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Topic: Clathrate hydrate

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	MBARI - Ocean Chemistry of Greenhouse Gases
		Gas hydrates are a solid ice-like phase formed at low temperature and high pressure by van der Waals forces between gas and water molecules, with the "host" water molecules forming a molecular cage which confines the "guest" gas molecules through their mutual electrostatic interaction.
		In the ocean, gas hydrates composed dominantly of methane are common constituents of the shallow marine geosphere (Kvenvolden, 1993), and they occur both in deep sedimentary structures (Dickens et al., 1997), and as outcrops on the ocean floor (MacDonald et al., 1994).
		Gas hydrate formation in the ocean does not involve shaking, and ice crystals are not part of the natural deep sea environment, and therefore laboratory experiments carried out to date have not been able to simulate natural processes.
	www.mbari.org /ghgases/geochem/gas_hydrates.htm (517 words)

	Methane clathrate information - Search.com
		Methane clathrate, also called methane hydrate or methane ice, is a form of water ice that contains a large amount of methane within its crystal structure (a clathrate hydrate).
		Methane hydrates are believed to form by migration of gas from depth along geological faults, followed by precipitation, or crystallization, on contact of the rising gas stream with cold sea water.
		Methane clathrates remain stable at temperatures up to 18 °C. The average methane clathrate hydrate composition is 1 mole of methane for every 5.75 moles of water, though this is dependent on how many methane molecules "fit" into the various cage structures of the water lattice.
	www.search.com /reference/Methane_clathrate (1365 words)

	ILL : ANNUAL REPORT 2001
		Clathrate hydrates are non-stoichiometric inclusion compounds encaging small, usually apolar molecules in a framework of hydrogen-bonded water molecules.
		One of the major unknowns in gas hydrate research in general and for CH hydrate in particular is the occupancy of the small and large cages as a function of pressure and temperature.
		Clathrate hydrates form very small crystallites of a few µm size and are completely texture free thus forming ideal powders for diffraction studies.
	www.ill.fr /AR-01/p-42.htm (1320 words)

	Werner F. Kuhs: Clathrate Hydrates (Site not responding. Last check: 2007-10-12)
		Clathrate hydrates constitute a class of solids in which the guest molecules occupy, fully or partially, cages in host structures made up of H-bonded water molecules.
		Clathrates are believed to occur in large quantities on some outer planets binding gas at fairly high temperatures, which is an interesting issue for planetologists.
		Yet this is not the only area of interest in the field of gas hydrates: They may be used as a cheaper alternative of gas storage and transport as compared to liquefied gas, and gas hydrates may be used in the desalination of sea water.
	peggy.uni-mki.gwdg.de /docs/Kuhs/clathrate_hydrates.html (2118 words)

	Clathrates - little known components of the global carbon cycle
		In the oceans, gas hydrates are found on the outer continental margins, where the supply of organic material is high enough to generate enough methane, and water temperatures are close to freezing.
		The basal zone of the gas hydrate becomes under-consolidated, possibly over-pressured because of the release of the methane, leading to the development of a zone with low shear strength where failure could be triggered and massive landslides could occur.
		Overall decreasing methane hydrate reservoirs (e.g., as a result of fluctuating sea levels during glacial -interglacial alternation) thus lead to a secular trend towards a lighter carbon isotopic signature of the ocean-atmosphere reservoir.
	ethomas.web.wesleyan.edu /ees123/clathrate.htm (2582 words)

	Science News Online (11/9/96): The Mother Lode of Natural Gas
		Although chemists first discovered gas hydrates in the early part of the 19th century, geoscientists have only recently started documenting their existence in underground deposits and exploring their importance as a potential fuel.
		Because of the scarcity of direct hydrate measurements at the time, the estimates rested on indirect seismic studies, which probe the ocean bottom sediments with blasts of sound that reflect off hidden layers.
		The cost of accessing hydrates has served as a barrier in the past, but some energy-hungry nations lacking conventional fossil fuels are extremely interested in future use of hydrates.
	www.sciencenews.org /pages/sn_arch/11_9_96/bob1.htm (1970 words)

	Clathrate hydrates (Site not responding. Last check: 2007-10-12)
		Clathrate ices form from water and non-stoichiometric amounts of small non-polar molecules (hence usually gaseous) under moderate pressure (typically of a few MPa) and at cold temperatures (typically close to 0°C, but increased pressure raises the melting point).
		During formation and dissociation, the solid clathrates interact significantly with the structure of the neighboring aqueous solution [904].
		At very high pressures, clathrate hydrates show complex phase behavor, often giving filled hexagonal ice [1142] with the smaller guest molecules/atoms, then at higher pressures they break down to give high density ice and a solid phase formed by the guest molecules (e.g.
	www.lsbu.ac.uk /water/clathrat2.html (597 words)

