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Intense sources of very cold neutrons (VCNs) would be beneficial for various neutron scattering techniques and low-energy particle physics experiments. Binary clathrate hydrates hosting deuterated tetrahydrofuran (THF-d) and dioxygen show promise as potential moderators for such sources due to a rich spectrum of localized low-energy excitations of the encaged guest molecules. In this article, we present a reliable manufacturing technique for such hydrates. Neutron diffraction data confirm their clathrate structure as type II (CS-II), determine their purity, and cage occupancy. Furthermore, we present data on the thermal expansivity of THF-d– and THF-d–O2clathrates, drawing attention to them as an interesting case study for the complex structure and dynamics of this class of material. [ABSTRACT FROM AUTHOR]

On Earth, natural hydrates are mostly encountered in clay‐rich sediments. Yet their formation processes in such matrices remain poorly understood. Achieving an in‐depth understanding of how methane hydrates accumulate on continental margins is key to accurately assess (a) their role in sustaining the development of some chemosynthetic communities at cold seeps, (b) their potential in terms of energy resources and geohazards, and (c) the fate of the methane releases, a powerful greenhouse gas, in this changing climate. This study investigated the formation of methane hydrates and their gas storage capacity (GSC) in clay‐rich sediments. A set of hydrate experiments were performed in matrices composed of sand, illite‐rich clay, and montmorillonite‐rich clay at different proportions aiming to determine the role of mineralogy on hydrate formation processes. The experiments demonstrate that a clay content of 10% in a partially water saturated sand/clay mixture increases the induction time by ∼60%, irrespective of the nature of the clay used. The increase in water saturation in the two matrices promotes hydrate formation. Micro‐Raman spectroscopic analyses reveal that increasing the clay content leads to a decrease in the hydrate small‐cage occupancy, with an impact on the storage capacity. Finally, the analyses of collected natural samples from the Black Sea (off Romania) enable us to estimate the GSC of the deposit. Our estimates is different from previous ones, and supports the importance of coupling multiscale properties, from the microscale to the geological scale, to accurately assess the total amount of methane hosts in hydrate deposits worldwide. Plain Language Summary: Natural gas hydrates are amongst the largest methane reservoirs on Earth. They are sensitive to temperature increase. Societal and environmental concerns surrounding natural gas hydrates pertain to their decomposition, and in particular to the amount of gas they may release and its fate: can it trigger geohazards, or jeopardize the development of unique chemosynthetic communities encountered on continental margins? In‐depth knowledge of hydrate formation processes and properties are essential to provide reliable answers to these questions. The majority of hydrate deposits are characterized by clay‐rich sediments. We led a comprehensive study coupling fine microstructural analyses of both natural and synthetic hydrate samples with macroscale laboratory experiments within different matrices to show how clays can affect their formation kinetics and storage capacity. We found that even a small amount of clay can significantly change the formation kinetics of hydrates, and the matrix mineralogy affects their storage capacity. This study is crucial with a view to accurately assessing the amount of methane trapped in hydrate deposits, and for improved prediction of the consequences of their decomposition on the environment in a changing climate. Key Points: Clay content and clay mineralogy significantly affect the induction time of methane hydrate formation as well as the hydrate morphologyIllite‐rich clays reduce the cage occupancy of hydrates and thus the resulting gas storage capacity (GSC)Microscale analyses underpins the need to characterize microscopic properties of hydrates to estimate GSC [ABSTRACT FROM AUTHOR]

Clathrate hydrates are crystalline compounds consisting of water molecules forming cages (so-called "host") inside of which "guest" molecules are encapsulated depending on the thermodynamic conditions of formation (systems stable at low temperature and high pressure). These icelike systems are naturally abundant on Earth and are generally expected to exist on icy celestial bodies. Carbon monoxide hydrate might be considered an important component of the carbon cycle in the solar system since CO gas is one of the predominant forms of carbon. Intriguing fundamental properties have also been reported: the CO hydrate initially forms in the sI structure (kinetically favored) and transforms into the sII structure (thermodynamically stable). Understanding and predicting the gas hydrate structural stability then become essential. The aim of this work is, thereby, to study the structural and energetic properties of the CO hydrate using density functional theory (DFT) calculations together with neutron diffraction measurements. In addition to the comparison of DFT-derived structural properties with those from experimental neutron diffraction, the originality of this work lies in the DFT-derived energy calculations performed on a complete unit cell (sI and sII) and not only by considering guest molecules confined in an isolated water cage (as usually performed for extracting the binding energies). Interestingly, an excellent agreement (within less than 1% error) is found between the measured and DFT-derived unit cell parameters by considering the Perdew-Burke-Ernzerhof (denoted PBE) functional. Moreover, a strategy is proposed for evaluating the hydrate structural stability on the basis of potential energy analysis of the total nonbonding energies (i.e., binding energy and water substructure nonbonding energy). It is found that the sII structure is the thermodynamically stable hydrate phase. In addition, increasing the CO content in the large cages has a stabilizing effect on the sII structure, while it destabilizes the sI structure. Such findings are in agreement with the recent experimental results evidencing the structural metastability of the CO hydrate. [ABSTRACT FROM AUTHOR]

