Synthesis of Mg2FeH6 by reactive mechanical alloying: formation and decomposition properties

Gennari, F.C.; Castro, Federico de; Andrade-Gamboa, J.

doi:10.1016/s0925-8388(01)02009-6

Cited by 127 publications

(118 citation statements)

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“…The activation energy of the desorption of pure Mg 2 FeH 6 prepared by sintering can also be estimated as 165:7 AE 8:4 kJ mol À1 . The result is similar with the result 174 AE 36 kJ mol À1 H 2 for Mg 2 FeH 6 which has been reported by Gennari et al 7) Compared with the sintering sample, the activation energy of the desorption of pure Mg 2 FeH 6 prepared by RMA is much smaller, which should be contributed to the crystallite sizes reduction and crystal structure modification by ball milling. As the particle size of Synthesis and Hydrogen Storage Behaviour of Pure Mg 2 FeH 6 at Nanoscalethe sintering sample is much smaller than that of the RMA samples, it is suggested that decrease of crystallite size played a more important role compared with particle size for enhancing desorption property of Mg 2 FeH 6 .…”

Section: Resultssupporting

confidence: 90%

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Synthesis and Hydrogen Storage Behaviour of Pure Mg2FeH6 at Nanoscale

et al. 2011

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Pure Mg 2 FeH 6 compounds with two different morphologies have been successfully synthesized directly by mechanical milling (MM) and sintering of a mixture of 2Mg+Fe nanoparticles under an H 2 atmosphere, respectively. The successful preparation of pure Mg 2 FeH 6 can be attributed to the small particle sizes of Mg and Fe nanoparticles prepared by hydrogen plasma-metal reaction (HPMR), which provides shorter diffusion distance for hydrogen and the metals. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) results show that the Mg 2 FeH 6 synthesized by mechanical milling has larger particle size but smaller crystallite size compared with the Mg 2 FeH 6 synthesized by sintering. The Mg 2 FeH 6 synthesized by mechanical milling can desorb more than 4.5 mass% hydrogen in 10 min under an initial hydrogen pressure of 0.001 bar at 573 K. Compared with the Mg 2 FeH 6 synthesized by sintering under the same conditions as the Mg 2 FeH 6 synthesized by mechanical milling, it is suggested that decrease of crystallite size is beneficial for enhancing desorption property of Mg 2 FeH 6 .

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Section: Resultssupporting

confidence: 90%

“…For the preparation of Mg 2 FeH 6 compounds, many methods such as sintering the 2Mg+Fe mixture under high pressure hydrogen 5,6) and mechanical milling the 2Mg+Fe or 2MgH 2 +Fe mixture [7][8][9][10][11][12][13][14] have been developed. The Mg 2 FeH 6 compound has been first synthesized and described in 1984.…”

Section: Introductionmentioning

confidence: 99%

Synthesis and Hydrogen Storage Behaviour of Pure Mg2FeH6 at Nanoscale

et al. 2011

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“…An example is the formation of Mg 2 FeH 6 [233]. This class of metal hydrides could be synthesized by high hydrogen pressure [234], thin films [235] or ball milling [236][237][238][239]. In the case of thin films, metastable phases could be stabilized by the high stresses due to the clamping of the material to the substrate [201,240,241].…”

