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In this study, the effects of partial substitution of Fe, in the ZrFe 2 -system alloys, by Cr or V are presented. The two studied alloys, ZrFe 1.8 V 0.2 and ZrFe 1.8 Cr 0.2 , have been synthesized by high frequency induction-levitation melting under inert Ar atmosphere. The induction furnace was equipped with a water-cooled copper crucible that permits the rapid solidification of the alloy after the melting. The crystal structures of the investigated alloys have been studied by the Rietveld analysis of the obtained X-ray diffraction (XRD) patterns. The microstructure has been observed by a scanning electron microscope (SEM) on polished samples of the alloys. Their hydriding properties have been studied with a high pressure Sievert's type apparatus, up to 200 bar. All pressure–composition–temperature (PCT) measurements have been obtained at 20, 60 and 90 °C. Two high temperature activation cycles have been conducted prior to PCT measurements. The results showed almost the same uptake for the alloys after identical activation and lowering of the plateau pressure in both cases. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogen is a promising alternative energy carrier that can potentially facilitate the transition from fossil fuels to sources of clean energy because of its prominent advantages such as high energy density (142 MJ kg−1), great variety of potential sources (for example water, biomass, organic matter), and low environmental impact (water is the sole combustion product). However, due to its light weight, the efficient storage of hydrogen is still an issue investigated intensely. Various solid media have been considered in that respect among which magnesium hydride stands out as a candidate offering distinct advantages. Recent theoretical work indicates that MgH2 becomes less thermodynamically stable as particle diameter decreases below 2 nm. Our DFT (density functional theory) modeling studies have shown that the smallest enthalpy change, corresponding to 2 unit-cell thickness (1.6 Å Mg/3.0Å MgH2) of the film, is 57.7 kJ/molMg. This enthalpy change is over 10 kJ/molMg smaller than that of the bulk. It is important to note that the range of enthalpy change for systems that are suitable for mobile storage applications is 15–24 kJ/molH at 298 K. The important key for the development of air-stable Mg-nanocrystals is the use of PMMA (polymethylmethacrylate) as an encapsulation agent. In our work we use laser ablation, a non-electrochemical method, for producing well-dispersed nanoparticles without the presence of any long-range aggregation. The observed improved hydrogenation characteristics of the polymer-stable Mg-nanoparticles are associated to the preparation procedure and in any case the polymer-laser ablation is a new approach for the production of air-protected and inexpensive Mg-nanoparticles. [Copyright &y& Elsevier]

Abstract: In boron-substituted melt-spun Sm(Co,Fe,Cu,Zr)7.5-type alloys a nanocomposite microstructure and high coercivities in both as-spun and short-time annealed ribbons can be obtained. In the present study three different compositions, namely Sm(Co0.73Fe0.1Cu0.09Zr0.04B0.04)7.5, Sm(Co0.70Fe0.1Cu0.12Zr0.04B0.04)7.5 and Sm(Co0.70Fe0.1Ni0.12Zr0.04B0.04)7.5 have been examined in order to investigate the influence of composition on the magnetic properties and the microstructure. Melt-spun ribbons have been obtained and annealing has been followed under argon atmosphere for 30–75min at 600–870°C. For the as-spun ribbons the TbCu7-type of structure and fcc-Co as a secondary phase have been identified in the X-ray diffraction patterns. For the annealed ribbons above 700°C the 1:7 phase transforms into 2:17 and 1:5 phases. The TEM studies have shown a homogeneous nanocrystalline microstructure with average grain size of 30–80nm. Coercivity values of 15–27kOe have been obtained from hysteresis loops traced in non-saturating fields. The coercivity decreases with temperature, but it is sufficiently large to maintain values higher than 5kOe at 380°C. [Copyright &y& Elsevier]

Abstract: In this work we investigate the effect of hydrogen absorption/desorption at 0 and 25  C on the structural, magnetic and microstructural characteristics of bulk samples with Sm(Co0.6Fe0.2Zr0.16B0.04)7.5 and Sm(Co0.74Fe0.1Cu0.12Zr0.04)8 stoichiometries. The B-doped sample absorbs 0.8 wt.% at room temperature under 15 bar of hydrogen pressure while the B-free one absorbs less than 0.01 wt.% under the same conditions. The B-free bulk sample has  kOe while after hydrogenation this value increases slightly. Hydrogenation of the B-free bulk sample results in stronger dipolar interactions between the hard grains, as revealed from plots. SEM with EDAX was used in order to examine the composition and surface morphology of bulk samples. [Copyright &y& Elsevier]

Abstract: Titanium borates show promising hydrogen storage characteristics. Structural relaxation around individual hydrogen atoms and the binding energies are studied by means of the density functional theory methods for a number of hydrogenated TiB2 , TiB and Ti2B structures. Starting with the possible symmetric hydrogen sites a random structure searching has been performed, in addition to locate all energetically stable adsorption sites. It is shown that for the three bulk compounds considered, the lowest binding energies are obtained for TiB2 (in the 0.3–1.8 eV range), the largest for Ti2B (in the 3.9–4.7 eV range), while for TiB they are intermediate (in the 2.8–3.5 eV range). Calculations performed on hydrogenated Ti2B result in two energetically stable sites for two different starting environments, suggesting a possible soft mode solution. [Copyright &y& Elsevier]