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OS6A-8:DETERMINATION OF HIGH-PRESSURE PHASES IN HYDROGEN HYDRATES
发布时间:2014-07-28
Grigory SMIRNOV, Vladimir STEGAILOV
Joint Institute for High Temperatures of the Russian Academy of Sciences, RUSSIA; Moscow Institute of Physics and Technology (State University), IRUSSIA
Gas hydrates are crystalline water-based inclusion compounds in which guest molecules are trapped inside cavities of the hydrogen-bonded water network. Several clathrates and filled-ice structures are known. Structure type primarily depends on guest size, temperature and pressure. Phase diagram of H2+H2O system has attracted great interest due to possibility of hydrogen storage and transportation. The pure hydrogen hydrates form at very high pressure, however, the addition of a promoter molecule, for example, tetrahydrofuran or methane, significantly reduce the formation pressure. Practical usage of hydrogen hydrates requires knowledge of phase diagram in a wide range of pressures and temperatures.
A new clathrate phase of water−hydrogen systems was reported by Efimchenko et al. [1] at about 253 K and 5 kbar and by Strobel et al.[2] at about 170 K and 7 kbar. X-ray diffraction patterns were similar in both cases. However, the structure of the new phase could not be well-resolved. Efimchenko et al. suggested that the new clathrate has trigonal symmetry (P3112) with a = 6.33 Å and c = 6.20 Å and called their variant a C0 structure. Strobel et al. proposed two more structures, the tetragonal sT′ structure (P42/mnm) with a = 6.25 Å and c = 10.67 Å and the α-quartz trigonal structure (P3221) with a = 6.24 Å and c = 6.18 Å. This work is devoted to the clarification of the experimental puzzle of the new HH structure using atomistic computational models. We use our preliminary experience in methane hydrate clathrates stability studies [3]. We find structures that are stable at the temperature and pressure assumed for the new phase [4].
[1] Efimchenko V.S. et al. New phase in the water–hydrogen system. J. Alloys Compd. 2011;509:S860-S863.
[2] Strobel T.A., Somayazulu M., Hemley R.J. Phase Behavior of H2 + H2O at High Pressures and Low Temperatures. J. Phys. Chem. C 2011;115:4898–4903.
[3] Smirnov G.S., Stegailov V.V. Melting and superheating of sI methane hydrate: Molecular dynamics study. J. Chem. Phys. 2012;136:044523.
[4] Smirnov G.S., Stegailov V.V. Toward Determination of the New Hydrogen Hydrate Clathrate Structures // J. Phys. Chem. Lett. 2013;4:3560–3564.
Joint Institute for High Temperatures of the Russian Academy of Sciences, RUSSIA; Moscow Institute of Physics and Technology (State University), IRUSSIA
Gas hydrates are crystalline water-based inclusion compounds in which guest molecules are trapped inside cavities of the hydrogen-bonded water network. Several clathrates and filled-ice structures are known. Structure type primarily depends on guest size, temperature and pressure. Phase diagram of H2+H2O system has attracted great interest due to possibility of hydrogen storage and transportation. The pure hydrogen hydrates form at very high pressure, however, the addition of a promoter molecule, for example, tetrahydrofuran or methane, significantly reduce the formation pressure. Practical usage of hydrogen hydrates requires knowledge of phase diagram in a wide range of pressures and temperatures.
A new clathrate phase of water−hydrogen systems was reported by Efimchenko et al. [1] at about 253 K and 5 kbar and by Strobel et al.[2] at about 170 K and 7 kbar. X-ray diffraction patterns were similar in both cases. However, the structure of the new phase could not be well-resolved. Efimchenko et al. suggested that the new clathrate has trigonal symmetry (P3112) with a = 6.33 Å and c = 6.20 Å and called their variant a C0 structure. Strobel et al. proposed two more structures, the tetragonal sT′ structure (P42/mnm) with a = 6.25 Å and c = 10.67 Å and the α-quartz trigonal structure (P3221) with a = 6.24 Å and c = 6.18 Å. This work is devoted to the clarification of the experimental puzzle of the new HH structure using atomistic computational models. We use our preliminary experience in methane hydrate clathrates stability studies [3]. We find structures that are stable at the temperature and pressure assumed for the new phase [4].
[1] Efimchenko V.S. et al. New phase in the water–hydrogen system. J. Alloys Compd. 2011;509:S860-S863.
[2] Strobel T.A., Somayazulu M., Hemley R.J. Phase Behavior of H2 + H2O at High Pressures and Low Temperatures. J. Phys. Chem. C 2011;115:4898–4903.
[3] Smirnov G.S., Stegailov V.V. Melting and superheating of sI methane hydrate: Molecular dynamics study. J. Chem. Phys. 2012;136:044523.
[4] Smirnov G.S., Stegailov V.V. Toward Determination of the New Hydrogen Hydrate Clathrate Structures // J. Phys. Chem. Lett. 2013;4:3560–3564.
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