Transformations in Methane Hydrates

Detailed study of pure methane hydrate in a diamond cell with in situ optical, Raman, and x-ray microprobe techniques reveals two previously unknown structures, structure II and structure H, at high pressures. The structure II methane hydrate at 250 MPa has a cubic unit cell of a = 17.158(2) Å and v...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2000-12, Vol.97 (25), p.13484-13487
Main Authors: Chou, I M, Sharma, A, Burruss, R C, Shu, J, Mao, H, Hemley, R J, Goncharov, A F, Stern, L A, Kirby, S H
Format: Article
Language:English
Subjects:
Chemistry
Crystals
Hydrates
Ice
Isochores
Marine
Methane
Molecules
Physical Sciences
Sediments
Single crystals
Water pressure
Wave diffraction
X ray diffraction
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Summary:Detailed study of pure methane hydrate in a diamond cell with in situ optical, Raman, and x-ray microprobe techniques reveals two previously unknown structures, structure II and structure H, at high pressures. The structure II methane hydrate at 250 MPa has a cubic unit cell of a = 17.158(2) Å and volume V = 5051.3(13) Å3; structure H at 600 MPa has a hexagonal unit cell of a = 11.980(2) Å, c = 9.992(3) Å, and V = 1241.9(5) Å3. The compositions of these two investigated phases are still not known. With the effects of pressure and the presence of other gases in the structure, the structure II phase is likely to dominate over the known structure I methane hydrate within deep hydrate-bearing sediments underlying continental margins.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.250466497