1,721,053 research outputs found
Hydrogen storage in MgH2 matrices: An ab-initio study of Mg-MgH2 interface
No full textWe studied the atomic-level structure of a model Mg-MgH2 interface by means of the Car-Parrinello molecular dynamics method (CPMD). The interface was characterized in terms of total energy calculations, and an estimate of the work of adhesion was given, in good agreement with experimental results on similar systems. Furthermore, the interface was studied in a range of temperatures of interest for the desorption of hydrogen. We determined the diffusivity of atomic hydrogen as a function of the temperature, and give an estimate of the desorption temperature. © (2008) Trans Tech Publications, Switzerland
Ex situ integration of iron oxide nanoparticles onto exfoliated expanded graphite flakes in aqueous suspension
No full textHybrid structures composed of exfoliated expanded graphite (EG) and iron oxide nanocrystals were produced by an ex situ process. The iron oxide nanoparticles coated with meso-2,3-dimercaptosuccinic acid (DMSA), or poly(acrylic acid) (PAA) were integrated onto the exfoliated EG flakes by mixing their aqueous suspensions at room temperature under the support of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysuccinnimide (NHS). EG flakes both naked and functionalized with branched polyethylenimine (PEI) were employed. Complete integration of the two constituents was achieved and stability was maintained for more than 12 months. No preferential spatial distribution of anchoring sites for attachment of iron oxide nanoparticles was observed, regardless of whether the EG flakes were used naked or functionalized with PEI molecules. The structural and physicochemical characteristics of the exfoliated expanded graphite and its hybrid nanostructures were investigated by SEM, TEM, FTIR and Raman techniques
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No full textHydrogenation-induced microstructure evolution in as cast and severely deformed Mg-10 wt.% Ni alloy
No full textWe determined the kinetics of hydrogen absorption of the hypoeutectic Mg-10 wt.% Ni alloy in the as-cast state and after processing by four passes of equal channel angular pressing (ECAP). While during the first hydrogenation cycle the ECAP-modified alloy exhibited faster absorption than its as-cast counterpart, this advantage was lost after the second hydrogenation cycle; parity was regained after six cycles. We attributed these differences in the hydrogen absorption kinetics to the formation of large (tens of micrometers) faceted Mg crystals observed during the first hydrogenation cycle. These crystals were significantly larger in the ECAP-modified alloy than in its as-cast counterpart. We discussed the growth of large Mg crystals during hydrogenation in terms of self-diffusion of Mg atoms driven by the metal-hydride transformation stress. The larger size of these crystals in the ECAP-processed alloy was attributed to the acceleration of diffusion by ECAP. Our metallographic studies revealed a number of microstructural changes in the alloys upon hydrogenation, such as cracking, accumulation of plastic strain in large Mg crystals, and re-distribution of the dispersed particles of Mg2Ni phase in the partly hydrogenated alloys. © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights
Effects of the compaction pressure and of the cycling process on kinetics and microstructure of compacted MgH2-based mixtures
No full textMaterials to be used in tanks for hydrogen storage should have suitable thermal properties otherwise their performances in term of kinetics and hydrogen capacity would rapidly decrease during exercise. For these reason in this work ball milled powders of MgH2 with Nb2O5 as catalyst and Expanded Natural Graphite (ENG) have been compacted at different pressures in the range between 100 and 600 MPa. The pellets were tested until 50 cycles after which the material was able to absorb and desorb hydrogen without significant reduction in maximum capacity. The mechanical stability of these compacted systems during repeated cycling under hydrogen pressure is discussed together with the modifications of the microstructure. The compaction pressure revealed to affect largely the distribution of ENG in the pellets and their mechanical stability upon cycling while this parameter have only a slight effect on the sorption kinetics. Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD) and volumetric Sievert's type apparatus have been used to characterize the samples. Copyright © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved
Hydrogen storage properties of Pd-doped thermally oxidized single wall carbon nanohorns
