Klein, Helmut

[["dc.bibliographiccitation.firstpage","1381"],["dc.bibliographiccitation.issue","3"],["dc.bibliographiccitation.journal","Journal of the American Ceramic Society"],["dc.bibliographiccitation.lastpage","1392"],["dc.bibliographiccitation.volume","101"],["dc.contributor.author","Neher, Sigmund H."],["dc.contributor.author","Klein, Helmut"],["dc.contributor.author","Kuhs, Werner F."],["dc.date.accessioned","2020-12-10T18:28:54Z"],["dc.date.available","2020-12-10T18:28:54Z"],["dc.date.issued","2017"],["dc.identifier.doi","10.1111/jace.2018.101.issue-3"],["dc.identifier.issn","0002-7820"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/76448"],["dc.language.iso","en"],["dc.notes.intern","DOI Import GROB-354"],["dc.title","Determination of crystal size distributions in alumina ceramics by a novel X-ray diffraction procedure"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","1"],["dc.bibliographiccitation.issue","1-4"],["dc.bibliographiccitation.journal","Marine Geology"],["dc.bibliographiccitation.lastpage","14"],["dc.bibliographiccitation.volume","244"],["dc.contributor.author","Bohrmann, Gerhard"],["dc.contributor.author","Kuhs, Werner F."],["dc.contributor.author","Klapp, Stephan A."],["dc.contributor.author","Techmer, Kirsten S."],["dc.contributor.author","Klein, Helmut"],["dc.contributor.author","Murshed, M. Mangir"],["dc.contributor.author","Abegg, Fritz"],["dc.date.accessioned","2018-11-07T10:57:49Z"],["dc.date.available","2018-11-07T10:57:49Z"],["dc.date.issued","2007"],["dc.description.abstract","The state of preservation of natural gas hydrate samples, recovered from 6 sites drilled during ODP Leg 204 at southern summit of Hydrate Ridge, Oregon Margin, has been investigated by X-ray diffraction (XRD) and cryo-scanning-electron-inicroscopy (cryo-SEM) techniques. A detailed characterization of the state of decomposition of gas hydrates is necessary since no pressurized autoclave tools were used for sampling and partial dissociation must have occurred during recovery prior to the quench and storage in liquid nitrogen. Samples from 16 distinct horizons have been investigated by synchrotron X-ray diffraction measurements at HASYLAB/ Hamburg. A full profile fitting analysis (\"Rietveld method\") of synchrotron XRD data provides quantitative phase determinations of the major sample constituents such as gas hydrate structure I (sI), hexagonal ice (Ih) and quartz. The ice content (Ih) in each sample is related to frozen water composed of both original existing pore water and the water from decomposed hydrates. Hydrate contents as measured by diffraction vary between 0 and 68 wt.% in the samples we measured. Samples with low hydrate content usually show micro-structural features in cryo-SEM ascribed to extensive decomposition. Comparing the appearance of hydrates at different scales, the grade of preservation seems to be primarily correlated with the contiguous volume of the original existing hydrate; the dissociation front appears to be indicated by micrometer-sized pores in a dense ice matrix. (c) 2007 Elsevier B.V. All rights reserved."],["dc.identifier.doi","10.1016/j.margeo.2007.05.003"],["dc.identifier.isi","000250150800001"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/50340"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Elsevier Science Bv"],["dc.relation.issn","0025-3227"],["dc.title","Appearance and preservation of natural gas hydrate from Hydrate Ridge sampled during ODP Leg 204 drilling"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","1437"],["dc.bibliographiccitation.issue","6"],["dc.bibliographiccitation.journal","Journal of Applied Crystallography"],["dc.bibliographiccitation.lastpage","1439"],["dc.bibliographiccitation.volume","52"],["dc.contributor.author","Neher, Sigmund H."],["dc.contributor.author","Klein, Helmut"],["dc.contributor.author","Kuhs, Werner F."],["dc.date.accessioned","2020-12-10T18:25:57Z"],["dc.date.available","2020-12-10T18:25:57Z"],["dc.date.issued","2019"],["dc.identifier.doi","10.1107/S1600576719012159"],["dc.identifier.eissn","1600-5767"],["dc.identifier.pmid","31798363"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/17179"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/75893"],["dc.notes.intern","DOI Import GROB-354"],["dc.notes.intern","Merged from goescholar"],["dc.rights.uri","https://goescholar.uni-goettingen.de/licenses"],["dc.title","FXD-CSD-GUI : a graphical user interface for the