Gas hydrates at high pressure

The behaviour of gas hydrates at high pressure is of wide interest and importance. Gas hydrates are stablised by water-gas repulsive interactions. Information on the effect of changing density on these water-gas interactions provides fundamental insight into the nature of the water potential. Gas hydrates are also widely found in nature and systems like the ammonia-water and methane-water systems form the basis of 'mineralogy' of planetary bodies like Saturn's moon Titan. Finally, gas hydrates offer the possibility of cheap environmentally inert transportation and storage for gases like carbon dioxide and hydrogen. We have been carrying out investigations of a range of gas hydrates at high pressure using neutron and x-ray diffraction as well as other techniques. Results from these studies including; the phase diagram of the ammonia water system, the occupancies of hexgonal clathrate structures, and new structures in the carbon dioxide water system, will be presented.

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High-pressure / High-temperature Behavior of the Methane-Ammonia- Water System up to 3 GPa

Zeitschrift für Naturforschung B ◽

10.1515/znb-2006-1215 ◽

2006 ◽

Vol 61 (12) ◽

pp. 1573-1576 ◽

Cited By ~ 13

Author(s):

Alexander Kurnosov ◽

Leonid Dubrovinsky ◽

Alexei Kuznetsov ◽

Vladimir Dmitriev

Keyword(s):

High Pressure ◽

Melting Temperature ◽

Water System ◽

Hydrate Formation ◽

Clathrate Hydrates ◽

Ammonia Water ◽

High Pressure High Temperature ◽

In Situ Experiments ◽

Diamond Anvil ◽

Methane Clathrate

Melting phase relations in the methane-ammonia-water system up to 3 GPa have been obtained in a series of in situ experiments in externally heated diamond anvil cells. The melting temperature of methane clathrate hydrates increases rapidly above pressures of ~ 1.5 GPa, and does not appear to be significantly affected by the presence of ammonia. The reaction of the hydrate formation at pressures 2 - 3 GPa is kinetically impeded. Our data show that the high-pressure methane hydrate has the maximum melting temperature among the clathrate hydrates studied so far.

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High pressure synthesis of phosphine from the elements and the discovery of the missing (PH3)2H2 tile

Nature Communications ◽

10.1038/s41467-020-19745-2 ◽

2020 ◽

Vol 11 (1) ◽

Author(s):

Matteo Ceppatelli ◽

Demetrio Scelta ◽

Manuel Serrano-Ruiz ◽

Kamil Dziubek ◽

Gaston Garbarino ◽

...

Keyword(s):

High Pressure ◽

Materials Science ◽

Metallic Elements ◽

X Ray Diffraction ◽

Energy Conversion And Storage ◽

Diamond Anvil ◽

Bond Theory ◽

Pressure Synthesis ◽

And Storage ◽

Significant Chemical

AbstractHigh pressure reactivity of phosphorus and hydrogen is relevant to fundamental chemistry, energy conversion and storage, and materials science. Here we report the synthesis of (PH3)2H2, a crystalline van der Waals (vdW) compound (I4cm) made of PH3 and H2 molecules, in a Diamond Anvil Cell by direct catalyst-free high pressure (1.2 GPa) and high temperature (T ≲ 1000 K) chemical reaction of black phosphorus and liquid hydrogen, followed by room T compression above 3.5 GPa. Group 15 elements were previously not known to form H2-containing vdW compounds of their molecular hydrides. The observation of (PH3)2H2, identified by synchrotron X-ray diffraction and vibrational spectroscopy (FTIR, Raman), therefore represents the discovery of a previously missing tile, specifically corresponding to P for pnictogens, in the ability of non-metallic elements to form such compounds. Significant chemical implications encompass reactivity of the elements under extreme conditions, with the observation of the P analogue of the Haber-Bosch reaction for N, fundamental bond theory, and predicted high pressure superconductivity in P-H systems.

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