No full textSingle wall carbon nanohorns as well as their thermally oxidized derivatives were decorated with Pd nanoparticles and their H2 sorption performance was examined at 298 K up to 20 bar. The specific surface area of the nanohorns was increased through air oxidation, while both the thermal treatment and the metal doping led to the enhancement of the H2 uptake. The higher uptake of the hybrid materials could not be attributed only to the additive effect of the carbon support and Pd content suggesting the existence of a cooperative mechanism between the metal particles and the carbon surface. This weak chemisorption process was found to be fully reversible after mild heating; still, its contribution to the overall H2 uptake was not found to be of great significance. © 2014 Elsevier B.V. All rights reserved
A step forward to the dehydrogenation reversibility of amine-borane adducts by coupling sodium and hydrocarbon groups
No full textMechanochemistry has played an important role in the synthesis of many novel compounds, in particular within the field of materials for solid state hydrogen storage applications. This work investigates reactive milling of ethane 1,2-di-amineborane (EDAB) and sodium hydride which yields the evolution of one equivalent of hydrogen and the formation of a novel compound (named NaEDAB) as evidenced by X-ray diffraction analyses. We postulate for this compound the chemical formula NaB2C2N2H13. The thermolysis of NaEDAB below 400 °C releases about 8 wt.% pure hydrogen, without producing foaming. Moreover, sodium addition significantly modifies hydrogen desorption enthalpies, giving rise to milder exothermic H2 release at moderate temperatures with respect to neat EDAB, as well as an endothermic desorption process at higher temperature. This result opens novel and promising perspectives towards the reversible hydrogenation of these compounds. © 2014 Hydrogen Energy Publications, LLC
Skin nitric oxide and its metabolites are increased in non-burned skin after thermal injuries: Shock 22(3):278-282, 2004
No full textLocal and systemic inflammation can lead to progression of burn wounds, converting second- to third-degree wounds or extending the burn to adjacent areas. Previous studies have suggested that the skin is an important site of production of nitric oxide (NO), synthesized by inducible nitric oxide synthase (iNOS) activation after injury. NO increases in burned wounds, but its formation in noninjured skin has not been investigated. We hypothesized that after severe burns, NO and cytotoxic peroxynitrite would increase in noninjured skin. We also tested the hypothesis that BBS-2, a specific inhibitor of iNOS, would impair NO formation after burn. Thirteen female sheep were randomized into burn injury and smoke inhalation (n = 5, group 1), burn and smoke treated with BBS-2 (n = 3, group 2), and sham (saline treatment, no injury) (n = 5, group 3). All the animals, including the sham-injury group, were mechanically ventilated for 48 h. Samples of nonburned skin and plasma were collected from each animal, and levels of NO and its metabolites were evaluated using a NO chemiluminescent detector. Nitrotyrosine and iNOS expression were determined in the skin by Immunoperoxidase staining, and scoring of masked slides (epidermis, hair follicles, vessels, glands, and stroma) was performed. Skin NO and metabolites significantly increased in the burn and smoke injury group, and this was inhibited by BBS-2. Nitrotyrosine expression also increased significantly in the skin of burned animals. BBS-2 prevented the increase of NOx but not the increase of nitrotyrosine expression in skin. Plasma levels of NO increased in burned animals when compared with sham, but this increase was not significant. The increase of NO and its metabolites after burn in noninjured skin is followed by a significant increase in peroxynitrite, a potent cytotoxic mediator
Microstructure and morphology changes in MgH2/expanded natural graphite pellets upon hydrogen cycling
No full textCompacted mixtures based on ball-milled magnesium hydride (MgH2) have gained significant research interest as suitable materials for hydrogen storage tanks. The issue related to their stability during practical service conditions is one of paramount relevance. In this work, we investigate the microstructure and morphology of pellets obtained by the compaction of ball-milled MgH2/Nb2O5 powders mixed with expanded natural graphite. The pellets are subjected to repeated hydrogen sorption cycles to measure hydrogen storage properties and its stability with cycling. Moreover, the effect of air-exposure on the hydrogen sorption behavior is studied. Electron microscopy observations of as-prepared and cycled pellets point to a dramatic modification of the material's microstructure upon repeated hydrogen cycling. In particular, the appearance of MgH2 particles depleted of the Nb2O5 catalyst and the formation of hollow MgO shells are highlighted. These findings are discussed by a simple model which takes into account the basic mechanisms intervening during the metal-hydride transformation in the pellet. © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved
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