Theoretical calculation of hydrogen desorption energies of calcium hydride clusters

Recently calcium hydride has attracted attention as a possible component in ternary complex hydrides such as Ca(AlH₄)₂, Ca₂SiH_x and quaternary complex hydrides of the type Li–B–Ca–H. Although in bulk form CaH₂ decomposes reversibly above 600° centigrade we were motivated to see whether calcium hydride in cluster form has properties suitable for hydrogen storage. We report here the results of DFT calculations using VASP^® package for clusters Ca_nH_2n with n = 1, 2, 3, 4, 6, 8, 10, 12, 14, 16, 20 to get the ground state geometries, energies, bond lengths, and desorption energies, after molecular dynamics optimization. The desorption energy vs. cluster size n curve showed that the desorption energy goes up sharply to ∼1.4 eV per H₂ for n up to 4, followed by a broad maximum of ∼1.8 eV per H₂ around n = 12–14, and then tapers off to a nearly constant value of 1.6 eV per H₂ approximating bulk behavior, which compares favorably with previously reported results. Comparison of these results with those of Mg_nH_2n shows that Ca_nH_2n has a lesser potential as a hydrogen storage medium.     

Processing of duplex stainless steel by WEDM

This study investigates the manufacturing process of 2205 duplex stainless steel by wire electrical discharge machining where the effects of pulse-on time (PONT), wire tension and pulse-off time (POFT) on surface finish, kerf width, and material removal rate (MRR). It was found that the kerf width was unchanged with the change of PONT at long pulse-of time and higher wire tension. However, it decreased initially and then increased due to the rise of PONT at low values of wire tension and POFT. Low wire tension and PONT, POFT and contributed towards widest kerf. Longer PONT increased MRR due to higher machining/processing speed. Lower wire tension and shorter POFT increased MRR more than that of higher wire tension and POFT. Craters and recast layer were on the machined surfaces at all machining conditions. Increased PONT raised surface roughness at the lower POFT and tension in the wire. The surface finish at high wire tension and longer PONT is always better than that at smaller PONT and lower tension in the wire. The microstructure underneath the recast layer remains unchanged and the failure of wire electrode occurred at higher wire tension, longer PONT and shorter POFT.     

Effects of Ti-based catalysts and synergistic effect of SWCNTs-TiF3 on hydrogen uptake and release from MgH2

The present investigations are focused on the effect of different Ti-based catalysts (Ti, TiO₂, TiCl₃ and TiF₃) on de/re-hydrogenation characteristics of nanocrystalline MgH₂. Desorption temperature of milled MgH₂ lowers from 380 to 350, 340, 310 and 260 °C with the addition of Ti, TiO_2, TiCl₃ and TiF₃ respectively. The rehydrogenation characteristics are also improved through the deployment of Ti-based catalysts. Among all Ti based additives, TiF₃ is found to be the most effective catalyst for hydrogen sorption from nano MgH₂. The better catalytic effect of TiF₃ over other Ti-based catalyst can be explained on the basis of temperature programmed reduction (TPR) studies. TPR experiments performed for different Ti additives, reveals that there is no oxidation/reduction reaction below 400 °C except for TiF₃. The TPR profile of TiF₃ shows some oxidation/reduction reaction exhibits at 200 °C. In order to further improve the sorption characteristics and cyclability of TiF₃ catalyzed nano MgH₂, we have investigated the effect of SWCNTs in MgH₂+TiF₃ sample. De/rehydrogenation characteristics reveal the synergistic effect of SWCNTs and TiF₃ in MgH₂+TiF₃ sample. The details of the improvement in sorption behavior of MgH₂–TiF₃ in presence of SWCNTs are described and discussed.     

Synthesis and characterization of novel ion-exchange resin based on polyimide containing 8-hydroxyquinoline as a pendent groups

Novel ion-exchange resin (PBMDDMCMHQ polyimide) having 8-hydroxyuinoline as a pendent groups was prepared using phenylenebismaleimide-diamine polyimide (PBMDDM) and 5-chloromethyl-8-hydroxyquinoline hydrochloride (CMHQ). Phenylenebismaleimide-diamine polyimide (PBMDDM) was prepared by Michael addition reaction of 1,3-phenylenebismaleimide (PBM) and 4,4’-diaminodiphenyl methane (DDM). The resulting ion-exchange resin was characterized by spectral techniques. Polymeric metal chelates of ion-exchange resin were also prepared using transition metal ions Zn(II), Cu(II), Ni(II), Co(II) and Mn(II), and were duly characterized. Ion-exchange properties of ion-exchange resin (PBMDDMCMHQ) for Fe(III), Zn(II), Ni(II) and Cu(II) metal ions were also studied by batch-equilibration method. The produced ion-exchange resin (PBMDDMCMHQ) has thermal stability up to 220°C and can be used over a wide pH range. It has good metal up take capacity at varying pH range and can be recycled.     

Effect of Ce Doping on the Magnetic Properties of NiFe2O4 Nanoparticles

In the present work, effect of different concentration of Ce ions on the magnetic properties of nickel ferrite nanoparticles is discussed. A series of NiCe _x Fe_2?x O₄ (x=0.0–0.10) samples were prepared by a chemical route. XRD patterns show that all the samples are in pure spinel phase except that with x=0.10. This indicates that rare earth ions have limited solubility in the spinel lattice. Magnetic properties are studied by electron paramagnetic resonance spectroscopy (EPR) and the results are explained in terms of a magnetic moment obtained by a vibrating sample magnetometer. Mössbauer spectroscopy was performed to have an idea about the distribution of ions between the tetrahedral and octahedral sites. Magnetic moment is found to decrease after doping with Ce ions. It was found that the samples show mixed spinel nature rather than the pure inverse character. Doping with Ce ions reduces the EPR linewidth of pure nickel ferrite, which indicates that eddy current losses are reduced.     

Correction to: Wideband Antipodal Vivaldi Antenna Using Metamaterial for Micrometer and Millimeter Wave Applications

Journal of Infrared, Millimeter, and Terahertz Waves -     

Vacuum Microwave Treatment of Potato Starch and the Resultant Modification of Properties

The study focuses on the vacuum microwave treatment of low‐moisture potato starch. Typical temperature and drying profiles are presented and explained with the help of other process parameters such as sample weight, pressure, incident and absorbed microwave power. Subsequently water absorption capacity of vacuum microwave treated and conduction heated samples was investigated at 55 °C. During vacuum microwave treatment, 50 g samples were treated with incident powers of 460, 500 and 750 W at 3800 Pa for durations between 30 and 300 s. Water absorption capacity increased exponentially with the net absorbed energy but could not be functionally correlated to end temperature and incident power. During conduction heating, starch samples were treated at temperature values of 120, 130, 140, 150 and 160 °C, till constant weight. The water absorption capacity was observed to increase with increase in treatment temperature.     

Design and Development of a Self-Powered Wearable Device for a Tele-Medicine Application

Wireless Personal Communications - Most of the existing searchable encryption scheme allows the user to search for the encrypted data with the support of Boolean search and this scheme are not so...     

Effect of Size,Content and Shape of Reinforcements on the Behavior of Metal Matrix Composites (MMCs) Under Tension

Journal of Materials Engineering and Performance - The objective of this research was to investigate the mechanical behavior of metal matrix composites (MMCs) 6061 aluminum, reinforced with silicon...