X-ray-diffraction-based determination of crystallite size distributions"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","116"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","Marine and Petroleum Geology"],["dc.bibliographiccitation.lastpage","125"],["dc.bibliographiccitation.volume","27"],["dc.contributor.author","Klapp, Stephan A."],["dc.contributor.author","Bohrmann, Gerhard"],["dc.contributor.author","Kuhs, Werner F."],["dc.contributor.author","Murshed, M. Mangir"],["dc.contributor.author","Pape, Thomas"],["dc.contributor.author","Klein, Helmut"],["dc.contributor.author","Techmer, Kirsten S."],["dc.contributor.author","Heeschen, Katja U."],["dc.contributor.author","Abegg, Friedrich"],["dc.date.accessioned","2018-11-07T08:48:06Z"],["dc.date.available","2018-11-07T08:48:06Z"],["dc.date.issued","2010"],["dc.description.abstract","Gas hydrate samples from various locations in the Gulf of Mexico (GOM) differ considerably in their microstructure. Distinct microstructure characteristics coincide with discrete crystallographic structures, gas compositions and calculated thermodynamic stabilities. The crystallographic structures were established by X-ray diffraction, using both conventional X-ray sources and high-energy synchrotron radiation. The microstructures were examined by cryo-stage Field-Emission Scanning Electron Microscopy (FE-SEM). Good sample preservation was warranted by the low ice fractions shown from quantitative phase analyses. Gas hydrate structure II samples from the Green Canyon in the northern GOM had methane concentrations of 70-80% and up to 30% of C-2-C-5 of measured hydrocarbons. Hydrocarbons in the crystallographic structure I hydrate from the Chapopote asphalt volcano in the southern GOM was comprised of more than 98% methane. Fairly different microstructures were identified for those different hydrates: Pores measuring 200-400 nm in diameter were present in structure I gas hydrate samples; no such pores but dense crystal surfaces instead were discovered in structure II gas hydrate. The stability of the hydrate samples is discussed regarding gas composition, crystallographic structure and microstructure. Electron microscopic observations showed evidence of gas hydrate and liquid oil co-occurrence on a micrometer scale. That demonstrates that oil has direct contact to gas hydrates when it diffuses through a hydrate matrix. (C) 2009 Elsevier Ltd. All rights reserved."],["dc.identifier.doi","10.1016/j.marpetgeo.2009.03.004"],["dc.identifier.isi","000272308200010"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/21128"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Elsevier Sci Ltd"],["dc.relation.issn","0264-8172"],["dc.title","Microstructures of structure I and II gas hydrates from the Gulf of Mexico"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","85"],["dc.bibliographiccitation.issue","1-4"],["dc.bibliographiccitation.journal","Marine Geology"],["dc.bibliographiccitation.lastpage","94"],["dc.bibliographiccitation.volume","274"],["dc.contributor.author","Klapp, Stephan A."],["dc.contributor.author","Hemes, Susanne"],["dc.contributor.author","Klein, Helmut"],["dc.contributor.author","Bohrmann, Gerhard"],["dc.contributor.author","MacDonald, Ian"],["dc.contributor.author","Kuhs, Werner F."],["dc.date.accessioned","2018-11-07T08:40:22Z"],["dc.date.available","2018-11-07T08:40:22Z"],["dc.date.issued","2010"],["dc.description.abstract","Methane hydrates are present in marine seep systems and occur within the gas hydrate stability zone. Very little is known about their crystallite sizes and size distributions because they are notoriously difficult to measure. Crystal size distributions are usually considered as one of the key petrophysical parameters because they influence mechanical properties and possible compositional changes, which may occur with changing environmental conditions. Variations in grain size are relevant for gas substitution in natural hydrates by replacing CH(4) with CO(2) for the purpose of carbon dioxide sequestration. Here we show that crystallite sizes of gas hydrates from some locations in the Indian Ocean, Gulf of Mexico and Black Sea are in the range of 200-400 mu m; larger values were obtained for deeper-buried samples from ODP Leg 204. The crystallite sizes show generally a log-normal distribution and appear to vary sometimes rapidly with location. (C) 2010 Elsevier B.V. All rights