Papers by Keyword: LaNi₅

Abstract: The reflectivity, loss function, refractive index, extinction coefficient and dielectric function of the LaNi₅ and LaNi_4.5Sn_0.5 intermetallic compounds are investigated through the plane-wave pseudo-potential method based on the density functional theory. The effects of Sn impurity are discussed and some interesting features are found in the low frequency region. Some important optical properties such as static dielectric constant and static refractive index are obtained. The equation [n (0)]²=ε₁(0) is satisfied according to our calculation, which indicates that our results are correct and reasonable. Nevertheless, the calculated results need to be testified in the future due to the lack of experimental data.

Abstract: A new technique was proposed for preparation of LaNi5 powder by direct electrolytic deoxidation of solid La₂O₃–NiO mixture oxides in molten CaCl₂–NaCl. Oxides pellets was sintered and used as cathode. High – density graphite was used as anode. Electrolysis was performed. Current change during electrolysis was recorded. XRD was used to analyse the composition of products. SEM was used to analysis surface and cross section of pellets before sintering, after sintering and after electrolysis. The preparation mechanism and the influences of sintering temperature and cell voltage on electrolytic deoxidation was studied. Results show that the optimum conditions to prepare LaNi₅ are：NiO-La₂O₃（Ni:La=5:1）pellets are formed at 30MPa, sintered at 850°C for 5h, electrolyzed under 3.2V in CaCl₂–NaCl melt at 850°C for more than 12 hours.

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: Employing the first principles discrete variational method(DVM), we investigated the electronic structure of LaNi5 hydrogen storage alloys containing various alloying elements, M=Mn,Fe,Co. The results showed that s electrons of H mainly interact with s electrons of hydride-non-forming element Ni, though hydride forming element La have stronger affinity to hydrogen atom. And alloying elements strengthened the bond between B-H, so decreased the capacity of doped-system.

Abstract: Hydrogen absorption-desorption cycling induced by pressure change in a closed system were carried out with LaNi5, La0.7Ce0.3Ni4Cu and TiFe0.9Ni0.1 alloys. PC isotherms measured during the cycling showed some changes in hydrogen storage capacity, plateau pressure and hysteresis of the alloys. . The half capacity life of LaNi5 alloy can be projected as 70,000 cycles for room temperature pressure cycling. When La0.7Ce0.3Ni4Cu alloy was pressure cycled both of the plateau pressures were decreased significantly and continuously. TiFe0.9Ni0.1 alloy showed a good resistance to cyclic degradation. Heat treatments of the degraded alloys under 1 atm of hydrogen gas recovered most of the hydrogen storage properties to the initial level even though they were degraded again more rapidly upon subsequent cycling.