Falenty, Andrzej

[["dc.bibliographiccitation.firstpage","231"],["dc.bibliographiccitation.issue","7530"],["dc.bibliographiccitation.journal","Nature"],["dc.bibliographiccitation.lastpage","+"],["dc.bibliographiccitation.volume","516"],["dc.contributor.author","Falenty, Andrzej"],["dc.contributor.author","Hansen, Thomas C."],["dc.contributor.author","Kuhs, Werner F."],["dc.date.accessioned","2018-11-07T09:31:19Z"],["dc.date.available","2018-11-07T09:31:19Z"],["dc.date.issued","2014"],["dc.description.abstract","Gas hydrates are ice-like solids, in which guest molecules or atoms are trapped inside cages formed within a crystalline host framework (clathrate) of hydrogen-bonded water molecules(1). They are naturally present in large quantities on the deep ocean floor and as permafrost, can form in and block gas pipelines, and are thought to occur widely on Earth and beyond. A natural point of reference for this large and ubiquitous family of inclusion compounds is the empty hydrate lattice(1-6), which is usually regarded as experimentally inaccessible because the guest species stabilize the host framework. However, it has been suggested that sufficiently small guests may be removed to leave behind metastable empty clathrates(7,8), and guest-free Si-and Ge-clathrates have indeed been obtained(9,10). Here we show that this strategy can also be applied to water-based clathrates: five days of continuous vacuum pumping on small particles of neon hydrate (of structure sII) removes all guests, allowing us to determine the crystal structure, thermal expansivity and limit of metastability of the empty hydrate. It is the seventeenth experimentally established crystalline ice phase(11), ice XVI according to the current ice nomenclature, has a density of 0.81 grams per cubic centimetre (making it the least dense of all known crystalline water phases) and is expected(7,12) to be the stable low-temperature phase of water at negative pressures (that is, under tension). We find that the empty hydrate structure exhibits negative thermal expansion below about 55 kelvin, and that it is mechanically more stable and has at low temperatures larger lattice constants than the filled hydrate. These observations attest to the importance of kinetic effects and host-guest interactions in clathrate hydrates, with further characterization of the empty hydrate expected to improve our understanding of the structure, properties and behaviour of these unique materials."],["dc.description.sponsorship","Bundesministeriums fur Bildung und Forschung (BMBF)"],["dc.identifier.doi","10.1038/nature14014"],["dc.identifier.isi","000346383500041"],["dc.identifier.pmid","25503235"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/31515"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Nature Publishing Group"],["dc.relation.issn","1476-4687"],["dc.relation.issn","0028-0836"],["dc.title","Formation and properties of ice XVI obtained by emptying a type sII clathrate hydrate"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","s415"],["dc.bibliographiccitation.issue","a1"],["dc.bibliographiccitation.journal","Acta Crystallographica Section A Foundations and Advances"],["dc.bibliographiccitation.lastpage","s415"],["dc.bibliographiccitation.volume","72"],["dc.contributor.author","Ranieri, Umbertoluca"],["dc.contributor.author","Bove, Livia E."],["dc.contributor.author","Klotz, Stefan"],["dc.contributor.author","Hansen, Thomas C."],["dc.contributor.author","Koza, Michael M."],["dc.contributor.author","Gillet, Philippe"],["dc.contributor.author","Wallacher, Dirk"],["dc.contributor.author","Falenty, Andrzej"],["dc.contributor.author","Kuhs, Werner F."],["dc.date.accessioned","2020-12-10T18:26:01Z"],["dc.date.available","2020-12-10T18:26:01Z"],["dc.date.issued","2016"],["dc.identifier.doi","10.1107/S205327331609392X"],["dc.identifier.issn","2053-2733"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/75917"],["dc.notes.intern","DOI Import GROB-354"],["dc.title","Neutron diffraction on methane and hydrogen hydrates under high pressure"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","4022"],["dc.bibliographiccitation.issue","10"],["dc.bibliographiccitation.journal","The Journal of Physical Chemistry C"],["dc.bibliographiccitation.lastpage","4032"],["dc.bibliographiccitation.volume","115"],["dc.contributor.author","Falenty, Andrzej"],["dc.contributor.author","Genov, Georgi"],["dc.contributor.author","Hansen, Thomas