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A study of the LiNH2 - MgH2 system for solid state hydrogen storage
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The influence of different high energy milling times and of the addition of catalysts such as Nb2O5, TiCl3 and graphite on the hydrogen absorption/desorption (A/D) kinetics of a mixture of 2LiNH2 + 1.1MgH2 has been studied in the temperature range 220–240 °C. It is found that a prolonged milling time is effective in improving the A/D kinetics, irrespective of the presence or not of any kind of tested additive. The enthalpy of decomposition reaction results to be about 40.4 kJ/mol, as derived from van’t Hoff plot using the values of the plateau pressures measured in desorption mode. This thermodynamic parameter fits well with the current literature data
Structure and hydrogen storage properties of MgH2 catalysed with La2O3
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The catalytic effect of the addition of lanthanum oxide (La2O3), in the range 0.5–2.0 mol%, on the hydrogen storage properties of MgH2 prepared by ball milling has been studied. The addition of La2O3 reduces the formation during milling of the metastable orthorhombic γ-MgH2 phase. The desorption rate of samples with 1 and 2 mol% La2O3 comes out to be about 0.010 wt% per second at 573 K under an hydrogen pressure of 0.3 bar, better than for sample with 0.5 mol% La2O3. The presence of LaH3 after hydrogenation/dehydrogenation cycles has been observed in all samples. The sample with 1 mol% of La2O3 gives a lower hysteresis factor compared with sample with 2 mol%
Study of Mg-based materials to be used in a functional solid state hydrogen reservoir for vehicular applications
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Powders mixtures of nanosized MgH2 and suitable additives, obtained by high energy milling, have been studied as materials to be used in a functional solid state hydrogen reservoir. A prototype of a two stages reservoir is under development (patent pending). The hydrogen release from the main stage, with high capacity Mg-based hydrides, is primed by a primer stage containing commercial hydrides able to operate at room temperature
Mössbauer study of Mg-Ni(Fe) alloys processed as materials for solid state hydrogen storage
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Mg-Ni-Fe magnesium-rich intermetallic compounds were prepared following two distinct routes. A Mg88Ni11Fe1 sample (A) was prepared by melt spinning Mg-Ni-Fe pellets and then by high-energy ball milling for 6 h the obtained ribbons. A (MgH2)88Ni11Fe1 sample (B) was obtained by high-energy ball milling for 20 h a mixture ofNi, Fe and MgH2 powders in the due proportions. A SPEX8000 shaker mill with a 10∶1 ball to powder ratio was used for milling in argon atmosphere. The samples were submitted to repeated hydrogen absorption/desorption cycles in a Sievert type gas-solid reaction controller at temperatures in the range 520÷590 K and a maximum pressure of 2.5 MPa during absorption. The samples were analysed before and after the hydrogen absorption/ desorption cycles by X-ray diffraction and Mössbauer spectroscopy. The results concerning the hydrogen storage properties of the studied compounds are discussed in connection with the micro-structural characteristics found by means of the used analytical techniques. The improved kinetics of hydrogen desorption for sample A, in comparison to sample B, has been ascribed to the different behaviour of iron atoms in the two cases, as proved by Mössbauer spectroscopy. In fact, iron results homogeneously distributed in sample A, partly at the Mg2Ni grain boundaries, with catalytic effect on the gas-solid reaction; in sample B, instead, iron is dispersed inside the hydride powder as metallic iron or superparamagnetic iron
Moessbauer study of Mg-Ni(Fe) alloys processed as materials for solid state hydrogen storage
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Hydrogen storage in Mg-Ni-Fe compounds prepared by melt spinning and ball milling
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Magnesium-rich Mg–Ni–Fe intermetallic compounds have been prepared by two different routes: (a) short time ball milling of ribbons obtained by melt spinning; (b) long time ball milling of a mixture of MgH2, Ni and Fe powders. The first type of samples displays an hydrogen desorption kinetics better than the second one. Pressure composition isotherm measurements exhibit for both type of samples two plateaux, the lower and wider corresponding to the MgH2 phase and the upper and shorter corresponding to the Mg2NiH4 phase. The presence of the two types of hydrides is confirmed by X-ray diffraction analysis. Mössbauer spectroscopy shows that in melt spun and subsequently milled samples iron is mainly in a disordered structure and segregates after hydrogenation, while in directly milled powders remains mainly unalloyed. After multiple hydrogen absorption/desorption cycles the main part of iron is in metallic state in samples of both types, those of first type preserving better hydrogen desorption kinetics
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