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Title: The structure of CO 2 hydrate between 0.7 and 1.0 GPa

A deuterated sample of CO 2 structure I (sI) clathrate hydrate (CO 2 ∙ 8.3 D 2O) has been formed and neutron diffraction experiments up to 1.0 GPa at 240 K were performed. The sI CO 2 hydrate transformed at 0.7 GPa into the high pressure phase that had been observed previously by Hirai, et al. (J. Phys. Chem. 133, 124511 (2010)) and O. Bollengier et al. (Geochim. Cosmochim. AC. 119, 322 (2013)), but which had not been structurally identified. The current neutron diffraction data were successfully fitted to a filled ice structure with CO 2 molecules filling the water channels. This CO 2+water system has also been investigated using classical molecular dynamics and density functional ab initio methods to provide additional characterization of the high pressure structure. Both models indicate the water network adapts an MH-III ‘like’ filled ice structure with considerable disorder of the orientations of the CO 2molecule. Furthermore, the disorder appears be a direct result of the level of proton disorder in the water network. In contrast to the conclusions of Bollengier et al. our neutron diffraction data shows that the filled ice phase can be recovered to ambient pressure (0.1 MPa) at 96 K, andmore » recrystallization to sI hydrate occurs upon subsequent heating to 150 K, possibly by first forming low density amorphous ice. Unlike other clathrate hydrate systems, which transform from the sI or sII structure to the hexagonal structure (sH) then to the filled ice structure, CO 2 hydrate transforms directly from the sI form to the filled ice structure.« less
Authors:
 [1] ;  [2] ;  [3] ;  [3] ;  [4] ;  [1]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Neutron Scattering Science Division
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Neutron Scattering Science Division; Carnegie Inst. of Washington, Washington, DC (United States). Geophysical Lab.
  3. National Research Council of Canada (NRC), Ottawa, ON (Canada)
  4. Carnegie Inst. of Washington, Washington, DC (United States). Geophysical Lab.
Publication Date:
Grant/Contract Number:
AC05-00OR22725; SC0001057
Type:
Accepted Manuscript
Journal Name:
Journal of Chemical Physics
Additional Journal Information:
Journal Volume: 141; Journal Issue: 17; Journal ID: ISSN 0021-9606
Publisher:
American Institute of Physics (AIP)
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source (SNS)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
OSTI Identifier:
1286804
Alternate Identifier(s):
OSTI ID: 1224280