C."],["dc.contributor.author","Kuhs, Werner F."],["dc.contributor.author","Salamatin, Andrey N."],["dc.date.accessioned","2018-11-07T08:58:05Z"],["dc.date.available","2018-11-07T08:58:05Z"],["dc.date.issued","2011"],["dc.description.abstract","The gas hydrate growth from frostlike powders composed of micrometer-sized ice particles does not start with hydrate shell formation, because the initial hydrate film thickness established in earlier work exceeds the ice particle dimensions. In this limiting case, the ice, grains are directly consumed by a growing nucleus created on the particle surface. The conventional Johnson-Mehl-Avrami-Kolmogorov (JM-AK) model,(1) which considers (re-) crystallization reactions phenomenologically in terms of the constituent nucleation and subsequent growth processes, cannot be directly applied to the hydrate formation from frost due to the assumption of an infinitely large domain of crystallization. We present here a modified approach to account for the small particle sizes of the starting material and extend the existing theory of gas hydrate formation from monodisperse ice powders(3-5) to the low-temperature and low-ice-particle-size limit. This approach may also prove to be very useful for applying chemical reactions starting on the surface of nanomaterials. In situ neutron scattering was used to obtain the experimental degree of transformation as a function of temperature between 185 and 195 K. The data were analyzed with the modified JMAK model constrained by information from cryo-SEM and BET measurements. Based on the obtained activation energies for hydrate nucleation and growth, an estimate is given for the probability of formation of CO2 hydrates at conditions relevant for Mars; a direct reaction of CO2 gas with water frost is considered to be very unlikely on the Martian surface under current conditions."],["dc.identifier.doi","10.1021/jp1084229"],["dc.identifier.isi","000288113400026"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/23558"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Amer Chemical Soc"],["dc.relation.issn","1932-7447"],["dc.title","Kinetics of CO2 Hydrate Formation from Water Frost at Low Temperatures: Experimental Results and Theoretical Model"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","054301"],["dc.bibliographiccitation.issue","5"],["dc.bibliographiccitation.journal","The Journal of Chemical Physics"],["dc.bibliographiccitation.volume","144"],["dc.contributor.author","Hansen, Thomas C."],["dc.contributor.author","Falenty, A."],["dc.contributor.author","Kuhs, Werner F."],["dc.date.accessioned","2018-11-07T10:18:18Z"],["dc.date.available","2018-11-07T10:18:18Z"],["dc.date.issued","2016"],["dc.description.abstract","The lattice constants of hydrogenated and deuterated CH4-, CO2-, Xe- (clathrate structure type I) and N-2-hydrates (clathrate structure type II) from 10 K up to the stability limit were established in neutron-and synchrotron diffraction experiments and were used to derive the related thermal expansivities. The following results emerge from this analysis: (1) The differences of expansivities of structure type I and II hydrates are fairly small. (2) Despite the larger guest-size of CO2 as compared to methane, CO2-hydrate has the smaller lattice constants at low temperatures, which is ascribed to the larger attractive guest-host interaction of the CO2-water system. (3) The expansivity of CO2-hydrate is larger than for CH4-hydrate which leads to larger lattice constants for the former at temperatures above similar to 150 K; this is likely due to the higher motional degrees of freedom of the CO2 guest molecules. (4) The cage occupancies of Xe-and CO2-hydrates affect significantly the lattice constants. (5) Similar to ice Ih, the deuterated compounds have generally slightly larger lattice constants which can be ascribed to the somewhat weaker H-bonding. (6) Compared to ice Ih, the high temperature expansivities are about 50% larger; in contrast to ice Ih and the empty hydrate, there is no negative thermal expansion at low temperature. (7) A comparison of the experimental results with lattice dynamical work, with models based on an Einstein oscillator model, and results from inelastic neutron scattering suggest that the contribution of the guest atoms' vibrational energy to