hydrate dissociation plays a role in the kinetic stability and metastability of the hydrate. Among these gas hydrates, CO + CH4 and CO + CO2 hydrates were preserved at temperatures just below 273 K, which is the self-preservation phenomenon. These results contribute to a comprehensive understanding of the dissociation mechanism of gas hydrates below the melting point of ice, which is crucial for understanding the kinetic stability of naturally occurring gas hydrates in the universe, as well as gas storage by gas hydrates under thermodynamically metastable conditions.

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Structures of Canonical Clathrate Hydrates

Cited by 5 publications

References 86 publications

Discovery of the final primitive Frank-Kasper phase of clathrate hydrates

Discovery of the final primitive Frank-Kasper phase of clathrate hydrates

Multi-phase retrieval of methane hydrate in natural sediments by cryogenic x-ray computed tomography

Dissociation Kinetics and Metastability of Carbon Monoxide Hydrates Correlating with Phase Change in Water Ice

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