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Étude du système Fe–Ti–V et de ses applications au stockage de l'hydrogène

Abstract : In order to stop the current climatic disturbance due to the large scale use of fossil fuels as a source of energy, a transition towards less carbon dioxide emitting energies is necessary. Hydrogen, a carbon dioxide neutral energy carrier, could play an important role. However, its thermodynamic properties prevent from storing it pure under moderate pressure in a reasonable volume in order to feed a vehicle. Metallic hydride storage seems to be a promising solution to this problem. Vanadium based body centered cubic alloys being light compared to rare earth based alloys used since the 1970s, the purpose of this work is the study of the hydrogenation properties (equilibrium pressure and absorption capacity in particular) of Fe–Ti–V system alloys. Since the compounds to be investigated have to take the body centered cubic structure, but the solubility limit of iron in this phase of the Fe–Ti–V system is not reliably documented, the first part of this work consisted in deepening the equilibrium diagram knowledge by determining the isothermal sections at 1000 °C and 1200 °C. With this aim in view, bulk samples were synthesized by arc melting followed by an annealing in a resistive furnace. The phase relations were systematically analysed by means of powder X-ray diffraction and electron probe microanalysis. Thanks to these techniques, we showed that after annealing at 1000 °C, the solubility limit of iron in a Ti–V alloy exceeds 15 at.% for any ratio Ti/V < 1. A quasi-peritectic reaction at 1140 °C could also be evidenced and a liquidus surface projection is proposed, based on microstructural analyses. The second part of this work consisted in the study of the hydrogenation properties of body centered cubic samples. The majority of the studied compounds showed a total capacity at ambient temperature of 1.7 H/M, corresponding to 3.4 wt.%, or 140 g/L, and the reversible capacity of the sample of composition Ti10V88Fe2 amounts to 0.98 H/M, corresponding to 1.93 wt.%, or 82,5 g/L (density higher than that of liquid hydrogen). There is a linear relationship, which was determined, between the alloy compositions and the hydrogenation enthalpy. We can thus, depending on the chosen composition, obtain equilibrium pressures ranging from 0.1 bar to more than 100 bar. A structural study by means of X-ray diffraction for low hydrogen concentrations pointed out the unit cell distortion from body centered cubic to body centered tetragonal by increasing hydrogen concentration. Furthermore, absorption kinetics of the body centered cubic samples is interesting, since 90 % of the total capacity is absorbed within one minute. On the other hand, a slowing down of the kinetics is observed when a large number of hydriding – dehydriding cycles is applied. However, this kind of alloy remains promising for hydrogen storage applications.
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https://tel.archives-ouvertes.fr/tel-00442963
Contributor : Blaise Massicot <>
Submitted on : Friday, December 25, 2009 - 2:20:18 PM
Last modification on : Wednesday, December 4, 2019 - 4:39:00 PM
Long-term archiving on: : Friday, June 18, 2010 - 12:06:48 AM

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Blaise Massicot. Étude du système Fe–Ti–V et de ses applications au stockage de l'hydrogène. Matériaux. Université Paris-Est, 2009. Français. ⟨tel-00442963⟩

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