Search

Abstract: Ball milling techniques were used to introduce both fluorine and catalytic transition metals (Fe, Ni) into MgH2 nanograined powders. XRD was carried out to follow the structural evolution upon milling, whereas the thermal stability against H-desorption was investigated by DSC and TG analysis. The latter showed that fluorine additions with the Fe catalyst effectively decrease the desorption temperature to about 500 K. Results on the absorption/desorption kinetics, which was investigated by volumetric techniques, are presented and discussed with respect to both the simultaneous catalytic activity of Fe or Ni with F and the effect of solid-state processes which may occur upon mechanical alloying. [Copyright &y& Elsevier]

The hydrogen storage properties of a 2:1 mol ratio of MgH 2 and Fe with or without 10 wt.% of LiBH 4 were investigated. Two doping methods were used: the first one consisted of two steps: first the 2MgH 2 + Fe mixture was ball milled for 10 h and subsequently LiBH 4 was added and milling resumed for 1 more hour. In the second method all materials were mixed and ball milled for 10 h. The first method produced materials with an hydrogen dehydrogenation capacity of 2.69 wt.% at 623 K and that could re-absorb 2.93 wt.% H 2 . The materials made by the second method presented a hydrogen dehydrogenation capacity of 2.98 wt.% at 623 K and re-absorbed 3.10 wt.% H 2 . For both methods, the rehydrided sample consisted only of MgH 2 . The reversibility of the reaction was enhanced with the LiBH 4 , but this additive, by acting as a catalyst for the formation of MgH 2 , precludes the formation of Mg 2 FeH 6 . [ABSTRACT FROM AUTHOR]

Abstract: The hydrogen absorption ability of the non-absorbing Al-rich ZrAl2 compound was examined after reducing its particles-size to the nanometer regime. The hydrogen abstinence of bulk ZrAl2 has been previously related to its excessive elastic shear stiffening. The particle size of ZrAl2 was reduced by attrition milling and cryomilling. The minimal average particle size was estimated from powder X-ray diffraction analysis to be in the range of 10–20nm. The hydrogen absorption of the milled compounds was measured in different hydrogenation systems at hydrogen pressures between ∼6MPa and ∼2GPa. In all the cases the hydrogen absorption was negligible. In addition, there was a reduction of the hydrogen absorption capacity of nanosized Zr(Al0.5Co0.5)2 as compared to the corresponding bulk compound at the same conditions. We suggest, in view of our and other results, that no significant improvement of the thermodynamics (unlike the kinetics) of the hydrogen absorption can be achieved via the nanoparticle avenue. [Copyright &y& Elsevier]

Abstract: Mg–Ti–Ni composite with nominal composition (Mg0.8Ti0.2)2Ni was produced by mechanical milling at liquid nitrogen temperature (cryomilling). The as-milled composite revealed low-temperature hydrogen absorption ability with slow kinetics. The highest value of hydrogen absorption capacity of 2.5wt.% was measured at 373K and the hydrogenation proceeds simultaneously with a transformation from a crystalline to an amorphous state. Desorption is not found to occur below 530K. A possible mechanism of hydrogenation at low temperatures is proposed. [Copyright &y& Elsevier]

On the basis of DFT results on the ideal amount of Zn required to dissolute into the α-phase of Mg(BH 4 ) 2 (space group P 6 1 22) and experimental results recently presented in the literature, mixtures of α-Mg(BH 4 ) 2 and ZnCl 2 have been prepared by ball-milling, reactive milling and cryo-milling in Mg:Zn starting ratios of 1:0.33, 1:0.2 and 1:0.1. Samples have been characterized with different experimental techniques (PXD, TGA, TPD with RGA and desorption kinetics in a Sieverts apparatus). All the as-milled samples exhibited a H 2 release beginning approximately at 125 °C, indicating a significant decrease in the decomposition temperature compared to pure Mg(BH 4 ) 2 . With the exception of the Mg(BH 4 ) 2 −0.33ZnCl 2 sample ball-milled under 1 bar Ar for 3 h that showed a small B 2 H 6 release around 120 °C, all samples are free of B 2 H 6 emissions. Results from desorption kinetics at 195 °C suggest a strong relation between the amount of ZnCl 2 in the starting mixture and the weight loss. [ABSTRACT FROM AUTHOR]