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- Un clathrate, du grec klathron qui signifie fermeture, est
un composé chimique constitué d'un "complexe d'inclusion" formé d'une
ou plusieurs molécules d'eau (liées entre elles par des liaisons
hydrogène) dites "molécules-hôtes" qui emprisonnent une autre molécule
de gaz (dite "molécules invitées") dans une sorte de cage moléculaire
- L'hydrate de méthane, la glace qui s'enflamme est le
clathrate le plus connu du public. Il est connu comme source de
méthane, puissant gaz à effet de serre, pour ses propriétés étonnantes.
Lors de la catastrophe de Deepwater Horizon, c'est la formation de
clathrate dans le matériel disposé au-dessus de la tête de puits qui a
empêché son fonctionnement
- Clathrate hydrates (or gas clathrates, gas hydrates,
clathrates, hydrates, etc.) are crystalline water-based solids
physically resembling ice, in which small non-polar molecules
(typically gases) or polar molecules with large hydrophobic moieties
are trapped inside "cages" of hydrogen bonded water molecules. In other
words, clathrate hydrates are clathrate compounds in which the host
molecule is water and the guest molecule is typically a gas or liquid.
Without the support of the trapped molecules, the lattice structure of
hydrate clathrates would collapse into conventional ice crystal
structure or liquid water. Most low molecular weight gases (including
O2, H2, N2, CO2, CH4, H2S, Ar, Kr, and Xe), as well as some higher
hydrocarbons and freons will form hydrates at suitable temperatures and
pressures. Clathrate hydrates are not chemical compounds as the
sequestered molecules are never bonded to the lattice. The formation
and decomposition of clathrate hydrates are first order phase
transitions, not chemical reactions. Their detailed formation and
decomposition mechanisms on a molecular level are still not well
understood.[1][2] Clathrate hydrates were first documented in 1810 by
Sir Humphry Davy.[3]
Clathrates have been found to occur naturally in large quantities.
Around 6.4 trillion (i.e. 6.4x1012) tonnes of methane is trapped in
deposits of methane clathrate on the deep ocean floor.[4] Such deposits
can be found on the Norwegian continental shelf in the northern
headwall flank of the Storegga Slide. Clathrates can also exist as
permafrost, as at the Mallik gas hydrate field in the Mackenzie Delta
of northwestern Canadian Arctic. These natural gas hydrates are seen as
a potentially vast energy resource, but an economical extraction method
has so far proven elusive. Hydrocarbon clathrates cause problems for
the petroleum industry, because they can form inside gas pipelines
often resulting in plug formation. Deep sea deposition of carbon
dioxide clathrate has been proposed as a method to remove this
greenhouse gas from the atmosphere and control climate change.
Clathrates are suspected to occur in large quantities on some outer
planets, moons and trans-Neptunian objects, binding gas at fairly high
temperatures.
> clathrate
- Complexe de molécules formant une cage enfermant une
molécule hôte (des clathrates sans molécule hôte ont toutefois été
synthétisés). Le mot vient du grec klathron, signifiant clos.
Le clathrate le plus connu est l'hydrate de méthane, ce dernier étant
la molécule hôte. Cette « glace qui brûle » (quand elle dégage son
méthane inflammable) n'est stable qu'à pression élevée. On en trouve
des stocks profondément enfouis dans le sous-sol, notamment sous le
fond des océans.

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