Digital Light Processing (DLP) allows the fast realization of 3D objects with high spatial resolution. However, DLP is limited to transparent resins, and therefore not well suited for printing electrically conductive materials. Manufacturing conductive materials will significantly broaden the spectrum of applications of the DLP technology. But conductive metals or carbon‐based fillers absorb and scatter light; inhibiting thereby photopolymerization, and lowering resolution. In this study, UV transparent liquid crystal graphene oxide (GO) is used as precursor for generating in situ conductive particles. The GO materials are added to a photopolymerizable resin via an original solvent exchange process. By contrast to earlier contributions, the absence of drying during the all process allows the GO material to be transferred as monolayers to limit UV scattering. The absence of UV scattering and absorption allows for fast and high‐resolution 3D printing. The chosen resin sustain high temperature to enable an in situ efficient thermal reduction of GO into reduced graphene oxide (rGO) that is electrically conductive. The rGO particles form percolated networks with conductivities up to 1.2 × 10−2 S m−1. The present method appears therefore as a way to reconcile the DLP technology with the manufacturing of 3D electrically conductive objects. [ABSTRACT FROM AUTHOR]

The self-consistent-charges density-functional tight-binding (SCC-DFTB) method is used to investigate the behavior of ammonium cyanate in the solid state under high pressure. The results have shown that the transformation of ammonium cyanate into urea is strongly exothermic.

Confocal Raman microspectrometry is used to study the C-Br stretching band for the gauche end-group conformation of the 1,8-dibromooctane guest molecules, allowing an assessment of possible changes in the conformational properties of the guest molecules as a consequence of the exchange process. The wider implications are discussed in relation to fundamental aspects of the molecular transport process in the crystalline solid.

Three electron reduced Mn12 complexes are examined with the help of inelastic neutron scattering (INS) spectroscopy. The extent of electron reduction and the axial anisotropy parameter of the cluster display an approximately linear relationship.

Our recent Communication suggested that ammonia in aqueous solution may preferentially destabilize large cages in methane clathrate hydrates. A Comment favored ammonia incorporation instead, but it did not accurately describe our proposed mechanism and relied primarily on studies conducted in different chemical systems and/or which used other preparation methods. [ABSTRACT FROM AUTHOR]

The inter-cage hopping in a type II clathrate hydrate with different numbers of H2 and D2 molecules, from 1 to 4 molecules per large cage, was studied using a classical molecular dynamics simulation at temperatures of 80 to 240 K. We present the results for the diffusion of these guest molecules (H2 or D2) at all of the different occupations and temperatures, and we also calculated the activation energy as the energy barrier for the diffusion using the Arrhenius equation. The average occupancy number over the simulation time showed that the structures with double and triple large-cage H2 occupancy appeared to be the most stable, while the small cages remained with only one guest molecule. A Markov model was also calculated based on the number of transitions between the different cage types. [ABSTRACT FROM AUTHOR]

The incorporation of ammonia inside methane clathrate hydrate is of great interest to the hydrate chemistry community. We investigated the phase behavior of methane clathrate formed from aqueous ammonia solution. Ammonia's presence decreases methane occupancy in the large cages, without definitive Raman spectroscopic evidence for its incorporation inside the structure. [ABSTRACT FROM AUTHOR]

NH4(C6H5)4B represents a prototypical system for understanding aromatic H bonds. In NH4(C6H5)4B an ammonium cation is trapped in an aromatic cage of four phenyl rings and each phenyl ring serves as a hydrogen bond acceptor for the ammonium ion as donor. Here the dynamical properties of the aromatic hydrogen bond in NH4(C6H5)4B were studied by quasielastic incoherent neutron scattering in a broad temperature range (20≤=T≤=350 K). We show that in the temperature range from 67 to 350 K the ammonium ions perform rotational jumps around C3 axes. The correlation time for this motion is the lifetime of the “transient” H bonds. It varies from 1.5 ps at T=350 K to 150 ps at T=67 K. The activation energy was found to be 3.14 kJ/mol, which means only 1.05 kJ/mol per single H bond for reorientations around the C3 symmetry axis of the ammonium group. This result shows that the ammonium ions have to overcome an exceptionally low barrier to rotate and thereby break their H bonds. In addition, at temperatures above 200 K local diffusive reorientational motions of the phenyl rings, probably caused by interaction with ammonium-group reorientations, were found within the experimental observation time window. At room temperature a reorientation angle of 8.4°±2° and a correlation time of 22±8 ps were determined for the latter. The aromatic H bonds are extremely short lived due to the low potential barriers allowing for molecular motions with a reorientational character of the donors. The alternating rupture and formation of H bonds causes very strong damping of the librational motion of the acceptors, making the transient H bond appear rather flexible. [ABSTRACT FROM AUTHOR]

