The Experts below are selected from a list of 39 Experts worldwide ranked by ideXlab platform
Koichi Momma - One of the best experts on this subject based on the ideXlab platform.
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transformation pathways and isothermal compressibility of a mtn type clathrasil using penetrating and non penetrating fluids
Microporous and Mesoporous Materials, 2019Co-Authors: Katharina S Scheidl, Koichi Momma, H Effenberger, Takehiko Yagi, Ronald MiletichAbstract:Abstract The high-pressure behavior of the natural MTN-type clathrasil chibaite was investigated with in situ single-crystal X-ray diffraction and Raman spectroscopy under hydrostatic pressures up to 10.3 GPa. The experiments were conducted in diamond-anvil cells using 4:1 methanol-ethanol mixture (ME), helium (He) and neon (Ne) as pressure-transmitting media. The pressure dependent unit-cell volumes of the room-pressure polymorph yield an isothermal bulk modulus KT0 = 25.75 (19) GPa for the compression in the non-penetrating ME fluid. Due to the penetration of the Ne and He atoms into the cages of the framework, the crystal structure is significantly stiffened resulting in KT0 = 42.5 (1.2) GPa (Ne) and KT0 = 58 (2) GPa (He). Under the influence of pressure both the evolution of the Raman spectra and the change in cell metrics indicate a distortion of the lattice without leading to a complete pressure-induced amorphization, as observed for many comparable porous structures. Compressed in the non-penetrating ME, the cubic F d 3 ¯ m framework of chibaite undergoes a first transformation step in the pressure range between 1.7 GPa and 2.2 GPa and a second one between 3.9 GPa and 4.3 GPa. The accompanied formation of crystal domains did not allow a reliable determination of the distorted crystal structures. The unit-cell parameters might suggest a monoclinic metric for pressures >1.7 GPa and a monoclinic or tetragonal metric for pressures >3.9 GPa. However, in some samples even the co-existence of crystal domains of a different degree of lattice distortions has been proved.
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New silica clathrate minerals that are isostructural with natural gas hydrates
Nature Communications, 2011Co-Authors: Koichi Momma, Katsumi Nishikubo, Chibune Honma, Yoshihiro Furukawa, Takuji Ikeda, Toshiro Nagase, Masayuki Takada, Naoki Takahashi, Yasuhiro KudohAbstract:Silica clathrate compounds (Clathrasils) and clathrate hydrates are structurally analogous because both materials have framework structures with cage-like voids occupied by guest species. The following three structural types of clathrate hydrates are recognized in nature: cubic structure I (sI); cubic structure II (sII); and hexagonal structure H (sH). In contrast, only one naturally occurring silica clathrate mineral, melanophlogite (sI-type framework), has been found to date. Here, we report the discovery of two new silica clathrate minerals that are isostructural with sII and sH hydrates and contain hydrocarbon gases. Geological and mineralogical observations show that these silica clathrate minerals are traces of low-temperature hydrothermal systems at convergent plate margins, which are the sources of thermogenic natural gas hydrates. Given the widespread occurrence of submarine hydrocarbon seeps, silica clathrate minerals are likely to be found in a wide range of marine sediments.
Yasuhiro Kudoh - One of the best experts on this subject based on the ideXlab platform.
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New silica clathrate minerals that are isostructural with natural gas hydrates
Nature Communications, 2011Co-Authors: Koichi Momma, Katsumi Nishikubo, Chibune Honma, Yoshihiro Furukawa, Takuji Ikeda, Toshiro Nagase, Masayuki Takada, Naoki Takahashi, Yasuhiro KudohAbstract:Silica clathrate compounds (Clathrasils) and clathrate hydrates are structurally analogous because both materials have framework structures with cage-like voids occupied by guest species. The following three structural types of clathrate hydrates are recognized in nature: cubic structure I (sI); cubic structure II (sII); and hexagonal structure H (sH). In contrast, only one naturally occurring silica clathrate mineral, melanophlogite (sI-type framework), has been found to date. Here, we report the discovery of two new silica clathrate minerals that are isostructural with sII and sH hydrates and contain hydrocarbon gases. Geological and mineralogical observations show that these silica clathrate minerals are traces of low-temperature hydrothermal systems at convergent plate margins, which are the sources of thermogenic natural gas hydrates. Given the widespread occurrence of submarine hydrocarbon seeps, silica clathrate minerals are likely to be found in a wide range of marine sediments.
Ronald Miletich - One of the best experts on this subject based on the ideXlab platform.
