Search results for "clathrate"

Microstructural evolution of gas hydrates in sedimentary matrices observed with synchrotron X-ray computed tomographic microscopy

2015

The formation process of gas hydrates in sedimentary matrices is of crucial importance for the physical and transport properties of the resulting aggregates. This process has never been observed in situ at submicron resolution. Here we report on synchrotron-based microtomographic studies by which the nucleation and growth processes of gas hydrate were observed at 276 K in various sedimentary matrices such as natural quartz (with and without admixtures of montmorillonite type clay) or glass beads with different surface properties, at varying water saturation. Both juvenile water and metastably gas-enriched water obtained from gas hydrate decomposition was used. Xenon gas was employed to enha…

Ab initiolattice dynamical studies of silicon clathrate frameworks and their negative thermal expansion

2014

The thermal and lattice dynamical properties of seven silicon clathrate framework structures are investigated with ab initio density functional methods (frameworks I, II, IV, V, VII, VIII, and H). The negative thermal expansion (NTE) phenomenon is investigated by means of quasiharmonic approximation and applying it to equal time displacement correlation functions. The thermal properties of the studied clathrate frameworks, excluding the VII framework, resemble those of the crystalline silicon diamond structure. The clathrate framework VII was found to have anomalous NTE temperature range up to 300 K and it is suitable for further studies of the mechanisms of NTE. Investigation of the displa…

Spontaneous cocrystal hydrate formation in the solid state: crystal structure aspects and kinetics

2013

Kinetics of anhydrous cocrystal hydration and that of cocrystal monohydrate formation from starting compounds in the solid state are studied as a function of RH and time. The propensity of the anhydrate to hydration is related to the crystal structures of anhydrous and hydrated forms.

CCDC 127933: Experimental Crystal Structure Determination

2001

Related Article: S.Kiviniemi, M.Nissinen, M.T.Lamsa, J.Jalonen, K.Rissanen, J.Pursiainen|2000|New J.Chem.|24|47|doi:10.1039/a907608e

CCDC 104283: Experimental Crystal Structure Determination

1997

Related Article: J.Ratilainen, K.Airola, M.Nieger, M.Bohme, J.Huuskonen, K.Rissanen|1997|Chem.-Eur.J.|3|749|doi:10.1002/chem.19970030515

Acetonitrile inclusion complexes of piperazine-based macrocycles

1995

New piperazine-based macrocycles with single small cavities were prepared by using high dilution technique. The inclusion of acetonitrile into the cavity (7, 8) or clathrate formation (3) was studied by 1H-NMR spectroscopy in solution and by X-ray diffraction in the crystalline state. The cycle 3 forms a molecular cleft, a molecular pocket, where the acetonitrile molecule is held by four weak N…H interactions reinforcing the clathrate formation. The cycles 7 and 8 contain a rigid cavity for an exact sterical fit with the methyl group of a linear compound like acetonitrile. The acetonitrile inclusion complex with 7 proved to be stable under normal conditions and was studied by means of therm…

A similar to 32-70 K FORMATION TEMPERATURE RANGE FOR THE ICE GRAINS AGGLOMERATED BY COMET 67 P/CHURYUMOV-GERASIMENKO

2015

Grand Canonical Monte Carlo simulations are used to reproduce the N$_2$/CO ratio ranging between 1.7 $\times$ 10$^{-3}$ and 1.6 $\times$ 10$^{-2}$ observed {\it in situ} in the Jupiter family comet 67P/Churyumov-Gerasimenko by the ROSINA mass spectrometer aboard the Rosetta spacecraft, assuming that this body has been agglomerated from clathrates in the protosolar nebula. Simulations are done using an elaborated interatomic potentials for investigating the temperature dependence of the trapping within a multiple guest clathrate formed from a gas mixture of CO and N$_2$ in proportions corresponding to those expected for the protosolar nebula. By assuming that 67P/Churyumov-Gerasimenko agglom…

Isolation of the CH3˙ rotor in a thermally stable inert matrix: first characterization of the gradual transition from classical to quantum behaviour …

2014

International audience; Matrix isolation is a method which plays a key role in isolating and characterizing highly reactive molecularradicals. However, the isolation matrices, usually composed of noble gases or small diamagnetic molecules,are stable only at very low temperatures, as they begin to desegregate even above a few tens of Kelvin.Here we report on the successful isolation of CH3 radicals in the cages of a nearly inert clathrate–SiO2matrix. This host is found to exhibit a comparable inertness with respect to that of most conventionalnoble gas matrices but it is characterized by a peculiar thermal stability. The latter property is related to thecovalent nature of the host material a…

2016

Abstract. To date, very little is known about the distribution of natural gas hydrates in sedimentary matrices and its influence on the seismic properties of the host rock, in particular at low hydrate concentration. Digital rock physics offers a unique approach to this issue yet requires good quality, high-resolution 3-D representations for the accurate modeling of petrophysical and transport properties. Although such models are readily available via in situ synchrotron radiation X-ray tomography, the analysis of such data asks for complex workflows and high computational power to maintain valuable results. Here, we present a best-practice procedure complementing data from Chaouachi et al.…

Nitrogen Hydrate Cage Occupancy and Bulk Modulus Inferred from Density Functional Theory-Derived Cell Parameters

2021

International audience; Gas clathrate hydrate solid materials, ubiquitous in nature as found either on the ocean floor, permafrost on the Earth, or in extraterrestrial planets and comets, are also technologically relevant, for example, in energy storage or carbon dioxide sequestration. Nitrogen hydrate, in particular, is of great interest as a promoter of the kinetics of the methane replacement reaction by carbon dioxide in natural gas hydrates. This hydrate may also appear in the chemistry of planets wherever nitrogen constitutes the majority of the atmosphere. A fine understanding of the stability of this hydrate under various thermodynamic conditions is thus of utmost importance to asses…