Scanning Electron Microscopy investigations of laboratory-grown gas clathrate hydrates formed from melting ice, and comparison to natural hydrates
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Laura A. Stern
,
Stephen H. Kirby
Abstract
Scanning electron microscopy (SEM) was used to investigate grain texture and pore structure development within various compositions of pure sI and sII gas hydrates synthesized in the laboratory, as well as in natural samples retrieved from marine (Gulf of Mexico) and permafrost (NW Canada) settings. Several samples of methane hydrate were also quenched after various extents of partial reaction for assessment of mid-synthesis textural progression. All laboratory-synthesized hydrates were grown under relatively high-temperature and high-pressure conditions from rounded ice grains with geometrically simple pore shapes, yet all resulting samples displayed extensive recrystallization with complex pore geometry. Growth fronts of mesoporous methane hydrate advancing into dense ice reactant were prevalent in those samples quenched after limited reaction below and at the ice point. As temperatures transgress the ice point, grain surfaces continue to develop a discrete “rind” of hydrate, typically 5 to 30 μm thick. The cores then commonly melt, with rind microfracturing allowing migration of the melt to adjacent grain boundaries where it also forms hydrate. As the reaction continues under progressively warmer conditions, the hydrate product anneals to form dense and relatively pore-free regions of hydrate grains, in which grain size is typically several tens of micrometers. The prevalence of hollow, spheroidal shells of hydrate, coupled with extensive redistribution of reactant and product phases throughout reaction, implies that a diffusion-controlled shrinking-core model is an inappropriate description of sustained hydrate growth from melting ice. Completion of reaction at peak synthesis conditions then produces exceptional faceting and euhedral crystal growth along exposed pore walls. Further recrystallization or regrowth can then accompany even short-term exposure of synthetic hydrates to natural ocean-floor conditions, such that the final textures may closely mimic those observed in natural samples of marine origin. Of particular note, both the mesoporous and highly faceted textures seen at different stages during synthetic hydrate growth were notably absent from all examined hydrates recovered from a natural marine-environment setting.
© 2015 by Walter de Gruyter Berlin/Boston
Articles in the same Issue
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Articles in the same Issue
- Introductory overview: Hydrate knowledge development
- Scanning Electron Microscopy investigations of laboratory-grown gas clathrate hydrates formed from melting ice, and comparison to natural hydrates
- Dynamics of trimethylene oxide in a structure II clathrate hydrate
- The stability of methane hydrates in highly concentrated electrolyte solutions by differential scanning calorimetry and theoretical computation
- The effect of elevated methane pressure on methane hydrate dissociation
- Methane hydrate formation in partially water-saturated Ottawa sand
- Methanol—inhibitor or promoter of the formation of gas hydrates from deuterated ice?
- Investigating the performance of clathrate hydrate inhibitors using in situ Raman spectroscopy and differential scanning calorimetry
- Physical properties and rock physics models of sediment containing natural and laboratory-formed methane gas hydrate
- Experimental studies on the formation of porous gas hydrates
- Investigation of jet breakup and droplet size distribution of liquid CO2and water systems—implications for CO2hydrate formation for ocean carbon sequestration
- Measurement of clathrate hydrate precipitation from CO2solution by a nondestructive method
- Influence of water thermal history and overpressure on CO2-hydrate nucleation and morphology
- Growth-controlling processes of CO2gas hydrates
- Thermodynamic prediction of clathrate hydrate dissociation conditions in mesoporous media
- Modeling dynamic marine gas hydrate systems
- Late-stage, high-temperature processesing in the Allende meteorite: Record from Ca,Fe-rich silicate rims around dark inclusions
- Partitioning of Sr, Ba, Rb, Y, and LREE between alkali feldspar and peraluminous silicic magma
- Nondestructive three-dimensional element-concentration mapping of a Cs-doped partially molten granite by X-ray computed tomography using synchrotron radiation
- A theoretical study of structural factors correlated with 23Na NMR parameters
- Metamorphic formation of Sr-apatite and Sr-bearing monazite in a high-pressure rock from the Bohemian Massif
- Ultra-deep origin of garnet peridotite from the North Qaidam ultrahigh-pressure belt, Northern Tibetan Plateau, NW China
- Letter. Novel high-pressure behavior in chlorite: A synchrotron XRD study of clinochlore to 27 GPa
- Letter. Periodic precipitation pattern formation in hydrothermally treated metamict zircon
- A high pressure X-ray diffraction study of aragonite and the post-aragonite phase transition in CaCO3
