Atoms and molecules <0.9 nm in diameter can be incorporated in the cages formed by hydrogen-bonded water molecules making up the crystalline solid clathrate hydrates. For these materials crystallographic structures generally fall into 3 categories, which are 2 cubic forms and a hexagonal form. A unique clathrate hydrate structure, previously known only hypothetically, has been synthesized at high pressure and recovered at 77 K and ambient pressure in these experiments. These samples contain Xe as a guest atom and the details of this previously unobserved structure are described here, most notably the host-guest ratio is similar to the cubic Xe clathrate starting material. After pressure quench recovery to 1 atmosphere the structure shows considerable metastability with increasing temperature (T <160 K) before reverting back to the cubic form. This evidence of structural complexity in compositionally similar clathrate compounds indicates that the reaction path may be an important determinant of the structure, and impacts upon the structures that might be encountered in nature.high pressure ͉ ice ͉ clathrate hydrate C lathrate hydrates are crystalline inclusion compounds composed of water molecules hydrogen-bonded to form cages of several types that, when stacked together, fill 3-dimensional space. Most hydrates belong to 3 structural families, 2 cubic forms known as sI and sII (1), and one hexagonal form known as sH (2-4). Species such as Ar, Kr, Xe and methane form sI or sII hydrate, whereas sH is unique in that it requires all types of cages (both small and large) to contain guest species for lattice stability (5). All 3 structures, containing methane, other hydrocarbons, H 2 S and CO 2 , O 2 and N 2 have been found in the geosphere, with sI methane hydrate by far the most abundant. At high pressures (P Ͼ 0.7 kbar) small guests (Ar, Kr, Xe, methane) are also thought to form sH hydrate with multiple occupancy of the largest cage in the hydrate (6-8). It has been proposed that the high-pressure methane hydrate of sH plays a role in the outer solar system, including formation models for Titan (9, 10).From a global perspective, natural gas clathrate hydrates are seen as a major energy resource, a potential climate change material and as a geohazard. In the natural gas industry, the prevention of gas hydrate blockages in pipelines is a major concern. From a climate change perspective the decomposition of natural gas hydrate can release large amounts of methane into the atmosphere, but paradoxically hydrates also have a potential for sequestration of anthropogenic greenhouse gases. Furthermore, clathrate hydrates have been explored for hydrogen storage.In standard hydrate notation (where D ϭ dodecahedral, T ϭ tetrakaidecahedral, P ϭ pentakaidecahedral, H ϭ hexakaidecahedral, and E ϭ eicosahedral; and for example 5 12 ϭ 12 5-sided faces), each of the cubic structures are made up of small and large water cages denoted as D (5 12 ) For many years it was thought that hydrate structures were predictable, phase equilibriu...

Graphene oxide (GO) is a type of twodimensional nanomaterial with a single-atom thickness. GO sheets contain pristine regions, oxidized regions, and a small fraction of holes. By stacking GO sheets together, a GO membrane can be fabricated with sufficient mechanical strength. The interlayer nanocapillary network formed from connected interlayer spaces, together with the gaps between the edges of noninterlocked neighboring GO sheets and cracks or holes of the GO sheet, provides passage for molecules or ions to permeate through the GO membrane in an aqueous solution. The characteristics of molecules or ions (e.g., their size, charge, and the interaction with the GO membrane) affect the separation performance of the GO membrane. The contribution of gaps between neighboring GO sheets for separation can be adjusted by changing the GO sheet size and the GO membrane thickness. The interlayer space of the GO membrane can be adjusted by changing the water pH and modifying or reducing the GO sheets to obtain the desired separation performance. The production of the GO membrane is easily scalable and relatively inexpensive, indicating that the GO membrane has promising potential for applications such as water treatment, desalination, anticorrosion, chemical resistance, and controlled release coatings.

