Titanium-functional group complexes for high-capacity hydrogen storage materials

Using first-principles density-functional electronic structure calculations, we propose functionalized organic molecules decorated with titanium atoms as high-capacity hydrogen storage materials. We study six kinds of functional groups which form complexes with Ti atoms and find that each complex is capable of binding up to six H₂ molecules. Among such complexes, Ti-decorated ethane-1,2-diol can store H₂’s with the maximum gravimetric density of 13 wt% and, under ambient conditions, a practically usable capacity of 5.5 wt%. We also present various forms of storage materials which are obtained by modifying well-known nanomaterials using Ti-functional group complexes.     

Synergistic effects in hydrogen-helium bubbles

The detrimental effects of hydrogen and helium on structural materials undergoing irradiation are well documented, if not well understood. There is experimental evidence to suggest that a synergistic effect between the two elements exists, which results in increased damage when both are present. This situation is expected in the next generation of fusion and fission reactors, so a fundamental understanding of these synergistic interactions is needed to predict materials performance. We perform atomistic simulations of hydrogen and helium bubbles in body-centered cubic iron to determine the mechanism behind this effect. We first develop an interatomic potential suitable for describing the interactions between hydrogen and helium. Through analysis of the energetics and structure of these bubbles, we explain the observed synergy as a consequence of bubble growth through helium induced loop punching, aided by the presence of hydrogen, instead of as a direct interaction between hydrogen and helium. The hydrogen benefits from an increased area of free surface on which to bind.     

Reduction of surface hydrogen on ultra cold neutron container materials by ion bombardement

The hydrogen concentration near to the surface of some typical ultra cold neutron container materials has been measured with theH(¹¹ B, ) 2 reaction. The concentration of 2 – 3 × 10¹⁶ H atoms/cm² is in agreement with results obtained by other methods. Using theoretical neutron scattering cross sections we confirm that at room temperature the experimentally known high UCN reflection loss rate could be caused by the measured concentration of hydrogen. The original hydrogen content has been reduced by ion bombardment to about one tenth of its original value. The redeposition of hydrogen has been studied as a function of the residual pressure. We conclude that it is possible to produce by sputtering container surfaces with hydrogen (and other surface impurity) contents sufficiently low and stable to test directly with UCN whether their losses are mainly due to upscattering on impurities or not.     

Effect of ion implantation on the chemical composition and structure of surface layers of heat-resistant alloys

We present a critical analysis of literature data devoted to the effect of ion implantation on the physicochemical state of surface layers of heat-resistant materials. We pay special attention to the problem of choosing the type of ions to be implanted, the bombardment conditions, and the finishing heat treatment with the goal of achieving the optimal level of operating properties. We show that for complex heterogeneous systems, the optimal treatment conditions can be estimated by methods of local equilibrium thermodynamics, chemical kinetics, and the theory of interaction of fast ions with solids using the basic principles of bulk alloying of heat-resistant alloys. We consider the characteristics features of continuous and pulsed implantation in heat-resistant materials. We formulate the requirements for techniques for investigating the chemical composition and the structural phase state of the near-surface regions of the bombarded targets. Analysis of the literature data on the effect of the bombardment conditions on the structure of the metals has shown that the data are ambiguous, that different authors use different terminology, and that the question of the phenomenology of the long-range effect is under dispute.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 72–91, May, 1994.     

Use of novel carbon-nanofiber-doped carbon liquid crystals as suitable adsorbents for hydrogen storage

Over the last few years a number of groups have been exploring the possibilities and limitations associated with using adsorption on newly developed materials for the storage of hydrogen. Here we report the results of hydrogen adsorption investigations on a newly synthesized form of carbon nanofiber-doped carbon liquid crystals. This material shows a marked increase in specific surface area upon activation with water vapor, leading to activated samples that are capable of adsorbing hydrogen upto 3.5% by weight at 77.3 K, at moderate pressures. The possibility of higher adsorption (6.5 wt.%) in these materials is also discussed. PACS 68.43.-h; 68.43.De; 68.60.-p     

Pseudofermion ferromagnetism in the Kondo lattices: a mean-field approach

Research into new materials to be used as hydrogen reservoirs is necessary, the increasing demand of energy in the world should be covered progressively by clean energies, trying not to pollute the environment. With this work we wish to contribute to the knowledge of the different saline hydrides and the possibility of using these as hydrogen reservoirs. We performed a systematic study on these materials. In this work we used different ab-initio codes to study several compounds of lithium and beryllium with hydrogen.     