thermal expansion is important, most prominently for CO2-and Xe-hydrates. (C) 2016 AIP Publishing LLC."],["dc.description.sponsorship","BMBF; DFG-grant [Ku 920/11]"],["dc.identifier.doi","10.1063/1.4940729"],["dc.identifier.isi","000369893900016"],["dc.identifier.pmid","26851915"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/41408"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Amer Inst Physics"],["dc.relation.issn","1089-7690"],["dc.relation.issn","0021-9606"],["dc.title","Lattice constants and expansivities of gas hydrates from 10 K up to the stability limit"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","5681"],["dc.bibliographiccitation.issue","9"],["dc.bibliographiccitation.journal","Energy & Fuels"],["dc.bibliographiccitation.lastpage","5691"],["dc.bibliographiccitation.volume","29"],["dc.contributor.author","Salamatin, Andrey N."],["dc.contributor.author","Falenty, A."],["dc.contributor.author","Hansen, Thomas C."],["dc.contributor.author","Kuhs, Werner F."],["dc.date.accessioned","2018-11-07T09:52:11Z"],["dc.date.available","2018-11-07T09:52:11Z"],["dc.date.issued","2015"],["dc.description.abstract","The shrinking-core model of the formation of gas hydrates from ice spheres with well-defined geometry gives experimental access to the gas permeation in bulk hydrates which is relevant to their use as energy storage materials, their exploitation from natural resources, as well as to their role in flow assurance. Here we report on a new approach to model CO2 dathration experiments in the temperature range from 230 to 272 K. We develop a comprehensive description of the gas permeation based on the diffusion along the network of polyhedral cages, some of them being empty. Following earlier molecular dynamics simulation results, the jump from a cage to one of its empty neighbors is assumed to proceed via a \"hole-in-cage-wall\" mechanism involving water vacancies in cage walls. The rate-limiting process in the investigated temperature range can be explained by the creation of water-vacancy-interstitial pairs. The gas diffusion leads to a time-dependent cage filling which decreases across the hydrate layer with the distance from the particle surface. The model allows a prediction of the time needed for a complete conversion of ice spheres into clathrate as well as the time needed for a full equilibration of the cage fillings. The findings essentially support our earlier results obtained in the framework of a purely phenomenological permeation model in terms of the overall transformation kinetics, yet it provides for the first time insight into the cage equilibration processes. The diffusion of CO2 molecules through bulk hydrate is found to be about three to four times faster in comparison with the CH4 case."],["dc.identifier.doi","10.1021/acs.energyfuels.5b01217"],["dc.identifier.isi","000363068200023"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/36063"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Amer Chemical Soc"],["dc.relation.issn","1520-5029"],["dc.relation.issn","0887-0624"],["dc.title","Guest Migration Revealed in CO2 Clathrate Hydrates"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.issue","27"],["dc.bibliographiccitation.journal","PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA"],["dc.bibliographiccitation.volume","110"],["dc.contributor.author","Kuhs, Werner F."],["dc.contributor.author","Sippel, Christian"],["dc.contributor.author","Falenty, Andrzej"],["dc.contributor.author","Hansen, Thomas C."],["dc.date.accessioned","2018-11-07T09:22:31Z"],["dc.date.available","2018-11-07T09:22:31Z"],["dc.date.issued","2013"],["dc.format.extent","E2440"],["dc.identifier.doi","10.1073/pnas.1305830110"],["dc.identifier.isi","000321978000004"],["dc.identifier.pmid","23980282"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/29354"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Natl Acad Sciences"],["dc.relation.issn","0027-8424"],["dc.title","Reply to Bogdan et al.: \"Cubic ice\" in cirrus clouds under dry and wet conditions"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.subtype","letter_note"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","21259"],["dc.bibliographiccitation.issue","52"],["dc.bibliographiccitation.journal","PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA"],["dc.bibliographiccitation.lastpage","21264"],["dc.bibliographiccitation.volume","109"],["dc.contributor.author","Kuhs, Werner