The effect of ZnO addition on the electrochemical properties of the LaNi3.55Mn0.4Al0.3Co0.2Fe0.55 electrode used in nickel–metal hydride batteries

Journal of Solid State Electrochemistry - The studied electrochemical properties of the LaNi3.55Mn0.4Al0.3Co0.2Fe0.55 alloy showed a rather poor performance. To improve them, ZnO, a doping agent at...     

Phase structure and electrochemical characteristics of CaNi4.7Mn0.3 hydrogen storage alloy by mechanical alloying

Journal of Solid State Electrochemistry - In this paper, we study systematically the effect of ball/powder weight ratio on the morphological, structural, and electrochemical properties of...     

Kinetic and thermodynamic studies of hydrogen storage alloys as negative electrode materials for Ni/MH batteries: a review

This paper reviews the present performances of intermetallic compound families as materials for negative electrodes of rechargeable Ni/MH batteries. The performance of the metal-hydride electrode is determined by both the kinetics of the processes occurring at the metal/solution interface and the rate of hydrogen diffusion within the bulk of the alloy. Thermodynamic and electrochemical properties for each hydride compound family will be reported. The steps of hydrogen absorption/desorption such as charge-transfer and hydrogen diffusion for evaluating the electrochemical properties of hydrogen storage alloys are discussed. Exchange current density (I ₀) and hydrogen diffusion coefficient (D _H) are the two most important parameters for evaluating the electrochemical properties of metal hydride electrode. The values of the two parameters for a number of hydrogen storage alloys are compared. The relationship between alloy composition and electrochemical properties is noted and evaluated.     

Ab initio calculations of structural,electronic, optical and thermodynamic properties of alkaline earth tellurides BaxSr1−XTe

Structural, electronic and thermodynamic properties of SrTe and BaTe compounds and their ternary mixed crystals Ba_xSr_1−xTe in the rock-salt structure have been studied with density functional theory (DFT), whereas the optical properties have been obtained by using empirical methods such as the modified Moss relation. The exchange-correlation potential was calculated using the generalized gradient approximation (GGA) of Perdew–Burke–Ernzerhof (PBE) and the local density approximation (LDA) of Teter–Pade (TP). In the present work, we used the virtual-crystal approximation (VCA) to study the effect of composition (x). The calculated lattice parameters at equilibrium volume and the bulk modulus for x=0 and x=1 are in good agreement with the literature data. Furthermore, the Ba_xSr_1−xTe alloys are found to be an indirect band gap semiconductor. In addition, we have also predicted the heat capacities (C_V), the entropy(S), the internal energy (U) and the Helmholtz free energy (F) of the parent compounds SrTe and BaTe.     

Structural and electrochemical properties of TiFe alloys synthesized by ball milling for hydrogen storage

The binary TiFe alloy was synthesized by mechanical alloying (MA) under argon atmosphere at room temperature. The effect of ball to powder weight ratio on the microstructures was characterized by X-ray diffraction (XRD). The effect of milling time on the electrochemical and activation properties was investigated by scanning electron microscope (SEM), galvanostatic charging and discharging, constant potential discharge, and potentiodynamic polarization techniques. Relationships between electrochemical properties, such as polarization, variation of electrochemical discharge capacity, \( \frac{D_{\mathrm{H}}}{a^2} \) ratio exchange current density, and Nernst potential and alloy compositions were evaluated. XRD results showed that with increasing ball to powder weight ratio, the amorphization process is accelerating and powders milled with a ratio of 1:8 have the highest conversion rate to TiFe. SEM observations reveal that particles show cleavage fracture morphology and size distribution is generally normalized. TiFe milled during 40 h was easily activated within 5 cycles and showed the best discharge capacity equal to 147 mAh g^?1. A good cycling was observed after 20 cycles at ambient temperature for the alloy milled for 30 h. A correlation between alloy composition, \( \frac{D_{\mathrm{H}}}{a^2} \) report, exchange current density, and Nernst potential on one hand and the variation of the electrochemical discharge capacity during cycling for different milling times on the other hand was observed.     

Microstructure and magnetic properties of atmospheric plasma sprayed Fe–40Al coating obtained from nanostructured powders

Amorphous and nanocrystalline materials have attracted much interest in the field of new materials design because of their excellent mechanical and physical properties as well as their magnetic properties. In this work, Fe–40Al coatings were prepared from nanostructured feedstock with a very low degree of order using atmospheric plasma spraying. Scanning electron microscopy, X-ray diffraction, and magnetic measurements were used to investigate microstructure, phase structure, and magnetic properties of the coatings. The results showed that Fe–40Al coating presented a ferromagnetic character due to partial structure with a low degree of order and unmelted nanostructured particles retained from the feedstock. Moreover, the heterogeneous magnetic properties were found in the parallel and vertical direction of the coating.     

A comparative study between slow electrons and positrons transport in solid thin films

In this work, we have conducted a comparative study between the transport of electrons and positrons in aluminum and gold solid thin films, in the examined primary energy range (0-4 keV), by using the Monte Carlo method. This comparative study has been used for three transport phenomena: transmission, absorption and backscattering and it will be useful for experimenters to choose between electron or positron beams for thin film characterizations. Here, we have calculated quantities such as absorption probability, mean penetration depth, transmission probability, transmission energy distributions and backscattering coefficient, for both electron and positron. The agreement between our results and the available experimental data is found to be good within the limits of the statistical accuracy.     

Backscattering coefficients for low energy electrons and positrons impinging on metallic thin films: scaling study

Thin films Backscattering Coefficients (BSCs) for 1 to 4 keV electron and positron normally incident beams are stochastically modeled and calculated by the Monte Carlo method. We suggest a new function BSC(δ) depending only of one free parameter (to be determined) and which can describe very well the variation of the backscattering coefficient versus the film thickness (δ). Moreover, this paper aims at discussing the observed differences between the electron and positron properties impinging on solid targets.