<i>In situ</i> structural properties of N2-, O2-, and air-clathrates by neutron diffraction

Chazallon, Bertrand; Kuhs, Werner F.

doi:10.1063/1.1480861

Cited by 134 publications

(134 citation statements)

References 67 publications

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“…The complexity of the problem generally depends on the number of atoms to be located in the asymmetric unit. Consequently, many crystal structures of gas hydrates have been solved by assuming the center of the disordered guest molecules to be at the center of the cages [26][27][28][29][30][31][32][33][34][35][36] and by using the Rietveld refinement technique. 37 Recently, significant advances have been made in other approaches to solving structures from powder diffraction data.…”

Section: Introductionmentioning

confidence: 99%

Direct Space Methods for Powder X-ray Diffraction for Guest−Host Materials: Applications to Cage Occupancies and Guest Distributions in Clathrate Hydrates

et al. 2009

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Structural determination of crystalline powders, especially those of complex materials, is not a trivial task. For non-stoichiometric guest-host materials, the difficulty lies in how to determine dynamical disorder and partial cage occupancies of the guest molecules without other supporting information or constraints. Here, we show how direct space methods combined with Rietveld analysis can be applied to a class of host-guest materials, in this case the clathrate hydrates. We report crystal structures in the three important hydrate crystal classes, sI, sII, and sH, for the guests CO 2 ,C 2 H 6 ,C 3 H 8 , and methylcyclohexane + CH 4 . The results obtained for powder samples are found to be in good agreement with the experimental data from single crystal X-ray diffraction and 13 C solid-state NMR spectroscopy. This method is also used to determine the guest disorder and cage occupancies of neohexane and tert-butyl methyl ether binary hydrates with CH 4 in the structure H clathrate hydrates. The results are found to be in good agreement with the results from the 13 C solid-state NMR and molecular dynamics simulations. It is demonstrated that the ab initio crystal structure determination methodology reported here is able to determine absolute cage occupancies and the dynamical disorder of guest molecules in clathrate hydrates from powdered crystalline samples.

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Section: Introductionmentioning

confidence: 99%

Direct Space Methods for Powder X-ray Diffraction for Guest−Host Materials: Applications to Cage Occupancies and Guest Distributions in Clathrate Hydrates

et al. 2009

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“…The cage occupancy și,J needs to be determined from a convenient hydrate model, e.g., ref. [3][4][5]12,13] or experimentally by diffraction methods [14][15][16]. Tables 1 and 2 summarize experimental data points available for the lattice parameter of sI hydrates and sII hydrates, respectively.…”

Section: Volume Of Gas Hydratesmentioning

confidence: 99%

Temperature and pressure correlation for volume of gas hydrates with crystal structures sI and sII

et al. 2017

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Abstract. The temperature and pressure correlations for the volume of gas hydrates forming crystal structures sI and sII developed in previous study [Fluid Phase Equilib. 427 (2016) 268-281], focused on the modeling of pure gas hydrates relevant in CCS (carbon capture and storage), were revised and modified for the modeling of mixed hydrates in this study. A universal reference state at temperature of 273.15 K and pressure of 1 Pa is used in the new correlation. Coefficients for the thermal expansion together with the reference lattice parameter were simultaneously correlated to both the temperature data and the pressure data for the lattice parameter. A two-stage Levenberg Marquardt algorithm was employed for the parameter optimization. The pressure dependence described in terms of the bulk modulus remained unchanged compared to the original study. A constant value for the bulk modulus B0 = 10 GPa was employed for all selected hydrate formers. The new correlation is in good agreement with the experimental data over wide temperature and pressure ranges from 0 K to 293 K and from 0 to 2000 MPa, respectively. Compared to the original correlation used for the modeling of pure gas hydrates the new correlation provides significantly better agreement with the experimental data for sI hydrates. The results of the new correlation are comparable to the results of the old correlation in case of sII hydrates. In addition, the new correlation is suitable for modeling of mixed hydrates.

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“…Four of these five molecules (CO, CH 4 , CO 2 , H 2 S) form individually a SI structure of clathrate (Davidson et al 1987;Dartois 2011;Handa 1986b;Anderson 2003;Miller 1961) and N 2 is the only one molecule forming a SII-structure (Chazallon & Kuhs 2002;Sloan & Koh 2008), leading to small differences in n hyd . All volatile molecules studied in this work are small enough to enter both the small and large cavities (Sloan & Koh 2008;Gabitto & Tsouris 2010).…”

Section: Thermodynamics Parameters Of Condensation and Clathrate Formmentioning

confidence: 99%

From stellar nebula to planetesimals

Marboeuf

Thiabaud

Alibert

et al. 2014

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Context. Solar and extrasolar comets and extrasolar planets are the subject of numerous studies in order to determine their chemical composition and internal structure. In the case of planetesimals, their compositions are important as they govern in part the composition of future planets. Aims. The present works aims at determining the chemical composition of icy planetesimals, believed to be similar to present day comets, formed in stellar systems of solar chemical composition. The main objective of this work is to provide valuable theoretical data on chemical composition for models of planetesimals and comets, and models of planet formation and evolution. Methods. We have developed a model that calculates the composition of ices formed during the cooling of the stellar nebula. Coupled with a model of refractory element formation, it allows us to determine the chemical composition and mass ratio of ices to rocks in icy planetesimals throughout in the protoplanetary disc. Results. We provide relationships for ice line positions (for different volatile species) in the disc, and chemical compositions and mass ratios of ice relative to rock for icy planetesimals in stellar systems of solar chemical composition. From an initial homogeneous composition of the nebula, a wide variety of chemical compositions of planetesimals were produced as a function of the mass of the disc and distance to the star. Ices incorporated in planetesimals are mainly composed of H 2 O, CO, CO 2 , CH 3 OH, and NH 3 . The ice/rock mass ratio is equal to 1 ± 0.5 in icy planetesimals following assumptions. This last value is in good agreement with observations of solar system comets, but remains lower than usual assumptions made in planet formation models, taking this ratio to be of 2-3.

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In situ structural properties of N2-, O2-, and air-clathrates by neutron diffraction

Cited by 134 publications

References 67 publications

Direct Space Methods for Powder X-ray Diffraction for Guest−Host Materials: Applications to Cage Occupancies and Guest Distributions in Clathrate Hydrates

Direct Space Methods for Powder X-ray Diffraction for Guest−Host Materials: Applications to Cage Occupancies and Guest Distributions in Clathrate Hydrates

Temperature and pressure correlation for volume of gas hydrates with crystal structures sI and sII

From stellar nebula to planetesimals

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