Papers by Keyword: Mg₂Ni

Abstract: A novel hydrogen storage material Mg₂Ni has been studied by the first-principle methods based on plane-wave pseudopotential theory. The corresponding electronic structure of hydrogen storage materials, Mg₂Ni, Mg₁₂Ni₅M₁ (M = Mn and Cu), and their hydride have also been investigated. The enthalpy of hydrogenation reaction is-65.07kJ/mol (H₂), which is in line with the experimental results. The stability of the new hydride alloy increased by substitution with Cu, and a small amount of alternative might be preventing powdering after several cycles. The Mn atom substitutes Ni atom of hydride alloy which would weaken the H-Ni bond, and the temperature of desorption decreased. The results will play an important role in practical application.

Abstract: In order to study the improvement mechanism of transition metal elements on Mg-based hydrogen storage alloys, especially for the structures and properties of hydrogen storage alloy Mg₂Ni, Ti and Zn substituted alloys Mg_2-mM_mNi,Mg₂Ni_1-nM_n (M=Ti and Zn, m, n=0.1667), and their hydrides Mg₂NiH₄,Mg_2-mM_mNiH₄,Mg₂Ni_1-nM_nH₄(M=Ti and Zn, m , n=0.125) have been investigated by first-principles. Through analyzing the results of the crystal structure, electron density distribution and density of states, the changes of structures and properties resulting from the adding of transition metal elements Ti and V of intermetallic Mg₂Ni and its hydride Mg₂NiH₄ were investigated. The results showed that the addition of transition metal elements can reduce the stability of the Mg₂Ni system to varying degrees and improve the dehydrogenation dynamics performance. Therefore, it may be considered that the substitution by transition metal elements in Mg-based hydrogen storage alloys is an effective technique to improve the thermodynamic behavior of hydrogenation/dehydrogenation in Mg-based hydrogen storage alloys (HSAs).

Abstract: Nanostructured Mg2Ni, Fe-doped and Ti-doped Mg2Ni alloys for hydrogen storage applications have been produced by means of Mechanically Activated Self-propagating High temperature Synthesis (MASHS). Different molar compositions of Fe and Ti (0.1; 0.3 and 0.5) have been studied in order to determine their influence in the hydrogen sorption properties. Different Mg-Ni based alloys have been tested in order to study their hydrogen sorption behavior. The hydrogenation was carried out in a Pressflow Gas Controller. Subsequently, the dehydrogenation process was conducted by means of a Differential Scanning Calorimetry (DSC) equipped with an H2 detector of the purged gas. The MASHS method has been demonstrated to be effective for the obtainment of nanostructured pure and doped Mg2Ni intermetallics. In addition, the materials produced showed hydrogen storage capacities superior to 4wt%, especially in the case of Fe-doped Mg2Ni and a slight reduction of desorption temperature was reached with Ti-doped Mg2Ni. Finally, the activation energy of the dehydrogenation process was evaluated and Ti-doped sample exhibited the lower activation energy value. Obtained results are promising for technological applications of Mg-based alloys.

Abstract: In this work, we have synthesized LaNi5/A and Mg2Ni/A (A = graphite, copper or palladium) nanocomposites. The A elements were distributed on the surface of ball milled alloy particles homogenously and role of these particles is to catalyze the dissociation of molecular hydrogen on the surface of studied alloy. Mechanical coating with graphite or palladium effectively reduced the degradation rate of the studied electrode materials. Results showed a significant broadening of the valence bands of studied nanocomposites compared to those obtained by theoretical band calculations. The reasons responsible for the band broadening of the nanocrystalline LaNi5- and Mg2Ni-type alloys are probably associated with a strong deformation of the nanocrystals in the mechanically alloyed (MA) samples. Normally the interior of the nanocrystal is constrained and the distances between atoms located at the grain boundaries expanded. The valence band spectra of the MA samples could be also broadened due to an additional disorder introduced during formation of the nanocrystalline structure.

Abstract: Nb addition was found to be beneficial to the electrode properties of mechanically alloyed Mg2Ni-based product in 6M KOH solution. Formation of Mg2Ni-based nanocrystalites occurred after 15 and 5h of milling using the initial binary and ternary powder mixtures with stoichiometric compositions of Mg2Ni and Mg1.75Nb0.25Ni, respectively. Further milling of the ternary mixture resulted in the formation of an amorphous phase which became dominant after 30h. Negative electrode made from ternary product after 20h of milling exhibited the highest initial discharge capacity and the longest discharge life. This electrode showed to have a microstructure consisting of nanocrystalline Mg2Ni and an amorphous phase.

Abstract: Structure, microstructure and hydriding properties of mechanically alloyed 2Mg-Ni mixture were investigated. Two different nanocomposites were synthesized by mechanical alloying (MA) in a low-energy planetary mill, namely MN100 (100 h of milling) and MN200 (200 h of milling). The formation of nanocrystalline Mg2Ni was detected as a function of the milling time. An appropriate combination of MA plus annealing under mild conditions accomplishes the complete formation of Mg2Ni phase. The pressure-composition isotherms of the two samples reveal different hydrogen storage capacities and plateau slopes. In addition, the low temperature Mg2NiH4 (LT) formed by hydriding/cooling of MN100 h decomposes at 190 °C, whereas this hydride produced from MN200 first transforms to the high temperature Mg2NiH4 and then decomposes near 245 °C. The differences in the hydriding/dehydriding properties of MN100 and MN200 were associated with the microstructure and structure of the phases formed during MA followed by heating under argon/hydrogen.

Abstract: Mg2-yAlyNi(y=0,0.2,0.3,0.4) and Mg2-aTiaNi (a=0.1,0.2,0.3,0.4) were successfully synthesized by two-step process. The phase composition, microstructure and morphology of the alloys were determined by XRD and SEM. It was found that their main phase was Mg2Ni and another phase, Mg3AlNi2, was observed when Mg in Mg2Ni was partially substituted by Al. The SEM observations showed a large amount of white grains were uniformly distributed in the matrix of the alloys substituted by Al, Ti and the variation of microstructure led to promoted electrochemical properties.

Abstract: Mg, Ni and Cu nanoparticles were prepared by hydrogen plasma-metal reaction method. Nanostructured Mg2Ni and Mg2Ni0.75Cu0.25 compound were successfully obtained using the metal nanoparticles. The synthesis mechanism, the structure and lattice parameter difference, and the hydrogen absorption behaviors of the two compounds were discussed.