Section: Reduction Of the Heat Of Formationmentioning

confidence: 99%

Metal Hydrides

Huot

2010

Handbook of Hydrogen Storage

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Metal hydrides are promising candidates for many stationary and mobile hydrogen storage applications. Presently, the most common use of metal hydrides is as anode material in commercial nickel-metal hydrides (Ni-MH) rechargeable batteries which have replaced conventional nickel-cadmium batteries in many applications. A wide variety of Ni-MH batteries are now on the market with cell sizes ranging from 30 mAh to 250 Ah [1,2]. Some other applications are: hydrogen compression [3], aircraft fire-detectors [4], isotope separation [5], and hydrogen getters for microelectronic packages. Hydride formation is also used in the HDDR process (hydrogenation-disproportionation-desorption-recombination) for the synthesis of magnetic materials such as Nd 2 Fe 14 B [6]. A striking application is as a component of cryocoolers for the ESA Planck mission [7]. Another exciting new application is the use of metal hydrides for switchable mirrors [8]. As we can see, metal hydrides have a wide range of applications. However, most research and development is targeted towards two applications: batteries and hydrogen storage. The former is now widely exploited but the latter is still facing many technical problems. The main advantages of storing hydrogen in a metal hydride are the high hydrogen volumetric densities (sometimes higher than in liquid hydrogen) and the possibility to absorb and desorb hydrogen with a small change in hydrogen pressure [9].The physics of hydrogen in elemental metals was reviewed at the end of the 1970s in thebooksHydrogeninMetals,volumesIandII [10,11].The1970s alsosawtheemergence of the important field of intermetallic compounds as hydride materials. An in-depth review of this field can be found in Hydrogen in Intermetallic Compounds volumes I, and II [12,13]. A review of the propertiesand applications of hydrogen in metals can befound in the third volume of Hydrogen in Metals [14]. The basic properties of the metal-hydrogen system are discussed from a fundamental point of view by Fukai [15]. Although initial studies on nanocrystalline and amorphous metal hydrides were initiated around the 1980s [16], the real emergence of nanocrystalline metal hydrides as a new class of Handbook of Hydrogen Storage. Edited by Michael Hirscher

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“…In the case of reactive milling, which means that milling is carried out under a hydrogen atmosphere, the reaction mixture is directly hydrogenated during the milling process. With this technique, Mg 2 FeH 6 was prepared starting from a mixture of 2 mole Mg and 1 mole Fe under a pressure of 0.5 MPa and reaction times of 100 h [214,215]. In a similar manner, Mg 2 CoH 5 was synthesized from a stoichiometric mixture of 2 mole MgH 2 and 1 mole Co under a hydrogen atmosphere of 0.1 MPa H 2 [216].…”

Section: Complex Transition Metal Hydrides J149mentioning

confidence: 99%

Complex Hydrides

and

Felderhoff

2010

Handbook of Hydrogen Storage

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Complex hydrides are salt-like materials in which hydrogen is covalently bound to the central atoms, in this way a crystal structure consisting of so-called complex anions is formed. In general, complex hydrides have the chemical formula A x Me y H z . Compounds where position A is preferentially occupied by elements of the first and second groups of the periodic table and Me is occupied either by boron or aluminum are well known and have been intensively investigated. However, another possibility is that complex hydrides are built by transition metal cations. Complex metal hydrides have been known for more than 50 years, but for many years they were not considered for reversible hydrogen storage due to the high kinetic barriers of the decomposition requiring high temperatures. The situation changed in 1997 when Bogdanovi c and Schwickardi discovered that the kinetic barrier of the decomposition of the complex metal hydride, NaAlH 4 , can be lowered by the addition of Ti catalysts and that the material becomes reversible close to acceptable technical conditions [1]. They further showed not only that catalysts can enhance the kinetics of dehydrogenation but also that rehydrogenation under moderate conditions becomes feasible. This breakthrough induced the publication of a tremendous number of papers focusing on the synthesis and the properties of complex hydrides. The major goal is to understand the basic steps of dehydrogenation and rehydrogenation and the role of catalysts. Many complex metal hydrides have high hydrogen gravimetric storage capacities and some of them are commercially available. Some complex hydride systems, such as Mg 2 FeH 6 and Al(BH 4 ) 3 , have an extremely high volumetric hydrogen density of up to 150 kg m À3 . Compared to liquid hydrogen with a volumetric density of 70 kg m À3 , the amount of hydrogen in such metal hydrides is much higher. This makes complex transition metal hydrides interesting as potential storage materials.Handbook of Hydrogen Storage. Edited by Michael Hirscher

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Synthesis of Mg2FeH6 by reactive mechanical alloying: formation and decomposition properties

Cited by 127 publications

References 15 publications

Synthesis and Hydrogen Storage Behaviour of Pure Mg<SUB>2</SUB>FeH<SUB>6</SUB> at Nanoscale

Synthesis and Hydrogen Storage Behaviour of Pure Mg<SUB>2</SUB>FeH<SUB>6</SUB> at Nanoscale

Metal Hydrides

Complex Hydrides

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