The tensile properties of a particulate reinforced al alloy in the temperature range -196–300 °c

The tensile properties of a particulate reinforced Al- Si-Mg alloy were determined in the temperature range — 196–300 °C. Microstructural coarsening of a peak aged (T61) material occurs at the higher temperatures (i.e. 200 and 300 °C), which, together with the test temperature, results in a considerable decrease in flow strength for both the composite and unreinforced alloy. However, the strengthening ratio (i.e. the ratio of composite to matrix strength, σ_c/σ_m actually increases with temperature. This effect is also observed when investigating the influence of test temperature alone (i.e. a stable matrix microstructure over the full temperature range). These results suggest that the primary relaxation mechanisms are damage accumulation and relaxation by plastic deformation of the matrix. There is no evidence of unrelaxed behaviour, even at −196 °C, and the strain rate used during testing is likely to be too high to allow diffusional relaxation to be operative at the higher temperatures     

A high-performance MPI implementation on a shared-memory vector supercomputer

In this article we recount the sequence of steps by which MPICH, a high-performance, portable implementation of the Message-Passing Interface (MPI) standard, was ported to the NEC SX-4, a high-performance parallel supercomputer. Each step in the sequence raised issues that are important for shared-memory programming in general and shed light on both MPICH and the SX-4. The result is a low-latency, very high bandwidth implementation of MPI for the NEC SX-4. In the process, MPICH was also improved in several general ways.     

Nanostructured SiC ceramics prepared by a new process—Crystallization of interfacial glass

Large bulk and fully dense SiC based nanoceramics with average grain size of 50 nm and 20–30 wt.% nanometer sized α-Sialon, Al_xSi_{3 − x}O₆ and α-SiO₂ interfacial phases were prepared by a new process, crystallization of interfacial glass, using LMAS glass-coated SiC powder as starting material. The process involves two major steps: densification by hot pressing, and crystallization of interfacial glass by annealing treatment. The densification was controlled by interfacial glass content, hot pressing temperature, and hot pressing pressure; density 99.8% theoretical being reached for SiC/30 wt. % glass nanoceramics hot-pressed at 1520 °C and 22 MPa for 30 min. The crystallization was complete and nearly all the interfacial glass was transformed into nanocrystalline phases after 800 °C and 900 °C for 5 h annealing treatments. Plastic flow and rearrangement of particles and interfacial glass infiltration are densification mechanisms. A large number of nanometer sized SiC powder particles serve as nucleating agents, e.g. hetero-nucleation, and are responsible for interfacial glass crystallization. A characteristic of the present process is that there is no SiC grain growth during densification and interfacial glass crystallization.     

Synthesis of Co(OH)2/graphene/Ni foam nano-electrodes with excellent pseudocapacitive behavior and high cycling stability for supercapacitors

Vertically aligned graphene nanosheets have been synthesized by radio-frequency plasma-enhanced chemical vapor deposition on nickel-foam current collectors and that have been used as substrates for cathodic electrodeposition of cobalt hydroxide nanosheets in Co(NO₃)₂ aqueous solution. Raman spectrum exhibits that high-quality graphene nanosheets have been synthesized. The composites have been characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, cyclic voltammetry and galvanostatic charge/discharge. It indicates that hexagonal Co(OH)₂ has a network microstructure, consisting of interlaced sheets with the thickness of 12 nm coated on the graphene nanosheets. The binder-free nano-electrode exhibits excellent pseudocapacitive behavior with pseudocapacitances of 693.8 and 506.2 Fg⁻¹ at current density of 2 and 32 Ag⁻¹, respectively, in a potential range of −0.1–0.45 V. The capacitance can retain about 91.9% after 3000 charge–discharge cycles at 40 Ag⁻¹, which is higher than that of Co(OH)₂/Ni foam (after 2000 cycles, 75.5% of initial capacitance remains). The introduction of graphene between Co(OH)₂ and Ni foam demonstrates an enhancement of electrochemical stability of the nano-electrodes.     

Room temperature synthesis of nanocrystalline silicon by aluminium induced crystallization for solar cell applications

The aim of this study is to synthesis large area, plastic compatible of p-type nanocrystalline silicon through conventional sputter system. The growth of and p-type doping of nanocrystalline silicon onto plastic substrates using D.C. magnetron sputtering was investigated. The film properties were examined by Raman spectroscopy, X-ray Diffraction, scanning electron microscopy and energy dispersive spectrometry. Nanocrystalline silicon was achieved with careful control of ion bombardment energy. Through a narrow experimental, window room temperature, nanocrystalline silicon can be synthesised on aluminium. It is believed the aluminium reduces the required energy for crystallite nucleation. PN junction was formed through sputtering of Al/Al–Si/n-type Si/AZO structure. The I–V characteristic showed good rectifying behaviour and confirms p-type doping via aluminium induced crystallization.     

