Papers by Keyword: Metal Hydride

Abstract: To address the issues of poor thermal conductivity and fragmentation of metal hydride particles undergoing hydriding/dehydriding reactions, a metal hydride-based composite material was developed. The active metal phase was embedded in a silica matrix and a graphite filler was incorporated by ball milling. A set of compact pellet samples at different composition were prepared and tested. Experimental data obtained from the thermal conductivity measurements shown that using powder graphite produced a quite linear increase in the thermal conductivity of the metal hydride – silica composite. Ongoing studies include composition optimization as well as long-term testing upon cycling of such metal hydride composites to evaluate their potentiality in technological hydrogen storage applications.

Abstract: After hydrogen desorption from hydrides based on crystal and partly amorphous CeNi3 compounds samples were obtained with a composition CeNi3Нx (x = 0.5, 0.9). All samples were investigated by X-ray diffraction under the usual conditions. It was revealed that samples after hydrogen desorption have hexagonal and orthorhombic structure of the metallic matrix with cell parameters close to the initial alloy CeNi3. Such structural behavior under hydrogen desorption is determined by the desorption conditions and depends on different hydrogen diffusion in the lattice.

Abstract: Hydrogen storage in reversible metal hydrides is attractive because it can be stored at relatively low pressures with a high volumetric density. In the present research work have been investigated compounds with nominal compositions Zr0.8Ti0.2Cr1.2V0.4Ni0.4 and Zr0.8Ti0.2Cr0.8V0.8Ni0.4 that have been prepared by arc-melting under argon atmosphere. Structural characteristics have been studied by using X-ray powder diffraction while the patterns have been analyzed by using the Rietveld analysis. A main hexagonal Laves phase MgZn2 (C14) and a secondary MgCu2 (C15)-type of, have been found in the powdered compounds. The bulk samples have composite microstructures but the V-rich is characterized by a dendritic microstructure. The high resolution scanning electron microscopy (HR-SEM) and energy dispersive X-ray analysis (EDAX) have been used for the morphology and quantitative analysis, respectively. Hydrogenations and dehydrogenations have been obtained after crucial activation procedure. The alloys were found to be more active under hydrogen after activation while the desorbed amount of hydrogen has been measured by using a Sievert-type apparatus.

Abstract: The goal of our studies is to find alloy compositions capable of high H capacity and reversible low temperature hydrogenation. In the present research work, specimens with nominal compositions Zr0.9Ti0.1Cr1.2V0.8 and Zr0.9Ti0.1Cr0.8V0.8Ni0.4 have been prepared by arc–melting under argon atmosphere. The microstructural properties of the samples were analyzed by XRD and SEM, while the corresponding microchemistry was determined by EDAX measurements. A two phase system was regularly obtained, with the main component being the hexagonal (C14) Laves phase. The presence of small amounts of Ni has been found to increase the alloy activity on hydrogen. Hydrogen activation was performed for both samples and charging-discharging properties were investigated in the temperature range between 20 oC and 100 oC by using a Sievert-type apparatus.

Abstract: The nanocrystalline Mg-based metal hydrides offer a breakthrough in prospects for practical applications. In this work, we study experimentally the structure, electrochemical properties and surface segregation effect of nanocrystalline and microcrystalline Mg2M alloys and Mg2M/M’ (M=Cu, Ni; M’=C, Ni, Pd) nanocomposites. These materials were prepared by mechanical alloying (MA). In the nanocrystalline Mg2Cu powder, discharge capacity up to 30 mA h g-1 was measured. It was found that nickel substituting copper in Mg2Cu1-xNix alloy greatly improved the discharge capacity of studied material. In nanocrystalline Mg2Ni powder, discharge capacities up to 100 mA h g-1 were measured. Additionally, it was found that mechanically coated Mg-based alloys with graphite, nickel or palladium have effectively reduced the degradation rate of the studied electrode materials. Finally, the properties of nanocrystalline alloys and their nanocomposites are compared to that of microcrystalline samples. X-ray photoelectron spectroscopy studies showed that the surface segregation of Mg atoms and valence band width in the nanocrystalline Mg2M alloy are greater compared to those observed in microcrystalline Mg2M. Especially, a strong surface segregation of Mg atoms was observed for the Mg2Ni/M’ composites. In that case, Mg atoms strongly segregate to the surface and form a Mg based oxide layer under atmospheric conditions. The lower lying Ni and M’ atoms form a metallic subsurface layer and could be responsible for the observed relatively high hydrogenation rate. Furthermore, the valence band broadening observed in the nanocrystalline Mg2Ni alloys and Mg2Ni/M’ composites could also significantly influence their hydrogenation properties.

Abstract: In this work, the (Zr-Ti)(Fe-Cr)2 based compounds have been synthesized while charging-discharging hydrogen ability has been examined. Relatively low hydrogen pressure has been used for the hydrogenation of the samples. After following the discharging procedure, a high desorbed amount of hydrogen ~180 (ml of H2)/(gr of the alloy) has been measured on the first 15 min by using a volumetric device. The crystal structure has been analyzed by means of x-ray diffraction (XRD) while a Rietveld analysis has been performed on the x-ray diffraction patterns and the characteristic MgZn2 type of structure has found to be the dominant phase in both compounds. The scanning electron microscopy (SEM) and energy dispersive x-ray analysis (EDX) have been used for microstructural studies and quantitative analysis, respectively. Magnetic measurements have been performed on the samples and a paramagnetic behaviour has found to be at room temperature.

Abstract: In this work we investigate the effect of hydrogen absorption/desorption at room temperature on the structural, magnetic and microstructural characteristics of Zr(Fe0.8Cu0.2)2 and Zr(Fe0.8Co0.1Cu0.1)2. Hydrating kinetics of the as cast bulk samples have been examined while in both samples an anomalous behavior at the absorption part of the P-C curve has been observed. Co doped sample absorbs higher hydrogen content at lower pressure. Crystal structure analysis has been performed by using the Rietveld method. Co free sample has saturation magnetization of 50.85 Am2/kg while Co doped sample has 54.04 Am2/kg at external field of 1.8 T. After hydrogenation the magnetization decreases. Thermomagnetic analysis in the range of 4.2 to 1100 K reveals that the Curie temperature of AB2 phases is in the range of 510 to 550 K. Scanning electron microscopy with energy dispersive x-ray spectroscopy was used in order to examine the composition and surface morphology of the bulk samples. The grain size reduces due to hydrogenation and this is attributed to the more hysteretic magnetization curve.