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transformation pathways and isothermal compressibility of a mtn type clathrasil using penetrating and non penetrating fluids
Microporous and Mesoporous Materials, 2019Co-Authors: Katharina S Scheidl, Koichi Momma, H Effenberger, Takehiko Yagi, Ronald MiletichAbstract:Abstract The high-pressure behavior of the natural MTN-type clathrasil chibaite was investigated with in situ single-crystal X-ray diffraction and Raman spectroscopy under hydrostatic pressures up to 10.3 GPa. The experiments were conducted in diamond-anvil cells using 4:1 methanol-ethanol mixture (ME), helium (He) and neon (Ne) as pressure-transmitting media. The pressure dependent unit-cell volumes of the room-pressure polymorph yield an isothermal bulk modulus KT0 = 25.75 (19) GPa for the compression in the non-penetrating ME fluid. Due to the penetration of the Ne and He atoms into the cages of the framework, the crystal structure is significantly stiffened resulting in KT0 = 42.5 (1.2) GPa (Ne) and KT0 = 58 (2) GPa (He). Under the influence of pressure both the evolution of the Raman spectra and the change in cell metrics indicate a distortion of the lattice without leading to a complete pressure-induced amorphization, as observed for many comparable porous structures. Compressed in the non-penetrating ME, the cubic F d 3 ¯ m framework of chibaite undergoes a first transformation step in the pressure range between 1.7 GPa and 2.2 GPa and a second one between 3.9 GPa and 4.3 GPa. The accompanied formation of crystal domains did not allow a reliable determination of the distorted crystal structures. The unit-cell parameters might suggest a monoclinic metric for pressures >1.7 GPa and a monoclinic or tetragonal metric for pressures >3.9 GPa. However, in some samples even the co-existence of crystal domains of a different degree of lattice distortions has been proved.
Katharina S Scheidl - One of the best experts on this subject based on the ideXlab platform.
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transformation pathways and isothermal compressibility of a mtn type clathrasil using penetrating and non penetrating fluids
Microporous and Mesoporous Materials, 2019Co-Authors: Katharina S Scheidl, Koichi Momma, H Effenberger, Takehiko Yagi, Ronald MiletichAbstract:Abstract The high-pressure behavior of the natural MTN-type clathrasil chibaite was investigated with in situ single-crystal X-ray diffraction and Raman spectroscopy under hydrostatic pressures up to 10.3 GPa. The experiments were conducted in diamond-anvil cells using 4:1 methanol-ethanol mixture (ME), helium (He) and neon (Ne) as pressure-transmitting media. The pressure dependent unit-cell volumes of the room-pressure polymorph yield an isothermal bulk modulus KT0 = 25.75 (19) GPa for the compression in the non-penetrating ME fluid. Due to the penetration of the Ne and He atoms into the cages of the framework, the crystal structure is significantly stiffened resulting in KT0 = 42.5 (1.2) GPa (Ne) and KT0 = 58 (2) GPa (He). Under the influence of pressure both the evolution of the Raman spectra and the change in cell metrics indicate a distortion of the lattice without leading to a complete pressure-induced amorphization, as observed for many comparable porous structures. Compressed in the non-penetrating ME, the cubic F d 3 ¯ m framework of chibaite undergoes a first transformation step in the pressure range between 1.7 GPa and 2.2 GPa and a second one between 3.9 GPa and 4.3 GPa. The accompanied formation of crystal domains did not allow a reliable determination of the distorted crystal structures. The unit-cell parameters might suggest a monoclinic metric for pressures >1.7 GPa and a monoclinic or tetragonal metric for pressures >3.9 GPa. However, in some samples even the co-existence of crystal domains of a different degree of lattice distortions has been proved.
Jacobus C Jansen - One of the best experts on this subject based on the ideXlab platform.
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high density storage of h2 in microporous crystalline silica at ambient conditions
Chemistry: A European Journal, 2007Co-Authors: Annemieke W C Van Den Berg, Paolo P Pescarmona, J Schoonman, Jacobus C JansenAbstract:Molecular hydrogen was encapsulated in the cages of clathrasil decadodecasil 3R (DD3R) during the hydrothermal synthesis of this microporous silicate. The crystalline structure of DD3R facilitates high-density hydrogen storage at ambient conditions. Prompt gamma activation analysis (PGAA) revealed that on average about one molecule of H2 is trapped in each (5(12)) cage of DD3R. The presence of molecular hydrogen inside the DD3R framework was confirmed by solid-state 1H NMR spectroscopy. Temperature-programmed decomposition (TPD) in combination with mass spectrometry showed that the encapsulated hydrogen is released upon decomposition of the clathrasil structure. This release can be promoted by the presence of water.