Raman spectroscopic investigations on natural samples from the Integrated Ocean Drilling Program (IODP) Expedition 311: Indications for heterogeneous compositions in hydrate crystals

Natural gas hydrates usually are found in the form of structure I, encasing predominantly methane in the hydrate lattices as guest molecules, sometimes also minor amount of higher hydrocarbons, CO 2 or H 2S. Raman spectroscopy is an approved tool to determine the composition of the hydrate phase. Th...

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Bibliographic Details
Published in:Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy Molecular and biomolecular spectroscopy, 2010-12, Vol.77 (5), p.973-977
Main Authors: Schicks, J.M., Ziemann, M.A., Lu, H., Ripmeester, J.A.
Format: Article
Language:English
Subjects:
Cascadia margin
Gas hydrates
IODP Expedition 311
Raman mapping
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Summary:Natural gas hydrates usually are found in the form of structure I, encasing predominantly methane in the hydrate lattices as guest molecules, sometimes also minor amount of higher hydrocarbons, CO 2 or H 2S. Raman spectroscopy is an approved tool to determine the composition of the hydrate phase. Thus, in this study Raman spectroscopic analyses have been applied to hydrate samples obtained from Integrated Ocean Drilling Program (IODP) Expedition 311 in two different approaches: studying the samples randomly taken from the hydrate core, and – as a new application – mapping small areas on the surface of clear hydrate crystals. The results obtained imply that the gas composition of hydrate, in terms of relative concentrations of CH 4 and H 2S, is not homogeneous over a core or even within a crystal. The mapping method yielded results with very high lateral resolution, indicating the coexistence of different phases with the same structure but different compositions within a hydrate crystal.
ISSN:1386-1425
DOI:10.1016/j.saa.2010.08.033