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Nanostructured Metal Hydrides for Hydrogen Storage Studied by In Situ Synchrotron and Neutron Diffraction
- Volodymyr Yartys, Roman Denys, Jan Petter Maehlen, Colin J Webb, Evan MacA Gray, Tomas Blach, Andrey A. Poletaev, Jan Ketil Solberg, Olivier Isnard
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- Journal:
- MRS Online Proceedings Library Archive / Volume 1262 / 2010
- Published online by Cambridge University Press:
- 01 February 2011, 1262-W04-01
- Print publication:
- 2010
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This work was focused on studies of the metal hydride materials having a potential in building hydrogen storage systems with high gravimetric and volumetric efficiencies of H storage and formed / decomposed with high rates of hydrogen exchange. In situ diffraction studies of the metal-hydrogen systems were explored as a valuable tool in probing both the mechanism of the phase-structural transformations and their kinetics. Two complementary techniques, namely Neutron Powder Diffraction (NPD) and Synchrotron X-ray diffraction (SR XRD) were utilised. High pressure in situ NPD studies were performed at D2 pressures reaching 1000 bar at the D1B diffractometer accommodated at Institute Laue Langevin, Grenoble. The data of the time resolved in situ SR XRD were collected at the Swiss Norwegian Beam Lines, ESRF, Grenoble in the pressure range up to 50 bar H2 at temperatures 20-400°C.
The systems studied by NPD at high pressures included deuterated Al-modified Laves-type C15 ZrFe2-xAlx intermetallics with x = 0.02; 0.04 and 0.20 and the CeNi5-D2 system. D content, hysteresis of H uptake and release, unit cell expansion and stability of the hydrides systematically change with Al content.
Deuteration exhibited a very fast kinetics; it resulted in increase of the unit cells volumes reaching 23.5 % for ZrFe1.98Al0.02D2.9(1) and associated with exclusive occupancy of the Zr2(Fe,Al)2 tetrahedra.
For CeNi5 deuteration yielded a hexahydride CeNi5D6.2 (20°C, 776 bar D2) and was accompanied by a nearly isotropic volume expansion reaching 30.1% (∆a/a=10.0%; ∆c/c=7.5%). Deuterium atoms fill three different interstitial sites including Ce2Ni2, Ce2Ni3 and Ni4. Significant hysteresis was observed on the first absorption-desorption cycle. This hysteresis decreased on the absorption-desorption cycling.
A different approach to the development of H storage systems is based on the hydrides of light elements, first of all the Mg-based ones. These systems were studied by SR XRD. Reactive ball milling in hydrogen (HRBM) allowed synthesis of the nanostructured Mg-based hydrides.
The experimental parameters (PH2, T, energy of milling, ball / sample ratio and balls size), significantly influence rate of hydrogenation. The studies confirmed (a) a completeness of hydrogenation of Mg into MgH2; (b) indicated a partial transformation of the originally formed -MgH2 into a metastable -MgH2 (a ratio / was 3/1); (c) yielded the crystallite size for the main hydrogenation product, -MgH2, as close to 10 nm. Influence of the additives to Mg on the structure and hydrogen absorption/desorption properties and cycle behaviour of the composites was established and will be discussed in the paper.
Oxidant stress: the role of nutrients in cell-lipoprotein interactions
- Denis Blache, Laurence Gesquière, Nadine Loreau, Phillipe Durand
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- Journal:
- Proceedings of the Nutrition Society / Volume 58 / Issue 3 / August 1999
- Published online by Cambridge University Press:
- 28 February 2007, pp. 559-563
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Oxidant stress is increasingly becoming an important hypothesis to explain the genesis of several pathologies, including cancer, atherosclerosis and also ageing. Beside a few rare genetic defects, dietary factors are thought to play a key role in the regulation of the production of reactive oxygenated species. An imbalance between nutrients, and in particular those involved in antioxidant status, could explain the onset of an enhanced production of free radicals. We will briefly review information concerning oxidation of lipids and lipoproteins which lead to atherothrombosis. We also present new findings supporting a role for blood platelets in generating oxidant species. New data are also described concerning the role of oxygenated derivatives of cholesterol, oxysterols, in cellular cholesterol efflux and NO production. Also, new developments relating to the influence of direct effects of free radicals on cellular cholesterol homeostasis are presented. Finally, the in vitro effects of butyrate, a natural short-chain fatty acid produced by bacterial fermentation, in the protection against free radical-mediated cytotoxicity are discussed. These data provide information on the mechanisms of dietary antioxidants in preventing oxidant stress.Résumé Au côté des rares cas d’origine génétique, les facteurs nutritionnels (déséquilibres alimentaires, déficience en nutriments antioxydants) jouent des rôles cruciaux dans la modulation de la production d’espèces actives de l’oxygène, conduisant à l’établissement d’un stress oxydant, situation métabolique de plus en plus reconnue comme susceptible d’être à l’origine de nombreuses pathologies comme les cancers, l’athérosclérose et également le vieillissement. Après avoir brièvement rappelé les données concernant l’oxydation des lipides et des lipoprotéines susceptibles de conduire au développement de l’athéro-thrombogenèse, nous présentons des données récentes et originales indiquant que les plaquettes sont en fait capables à l’instar d’autres cellules, de produire des formes actives de l’oxygène susceptibles de modifier les LDL. Des résultats originaux sont également exposés concernant l’effets des oxystérols, produits d’oxydation du cholestérol générés au cours de l’oxydation des LDL ou présents dans l’alimentation, sur deux paramètres importants comme l’efflux du cholestérol cellulaire et la production de monoxyde d’azote. De plus, des données nouvelles relatives à l’effets du stress oxydant et son inhibition par des antioxydants d’origine nutritionnelle sont exposées sur l’homéostasie du cholestérol cellulaire. Enfin, dans ce contexte, les effets potentiellement antiathérogènes d’un acide gras à courte chaîne produit par la fermentation bactérienne, le butyrate, sont décrits sur la protection de cellules en culture vis-à-vis d’un stress oxydant in vitro. Ces éléments contribuent à apporter de nouvelles informations renforçant la notion de fonctionnalité des nutriments dans la protection du stress oxydant en relation avec la pathogenèse.