Features of the plasma saturation of nanocrystalline and coarse-crystalline titanium samples with hydrogen and deuterium

We investigate the laws governing the saturation of nano- and coarse-crystalline Ti-6Al-4V alloy samples with hydrogen from high-frequency and glow discharge plasmas with a view to finding materials suitable for making hydrogen accumulators. We conclude that nanocrystalline Ti-6Al-4V alloy holds promise for creating hydrogen accumulators, and hydrogen plasma of high-frequency discharge origin is a cleaner hydrogen saturation medium than that of non-self-sustained discharge origin.     

Neutron powder diffraction of metal-organic frameworks for hydrogen storage

We review recent structural studies that we have undertaken aimed at elucidating the fundamental properties of metal-organic framework materials and their interactions with hydrogen. We have shown that exposing coordinatively unsaturated metal centers can greatly enhance the hydrogen binding energy and that they result in a significant increase of the surface packing density of adsorbed hydrogen molecules on materials’ surface. We will review some of the structural aspects of these materials, especially the adsorbed hydrogen molecule surface packing density in one type of metal-organic framework, MOF-74, which can be packed even denser than that in solid hydrogen.      

On the experimental determination of hydrogen momentum distributions at sources providing high energy neutrons

With the increased usable flux at high neutron energies of pulsed sources the measurement of momentum distributions enters a new range of feasibility and accuracy. It is shown that for the case of hydrogen which has many applications an additional gain is to be expected due to the insensitivity to monochromization. The optimization of the analyzer is discussed and a test experiment is proposed.     

Hydrogen defect-level pinning in semiconductors: the muonium equivalent

We have determined locations for the donor and acceptor levels of muonium in six semiconductor materials (Si, Ge, GaAs, GaP, ZnSe, and 6H-SiC) as a test of defect-level pinning for hydrogen. Within theoretical band alignments, our results indicate a common energy for the equilibrium charge-transition level Mu(+/-) to within experimental uncertainties. However, this is nearly 0.5 eV higher than the energy at which the equivalent level for hydrogen was predicted to be pinned. Corrections for zero-point energy account for only about 10% of this difference. We also report experimental results for the (negative-U) difference between donor and acceptor levels for Mu to be compared with calculated values for H impurities in the same materials.     

Energy of hydrogen dissolution in FCC hydrides of disordered Ti–V–Cr alloys according to density functional theory data

Ti–V–Cr alloys are hydrogen storage materials, but their characteristics, which are important for practical applications, depend strongly on composition. The search for an optimal composition with given characteristics requires the support of theoretical calculations of the electronic structure of alloys and their hydrides. In this paper, the interstitial energy and energy of hydrogen dissolution in the hydride of a ternary disordered Ti_0.33V_0.27Cr_0.4H_1.75 alloy with a face-centered cubic lattice were calculated within the framework of the density functional theory using the pseudopotential method. The deviation of the dissolution energy distribution from the Gaussian distribution is shown. Based on the data obtained for a particular hydride, the energy distributions of hydrogen dissolution in a number of hydrides of alloys (Ti_0.8Cr)_1–xV_x with x = 0.9, 0.8, 0.7, and 0.6 have been derived. A correlation was found between the theoretically calculated width of the energy distribution of hydrogen dissolution and the experimental slope of the pressure “plateau.”     

Investigation of planar photonic crystal band diagrams under the light cone using surface coupling techniques

We report experimental results for the band structure of 2-dimensional triangular photonic crystals etched in SOI wafers. Boundary conditions at the surface and at the border of the etched area of the slab, allow the excitation of guided modes via diffraction phenomena using surface coupling techniques and the determination of the structure band diagram above and below the light cone. These non-destructive techniques, usable for non-active materials, allow fast characterization of technical processes and the location in reciprocal space of areas with unique dispersion properties. PACS 42.70.Qs; 42.25.Fx; 81.70.Ex     

Proton conduction in α-alumina and its application to hydrogen sensor for molten metals

With a view to developing a new proton conducting solid electrolyte usable at more elevated temperatures, the proton conduction in α-alumina was examined by reviewing the historical literatures and our recent works. It was clarified that acceptor-doped α-alumina had the possibility to exhibit a certain amount of proton conduction when hydrogen or water vapor was contained in the surrounding. In the case of Mg-doped α-alumina, proton conduction was found to dominate in the considerably wide range of oxygen and hydrogen potentials at temperatures 1273–1673 K. The excellent performance of the hydrogen sensor for molten metals employing Mg-doped α-alumina was experimentally ascertained.     