reserved."],["dc.identifier.doi","10.1016/j.margeo.2010.03.007"],["dc.identifier.isi","000279524100007"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/19216"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Elsevier Science Bv"],["dc.relation.issn","0025-3227"],["dc.title","Grain size measurements of natural gas hydrates"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","207"],["dc.bibliographiccitation.issue","1-2"],["dc.bibliographiccitation.journal","Earth and Planetary Science Letters"],["dc.bibliographiccitation.lastpage","217"],["dc.bibliographiccitation.volume","299"],["dc.contributor.author","Klapp, Stephan A."],["dc.contributor.author","Murshed, M. Mangir"],["dc.contributor.author","Pape, Thomas"],["dc.contributor.author","Klein, Helmut"],["dc.contributor.author","Bohrmann, Gerhard"],["dc.contributor.author","Brewer, Peter G."],["dc.contributor.author","Kuhs, Werner F."],["dc.date.accessioned","2018-11-07T08:37:59Z"],["dc.date.available","2018-11-07T08:37:59Z"],["dc.date.issued","2010"],["dc.description.abstract","In underwater hydrocarbon seepage environments, gas hydrates are considered to play a significant role as shallow gas reservoirs and buffers for light hydrocarbon expulsion. Here we report on mixed hydrate structures from the Chapopote Knoll in the southern Gulf of Mexico and discuss several options on how a mixture of structure I (sI) and structure II (sII) gas hydrate may occur in nature. Locally resolving microscopic methods are needed to characterize the coexistence of different hydrate structures at geological hydrate deposits; we used Raman spectroscopy, X-ray diffraction, and gas chromatography for our investigations. Gas hydrates were found within the matrix and pores of the asphalts extruded at the seafloor. Two of the three hydrate pieces investigated comprised only sI, formed mostly from methane. In contrast, one piece comprised an intimate mixture of both sI and sII with sII representing ca. 25 wt.% and sI ca. 75 wt.% of the hydrate present. The two structures were closely associated within individual grain agglomerates. The crystallites of sII were significantly larger than of sI, suggesting differences in the nucleation density or different crystallite ages. The structural coexistence may be a result of one or more processes: i) de-mixing into two hydrate structures during the growth from the gas phase, which provides an additional degree of freedom for lowering the free energy in the system; ii) fractionated crystallization with a subsequently changing molecular composition; iii) crystallization from separated gas bubbles with different hydrocarbon compositions and water; and iv) partial transformation from sII to sI after hydrate nucleation, ceasing when a thermodynamically stable state was reached. The presented work will affect future assessments of natural hydrate deposits at thermogenic hydrocarbon systems, as it shows that both hydrate types I and II can be present at a certain geological site, and may provide a lingering strength to the system if conditions fall below the sI stability limit. This suggests that present worldwide hydrate occurrences are likely to be underestimated. (C) 2010 Elsevier B.V. All rights reserved."],["dc.identifier.doi","10.1016/j.epsl.2010.09.001"],["dc.identifier.isi","000284292100020"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/18668"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Elsevier Science Bv"],["dc.relation.issn","1385-013X"],["dc.relation.issn","0012-821X"],["dc.title","Mixed gas hydrate structures at the Chapopote Knoll, southern Gulf of Mexico"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","1352"],["dc.bibliographiccitation.issue","5"],["dc.bibliographiccitation.journal","Journal of Applied Crystallography"],["dc.bibliographiccitation.lastpage","1371"],["dc.bibliographiccitation.volume","51"],["dc.contributor.author","Neher, Sigmund H."],["dc.contributor.author","Klein, Helmut"],["dc.contributor.author","Kuhs, Werner F."],["dc.date.accessioned","2020-12-10T18:25:57Z"],["dc.date.available","2020-12-10T18:25:57Z"],["dc.date.issued","2018"],["dc.identifier.doi","10.1107/S1600576718010567"],["dc.identifier.eissn","1600-5767"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/75890"],["dc.notes.intern","DOI Import GROB-354"],["dc.title","A fast X-ray-diffraction-based method for the determination of crystal size distributions (FXD-CSD)"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dspace.entity.type","Publication"]]