	Water cluster architecture based on clathrate hydrates (Site not responding. Last check: 2007-10-12)
		Although both non-crystalline ES clusters and crystalline gas-containing clathrates both have similar inner-shell water clustering, the topology of the outer clustering is very different.
		The lack of evidence for the partial formation of crystalline clathrates in liquid water containing clathrate-forming solutes cannot, therefore, be used to indicate the lack of formation of other clathrate structuring as suggested by some authors.
		The use of such clathrate cages in the formation of solid gas hydrate ices is shown on another page.
	www.lsbu.ac.uk /water/clathrate.html (339 words)

	section2.htm
		Clathrate hydrates [1] are solid inclusion compounds composed of polyhedral water cavities, which incorporate guest molecules, including a wide variety of relatively small gas molecules as well as some liquids, such as tetrahydrofuran (THF).
		Vibrational spectroscopy provides a useful probe for studying the structural characteristics of hydrate samples because the vibrational motions of water molecules and guest molecules are different for structure I hydrate, structure II hydrate, a mixture of liquid water and hydrate former, and ice.
		In the case of THF hydrate, both water lattice modes and guest modes were monitored during hydrate crystallisation, while in the case of methane hydrate only the guest modes were monitored during the growth process.
	www.ijvs.com /volume6/edition1/section2.html (3208 words)

	Oilfield Glossary: Term 'hydrate'
		More generally, hydrates are compounds in which gas molecules are trapped within a crystal structure.
		Hydrates form in cold climates, such as permafrost zones and in deep water.
		To date, economic liberation of hydrocarbon gases from hydrates has not occurred, but hydrates contain quantities of hydrocarbons that could be of great economic significance.
	www.glossary.oilfield.slb.com /Display.cfm?Term=hydrate (173 words)

	Mooijer
		To justify the applicability and feasibility of clathrate hydrate technologies knowledge on fundamentals of phase behaviour and structure is essential.
		The clathrate hydrate phase behaviour, with its relation to structure, is described with the van der Waals - Platteeuw model.
		The implications for clathrate hydrate technologies of application of these components are assessed regarding the equilibrium conditions, storage capacity and formation mechanism.
	www.dct.tudelft.nl /pcmt/html/mooijer.html (1478 words)

	O.I. Levik Hydrate Site (Site not responding. Last check: 2007-10-12)
		Clarke, M.A.: Determination of the Intrinsic Kinetics of Gas Hydrate Decomposition by Particle-Size Analysis, University of Calgary, 2000.
		Jakobsen, T.: Clathrate Hydrates Studied by Means of Time-domain Dielectric Spectroscopy, University of Bergen, 1996.
		Mehta, A.P.: A Thermodynamic Investigation of Structure H Clathrate Hydrates, Colorado school of Mines, 1996.
	www.levik.no /hydrates.html (1591 words)

	Burning Ice Methane Hydrate, Titan, Hydrogen strage, Cassini Huygens
		Methane hydrate (MH), known as Burning Ice, is a special class of ice that contains methane molecules in cages or networks of hydrogen bonded water molecules.
		hydrate for hydrogen strage, inert gas hydrates with simplest structure, and CO hydrate for preventing green house effects.
		We are studying the physical properties of the newly discovered high pressure phases of methane hydrate by the first principles molecular dynamics simulations.
	www.iitaka.org /mh_e.html (627 words)

	Mechanical Engineering "Power & Energy," February 2005 -- "Buried Treasure," Feature Article
		Methane hydrate is the common term used for the most abundant natural form of clathrate hydrate, solid substances in which host molecules (in this case, water) form a solid lattice that encapsulates, without bonding, appropriately sized guest molecules.
		Researchers are now in general agreement that hydrates most often occur as discrete grains that form within pores and act as part of the framework of the sediment, rather than as grain coatings or cements.
		This new appreciation for the complexities of natural hydrates is a key step in reclassifying hydrates from a vaguely defined "resource of the future" to a recognized part of the nation's energy portfolio.
	www.memagazine.org /pefeb05/buriedt/buriedt.html (2347 words)

	Experimental Mineralogy on the Sea Floor
		Clathrate hydrates are considered to be one possible answer to the question of how humans could benignly re-package (sequester) the CO that we now dump in such huge abundance into the atmosphere due to the burning of carbon-based fossil fuels.
		Clathrate hydrates are minerals that occur naturally on the sea floor, most commonly as methane (i.e., CH, natural gas) clathrate hydrate.
		These data will provide a means of evaluating the long-term stability of the clathrate and its rate of conversion to dissolved CO in seawater.
	www.brynmawr.edu /Acads/Geo/geology/alumnae/JDP.html (873 words)

