High pressure cell for neutron diffraction investigations

Ivanov, A.; Litvin, D.F.; Савенко, Б. Н.; Smirnov, L. S.; Воронин, В. И.; Teplykh, А. Е.

doi:10.1080/08957959508200921

Cited by 17 publications

(7 citation statements)

References 3 publications

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“…The neutron diffraction experiments were performed using a piston−cylinder apparatus for in situ measurements . Neutron powder diffraction patterns were collected at room temperature and 80 and 900 MPa at research reactor IVV-2M (Yekaterinburg) 29 using a monochromatic neutron beam with λ = 1.5246 Å.…”

Section: Methodsmentioning

confidence: 99%

New Type of Phase Transformation in Gas Hydrate Forming System at High Pressures. Some Experimental and Computational Investigations of Clathrate Hydrates Formed in the SF₆−H₂O System

Анчаров

et al. 2006

J. Phys. Chem. B

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In this work, we present a new, previously unknown type of structure transformation in the high-pressure gas hydrates, which is related to the existence of two different isostructural phases of the sulfur hexafluoride clathrate hydrates. Each of these phases has its own stability field on the phase diagram. The difference between these hydrates consists of partial filling of small D cages by SF(6) molecules in the high-pressure phase; at 900 MPa, about half of small cages are occupied. Our calculations indicate that the increase of population of small cavities is improbable, therefore, at any pressure value, a part of the cavities remains vacant and the packing density is relatively low. This fact allowed us to suppose the existence of the upper pressure limit of hydrate formation in this system; the experimental results obtained confirm this assumption.

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Section: Methodsmentioning

confidence: 99%

New Type of Phase Transformation in Gas Hydrate Forming System at High Pressures. Some Experimental and Computational Investigations of Clathrate Hydrates Formed in the SF₆−H₂O System

Анчаров

et al. 2006

J. Phys. Chem. B

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“…The principal features of the HPC are published elsewhere (Gorski, Ivanov, Kuklin & Smirnov, 1995;Ivanov et al, 1995). The HPC is of the clampedpressure cylinder-piston type and works up to a hydros static pressure of 10 MPa.…”

Section: The High-pressure Cell (Hpc)mentioning

confidence: 99%

A Small-Angle Neutron Scattering Investigation of the TDMAO Micelle System at High Hydrostatic Pressure

Gorski¹,

Kalus²,

Куклин³

et al. 1997

J Appl Cryst

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The phase behaviour and phase transition of the tetradecyldimethylaminoxide micellar system TDMAO/ D20 have been investigated by small-angle neutron scattering (SANS) at temperatures T between 287 and 325 K, pressures up to P--842 MPa and at TDMAO concentrations of 55 and 102mmoll -~. A pressureinduced structural (shape) phase transition was observed for the whole pressure versus temperature range, with a slope of the transition line of dTm/dP ~-0.31 ° MPa -lThe reversibility and reproducibility of this phase change were tested. The SANS experiments showed a pressure-induced structural phase transition from a lowpressure phase (i), where rod-like micelles with a radius of R-1.94 4-0.03 nm were present, to a high-pressure phase (ii). An accurate determination of the structure of phase (ii) has not been possible up to now. In phase (ii)l,_ a discrete correlation peak in the Q range 1.8-2.2 nm was found.

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“…[23] The diffraction pattern was recorded at ambient temperature and a pressure of 0.8 GPa. Refinement of the structure was carried out using the FullProf program, [24] with the tetrahydrofuran molecule described as a rigid model.…”

