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1.
Reaction rates in the Mg2Ni---H2 system are still unclear, although they are needed for the process/optimization of hydrogen storage reactors. In this article, the rates of hydrogen absorption and desorption of the magnesium nickel alloy were investigated at different pressures up to 2.0 MPa using a constant-temperature thermogravimetric method. The powder of the alloy was microencapsulated with copper to improve the alloy properties (such as cycling strength) as a pretreatment. In the experiments, weight changes of the smallest amount possible of samples were monitored with the help of an ultra-accurate thermobalance, in order to avoid changes of the sample temperature due to the heat of the reaction. The reaction curves obtained revealed unique dependence of temperature and pressure and influence of thermal hysterisis. It is also possible that hydrogen-absorption and-desorption rates of this hydrogen storage alloy are expressed by the rate equation of first-order reversible reaction.  相似文献   
2.
Key experiments were carried out on the three Al–R–Mg (R=Gd,Dy,Ho) systems and the results obtained used for the thermodynamic optimisation reported in a separate paper in this issue [Caccasmani G, De Negri S, Saccone A, Ferro R. Intermetallics this issue.]. The samples were characterized by differential thermal analysis (DTA), X-ray powder diffraction (XRD), light optical microscopy (LOM), scanning electron microscopy (SEM) and quantitative electron probe microanalysis (EPMA). The isothermal sections at 400 °C are all characterized by extended homogeneity regions at a constant rare earth content. The extension of the (Mg,Al)R solid solution, cP2-CsCl type, varies with the R atomic number. Ternary compounds (τ) of Al2(R,Mg) stoichiometry (hexagonal Laves phases with MgNi2-type structure) have been found to exist at 400 °C in all the systems. Their temperatures of formation were detected by DTA measurements.  相似文献   
3.
Gallium activity in the B2 phase regions of both binary Co–Ga and ternary Co–Ga–Sb systems was measured by EMF method with stabilized zirconia solid electrolyte The temperature range was 1073–1273 K and Sb concentrations were 1, 2 and 3 mol fractions. Ga activity at 1173 and 1273 K increases sharply in Ga rich region and the addition of Sb to the CoGa phase increases Ga activity. Activity change corresponds to the lattice parameter change with Sb addition to the CoGa phase.  相似文献   
4.
C. Colinet 《Intermetallics》2003,11(11-12):1095
A large number of ab-initio calculations of energies of formation of intermetallic compounds have been performed in the last 15 years. The currently used methods are listed. The paper presents a review of the aluminium based compounds which have been studied. Comparisons of calculated and experimental enthalpies of formation are provided for aluminim-3d and-4d transition metal alloys at equiatomic composition. The modelling of the enthalpies of mixing of solid solutions based on a given lattice is described.  相似文献   
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6.
To improve the performance of a thermoelectric material CuGaTe2, element Ag is doped to replace element Ga and we investigate the electronic structure, phase stability, elastic and thermoelectric properties of CuGa1−xAgxTe2 (x = 0, 0.25 and 0.5) via first-principles method. The phase stability of CuGa1−xAgxTe2 is discussed by analyzing the formation energy, cohesive energy and elastic constants. The calculated sound velocities decrease with the increase of Ag content, which is favorable for reducing the lattice thermal conductivity. The analysis of band structures shows that the replacement of Ga by Ag makes CuGaTe2 undergo a direct-indirect semiconductor transition. The Ag doping induces steep density of states in valence band edge, which is beneficial for increasing the carrier concentration and improving thermoelectric performance of CuGaTe2.  相似文献   
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8.
Based on the density functional theory (DFT), the plane-wave pseudopotential method was used to calculate structural stabilities, electronic structures, and ferromagnetism of Fe3Si, Fe11NiSi4, Fe11CoSi4 and Fe11CrSi4 intermetallic compound. This study showed that the Fe11NiSi4 and Fe11CrSi4 phase are more stable than Fe3Si phase, especially Fe11NiSi4, but decreased with Fe11CoSi4 phase. Calculating the density of states and the Mulliken electronic populations showed that Fe11NiSi4 had the highest structural stability because of its Fermi level, which was close to the bottom of the pseudo-gap. Fe11NiSi4 also had the largest Mulliken population, which increased the metallic bonding of the alloying system. The total magnetic moments of Fe11NiSi4, Fe11CoSi4 and Fe11CrSi4 were 20.04μB, 19.98μB, and 18.81μB, respectively. These magnetic moments mainly originated from the 3d spin polarization of Fe and those of additional atoms.  相似文献   
9.
A new kinetic model is proposed to describe the isothermal oxidation of metals and alloys in the form of sphere, flat plate and fiber shape with considering oxidation induced volume change or Pilling–Bedworth Ratio. The effects of temperature, oxygen partial pressure, particle size, sample shape on the oxidation reaction fraction are analyzed in the model through a physical meaning explicit function. The oxidation experimental data of zinc powders and plates were used to check the model. The results show that the calculated curves agree well with the experimental data and the model can give a good theoretical prediction. All of these will be useful for studying the oxidation of intermetallics either.  相似文献   
10.
Ru-based high temperature shape memory alloys show different structures at different temperatures and composition. Equiatomic Ru–Ta and Ru–Nb show two subsequent phase transformations, but their individual influence is still unclear because of the difficulty of comparing the high temperature cubic phase, the intermediate tetragonal phase and the low temperature monoclinic phase. It is important to find a way to compare these structures in order to better understand the microstructure of these alloys and their shape memory behaviour. In order to get the necessary information the alloys have been investigated with neutron diffraction technique during in-situ heating up to about 1100 °C.This study shows the evolution of the lattice parameters and the shape of the unit cells at different temperatures for the three phases these materials exhibit. It proposes a way to compare the different structures and it gives a mathematical expression of the phase transformations. The ultimate goal of this work is to enable a better understanding of the deformation mechanisms in the unit cell and a possible anticipation of the existence of a shape memory effect in these systems.  相似文献   
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