In the perchloric acid clathrate hydrate HClO4·5.5H2O, the perchlorate anions are contained inside an aqueous host crystalline matrix, positively charged because of the presence of delocalized acidic protons. Our experimental results demonstrate that the microscopic mechanisms of proton conductivity in this system are effective on a time scale ranging from nanosecond to picosecond. In the present paper, we discuss more specifically on the relaxation processes occurring on a nanosecond time scale by combining high-resolution quasielastic neutron scattering and 1H pulse-field-gradient nuclear magnetic resonance experiments. The combination of these two techniques allows us to probe proton dynamics in both space and time domains. The existence of two types of proton dynamical processes has been identified. The slowest one is associated to long-range translational diffusion of protons between crystallographic oxygen sites and has been precisely characterized with a self-diffusion coefficient of 3.5×10-8 cm2/s at 220 K and an activation energy of 29.2±1.4 kJ/mol. The fastest dynamical process is due to water molecules’ reorientations occurring every 0.7 ns at 220 K with an activation energy of 17.4±1.5 kJ/mol. This powerful multitechnique approach provides important information required to understand the microscopic origin of proton transport in an ionic clathrate hydrate. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Confocal Raman microspectrometry is used for probing the kinetic aspects of the guest exchange process in a urea inclusion compound. The transport of the new pentadecane guest molecules along the tunnel has displayed a linear dependence on time, with the rate of the process in the region of 70-100 nm [s.sup.-1].

A series of quasielastic neutron scattering (QENS) experiments were carried out on cement pastes with water/cement ratio varying to investigate the interaction of water in the gel pores with the cement paste made from Portland cement. The results reveal that to a first approximation the QE response can be explained in terms of the diffusion of water within the gel pores within the paste and that QENS can be used to examine the interactions of the pore water to the pores structure in the paste.

A study is conducted to demonstrate that confocal Raman microspectrometry can be used successfully as an in situ probe of the transport process, yielding information on the spatial distribution of guest molecules and its time dependence. The focus is on the system in which the original and new guest molecules are 1,8-dibromoctane (DBO) and pentadecane (PD).

Hydrate-based CO2 trapping from CO2–N2 and CO2–CO gas mixtures is shown by Raman spectroscopy – the results are of interest for new separation and capture technology. A better trapping efficiency is measured for low CO2 concentrations and N2-based gas mixtures. Moreover, it is observed that CO molecules would impede hydrate formation from ice when a CO-enriched gas mixture is considered. [ABSTRACT FROM AUTHOR]

The article discusses the highlights of the 2006 United States-China Workshop Series on Neutron Science and Technology. The event took place in Beijing China from Noevmber 12-15, 2006 with moer than 150 participants. This event was sponsored by the National Science Foundation and other concerned organizations. The workshop involved several discussions about the issues and the future of neutron science and technology. It concluded with a panel discussion led by facility leaders covering research and development, neutronics and instrumentation development.

The occurrence of alkane-alkane guest exchange within the one-dimensional channels of the urea host structure in alkane/urea inclusion compounds is demonstrated using confocal Raman microspectrometry. With appropriate deuteration of one of the alkane guest components, this technique represents a powerful strategy for in situ characterization of the alkane-alkane guest exchange process. [ABSTRACT FROM AUTHOR]

The article discusses the Journées de la Diffusion Neutronique (JDN24), an annual meeting on neutron diffusion hosted by the French neutron scattering society "Société Française de la Neutronique (SFN)" in Carqueiranne, France from May 2-4, 2016. Topics include the presentation of topics on the fundamental physics of neutron, the session on the function of biological system on neutron scattering, and the aspects of neutron facilities in France.

