| 1. |
- Pistidda, C., et al.
(författare)
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Hydrogen storage systems from waste Mg alloys
- 2014
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 1873-2755 .- 0378-7753. ; 270, s. 554-563
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Tidskriftsartikel (refereegranskat)abstract
- The production cost of materials for hydrogen storage is one of the major issues to be addressed in order to consider them suitable for large scale applications. In the last decades several authors reported on the hydrogen sorption properties of Mg and Mg-based systems. In this work magnesium industrial wastes of AZ91 alloy and Mg-10 wt.% Gd alloy are used for the production of hydrogen storage materials. The hydrogen sorption properties of the alloys were investigated by means of volumetric technique, in situ synchrotron radiation powder X-ray diffraction (SR-PXD) and calorimetric methods. The measured reversible hydrogen storage capacity for the alloys AZ91 and Mg-10 wt.% Gd are 4.2 and 5.8 wt.%, respectively. For the Mg-10 wt.% Gd alloy, the hydrogenated product was also successfully used as starting reactant for the synthesis of Mg(NH2)(2) and as MgH2 substitute in the Reactive Hydride Composite (RHC) 2LiBH(4) + MgH2. The results of this work demonstrate the concrete possibility to use Mg alloy wastes for hydrogen storage purposes. (C) 2014 Elsevier B.V. All rights reserved.
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| 2. |
- Santoru, A, et al.
(författare)
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A new potassium-based intermediate and its role in the desorption properties of the K-Mg-N-H system.
- 2016
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Ingår i: Physical chemistry chemical physics : PCCP. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 18:5, s. 3910-3920
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Tidskriftsartikel (refereegranskat)abstract
- New insights into the reaction pathways of different potassium/magnesium amide-hydride based systems are discussed. In situ SR-PXD experiments were for the first time performed in order to reveal the evolution of the phases connected with the hydrogen releasing processes. Evidence of a new K-N-H intermediate is shown and discussed with particular focus on structural modification. Based on these results, a new reaction mechanism of amide-hydride anionic exchange is proposed.
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| 3. |
- Pistidda, C., et al.
(författare)
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Effect of the Partial Replacement of CaH2 with CaF2 in the Mixed System CaH2 + MgB2
- 2014
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 118:49, s. 28409-28417
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Tidskriftsartikel (refereegranskat)abstract
- In this work the effect of a partial replacement of CaH2 with CaF2 on the sorption properties of the system CaH2 + MgB2 has been studied. The first five hydrogen absorption and four desorption reactions of the CaH2 + MgB2 and 3CaH(2) + CaF2 + 4MgB(2) systems were investigated by means of volumetric measurements, high-pressure differential scanning calorimetric technique (HP-DSC), B-11 and 19F MAS NMR spectroscopy, and in situ synchrotron radiation powder X-ray diffraction (SR-PXD). It was observed that already during the mixing of the reactants formation of a nonstoichiometric CaF2-xHx solid solution takes place. Formation of the CaF2-xHx solid solution sensibly affects the overall hydrogen sorption reactions of the system CaH2 + MgB2.
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| 4. |
- Pistidda, C., et al.
(författare)
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First Direct Study of the Ammonolysis Reaction in the Most Common Alkaline and Alkaline Earth Metal Hydrides by in Situ SR-PXD
- 2015
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:2, s. 934-943
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Tidskriftsartikel (refereegranskat)abstract
- We report on the first in situ synchrotron radiation powder X-ray diffraction study (SR-PXD) of the ammonolysis reaction of selected alkaline and alkaline earth metal hydrides (i.e., LiH, NaH, KH, MgH2, and CaH2). The investigation was performed using an in situ SR-PXD pressure cell at an initial NH3 pressure of 6.5 bar in a range of temperature between room temperature (RT) and 350 degrees C. The results of this work give new important insights into the formation of metal amides and imides starting from the corresponding metal hydrides. LiH was observed to react with NH3 to form LiNH2 already at RT, and then it decomposes into Li2NH at 310 degrees C through the formation of nonstoichiometric intermediates of the Li1+-xNH2-x form. The formation of NaNH2 takes place nearly at RT (28 degrees C), and it melts at 180 degrees C. As for LiH, KH reacts with NH3 at RT to surprisingly form, what it seems to be, cubic KNH2. However, we believe this phase to be a solid solution of KH in KNH2. At high temperature, the possible formation of several solid solutions of K(NH2)(1-y)H-y with defined composition is also observed. The formation of Mg(NH2)(2) was observed to starts at around 220 degrees C, from the interaction beta-MgH2 and NH3. At 350 degrees C, when all beta-MgH2 is consumed, the formation of Mg(NH2)(2) stops and MgNH is formed by the reaction between beta-MgH2 and NH3. Our results indicate that the formation of the beta-MgH2 is a key step in the synthesis of Mg(NH2)(2) at low temperature (e.g., via ball milling technique). CaH2 was observed to react with NH3 at around 140 degrees C to form CaNH. At higher temperature the appearance of new reflections of possible Ca1+xNH phases, with the same crystalline structure of CaNH but with a smaller cell parameter was observed.
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