Hydrogen adsorption and desorption in carbon nanotube systems and its mechanisms

The hydrogen physisorption properties in single-walled carbon nanotube (SWNT) based materials were characterized. The SWNTs were highly purified and three useful pores for hydrogen physisorption were activated. Hydrogen was physisorbed in intra-tube pores at room temperature and the capacity was estimated to be about 0.3–0.4 wt.% at room temperature. The adsorption capacity can be explained by the Langmuir model. The intra-tube pores have large adsorption potential and this induces hydrogen physisorption at comparatively higher temperatures. This fact indicates the importance of fabricating sub-nanometer ordered pores for this phenomena. PACS 51.30.+i; 51.90.+r; 81.05.Tp; 81.07.De     

Optical Materials for the THz Range

Optics and Spectroscopy - The properties of optical materials usable in the terahertz (THz) spectral range, which is the boundary between the optical and radio ranges, are examined. The relevance...     

Precise calculation of transition frequencies of hydrogen and deuterium based on a least-squares analysis

We combine a limited number of accurately measured transition frequencies in hydrogen and deuterium, recent quantum electrodynamics (QED) calculations, and, as an essential additional ingredient, a generalized least-squares analysis, to obtain precise and optimal predictions for hydrogen and deuterium transition frequencies. Some of the predicted transition frequencies have relative uncertainties more than an order of magnitude smaller than that of the g factor of the electron, which was previously the most accurate prediction of QED.     

Improvement of field emission of graphite flakes using hydrogen thermal processing

In order to improve the field electron emission properties of the graphite, the carbon nanoparticles (CNPs) are synthesized on the micrographite flakes by hydrogen thermal processing. We spin the graphite solution on the silicon wafer and desiccate it, then produce the CNPs on the graphite flakes using hydrogen thermal processing in the furnace. The processing parameters such as the processing temperature, hydrogen flow rate and processing time, were varied to find the optimal conditions for the improvement of the field emission properties of the graphite flakes. The experimental results show that the field emission properties of the graphite flakes have glaring improvement after heat treatment owing to the increase of the defect density and the CNPs on above. The turn-on field was decreased from 7.7 of the untreated sample to 4.3 V/μm of the treated sample at the optimal processing conditions.     

应变对析氢反应催化剂TiC2性能影响的研究

应变工程是一种有效地用来调整原子薄膜材料的电子、磁性和光学性能的策略.利用第一性原理计算,我们表明应变也可以有效地调节Ti C₂的析氢反应(HER)的催化活性,这是电解水电化学制氢所必需的.我们主要考虑0-8%范围的拉伸应变,研究发现,在25%的氢覆盖率下双轴拉伸比单轴拉伸能更有效的提高HER活性,但b方向拉伸后的Ti C₂结构具有更高的氢最大覆盖率,且b方向的拉伸应变对不同氢覆盖率的Ti C₂单层片的催化性能都有很大的提高.电子结构计算表明,拉伸应变可以激活相对惰性的内部价电子,从而引起体系的失稳和催化活性的提高.在本工作中获得的见解可能有助于利用应变作为一种有效手段来提高二维材料的催化活性,并探索更有效地调整其电子结构和催化活性的新方法.     

Hydrogen Release and Room Temperature Creep for Vanadium Alloys Containing Hydrogen

Vanadium alloy has been taken as one of the candidate structural materials for fusion reactors because of its excellent high-temperature mecha nical performances, high thermal stress factor and low radioactivity. It is a kind of potential materials for hydrogen storage as well. Because operated in an environment conta!ning hydrogen and its isotopes or the neutron irradiation resulting transmutation product of H, the problem that H induced degradation of mechanical properties and hydrogen embrittlement has been being one of the key issues for the application for vanadium alloys.     

An improved approach for hydrogen analysis in metal samples using single laser-induced gas plasma and target plasma at helium atmospheric pressure

We report in this paper the results of an experimental study on hydrogen analysis of solid samples in high pressure helium ambient gas employing the basic scheme of laser induced breakdown spectroscopy (LIBS). It is shown that the metastable excited state of helium atom can be utilized to induce delayed excitation of the ablated hydrogen atoms, and thereby avoid the Stark broadening effect as well as overcoming the undesirable mismatch effect, which are responsible for inefficient excitation respectively. It is further demonstrated that for samples of high boiling-point materials such as zircaloy, successful hydrogen analysis can be achieved by a newly introduced double excitation technique employing single laser realized in a modified configuration of the conventional LIBS method. PACS 51-52