Filling Ices with Helium and the Formation of Helium Clathrate Hydrate.

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.

Fast methane diffusion at the interface of two clathrate structures.

Methane hydrates naturally form on Earth and in the interiors of some icy bodies of the Universe, and are also expected to play a paramount role in future energy and environmental technologies. Here we report experimental observation of an extremely fast methane diffusion at the interface of the two most common clathrate hydrate structures, namely clathrate structures I and II. Methane translational diffusion-measured by quasielastic neutron scattering at 0.

A Chiral Gas-Hydrate Structure Common to the Carbon Dioxide-Water and Hydrogen-Water Systems.

We present full in situ structural solutions of carbon dioxide hydrate-II and hydrogen hydrate C at elevated pressures using neutron and X-ray diffraction. We find both hydrates adopt a common water network structure. The structure exhibits several features not previously found in hydrates; most notably it is chiral and has large open spiral channels along which the guest molecules are free to move.

Dense Semi-Clathrates at High Pressure: A Study of the Water-tert-Butylamine System.

In situ high-pressure crystallization and diffraction techniques have been applied to obtain two very structurally distinct semi-clathrates of the tert-butylamine-water system with hydration numbers 5.65 and 5.8, respectively, thereby considerably reducing a notable hydration gap between the monohydrate and the 71/4 -hydrate that results when crystallization space is explored by temperature alone.

Formation and properties of ice XVI obtained by emptying a type sII clathrate hydrate.

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. 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, which is usually regarded as experimentally inaccessible because the guest species stabilize the host framework.

Extent and relevance of stacking disorder in "ice I(c)".

A solid water phase commonly known as "cubic ice" or "ice I(c)" is frequently encountered in various transitions between the solid, liquid, and gaseous phases of the water substance. It may form, e.g.

"Self-preservation" of CO(2) gas hydrates--surface microstructure and ice perfection.

Gas hydrates can exhibit an anomalously slow decomposition outside their thermodynamic stability field; the phenomenon is called "self-preservation" and is mostly studied at ambient pressure and at temperatures between approximately 240 K and the melting point of ice. Here, we present a combination of in situ neutron diffraction studies, pVT work, and ex situ scanning electron microscopy (SEM) on CO(2) clathrates covering a much broader p-T field, stretching from 200 to 270 K and pressures between the hydrate stability limit and 0.6 kPa (6 mbar), a pressure far outside stability.