F."],["dc.contributor.author","Sippel, Christian"],["dc.contributor.author","Falenty, Andrzej"],["dc.contributor.author","Hansen, Thomas C."],["dc.date.accessioned","2018-11-07T09:02:10Z"],["dc.date.available","2018-11-07T09:02:10Z"],["dc.date.issued","2012"],["dc.description.abstract","A solid water phase commonly known as \"cubic ice\" or \"ice Ic\" is frequently encountered in various transitions between the solid, liquid, and gaseous phases of the water substance. It may form, e. g., by water freezing or vapor deposition in the Earth's atmosphere or in extraterrestrial environments, and plays a central role in various cryopreservation techniques; its formation is observed over a wide temperature range from about 120 K up to the melting point of ice. There was multiple and compelling evidence in the past that this phase is not truly cubic but composed of disordered cubic and hexagonal stacking sequences. The complexity of the stacking disorder, however, appears to have been largely overlooked in most of the literature. By analyzing neutron diffraction data with our stacking-disorder model, we show that correlations between next-nearest layers are clearly developed, leading to marked deviations from a simple random stacking in almost all investigated cases. We follow the evolution of the stacking disorder as a function of time and temperature at conditions relevant to atmospheric processes; a continuous transformation toward normal hexagonal ice is observed. We establish a quantitative link between the crystallite size established by diffraction and electron microscopic images of the material; the crystallite size evolves from several nanometers into the micrometer range with progressive annealing. The crystallites are isometric with markedly rough surfaces parallel to the stacking direction, which has implications for atmospheric sciences."],["dc.description.sponsorship","Deutsche Forschungsgemeinschaft [Ku920/11]"],["dc.identifier.doi","10.1073/pnas.1210331110"],["dc.identifier.isi","000313627700034"],["dc.identifier.pmid","23236184"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/24616"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Natl Acad Sciences"],["dc.relation.issn","0027-8424"],["dc.title","Extent and relevance of stacking disorder in \"ice I-c\""],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","3194"],["dc.bibliographiccitation.issue","12"],["dc.bibliographiccitation.journal","The journal of physical chemistry letters"],["dc.bibliographiccitation.lastpage","3198"],["dc.bibliographiccitation.volume","9"],["dc.contributor.author","Kuhs, Werner F."],["dc.contributor.author","Hansen, Thomas C."],["dc.contributor.author","Falenty, Andrzej"],["dc.date.accessioned","2018-06-28T09:56:31Z"],["dc.date.available","2018-06-28T09:56:31Z"],["dc.date.issued","2018"],["dc.description.abstract","We have formed the long-sought He-clathrate. This was achieved by refilling helium into ice XVI, opening a new synthesis route for exotic forms of clathrate hydrates. The process was followed by neutron diffraction; structures and cage fillings were established. The stabilizing attractive van der Waals interactions are enhanced by multiple cage fillings with theoretically up to four helium atoms per large cage and up to one per small cage; He-clathrate hydrates can be considered as a solid-state equivalent of the clustering of small apolar entities dissolved in the liquid state of water. Unlike most other guests, helium easily enters and leaves the water cages at temperatures well below 100 K, hampering applications as a gas storage material. Despite the weak dispersive interactions, the inclusion of helium has a very significant effect on lattice constants; this is also established for helium inclusion in ice Ih and suggests that lattice parameters are arguably the most sensitive measure to gauge dispersive water-gas interactions."],["dc.identifier.doi","10.1021/acs.jpclett.8b01423"],["dc.identifier.pmid","29809013"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/15160"],["dc.language.iso","en"],["dc.notes.status","final"],["dc.relation.eissn","1948-7185"],["dc.title","Filling Ices with Helium and the Formation of Helium Clathrate Hydrate"],["dc.type","journal_article"],["dc.type.internalPublication","unknown"],["dspace.entity.type","Publication"]]