Section: Methodsmentioning

confidence: 99%

New Clathrate Hydrate Structure: High‐Pressure Tetrahydrofuran Hydrate with One Type of Cavity

et al. 2004

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Since the last decade interest in clathrate hydrates has increased mainly because of the finding of immense deposits of hydrocarbon gas hydrates (clathrates) in the Earth's crust. [1,2] For scientists, interest is augmented by prospective investigations into the types of water arrangement in supramolecular structures (water being the most abundant chemical compound on earth). Herein we report on a new type of polyhedral clathrate framework, which was detected in a high-pressure [D 8 ]tetrahydrofuran hydrate. Its peculiarity consists in there being only one type of framework-building polyhedral cavity.Clathrate hydrates are inclusion compounds where the host is a polyhedral framework built of hydrogen-bonded water molecules in which guest molecules are trapped. Hostguest interactions are usually van der Waals in nature. Structures of clathrate hydrates are classified by the type of water framework, which is considered to be a three-dimensional packing of polyhedral cages with tetra-, penta-, and hexagonal faces, oxygen atoms as vertices, and hydrogen bonds as edges. The cages can act as hosts to a variety of guest molecules, from inert gases to large organic molecules (including those with hydrophilic groups). The shape and size of the guest molecules define the structural type of hydrate formed. Among the clathrate hydrates which arise under ambient pressure, three structural types are prevalent: cubic structures I and II, and hexagonal structure III (structure H), and these have been considered in detail in the literature. [3][4][5] Reports have appeared on bromine hydrate, which was shown to have a structure previously found only in semiclathrate hydrates, [6] and the hydrate of dimethyl ether, which was found to have a quite new structure.[7] For a long time the question of the effect of pressure on the structure of the clathrate hydrate formed remained open. It was known that under a pressure of hundreds of MPa, high-pressure phases existed in almost all the water-guest systems studied, though information on their structures was lacking. [8][9][10][11][12] Systematic studies of clathrate hydrate structures carried out in situ under high pressures were developed only during the last few years. In 2002, two new structural types of clathrate hydrates were identified in water-methane and water-argon systems under high pressure. [13,14] Hydrates of the structural type first found in methane hydrate were then also found in waternitrogen and water-argon systems. [15,16] The hydrate of the structural type first found in argon hydrate was then also found in the water-nitrogen system.[15] The characteristic feature of the structures under ambient pressure was the presence of several types of polyhedral cages packed in the water framework without any noticeable distortion of the lengths and angles of the hydrogen bonds. In contrast, the new high-pressure structures are built from one type of spacefilling polyhedral cage (in methane hydrate they can be considered as a system of one-dimensional channels). Such polyhedron...

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High pressure cell for neutron diffraction investigations

Cited by 17 publications

References 3 publications

New Type of Phase Transformation in Gas Hydrate Forming System at High Pressures. Some Experimental and Computational Investigations of Clathrate Hydrates Formed in the SF₆−H₂O System

New Type of Phase Transformation in Gas Hydrate Forming System at High Pressures. Some Experimental and Computational Investigations of Clathrate Hydrates Formed in the SF₆−H₂O System

A Small-Angle Neutron Scattering Investigation of the TDMAO Micelle System at High Hydrostatic Pressure

New Clathrate Hydrate Structure: High‐Pressure Tetrahydrofuran Hydrate with One Type of Cavity

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High pressure cell for neutron diffraction investigations

Cited by 17 publications

References 3 publications

New Type of Phase Transformation in Gas Hydrate Forming System at High Pressures. Some Experimental and Computational Investigations of Clathrate Hydrates Formed in the SF6−H2O System

New Type of Phase Transformation in Gas Hydrate Forming System at High Pressures. Some Experimental and Computational Investigations of Clathrate Hydrates Formed in the SF6−H2O System

A Small-Angle Neutron Scattering Investigation of the TDMAO Micelle System at High Hydrostatic Pressure

New Clathrate Hydrate Structure: High‐Pressure Tetrahydrofuran Hydrate with One Type of Cavity

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New Type of Phase Transformation in Gas Hydrate Forming System at High Pressures. Some Experimental and Computational Investigations of Clathrate Hydrates Formed in the SF₆−H₂O System

New Type of Phase Transformation in Gas Hydrate Forming System at High Pressures. Some Experimental and Computational Investigations of Clathrate Hydrates Formed in the SF₆−H₂O System