	Clathrate Hydrate Structure
		There are two main clathrate hydrate structures: type I and type II.
		Structure I hydrate also contains larger tetrakaidecahedral cavities (consisting of twelve pentagonal and two hexagonal faces), which can accommodate guest molecules of up to 6.1 Å diameter.
		Structure II hydrate contains even larger hexakaidecahedral cavities (twelve pentagonal and four hexagonal faces) which can enclathrate guest molecules of up to 6.6 Å in diameter.
	chem.ps.uci.edu /~kcjanda/Janda/clathratecages.html (152 words)

	Methane Clathrate Hydrate Prospecting
		Methane hydrate deposits would be detected indirectly through thermal, magnetic, and electric measurements.
		Also, CH O is among the cleanest-burning fuels, and CH is the most efficient fuel because the carbon in CH is in its most reduced state.
		The method involves looking for a proxy for methane gas hydrate, by means of the combination of a thermal-analysis submethod and a field submethod that does not involve drilling.
	www.nasatech.com /Briefs/Dec03/NPO30257.html (209 words)

	Neutron Scattering Investigation of the Structure and Dynamics of Propylene Oxide Clathrate Hydrate (Site not responding. Last check: 2007-10-12)
		Clathrate hydrates (CHs) have attracted considerable interest recently, owing to their presence in vast "gas hydrate" deposits under the ocean floor, their detrimental formation in gas and oil pipelines, possible existence in extraterrestrial environments, but primarily because of their potential as an energy source and gas storage medium.
		The synthesis and measurement of gas hydrates require extreme conditions of pressure and temperature, however, CHs of water-soluble cyclic ethers form under considerably milder conditions and their study has contributed a great deal to what is known about the structure and dynamics of this class of inclusion compounds.
		Neutron diffraction and inelastic scattering studies of CHs of cyclic ethers tetrahydrofuran and trimethylene oxide provided early details on the structural distortions accompanying thermal expansion, the presence of distinct regions of low-temperature and high-temperature guest molecule dynamics, and correlations of these behaviors (and their temperature dependence) with the size of the guest.
	www.ncnr.nist.gov /seminars/2005/jones_2005.html (197 words)

	Compound clathrate hydrate on Titan's surface
		Large-scale multicomponent (compound) clathrate hydrate formation is stable relative to water ice on the surface of Titan.
		Compound clathrate hydrates are nonstoichiometric crystal of guest molecules trapped inside cages of varying sizes formed by latticeworks of water molecules.
		Water, whose availability is the main control to hydrate formation on Titan, moderates hydrate formation given its relatively small abundance compared to the other hydrate-forming components.
	www.agu.org /pubs/crossref/2005/2005JE002435.shtml (194 words)

	The Speculist: Fire and Ice -- The Risk
		Methane clathrate melts all the time, usually in small quantities that bubble up towards the ocean's surface.
		Looking at past changes is highly relevant to understanding future climate changes, particularly given the large increase in atmospheric greenhouse gas concentrations in the atmosphere due to historically recent human activities such as burning fossil fuels.
		One hypothesis, called the "Clathrate Gun" hypothesis, developed by James Kennett, professor of geological sciences at UCSB, proposes that past shifts from glacial to interglacial periods were caused by a massive decomposition of the marine methane hydrate deposits.
	www.blog.speculist.com /archives/000939.html (1722 words)

	Measurement of clathrate hydrate precipitation from CO2 solution by a nondestructive method -- Song et al. 89 (89): ...
		Measurement of clathrate hydrate precipitation from CO2 solution by a nondestructive method -- Song et al.
		Measurement of clathrate hydrate precipitation from CO solution by a nondestructive method
		of clathrate hydrate precipitation from CO solution using a
	ammin.geoscienceworld.org /cgi/content/abstract/89/8-9/1247 (228 words)

	Shuqiang Gao's Page (Site not responding. Last check: 2007-10-12)
		Clathrate hydrates are non-stoichiometric crystalline compounds consisting of
		Clathrate hydrates are important in flow assurance, sea floor stability, global
		supposed to interfer hydrate formation on molecular level.
	www.ruf.rice.edu /~saft/current_GS/Shuqiang/Shuqiang.html (247 words)

	Center for Hydrate Research (Site not responding. Last check: 2007-10-12)
		Ramesh A. Kini (2002) - NMR Studies of CH4, C2H6, and C3H8 Hydrates: Structure, Kinetics, and Thermodynamics
		Derek M. Kleehammer (2005) - Rheology of Hydrate Slurries: Ttransferability Between a Laboratory Viscometer and a Pilot Scale Flow Loop
		Douglas J. Turner (2003) - Sensitivity of Tetrahydrofuran Hydrate and Methane Hydrate Equilibria to Porous Media
	www.mines.edu /research/chs/theses.html (400 words)

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