Study on preparation and luminescent properties of Eu3+-doped LaAlO3 and GdAlO3

Eu³⁺-doped trigonal LaAlO₃ and orthorhombic GdAlO₃ phosphors have been successfully synthesized by sol–gel method. The crystallization processes of the phosphors have been characterized by X-ray diffraction (XRD) and thermogravimetry-differential scanning calorimetry (TG-DSC). The optical properties of these phosphors were investigated using the photoluminescence (PL) and photoluminescence excitation (PLE) spectra. The influences of the different structures and bonding of the hosts on the luminescence performance of Eu³⁺ ion-doped LaAlO₃ and GdAlO₃ were investigated in detail based on chemical bond theory. Under appropriate UV-radiation, the reddish orange light emitted from GdAlO₃:Eu³⁺ was brighter than that from LaAlO₃:Eu³⁺. Such a brightly luminescent phosphor could be considered as an ideal optical material for the development of new optical display systems.     

Tuning of crystal phase and luminescence properties of Gd2(MoO4)3:Dy3+ phosphors

The orthorhombic and monoclinic Gd₂(MoO₄)₃:Dy³⁺ were successfully synthesized by a hydrothermal process with a subsequent annealing treatment at 800 °C for 4 h. The crystal phase of Gd₂(MoO₄)₃:Dy³⁺ was controlled as a function of the pH value of the solution. The crystallization and microstructures of the samples were characterized by Powder X-ray diffraction (XRD) and scanning electron micrograph (SEM). Furthermore, the optical properties were investigated by the diffuse reflection, excitation and emission spectra. The mechanisms of different crystal phases affected on the luminescence properties of Gd₂(MoO₄)₃:Dy³⁺ were discussed. The electric dipole–dipole interaction between Dy³⁺ ions was identified as the main mechanism for the concentration quenching of the two structures. Finally, the chromatic natures of all the samples were analyzed in detail. The results indicate that the orthorhombic phosphor Gd_1.84(MoO₄)₃:Dy_0.16³⁺ can be considered as a suitable candidate for white light emitting diodes (W-LEDs).     

Experimental study on synthesizing TiO2 nanotube/polyaniline (PANI) nanocomposites and their thermoelectric and photosensitive property characterization

In this paper, TiO₂ nanotube/polyaniline (PANI) nanocomposites were made. The thermoelectric and photosensitive properties of the nanocomposites were studied. The effects of processing time, voltage, concentration of F^? ions and H₃PO₄ on the formation of TiO₂ nanotubes were investigated. The morphologies of the synthesized nanocomposites were revealed by scanning electron microscopy (SEM). The formation of polyaniline was confirmed by both Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). The optimum conditions for the formation of well-organized TiO₂ nanotubes are at 20 V for 60 min in the electrolyte containing 0.2 M fluorine ions. The highest absolute value of the Seebeck coefficient for the TiO₂ nanotube/polyaniline nanocomposites is 124 μV/K at 30 °C. Pure Ti foil does not show photosensitive property, while the TiO₂ nanotubes have strong photosensitivity.     

Double-perovskites A2FeMoO6−δ (A = Ca, Sr, Ba) as anodes for solid oxide fuel cells

Double-perovskites A₂FeMoO_6−δ (A = Ca, Sr, Ba) have been investigated as potential anode materials for solid oxide fuel cells (SOFCs). At room temperature, A₂FeMoO_6−δ compounds crystallize in monoclinic, tetragonal, and cubic structures for A = Ca, Sr, and Ba, respectively. A weak peak observed at around 880 cm⁻¹ in the Raman spectra can be attributed to traces of AMoO₄. XPS has confirmed the coexistence of Fe²⁺-Mo⁶⁺ and Fe³⁺-Mo⁵⁺ electronic configurations. Moreover, a systematic shift from Fe^2+/3+-Mo^6+/5+ to Fe²⁺-Mo⁶⁺ configuration is seen with increasing A-site cation size. A₂FeMoO_6−δ samples display distinct electrical properties in H₂, which can be attributed to different degrees of degeneracy of the Fe²⁺-Mo⁶⁺ and Fe³⁺-Mo⁵⁺ configurations. Ca₂FeMoO_6−δ is unstable in a nitrogen atmosphere, while Sr₂FeMoO_6−δ and Ba₂FeMoO_6−δ are stable up to 1200 °C. The thermal expansion coefficients of Sr₂FeMoO_6−δ and Ba₂FeMoO_6−δ are very close to that of La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM). The performances of cells with 300 μm thick LSGM electrolyte, double-perovskite SmBaCo₂O_5+x cathodes, and A₂FeMoO_6−δ anodes follow the sequence Ca₂FeMoO_6−δ < Ba₂FeMoO_6−δ < Sr₂FeMoO_6−δ. The maximum power densities of a cell with an Sr₂FeMoO_6−δ anode reach 831 mW cm⁻² in dry H₂ and 735 mW cm⁻² in commercial city gas at 850 °C, respectively.