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Title: Time-resolved x-ray diffraction and Raman studies of the phase transition mechanisms of methane hydrate

The mechanisms by which methane hydrate transforms from an sI to sH structure and from an sH to filled-ice Ih structure were examined using time-resolved X-ray diffractometry (XRD) and Raman spectroscopy in conjunction with charge-coupled device camera observation under fixed pressure conditions. The XRD data obtained for the sI–sH transition at 0.8 GPa revealed an inverse correlation between sI and sH, suggesting that the sI structure is replaced by sH. Meanwhile, the Raman analysis demonstrated that although the 12-hedra of sI are retained, the 14-hedra are replaced sequentially by additional 12-hedra, modified 12-hedra, and 20-hedra cages of sH. With the sH to filled-ice Ih transition at 1.8 GPa, both the XRD and Raman data showed that this occurs through a sudden collapse of the sH structure and subsequent release of solid and fluid methane that is gradually incorporated into the filled-ice Ih to complete its structure. This therefore represents a typical reconstructive transition mechanism.
Authors:
;  [1] ; ;  [2] ; ;  [3] ;  [4]
  1. Geodynamics Research Center, Ehime University, Matsuyama, Ehime 790-8577 (Japan)
  2. Japan Association of Synchrotron Radiation Institution, Harima 679-5198 (Japan)
  3. National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8569 (Japan)
  4. National Institute for Material Science, Tsukuba, Ibaraki 305-0044 (Japan)
Publication Date:
OSTI Identifier:
22415848
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 142; Journal Issue: 2; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; CHARGE-COUPLED DEVICES; CORRELATIONS; FLUIDS; GAS HYDRATES; ICE; METHANE; PHASE TRANSFORMATIONS; PRESSURE RANGE GIGA PA; RAMAN SPECTROSCOPY; SOLIDS; TIME RESOLUTION; X-RAY DIFFRACTION