Surfactant dry solution (DS) was prepared by mixing sodium dodecyl sulfate (SDS) solution, hydrophobic silica nanoparticles and air in a high speed blender. Flour-like SDS-DS combines the advantages of dispersed dry water and active SDS solution. Methane storage in clathrate hydrates using SDS-DS was investigated in a stainless steel vessel without stirring under the condition of 5.0 MPa and 273.2 K. The results demonstrated that highly dispersed SDS-DS could significantly enhance formation kinetics and storage capacity of methane hydrate. SDS-DS exhibited about the same methane storage capacity (172.96 m 3 •m-3) as dry water, but faster storage rates than dry water. Compared to SDS solution, SDS-DS had similar storage rates (7.44 m 3 •m-3 •min-1) and higher methane storage capacity under the relative low pressure. However, the aggregation of partial SDS-DS powders destroyed its original dispersive property after hydrate dissociation.

The effects of aluminum foam (AF, average pore size of 1000 μm) on formation and growth kinetic behaviors of methane hydrate with 0.03 wt % sodium dodecyl sulfate (SDS) were investigated in a 300 cm 3 stainless steel vessel without stirring under 4.2, 6.0, and 8.3 MPa and 273.15 K. AF is a porous metal medium possessing large rough surface and excellent thermal conductivity. The experimental results demonstrated that porous AF played an acceleration role in the initial formation and further growth of methane hydrate by promoting hydrate nucleation and facilitating the removal of hydration heat. When AF was used, not only was the induction time reduced but the formation and growth were also sped up significantly, compared to conditions without it. In addition, under the above three pressures, the maximum formation rates (R f,max ) were increased by enormous times, 52% and 23%, with the help of AF, respectively. The relatively low increment of R f,max under high pressure most likely was caused by AF's own limitations (pore size). AF with smaller pore size can be selected for further study.

Ni(0) nanoparticles (NPs) are unstable and tend to aggregate in water, which poses a considerable challenge in their catalytic application. To overcome these drawbacks, integrated Ni-noble metal bimetallic NPs with...

Ba 8 Si 46 is the archetype of the Si clathrates family. X-ray diffractions have revealed an unusual homothetic isostructural transition at ∼14-16 GPa. Raman experiments, however, suggested even more transitions at lower pressure. We present evidence showing that successive electronic topological transitions are responsible for the transformations. It is shown that the electronic structure of Ba 8 Si 46 is easily perturbed by the environment. Reverse Monte Carlo calculations and in-situ resistivity measurements revealed continual changes in the structure and electrical properties upon compression. This finding is corroborated by results of x-ray Raman scattering study in the vicinity of the Ba N 4,5 and Si L 2,3 absorption edges.

Thermal stability of composite cathodes for solid oxide fuel cells, the mixtures of (La0.8Sr0.2)0.95MnO3−δ (LSM) and (Y2O3)x(ZrO2)1−x (xYSZ, x = 3, 6, 8 and 10), is determined using in-situ neutron diffraction. Thanks to the most advanced high flux neutron source, our work highlights the visualization of the phase evolutions in heterogeneous material systems at high temperatures, along with the analysis of the diffusion activities of transition metal ions that reveal the reaction mechanism and kinetics. It is found that the tetragonal-to-cubic phase transition in YSZ at T > 900°C leads to a heterogeneous redistribution of Mn ions. The subsequent reaction of LSM and YSZ occurring at T > 1100°C is revealed as a three-stage kinetic process, yielding La2Zr2O7, SrZrO3 and MnO. The diffusion activities of Y, Mn and La ions in the heterogeneous systems at elevated temperatures are derived by the structural analysis, and the three-stage reaction of YSZ and LSM is found strongly correlated to ions' behaviors as functions of temperature.

For a finite-dimensional dynamical system, whose governing equations may or may not be analytically available, we show how to stabilize an unstable orbit in a neighborhood of a "fully"unstable fixed point (i.e., a fixed point at which all eigenvalues of the Jacobian matrix have modulus greater than unity). Only one of the unstable directions is to be stabilized via time-dependent adjustments of control parameters. The parameter adjustments can be optimized.