Clathrate hydrates are ice-like systems in which nanometric water cages encapsulate guest molecules. Functionalizing clathrate hydrates is an important issue, accomplished by playing with their chemical composition and their cage structure. In this issue, the cage occupancy and its kinetics constitute key information for future developments. In many aspects, nitrogen gas hydrate represents an interesting system not only for its applied relevance (e.g., gas separation and methane/carbon dioxide exchange), but also for its fundamental interest (e.g., structural metastability and kinetics). Thanks to the complementarity of neutron diffraction and Raman scattering, the vibrational signatures of the so-called SI and SII clathrate structures of the nitrogen hydrates are reviewed. Moreover, the investigation of the ageing of the SII structure is reported together with its interpretation in the frame of the Langmuir behavior of the cage filling at low temperature. The cage filling is monitored with the help of a time-dependent analysis of the Raman scattering signals (over several months). The SII large cage filling decreases with a kinetic rate of 5.9 ± 3.3 × 10 − 3 h−1 at 77 K and atmospheric pressure, so that equilibrium is reached after ca. eight weeks. Isotherm measurements of the guest Raman signatures lead to revealing a Langmuir constant higher in the small cage than in the large cage at 150 K. Such a behavior might thus be correlated with the nitrogen depletion with time, observed in the large cage of the SII nitrogen hydrate. [ABSTRACT FROM AUTHOR]

The bromomethane clathrate hydrate crystallizes into the type I structure with the six large cages and the two small cages both filled with bromomethane guest molecules. Dynamic properties of the guest molecules have been investigated by means of incoherent quasi-elastic neutron scattering (QENS) in temperatures between 50 K and 260 K at atmospheric pressure. These investigations provide direct experimental evidence about the fundamental aspect of rotational motions of the bromomethane molecules. A comprehensive study has been achieved through the analysis of the structure factors (i.e., the spatial extend of the motion) as well as of the QENS broadening (i.e., the characteristic time of the motion). Such analysis reveals the existence of two types of motions: methyl group rotations about the C–Br bond with activation energy of 0.19 ± 0.08 kJ/mol and whole molecule reorientations thermally activated above 100 K with activation energy of 4.3 ± 1.2 kJ/mol. At the lowest studied temperature (50 K), the methyl group rotates faster by almost one order of magnitude in the large cage (characteristic time of 1.25 ps) than in the small cage (characteristic time of 10 ps). Such results provide new experimental signatures of the cage occupancy by evidencing different Brownian dynamics for the guest molecules in small cages and those in large cages. [ABSTRACT FROM AUTHOR]

Among hydrogen storage materials, hydrogen hydrates have received a particular attention over the last decades. The pure hydrogen hydrate is generated only at extremely high-pressure (few thousands of bars) and the formation conditions are known to be softened by co-including guest molecules such as tetrahydrofuran (THF). Since this discovery, there have been considerable efforts to optimize the storage capacities in hydrates through the variability of the formation condition, of the cage occupancy, of the chemical composition or of the hydrate structure (ranging from clathrate to semi-clathrate). In addition to this issue, the hydrogen insertion mechanism plays also a crucial role not only at a fundamental level, but also in view of potential applications. This paper aims at studying the molecular hydrogen diffusion in the THF hydrate by in-situ confocal Raman microspectroscopy and imaging, and at investigating the impact of strong acid onto this diffusive process. This study represents the first report to shed light on hydrogen diffusion in acidic THF-H 2 hydrate. Integrating the present result with those from previous experimental investigations, it is shown that the hydrogen insertion in the THF hydrate is optimum for a pressure of ca . 55 bar at 270 K. Moreover, the co-inclusion of perchloric acid (with concentration as low as 1 acidic molecules per 136 water molecules) lead to promote the molecular hydrogen insertion within the hydrate structure. The hydrogen diffusion coefficient-measured at 270 K and 200 bar-is improved by a factor of 2 thanks to the acidic additive., (Copyright © 2020 Nguyen, Pétuya, Talaga and Desmedt.)

We designed and implemented an experimental methodology to investigate gas hydrate formation and growth around a water-guest meniscus in a thin glass capillary, thus mimicking pore-scale processes in sediments. The glass capillary acts as a high-pressure optical cell in a range of supercooling conditions from 0.1 °C, i.e., very close to hydrate dissociation conditions, to ∼35 °C, very near the metastability limit. Liquid or gaseous CO 2 is the guest phase in most of the experiments reported in this paper, and N 2 in a few of them. The setup affords detailed microscopic observation of the roles of the key parameters on hydrate growth and interaction with the substrate: supercooling and substrate wettability. At low supercooling (less than 0.5 °C), a novel hydrate growth process is discovered, which consists of a hollow crystal originating from the meniscus and advancing on the guest side along the glass, fed by a thick water layer sandwiched between the glass and this crystal.